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Assessment of the potential for integration of avian conservation with modern agricultural production

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Assessment of the potential for integration of avian conservation with modern agricultural production
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Jones, Gregory Alan
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Agriculture ( jstor )
Birds ( jstor )
Crops ( jstor )
Farms ( jstor )
Foraging ( jstor )
Insects ( jstor )
Pests ( jstor )
Species ( jstor )
Sunflowers ( jstor )
Vegetation ( jstor )
Dissertations, Academic -- Wildlife Ecology and Conservation -- UF ( lcsh )
Wildlife Ecology and Conservation thesis, Ph.D ( lcsh )
City of Gainesville ( local )
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Thesis (Ph.D.)--University of Florida, 2003.
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Includes bibliographical references.
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Printout.
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Vita.
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by Gregory Alan Jones.

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ASSESSMENT OF THE POTENTIAL FOR INTEGRATION OF AVIAN
CONSERVATION WITH MODERN AGRICULTURAL PRODUCTION















BY

GREGORY ALAN JONES


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA




























Copyright 2003

by

Gregory Alan Jones















ACKNOWLEDGMENTS

Funding for my research was provided by the Florida FIRST initiative of

the University of Florida's Institute of Food and Agricultural Sciences, the

Organic Farming Research Foundation, The Eastern Bird Banding Association,

The North American Bluebird Society, and the University of Florida's

Department of Wildlife Ecology and Conservation.

I am truly grateful for the collaborative assistance of the following

researchers: Dr. Kathryn Sieving, Dr. Michael Avery, Dr. Robert Meagher, Dr.

Kenneth Buhr, and Dr. Jennifer Gillett. I thank Dr. Avery, Kandy Rocca, and all

of the staff members at the USDA Denver Wildlife Research Center's Florida

Field Station, Gainesville, Florida, for use of their facilities, birds and their help in

conducting experiments. I also thank Dr. Meagher, Charlie Dillard and all of the

staff members at the USDA-ARS Insect Behavior & Biocontrol Unit, Gainesville,

Florida, for the help and provision of experimental materials. I thank the

following research assistants: Matt Reetz, Leonard Santisteban, and Kat Smith. I

thank the WEC staff members Caprice McRea, Monica Lindberg, Delores

Tillman, Laura Hayes, and Sam Jones for their kind help and friendship over the

past years.

A very special thank you goes to the members of my supervisory

committee for their guidance and support during pursuit of my degree: Dr.









Kathryn Sieving (Chair), Dr. George Tanner, Dr. Michael Avery, Dr. Douglas

Levey, and Dr. E. Jane Luzar. I will always be grateful for Dr. Sieving's

commitment, encouragement, and patience as I struggled through the process of

developing a research program and seeing it through to completion. I appreciate

the special attention and help provided to me by all of these people, each in their

own way over the years. I have very much enjoyed working with each of these

fine individuals.

I wish to relate my appreciation to Dean Jimmy Cheek and Associate

Dean E. Jane Luzar for providing me the opportunity to work with the students

and faculty in the College of Agricultural and Life Science's Honors Program. It

has been a great privilege and learning experience to be able to interact with the

brightest and the best of the college's students. I have been very fortunate to be

able to work and learn from some of the top teaching staff in the college as well in

this program. I am very grateful for these people's support over the past few

years.

I greatly appreciate the logistic cooperation of the following extension

agents Gary Brinen, Austin Tilton, David Denkins, Jacque Bremen, Marvin,

Anthony Drew, and David Holmes. I would also like to thank Marty Mesh and

the Florida Certified Organic Growers and Consumers, Inc. for their assistance.

The cooperation and participation of the following producers is gratefully

acknowledged as well: Larry and Greg Rogers, the Hauffler Brothers, Don King,

Andy Mulberry, W. K. Bagwell, Dennis Short, Kathy and Marvin Graham, Lois

Milton, Tommy Simmons, Bill Ogle, Bill Allen, Rosalie Koenig, Charles









Lybrand, Donald Appelbaum, Ed Parker, Charles Andrews, Joe Durando, Paul

Morris, Archer Christian, Cynthia Conolly, and Bikram Singh.

I would especially like to thank my fellow colleagues in Dr. Sieving's lab

for their fellowship over the years. Their reviews, sharing of ideas, and guidance

has truly been an important factor in the success of my graduate program. I have

enjoyed their friendship while I have been at the university and hope to continue

to be close to them in the future. Thanks Tom, Marcela, John, Traci, Matt, Mike

and Ivan.

Finally, I thank my wife Leigh and my two sons Ben and Zach for their

love, support and patience. I know I have not always been easy to live with,

especially at times when I was frustrated or stressed during the past few years. I

could not have achieved my academic or career goals without them. I love you

all. I also appreciate the love and support provided to me and my family by my

parents and especially my mother-in-law Jamie Schnabel.
















TABLE OF CONTENTS


Page

ACKNOWLEDGMENTS ............................... ... ........... iii

ABSTRACT .. ................................. ........... ............. viii

CHAPTERS

1 INTRODUCTION .................... ................... ............ 1

Economic Ornithology The First Attempt to Integrate Bird
Conservation and Agricultural Production ............................. 2
Effects of Agricultural Practices on Avian Populations ................. 4
Birds as Predators in Agroecosystems ..................................... 8
Examples of Experimental Work Investigating the Impact of
Birds on Insect Populations in Modem Agroecosystems ............ 10
Natural Systems Agriculture or Ecoagriculture .......................... 12
Research Needs ......................... ...... ........ .... 16
Conclusion ............ ............................... ... ........ 17

2 AVIAN BIODIVERSITY AND FUNCTIONAL INSECTIVORY
ON NORTH-CENTRAL FLORIDA FARMLANDS .............. 19

Introduction ...................... ................ ... ...... ..... ....... 19
M methods .............. ............... ........... ............... 23
Results ................ .... ...... ... ....... ...... 30
Discussion ................ ....................... .... .. .. 40

3 INTERCROPPING WITH SUNFLOWERS TO CREATE LOCAL
REFUGIA FOR AVIAN PREDATORS OF ARTHROPOD PESTS 50

Introduction ......................... .... ................... 50
M ethods .................. .... ............................ ..... 54
Results .................................................................. ...... 61
Discussion ......... ..... ..... ......................... ........ 76
Conclusion ..................... .................... .......... 82









4 PARASITIZED AND NON-PARASITIZED PREY SELECTIVITY
OF INSECTIVOROUS BIRDS: POTENTIAL FOR
AUGMENTATION OF CLASSICAL BIOCONTROL ............ 84

Introduction .............. ..................... ........ 84
M methods .......... .... ..... .............. ......... ........... 87
R results ............... .. ............. .. ........ ....... .... ... 95
Discussion ..................... ................ .. ...... .......... 96
Conclusion ............. ............. .................... 100

5 SUMMARY AND FUTURE RESEARCH NEEDS ................... 102

Summary ................ ...................... ................ .. 102
Future Research Needs ..... .................... ...... ............ 106
Conclusion ................... .. .. ........... .... .... ............ 107


LITERATURE CITED ................... ... ........ ..... ....... 109

APPENDICES

A BIRD SPECIES OBSERVED DURING CENSUS SURVEYS
IN NORTH-CENTRAL FLORIDA FARMLANDS ...... 128

B BIRD SPECIES OBSERVED ON ORGANIC FARMLANDS
OF NORTH-CENTRAL FLORIDA ....................... 133

C BENEFICIAL INSECTS OCCURRING ON SUNFLOWER
AND CROP VEGETATION ............................. 138


BIOGRAPHICAL SKETCH .................................... ............. 140














Abstract of Dissertation Presented to the Graduate School
Of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

ASSESSMENT OF THE POTENTIAL FOR INTEGRATION OF AVIAN
CONSERVATION WITH MODERN AGRICULTURAL PRODUCTION

By

Gregory Alan Jones

December 2003

Chair: Kathryn E. Sieving, Associate Professor
Major Department: Wildlife Ecology and Conservation


The overall goal of my research was to assess the potential for integrating

bird conservation on farmlands while enhancing production goals through

augmentation of insect pest control. Working on selected conventional and

organic farms in North-central Florida my study objectives were to: 1) assess

habitat characteristics on and adjacent to farms influencing avian species diversity

and insect-foraging activity, and to identify 'functional insectivores' on these

farms, 2) determine the effectiveness of sunflower intercrops as refugia for both

insectivorous birds and beneficial insects in cropped fields, and as tools to

enhance insect-foraging by birds in cropped areas, and 3) test the hypothesis that

insectivorous birds can potentially augment pest control programs involving

hymenopteran parasitoid predators, via preference for unparasitized over

parasitized prey.









Using a combination of bird surveys and focal foraging observations over

2 years, I determined that bird diversity in cropped and non-cropped habitats on

farms varied in the following ways: a) vegetation type in field borders

significantly influenced species richness per census point (F5,30 = 3.5, P = 0.013)

and in field borders (F5.30 = 3.8, P = 0.009), b) mixed crops generated

significantly greater bird densities per point (F,3o = 7.4, P = 0.011) and in cropped

fields (Fi,30 = 8.2, P = 0.008), and c) foraging activity and abundance of

functional insectivores were greatest in mixed crops (F1,29= 4.2, P = 0.051). In a

replicated, controlled field experiment I determined that intercropping rows of

sunflowers significantly increased densities of birds (F2," = 43.33, p< 0.001),

numbers of individuals (F.,, = 59.84, p < 0.001), and foraging time by individual

insectivores in crops (F,,,9 = 51.93, p < 0.001). Visual observations and stomach

samples confirmed that birds consumed economically important pest insects. In

experimental feeding trials, blackbirds exhibited no preference between

parasitized and non-parasitized lepidopteran larvae of similar body size (Wo =

139, p = 0.69) but a significant preference for larger non-parasitized prey (Wo =

248, p < 0.001). My study suggests that farmlands can be managed to enhance

wild bird populations and the potential that birds could augment pest control

programs in modem agricultural operations.















CHAPTER 1
INTRODUCTION


The relationship of birds to agricultural activities in the temperate zones of the

Northern Hemisphere has long been of interest to ornithologists both in the United

States and in Europe. Early naturalists published numerous papers describing careful

observations and thoughtful consideration of the relation of birds to crop production.

During its existence, multiple reports produced by the Section for Economic

Ornithology within the federal Department of Agriculture confirmed the utility of

birds as destroyers of pest insects, often recommending their classification as highly

beneficial to agriculture. However, with the advent of farm mechanization, synthetic

chemical pesticides, and the intensification of agricultural production, focus upon the

positive impact birds may have on agriculture waned and research interest regarding

the detrimental effect agriculture has on avian populations increased. Currently

ornithologists have suggested that change in agricultural practices and landscape

structure over the past few decades have reduced the occurrence of farmland habitat

elements many farmland species had traditionally utilized (O'Conner and Boone

1990, Freemark 1995, McLaughlin and Mineau 1995).

Rodenhouse et al. (1995) believe that agriculture has had a greater impact on

the status of Neotropical migratory birds than any other human activity. Additionally,

their review also shows that conservation measures benefiting avian species in









agricultural landscapes will be acceptable to farmers if management

recommendations have neutral or positive effects on food production. Sufficient

evidence has accumulated from studies in forest, grassland, orchard, and row

cropping systems that offers sufficient evidence that insectivorous birds may be of

economic value by enhancing production through predation of pest insects. Due to

this potential ecological role of birds in agroecosystems, several reviewers of past

work, including McFarlane (1976), Jackson (1979), and Kirk et al. (1996), suggest

birds should be considered as components of modem biological pest management

schemes. However, despite potential values of birds on farms, the theory and practice

of enhancing these native natural enemies by providing habitat for them within

cropping systems has been relatively neglected.

Ornithologists have an opportunity to propose management recommendations

favoring avian conservation within agricultural production systems by working within

interdisciplinary teams developing modem sustainable or natural systems agriculture

(Rodenhouse et al. 1995). As agricultural producers recognize the importance of a

structurally and biologically diverse fanned environment, ornithologists can institute

the resurrection of quality avian habitat within agroecosystems. Enlightened

management of farmlands can satisfy the needs of agriculture and numerous avian

species while providing mutual benefits (Rodenhouse et al. 1995).



Economic Ornithology The First Attempt to Integrate Bird Conservation
and Agricultural Production

Early naturalists in this country, such as Alexander Wilson, James Audubon,

and even Benjamin Franklin, became interested in bird behavior and made references









to the purely economic phases of bird life. Their writings repeatedly relate the value

of different species as destroyers of insects. After 1850, various researchers

interested in agriculture published numerous papers in agricultural journals and in

reports of agricultural and horticultural societies that described careful observations

and thoughtful considerations of the relation of birds to crop production (reviewed by

Weed and Dearborn 1935). Needless to say, these publications generated a great deal

of discussion as to the true utility of birds, because some bird species had long been

considered agricultural pests.

One of the results of the organization of the American Ornithologist's Union

(AOU; circa 1883) was the impetus it gave to the study of bird's food habits to

resolve questions of their utility as pest predators and the desirability of legislation

permitting the destruction of species popularly considered pests. At the request of the

AOU and researchers within the Department of Agriculture, congress appropriated

monies to establish a Section for Economic Ornithology (SEO) within the Division of

Entomology of the federal Department of Agriculture (McAtee 1933). The section

was responsible for the promotion of economic ornithology (or the study of the

interrelation of birds and agriculture), the investigation of avian food habits, the

investigation of both resident and migratory birds in relation to both insects and

plants, and publish reports thereon (McAtee, 1933, Weed and Dearborn 1935).

Research emphasis at this time consisted of the examination of the contents of

bird stomachs, together with observations of birds in the field. Multiple reports

produced by the SEO confirmed the utility of birds as destroyers of pest insects and

as important weed seed predators. Reports of this nature submitted to the USDA's









administrators often concluded that birds feed largely upon pest insects and should be

classified among the species highly beneficial to agriculture. The section later

developed into the original Biological Survey, and research of this kind continued

until the early 1930s (Weed and Dearborn 1935, Kirk et al. 1996). However, with the

advent of synthetic chemical pesticides in the 1940's, little work in this field has been

done (Kirk et al. 1996). Currently, avian research performed by the USDA focuses,

for the most part, upon control of crop damage by birds. While focus upon the

positive impact birds may have upon agriculture waned, research interest regarding

the detrimental effects agriculture has had on birds has increased since the 1940s.



Effects of Agricultural Practices on Avian Populations

Agricultural development since the 1700s has dramatically altered or

eliminated the natural landscape of the continental United States. Forests originally

covered about one-half of this region of North America, 40% was covered in

grasslands, and the remaining area was arid and barren (Cochrane 1993). Between

1790 and 1890, 300 million acres of virgin forests were cleared and an equal amount

of grasslands were plowed. Agriculture today comprises the largest landuse class

encompassing over 50% of the arable land area of the contiguous 48 states (USDA

1998). Currently, of the 1.9 billion acres of land in the U. S., some 350 400 million

acres are under intensive crop cultivation with approximately another 200 million

acres of marginal land at the ready to be put into this practice should prices warrant

its use (Cochrane 1993). While the conversion of natural landscapes to

agroecosystems in Europe occurred much earlier in history, this alteration took place









steadily across several centuries, and agricultural lands now comprise 41% of the land

area of the 15 countries of the European Union (Pain and Dixon 1997).

Agricultural practices on farmlands have changed drastically over the past 150

years. The concept of farm mechanization was widely accepted in the 1850s,

characterized by the use of cultivators, mowing machines, and reapers (Cochrane

1993). From this point farm machines evolved rapidly; increasing in size and

efficiency and incorporating both steam and then internal combustion power.

Increased size and efficiency of farm machinery in the post World War 2 years

allowed for the expansion of field size and homogenization in farmland structure.

During the period from 1935 to 1970, while the acreage of land under cultivation did

not change the number of farms declined from 6.8 million to 3 million via corporate

consolidation concomitantly with an intensification of production per unit area

(Cochrane 1993). This same phenomenon occurred in post World War 2 Europe

including increased field sizes, reductions or elimination of boundary features, and an

overall change in agricultural landscape structure (Pain and Dixon 1997).

Many researchers here in the U.S. have suggested that changes in agricultural

practices over the past few decades have reduced the favorability of agricultural

landscapes for foraging and nesting by many native and migrant species (Best 1986,

O'Conner and Boone 1990, Wamer 1992, Bollinger and Gavin 1992). The once

heterogeneous landscape found in agroecosystems composed ofwoodlots, ponds,

shelterbelts, wooded hedgerows and fencerows, and other such landscape elements

provided for an abundance and diversity of bird species. However, these landscapes

have become increasingly homogenized through the removal, fragmentation, and









isolation of these elements upon which many species had come to depend (O'Conner

and Boone 1990). For example, Gawlick and Bildstein (1990) attribute the decline of

Loggerhead Shrikes to loss of their preferred edge habitat in farm landscapes. This

same sentiment has been voiced by researchers in Europe relating that increased

specialization has reduced the prevalence of mixed farming and the habitat mosaics

inherent to traditional types of farming (O'Conner and Shrubb 1986, Baillie et al.

1997). Groppali (1993) related the percentage of eradication of tree rows and hedges

to expand cultivated parcels within his study area near Cremona, Italy, was 33% and

36% respectively over a 9-year period, 1980-1989. In these parcels where tree rows

and hedges had been removed, species diversity and numbers of nesting pairs of birds

were significantly reduced. In Britain, Baillie et al. (1997) found that more farmland

birds are declining than increasing, and more importantly, specialist farmland species

are declining more than generalists due to loss of preferred farmland habitat.

Within the U.S., resident and migratory landbird passerines, represented by

over 200 different species, constitute over 70% of the bird species that feed, roost, or

breed on agricultural lands (Rodenhouse et al. 1993). Most landbirds utilizing crop

fields and edges are Neotropical migrants, and agricultural practices have been

implicated in the decline of at least nine of these species currently listed as threatened

or endangered. Studies in U.S. farm landscapes have found the majority of bird

species utilizing agricultural lands are found in uncultivated areas. Highest species

richness and abundance have been documented in those areas with greatest vegetative

structure, including woody shrubs and trees. Avian richness and abundance are often

lower in grassed edge, and lowest in row cropped fields (Shalaway 1985, Best et al.









1990, Camp 1990). Therefore there appears to be a strong correlation between

decreasing species richness and abundance and decreasing structural diversity in farm

systems. Similar results have been obtained in European studies (Baillie et al. 1997).

Production practices associated with agricultural intensification are also

problematic for birds utilizing agricultural landscapes. Intensive agricultural

practices include greater working of the land with quick rotations or relay cropping,

cover crops replacing fallow rotations, increased livestock densities, and use of high

yielding cultivars requiring greater or more frequent fertilization and irrigation

(O'Connor and Boone 1990). Rodenhouse et al. (1993) indicated that Breeding Bird

Survey abundances of many bird species in agricultural landscapes have exhibited

significant negative associations with specific crops between 1973-1989, suggesting

detrimental cropping practices are being employed. Multiple quick crop rotations

within a year, or relay cropping, increases the frequency of disturbance during avian

breeding potentially causing direct injury to adults and nestlings. Injury and nest

destruction by farm machinery can occur during field preparation, planting, crop

management, and harvest operations. Individuals can also be harmed indirectly

through the application of herbicides and insecticides that alter vegetation structure

and the insect food base within and immediately surrounding cultivated parcels

(O'Conner and Boone 1990, Rodenhouse et al. 1993). In their publication Birds in

Europe, Tucker and Heath's (1994) analysis of the major threats to birds listed as

species of conservation concern showed that agricultural intensification affects more

species than any other threat.









Birds as Predators in Agroecosystems

While the detrimental effects of modem agriculture on birds has received

much attention, the importance of wild bird management to enhance the productivity

and sustainability of agriculture, or to maintain ecological integrity and biodiversity

in agroecosystems, has not been thoroughly investigated (Rodenhouse et al. 1993,

Kirk et al. 1996). Rodenhouse et al. (1993) suggest that the development of lower

input sustainable agriculture and acceptance of integrated pest management (IPM)

programs may offer opportunities for greater avian conservation in agroecosystems.

Most importantly, management of uncultivated habitats (where birds may thrive) to

preserve natural enemies of agricultural pests will become a central part of pest

management planning in IPM (Rosen et al. 1996). The conservation value for bird

species utilizing low-input agricultural landscapes will be realized through the

reestablishment of habitat (i.e. Woodlots, windbreaks, complex hedgerows, etc.) and

an increase in food resources enhancing both their survival and reproductive success.

Rodenhouse et al. (1995) believe that the key to acceptance of conservation measures

that benefit avian species in agricultural landscapes is that management

recommendations do not interfere with, and hopefully enhance, production. Here lies

an important opportunity for ornithologists. By illustrating that birds may be of

economic value by enhancing production through predation of pest insects, farmers

could be encouraged to consider providing habitat for these species in their cropping

systems and farm landscapes.

Studies relating individual pest species to individual bird species or groups of

species offer sufficient evidence that birds can and should be considered as an









important component of modem biological pest management schemes (Jackson

1979). Birds are important predators of many destructive forest insects and play an

important role in suppressing phytophagous insect populations in forest ecosystems

(reviewed by Takekawa et al. 1982, McFarlane 1986, Price 1987). Moreover, via

numerical and functional responses to insect outbreaks in North America birds are

potentially decreasing insect outbreak frequency and severity (Holling 1988, Dahlston

et al. 1990, Holmes 1990). Limitation of phytophagous insect biomass in these

systems may have an important effect upon primary productivity within forest

systems. For example, Marquis and Whelan (1994) have demonstrated that exclusion

of insectivorous birds from foraging on phytophagous pests of white oak in Missouri

significantly reduces long-term primary productivity of individual trees. Over several

years, trees harboring insectivorous birds had greater leaf area and stem elongation

than did trees where birds were excluded or in trees that were sprayed with

insecticide. Conceivably, birds utilizing agricultural areas could provide similar

biomass reduction and productivity benefits, which could be realized through

appropriate management practices (Rodenhouse et al. 1995, Kirk et al. 1996).

Over the past 10 years, field entomologists and agronomists have increasingly

recognized that conservation of natural enemies via management of non-cropped

habitats that support them is important to effective and successful biological control

in agricultural systems (Rosen et al. 1996). However, despite its demonstrated value,

the theory and practice of enhancing native natural enemies as integral components of

agroecosystems has been relatively neglected (Picket and Bugg 1998). If a low-input

productive balance is to be restored within agroecosystems, farmers must recognize









and make use of natural control of insect pests by providing for the needs of all

potential predators of pest insect within these systems. As was recognized long ago

by economic ornithologists, most birds that traditionally utilize agricultural areas may

be of great economic value by providing biological stability in agroecosystems.

Conservation of beneficial insectivorous birds through habitat enhancement on farms

could result in significant economic benefits to agricultural production by reducing

pest control costs and improve sustainability through reduced reliance upon persistent

toxic agrochemicals.



Examples of Experimental Work Investigating the Impact of Birds
on Insect Populations in Modern Agroecosystems

Since 1950, several studies have focused upon 2 pests of field crops, corn

borers and grasshoppers, utilizing exclosures to compare insect populations protected

from bird predation (Kirk et al. 1996). Both Floyd et al. (1971, 1969) and Black et al.

(1970) reported significantly lower survival of overwintering corn borer larvae found

in corn stalks exposed to bird predation compared to those present within exclosures.

As overwinter losses were normally low due to other factors, they concluded these

were destroyed via predation by birds [such as Northern Flickers (Colaptes auratus)]

observed feeding on corn stalks. Numbers of larvae removed compared with the

numbers remaining in infested stalks where birds had been excluded ranged from

45% to over 80% in these studies. Quiring and Timmins (1988) found similar results

of reduced corn borer larvae overwinter survival due to predation by American Crows

(Corvus brachyrhynchos) in southwestern Ontario, Canada. Additionally, corn borer









larvae removal was found to be greatest in those fields nearest one of the largest

known crow roosts in the region.

Exclusion studies of bird predation impact upon grasshoppers in rangeland

systems (frequently grasslands are interspersed with row cropping fields) have

produced mixed results. While Belovsky et al. (1990) determined birds had a minor

impact on grasshopper populations, other studies indicated that birds do affect

grasshopper densities and species richness. Joern (1986) concluded that avian

predation can have a significant impact on grasshopper populations through biomass

reduction and reduction of species diversity. Modeling this, Kirk et al. (1996)

estimated that a grasshopper-eating passerine family unit could consume 3.7 kg of

grasshopper biomass, or approximately 149,000 individuals per breeding season. In a

grassland system of Northwest China, numbers of breeding Rosy Starlings (Sturnus

roses) were increased after human made nesting sites with shrubby cover and water

were added (Olkowski and Zhang 1998). Researchers determined grasshopper

numbers were reduced from 42 to 2.3 per m2 within a 500 m radius around artificial

nesting structures by the end of the birds' breeding season (Chen 1986, Olkowski and

Zhang 1998).

Two recent exclosure studies have evaluated the impact of bird predation on

foliage arthropods in coffee plantations and lepidopteran pests in an orchard system.

Greenberg et al. (2000) found birds reduced the abundance of large arthropods on

coffee plants by 64-80%, compared to that those found on plants where birds were

excluded, depending on the coffee system type (shade or sun coffee). A significant

reduction in leaf damage to coffee plants was associated with this reduction in









arthropod biomass in both coffee systems. Mols and Visser (2002) found that

caterpillar damage levels to apples in orchards decreased with increased periods of

foraging by great tits (Parus major). Overall damage to apples by caterpillars was

reduced by measurable amounts improving yield, number of apples per tree,

compared to trees where great tits were excluded.

Both McFarlane (1976) and Kirk et al. (1996) conclude that strong

experimental evidence in forest and grassland systems suggests avian predation could

suppress crop insect pest populations at medium or low infestation levels,

representing an important ecological in agroecosystems would compliment integrated

pest management plans. While birds alone may not "regulate" insect pest

populations, combined with other forms of pest management, they promise to play an

important ecological role in agroecosystems (Kirk et al. 1996). Sympathetic

management is needed to stem the decline of farmland birds and enable them to

assume a mutualistic role with agricultural production.



Natural Systems Agriculture or Ecoagriculture

Agricultural modernization largely contradicts ecological principles.

Consequently modem, or "conventional", agroecosystems are inherently unstable,

plagued by recurrent pest outbreaks, pollution of water systems, soil erosion,

salinization, and other undesirable environmental and social costs (Altieri 1994).

Modem agriculture emphasizes artificial single species monocultures, requiring

constant human intervention to suppress ecological succession and maintain

productivity (Swift and Anderson 1993). Additionally, simplification of species









composition of biological communities both reduces their stability and results in

increased susceptibility of that community to invasion by undesirable species (Elton

1958, Crawley 1987). Therefore, conventional agriculture exists in a metastable

equilibrium regulated by enormous inputs of energy (Harwood 1990) and human

activity (Gliessman 1987). The inherent self-regulation of populations within natural

biotic communities is lost when humans modify community interactions and disrupt

coevolutionary processes (Tumbull 1969). Inherent limitations of species populations

within natural communities is a desirable attribute to incorporate into synthetic

agroecosystems (Tumbull 1969) and, in particular, enhancement of predator-prey

relationships characteristic of natural systems has a pivotal role to play in the

evolution of agriculture towards more environmentally sustainable systems in this

century (Atkinson and McKinlay 1997).

An ecosystem approach to agriculture emphasizes management of

agroecosystems in such a manner that sufficient food production will be sustainable

and of high quality with minimal environmental disturbance (Colby 1990, McNeely

and Scherr 2003). Utilizing this approach, it is believed that a multitude of beneficial

ecological processes can be incorporated into agroecosystems (Soule and Piper 1992).

The central idea for "ecological agriculture" is that the structures of native biological

communities are the most appropriate structural models for agriculture. Such

communities have developed and endured in particular environments as a result of

centuries of evolutionary selection for ecosystem function (The Land Institute 1999,

McNeely and Scherr 2003). Agricultural systems that are modeled after natural

ecosystems should exhibit many functional attributes and processes that stabilize









natural systems, including vegetation adapted to the local climate, closed nutrient

cycling, effective resource partitioning, soil preservation, and biological methods of

crop protection (Soule and Piper 1992). Therefore, by mimicking the local natural

vegetation structure of native biological communities, farmers can emulate a whole

package of patterns and processes that have developed over an evolutionary time

frame exhibited by these ecological systems. Additionally, rather than perfecting one

crop at a time, this holistic ecological perspective to agricultural production suggests

seeking out a collection of plants and animals that work well together. It is this

perspective of natural systems agriculture that provides a great opportunity for avian

conservation.

The potential exists to manage farm habitats to attract selected desirable

species in greater numbers in order to create a stable guild of insect predators, capable

of rapid aggregation to high density "hot spots" of colonizing pests, and capable of

switching to pest species from alternative foods (Helenius 1998). Methodologies that

promote the abundance and diversity of pest insect predators will not only

significantly contribute to non-chemical based crop protection but also provide

beneficial consequences in conserving biological diversity in agricultural landscapes.

Habitat management to enhance biological control of arthropod pests can provide

various environmental requisites to pest insect enemies (such as birds) including

modified climate, protective cover, nesting habitat, and supplementary foods (Pickett

and Bugg 1998). Colonization, dispersal by diffusion, and foraging movements of

beneficial predators can be influenced through habitat modifications within cropping

systems (Helenius 1998). For example, weedy vegetation strips within fields could









be arranged in such a way as to provide refuge and increase interspersion of foraging

predators within large cropped areas (Nentwig 1998). Modifying agricultural

landscapes, or "farmscaping," by adding features such as hedgerows, field margins,

shelterbelts, and roadside and watercourse plantings using native trees, shrubs,

perennial grasses, and herbaceous and annual broadleaf species can attract and sustain

beneficial arthropod pest predators (Bugg et al. 1998).

Ornithologists have an opportunity to propose management recommendations

favoring avian conservation within agricultural production systems by working within

interdisciplinary teams developing modem sustainable or ecoagriculture. The largely

unexplored diversity of avian insect predators that could be included in natural

biological regimes offers numerous possibilities for their use in cropping systems.

Birds of conservation concern, both resident and migratory, can benefit from

cropping systems and farmland habitat structure created to enhance insectivorous bird

use of agroecosystems. Through this effort, many habitat features and the structural

complexity once found within agricultural landscapes supporting avian species in the

past would be reintroduced. As agricultural producers recognize the importance of a

structurally and biologically diverse farmed environment, ornithologists can institute

the resurrection of quality avian habitat within agroecosystems. With enlightened

management of farmlands both the needs of agriculture and numerous avian species,

as well as other wildlife, can be satisfied and mutually beneficial (Rodenhouse et al.

1995).









Research Needs

Before we can propose that agricultural producers can truly employ birds in

pest management schemes we must not only know the relationship between insect

pests and avian species, we must have an understanding of the functional role birds

currently play in modem agroecosystems. With this understanding, management

recommendations for biological control enhancement can be developed by

manipulating populations of avian species identified as potentially beneficial

currently existing in, or that could be attracted to, these systems. Rodenhouse et al.

(1995) state that future research should focus upon identifying farmland structures

and agricultural practices that create and sustain avian populations. They explain that

studies of annual breeding productivity and survival of birds nesting in fields and

edges are few, potential source areas that may require protection or expansion have

not been identified, and the values of specific landscape elements and combinations

of elements have not been determined for agroecosystems. Therefore, they believe

that both field-scale and landscape scale studies need to be performed and integrated.

Kirk et al. (1996) believe that a consideration of birds should be part of any

economic cost/benefit assessment related to pest control programs and farm

landscapes should be managed with them in mind. They state that more

multidisciplinary studies are needed to examine: (1) the abundance and availability of

birds relative to various insect pest species, (2) avian diets and foraging habits to

determine quantitatively the site-specific level of predation on invertebrate pest

species compared to other arthropods, (3) integration of birds with other natural insect

enemies, and (4) management of farmland landscapes in ways that best augment









natural control of insect pests. Wratten et al. (1998) indicate the potential for the

expansion of research exploiting ecological knowledge in farmland management is

promising. They suggest that a better understanding is needed of 3 related processes:

(1) the spatial scale dynamics of beneficial insect predators on farmland, (2) the

potential negative effects of insect predator refugia, and (3) the mechanisms involved

in the functioning of within-field and border refugia for the enhancement of natural

enemies of insect pests in agroecosystems.



Conclusion

Ornithologists have suggested that change in agricultural practices and

landscape structure over the past few decades have reduced the favorability of

farmland habitat elements many farmland species had traditionally utilized.

Agricultural landscapes have become increasingly homogeneous through the

removal, fragmentation, and isolation of these elements upon which many species had

come to depend. Intensification of agriculture, resulting in changes in production

practices, has also been cited as being problematic for birds utilizing agricultural

landscapes. Direct injury to individuals and nest destruction can be caused by farm

machinery during cropping operations. Individuals may also be harmed indirectly

through the application of agrochemicals. Holistic ecological perspectives to

agricultural production of both sustainable and natural systems agriculture provide an

opportunity to promote the inclusion of suitable habitat in agricultural lands for avian

species. Farm habitats can be managed to attract desirable insect pest predator

species in greater numbers contributing to non-chemical based crop protection as well









as improve conservation of biological diversity in agricultural landscapes. Migratory

and resident species of conservation concern will also benefit from farm structure and

management created to enhance avian presence in agroecosystems.

Recommendations developed by the ornithological community integrating the

body of information defining the problems faced by farmland birds with research

illuminating the functional role birds play in these systems, can potentially reverse

agricultural practice-induced avian population declines. Aldo Leopold stated,


In its extreme form it [agriculture] is humanly desolate and economically
unstable. These extremes will someday die of their own too much, not
because they are bad for wildlife, but because they are bad for farmers.
When that day comes, the farmer will be asking us how to enrich the wildlife
of his community. (Leopold 1945, page 168)

As imperatives for agricultural shift from the single goal of increasing production per

acre to environmentally sustainable systems, an excellent opportunity exists to match

the aspirations of farmers with needs of birds of conservation concern.















CHAPTER 2
AVIAN BIODIVERSITY AND FUNCTIONAL INSECTIVORY ON NORTH-
CENTRAL FLORIDA FARMLANDS


Introduction

Although agroecosystems do not support the biodiversity of natural landscapes

they replace, under the right circumstances they can provide diverse ecological functions

in addition to habitat for wild species. In regions where urbanization is rampant (e.g.,

Florida) farmlands are often the only ecological buffer between natural ecosystems and

suburban sprawl (Evans and McGuire 1996, McNeeley and Scherr 2002). Reflecting

growing public concerns over scientific reports of agriculture's negative effects on

human and ecosystem health (e.g., Parsons et al. 2000) during the past decades, policy

makers have been responding with incentives to modify grower operations to reduce

negative environmental impacts and increase ecological values of farmlands (Ikard 1996,

D'Souza and Ikerd 1996). For example, USDA programs like SARE (Sustainable

Agriculture Research and Education) promote development of sustainable agricultural

practices through research partnerships between farmers and scientists

(http://www.sare.org/htdocs/sare/about.html). Additionally, the Farm Bill of 2002

provides farmers monetary incentives for conservation of soil, water, air, and biodiversity

(Farm Security and Rural Investment Act of 2002). Signs of change toward ecological

agriculture include an increase of 10% per year in US farmland acreage under certified

organic management (USDA 1996, 2000, 2001a). With the public, policy makers, and









farmers increasingly involved in exploring alternative agriculture, the need for research to

integrate production of ecological services, native biodiversity, and healthy foods is also

intensifying (Rodenhouse et al. 1995, McNeeley and Scherr 2002).

Wildlife conservation is a natural partner in cultivating ecological agriculture

(Vandermeer and Perfecto 1997, McNeeley and Scherr 2002), yet this partnership is

weak because conventional food production practices that are detrimental to biodiversity

still dominate, and because research has not been satisfying demands for information for

ecologically-oriented farm operations (Hess 1991, Alston and Reding 1998, Jacobson et

al. 2003). Habitat destruction for agricultural expansion remains the single most

important cause of biodiversity impoverishment the world over (Vitousek et al. 1997),

and if native biotas are to survive the coming decades of human population expansion,

agricultural production lands must improve their biodiversity-holding capacity (Pimental

et al. 1992, Hobbs and Norton 1996). Indications are that alternative agriculture practices

encourage native wildlife and protect ecosystem services better than conventional

production agriculture (Warburton and Klimstra 1984, Pimental et al. 1992, Uri et al.

1999, McNeely and Scheer 2002), in part because sustainable farming generates

heterogeneous vegetative environments with features (hedge rows, shelter belts, mixed

cropping systems, and plantings that host natural enemies of pest species; O'Conner and

Boone 1992) that encompass many recognized values for both wildlife and people (e.g.,

wild flowers, pollinators, and game; Daily 1997a). Conventional agriculture, however,

still dominates human landscapes in the developed world, to the detriment of native

biodiversity. For example in the U.S., over 200 native species of resident and migratory

birds feed, roost, or breed on agricultural lands (Rodenhouse et al. 1993), but many of









their populations decline by 50% or more where expansive monocropping systems with

short rotation periods, heavy chemical inputs, and intensive mechanization reign

(O'Conner and Shrubb 1986, Rodenhouse et al 1993, Freemark 1995, McLaughlin and

Mineau 1995; bird declines in Europe see, Pain and Dixon 1997, Pain and Pienkowski

1997, Ormerod and Watkinson 2000).

Ecological research on farmlands would help the shift to ecologically sustainable

agriculture, but research to foster ecological integrity on farms is scarce (Cochrane 1993,

McNeely and Scheer 2002), despite numerous encouraging factors: 1) considerable

public interest, 2) diverse ecological values of farmlands, 3) an enormous area on the

earth's surface in which to work (950 million acres in the U.S.; USDA 1999), 4) global

biodiversity conservation needs to prioritize farmlands, because current parks and

reserves are insufficient and, 5) farmlands are relatively easy to restore to native

ecosystems (Askins 2000, McNeely and Scheer 2002). One reason for lack of interest in

conservation research in agroecosystems is that agriculture is a business and ecologists

have largely failed to show how biodiversity conservation and ecological functionality

can realize economic benefits for growers (Daily 1997b, McNeely and Scheer 2002). A

priority area of interest to growers has always been pest control. Whereas bio-control

programs focus primarily on invertebrate predators on pests, little work has been done to

integrate vertebrate species into row crop agricultural systems. In this study I assessed

the potential that native bird species could serve as effective predators of pests. I

examined factors influencing avian species diversity on North-central Florida farmlands

and, in particular, factors that increased insect-eating activity by wild birds in cropped

fields. Goals for this study were two-fold: 1) to assess overall avian biodiversity (species









richness and densities) on a selection of conventional and certified organic farms, and

identify farm characteristics (management and vegetative structural features) correlated

with bird diversity, and 2) to identify 'functional insectivores' among the bird species

utilizing farmlands (or, those species that we observed to feed frequently on insect prey

in cropped fields), and to identify farm characteristics (management and vegetative

structural features) correlated with the densities of functional insectivores in cropped

fields.

Study Design

Certified organic farming is defined as crop production without the use of most

conventional pesticides, synthetic fertilizers, sewage sludge, or bio-engineered food

plants (USDA 2002). Other works have shown that both birds and insect biomass can be

higher on organic, or low input, than conventional farms (birds: Christensen et al. 1996,

Chamberlain et al. 1999, Freemark and Kirk 2001, Beecher et al. 2002; insects:

Dritschillo and Wanner 1980, Hald and Reddersen 1990, Brooks et al. 1995, O'Leske et

al. 1997, Feber et al. 1997 & 1998). Therefore, in this investigation of factors affecting

bird diversity, abundance, and insect foraging paired sampling sites were selected on both

organic and conventional farms. In addition to censusing the bird community over 2

years (2000 and 2001), extensive foraging observations were conducted on individual

birds in cropped areas, and both field scale features (crop type, field border vegetation)

and type of matrix adjacent to each sampled field were characterized as predictors of both

bird diversity and foraging activity on the two farm types. I define functional

insectivores as bird species that were observed most commonly feeding on insect prey

taken from crop vegetation. All of my study species have been classified in the literature









according to well-established foraging guilds (e.g., frugivore, insectivore, omnivore)

based on their most typical or average annual diet composition across the US (De Graaf

et al. 1985). However, many birds' diets vary with season, and both typical frugivores

and omnivores can be highly insectivorous during breeding efforts (Beal et al. 1941,

Martin et al. 1951, Ehrlich et al. 1988). Therefore, rather than using 'typical' dietary

guilds to classify how birds might be interacting with insect pests, I wanted to know

which species were frequently out in fields eating insects during the spring growing

seasons on the farms studied. The most abundant of these insect-foraging species were

designated as functional insectivores or those most likely to consume insect biomass

with positive economic outcomes for farming operations.


Methods

Research Site Selection

With the aid of University of Florida Cooperative Extension agents, and following

farmer participation in surveys (see Jacobsen et al. 2003), local producers were contacted

to obtain permission for conducting research on their properties. A total of 30 census

points were established on certified organic farms during April of 2000, and a paired

reference site for each of these points on a nearby conventional farm was established (n =

60 total points, 10 organic and 10 conventional farm properties) in an effort to match crop

types, habitat structure, field border types, and matrix vegetation where possible (after

Rogers and Freemark 1991, Christensen et al. 1996, Chamberlain 1999). In 2001, one of

the organic farms sampled in 2000 was not planted, thus 5 fewer points were used in the

second year of the study. The 20 farm properties ranged in size from 4 to 104 ha located

within Alachua, Gilchrist, Marion, and Jefferson Counties of North-central Florida.









Patterns of Bird Diversity

Census surveys

Surveys were used to estimate bird species richness and density in cropped and

non-cropped habitats on farms. Birds were censused utilizing point count methods

described in Bibby et al. (1992) with modifications recommended by Freemark and

Rogers (1995) to suit agricultural landscapes. Sampling points of 50 m radius (fixed)

were situated on the border of cropped fields with non-cropped areas (Figure 2-1).

Census points were at least 200 m apart if they occurred on any single farm management

unit. All points were sampled a minimum of 4 times between 25 April and June 30 in

both 2000 and 2001, and order of visitation to sites in the pair (organic vs. conventional)

and the order of points visited on each farm management unit were reversed each visit.

Censuses were conducted between dawn and 1100 EST on fair weather days. All birds

seen or heard within the 50 m fixed-radius during a 10 min period were recorded.

Registrations were recorded and mapped onto two 1800 semi-circles (in the cropped field

and the un-cropped area after Freemark and Rogers 1995; Figure 2-1). By marking the

locations of individuals and noting their movements on maps this minimized the potential

of double counting individuals during counts. By censusing in this manner, I quantified

bird occurrences, both within cropped areas close to field edges and in adjacent non-

cropped habitats.

I began counting 2-3 minutes after arriving at each station. Birds occurring

outside of the circles or flying overhead were noted (see below) but excluded from point

count data, with one exception; I considered swallows or purple martins flying low (< 10

m above vegetation) over fields to be 'using' them (since they are likely to be foraging on















































Figure 2-1. Aerial view of a farm site in Alachua Co. illustrating 50 m radius point count
circle positioned on the edge of a cropped field where cropped field and field border
habitat type were characterized. Matrix type adjacent to each field was characterized
within a 200 m radius semicircle at each census point (after Freemark and Kirk 2001).









insects; see Boutin et al. 1999). Birds flushed within a count circle as an observer

approached or left a station were counted if they were not otherwise recorded during the

count period. If a flock was encountered, it was followed after the end of the sampling

period (if needed) to determine its composition and size. Because sampling occurred

during the breeding seasons only, singing males observed repeatedly during counts were

assumed to be paired breeders and were counted as two individuals (after Bibby et al.

1992). Walk-abouts were conducted in cropped and non-cropped areas on each farm unit

following point counts (Freemark and Rogers 1995). Only species not noted during the

formal point counts were recorded during walk-abouts.

Habitat classification: field-scale features and adjacent matrix type

Habitat characteristics associated with each census point were assessed at field

edges and in surrounding matrix (Figure 2-1; refer to Table 2-1). Field scale

characteristics of the farms were classified within each 50 m census point and included

whole-farm management type (certified organic or conventional), crop diversity (mixed

or mono crops), and field border habitat types (see Table 2-1). Matrix types that

dominated the immediate area adjacent to fields sampled were characterized within a 200

m (6.3 ha) radius semi-circle adjacent to the cropped field edge (see Freemark and Kirk

2001, Figure 2-1, Table 2-1). The dominant matrix type was identified as the one habitat

type covering the largest area within the 200 m semi-circle. Area of each matrix type

was measured within the semicircle plot utilizing ESRI ArcView software and the Xtools

extension package (Oregon Dept. of Forestry 2001) and 1999 digital ortho quarter-quad

aerial photos obtained from the Florida Department of Environmental Protection. Of the









Table 2-1. Predictor and response variables used in analyses. The representative scale of
measurement for each predictor variable is indicated in column 3. See text for clarification.


Variable Categories Scale
Predictor Variables
Year 2000
2001
Farm type Conventional Whole Farm
Organic Whole farm
Crop Mono 50 m radius census plot
Diversity Mixed 50 m radius census plot
Border type Crop 50 m radius census plot
Hardwood 50 m radius census plot
Hedge 50 m radius census plot


Pasture 50 m radius census plot
Suburb 50 m radius census plot
Pine 50 m radius census plot
plantation
Matrix type Crop 200 m radius semicircle
Hardwood 200 m radius semicircle
Pasture 200 m radius semicircle
Suburb 200 m radius semicircle
Pine 200 m radius semicircle
plantation
Response Variables
Density 50 m radius census plot


Species richness 50 m radius census plot Total # of species counted
Insect-foraging observed ** 50 m radius census plot Categorical (yes / no)
* 3 measures taken: whole point count circle, crop half, and field border half of circle.
** Only in crop half of point count circle.


Definition


Time (2 levels) included as
repeated measure in analyses
Conventional management
Certified organic management
Single crop species in field
2 or more crop species in field
Cultivated field in production
Broad-leaved trees > 5 m tall
Linear strip of woody
vegetation
Improved grassland: grazed
Residential development
Slash pine trees > 5 m tall


Cultivated field in production
Broad-leaved trees > 5 m tall
Improved grassland: grazed
Residential development
Slash pine trees > 5 m tall




Mean # of birds / ha









five matrix types (Table 2-1), the mean coverage for each primary matrix type was never

less than 62% (max 90%) of the 200 m radius semi-circle.

Determination of functional insectivores

In order to identify those species exhibiting the greatest potential as arthropod

pest predators in cropping systems a minimum of two 1-hour ad libitum foraging

observation sessions per census point were conducted during each of the two breeding

seasons (Robinson and Holmes 1982, Rodenhouse and Best 1994). Observations were

taken within the cropped portions of the 50 m fixed-radius point count circles. Foraging

data included identification of species observed to take invertebrate prey from crop

vegetation. Birds were determined to be insect foragers if they perched on, or flew low

over, crop vegetation while taking insect prey at least one successful prey capture had

to be observed for a bird to be designated as a forager. I then selected functional

insectivores, or those species most likely to have an impact on insect pests in cropped

areas, in the following manner from among the species documented to be taking insects

in cropped fields the ten species were picked that also occurred in the greatest densities in

the cropped areas (from point counts). The factors (field and matrix characteristics;

Table 2-1) associated with the highest recorded densities of the ten functional

insectivores were then assessed in cropped fields that were sampled (see Data Analysis).

Data Analysis

Bird diversity

Because of my initial expectation that farm management would influence avian

biodiversity, avifaunal differences between the organic and conventional farm sites

sampled was broadly assessed, including species lists, comparisons of total species









counts with Breeding Bird Survey data and Audubon Society occurrence data from

Alachua County (where most of the farms were located). Total species counts for each

farm were determined by totaling the number of species detected on point counts, species

noted inside cropped areas but outside the fixed radius during point counts, and species

detected during search surveys (walk-abouts for 30 min).

In order to determine how field and matrix characteristics influenced bird species

richness and density only point count data was used and analyzed in the following way.

The number of individuals and species counted in each circle was averaged over all

counts done in each circle in each year. Count data by crop versus field border portions

of each count circle were also separated out. Thus, for each count circle the following 6

response variables were derived: mean number of species per count circle, mean number

of species in the field border vegetation, mean number of species in crop vegetation;

mean density of birds per count circle (standardized to # of birds / ha), mean density of

birds / ha of field border, and mean density of birds / ha of crop. The three density

variables and the three richness variables were submitted to two separate repeated

measures multivariate analysis of variance (RM-MANOVA) with the following predictor

variables: year (as the repeated measure), farm type, crop diversity, border type, and

matrix type (Table 2-1).

Functional insectivory

Finally, to understand what farm-scale habitat features might influence

insectivory in cropped fields a univariate repeated measures analysis of variance

(RMANOVA) model was applied with the same predictor variables as above, and density

of birds (ten functional insectivore species only) detected only in the crop half of count









circles as the response variable.



Results

Bird Species Richness on Organic versus Conventional Farms

In statistical models of factors influencing species richness, farm management

(organic versus conventional) was never a significant predictor. However, on average,

more bird species were observed on (and unique to) organic than conventionally managed

farms (Figure 2-2, see Appendix A). A total of 64 different bird species were recorded in

point count censuses during the first field season (1 May 30 June 2000). Sixty species

were observed in or near organic crops, 49 in or near conventional fields, 45 were

common to both farm types, 4 were unique to conventional and 15 to organic systems.

Seventy-four species were counted in 2001 (25 April 30 June). Sixty-six of these

species were observed in or near organic and 58 in or near conventionally managed

fields, 52 species were common to both farm types, and 6 were unique to conventional

systems, and 14 to organic systems (see Appendix A). Together, the species observed

using farmscapes of North-central Florida represented 82 % of resident and migratory

landbird species listed as breeders in Alachua County (where most of our samples were

taken; Alachua Audubon Society 2003) and nearly all of those species noted in recent

Breeding Bird Surveys along the two routes monitored in the same county (USGS 2001a,

USGS 2001b; FFWCC 2003; Figure 2-2). I observed 24 listed species on organic farms

(18 state listed, 6 federally listed), and 18 listed species on conventional farms (14 state, 4

federal; see Appendix A). Of the five farms with the most bird species, 3 were organic

and 2 conventional. Finally, all 10 of the functional insectivore species (abundant insect-










100



90-



) 80-
C.
0
S70
E

60


50


40
6 ) o o
o Jo C
0 0 0 0





Figure 2-2. Number of landbird species known to breed in Alachua County, FL (Alachua
County Audubon Society 2003) and species documented on the two Breeding Bird
Survey routes (# 25013 and 25113; USGS 2001a, USGS b, Florida Fish and Wildlife
Conservation Commission 2003) compared to the number of species observed in organic
and conventionally managed farmlands of north-central Florida during the breeding
seasons of 2000 and 2001 (1 May 30 June, 25 April 30 June, respectively).









eating species observed in cropped areas) were observed in both organic and

conventional fields (see below).

Factors Influencing Bird Community Structure

Species richness

A RM-MANOVA model was constructed in the following way: year (2 levels) as

the repeated measure; mean number of species per point, per crop half, and per border

half of point count circles as response variables; farm type, crop diversity, field border

type, adjacent matrix type as categorical predictors; all main effects and 2-way

interactions were specified using Type III sum of squares. No within-subjects contrasts

(year effects) were significant (at alpha = 0.05), and only field border type had a

significant influence on species richness (per point; F5,30 = 3.5, P = 0.013, and field

border half of the count circle; F5,30 = 3.8, P = 0.009; see Figure 2-3 caption for multiple

comparison tests).

Bird density variation

Using the same RM-MANOVA model as above, with three different response

variables (mean densities of birds per point, per crop, and per border half of count

circles), again no effects of year were found, and only crop diversity significantly

influenced bird densities (per point; F1,30 = 7.4, P = 0.011, and per crop half of the count

circle; Fi,30 = 8.2, P = 0.008); fields with more than one crop type had higher bird

densities (Figure 2-4). All other factors and interaction terms were non-significant. I

noted that the two most abundant species sampled were Northern Cardinal and Northern

Mockingbird. Since these two species numerically dominated the data, and both are

known to be edge and disturbance associated (Ehrlich et al. 1988, Derrickson and

















12-






8-







41






0-
crop hardwood


hedge


* Per Point
* In Crop


pasture pineplan suburb


Field Border Type



Figure 2-3. Mean number of species detected per point, and in crop half of point count
circles (both years averaged). Error bars = 1 SE. Multiple comparisons tests (LSD)
indicate the following: hardwood and hedge borders generated significantly more species
per point than crop, pasture, or pine plantation borders (P < 0.03); hardwood borders
generated more species in crops than all other border types except hedges (P < 0.05), and
hedge borders generated more species in crops than pasture and pine plantation (P <
0.03).


0

0
.0


E
z
E
10
B










* Per Point
U In Crop


"""-


I II
mono
Crop Diversity


Figure 2-4. Mean densities of birds (all species) detected per point, and per crop half of
point (years combined) in mono-cropped and poly-cropped fields. Error bars = 1 SE.


mix
mix









Breitwisch 1992, Halkin and Linville 1999), I decided to re-run this analysis without

them to get insights about abundance variation of species with other kinds of habitat

associations. The same RM-MANOVA model was re-applied and again found no effects

of year but significant effects of crop diversity on densities of birds in crops (FI,29 = 10.5,

P = 0.003; higher densities in mixed crops). Border vegetation type was also found to

significantly affect densities per point (F5,29 = 3.8, P = 0.01) and in the crop (F5,29 = 4.1, P

= 0.006; see Figure 2-5 caption for multiple comparison tests), and there was a significant

interaction between adjacent matrix and field border vegetation types on bird densities in

the crop (F6.29 = 2.5, P = 0.044; Figure 2-6). Given that I did not have all combinations of

border and matrix types represented in my point count sampling, multiple comparisons

could not be run on the interaction. However, of the combinations sampled, the greatest

numbers of birds were observed in crops that were bordered by hardwood with adjacent

pine plantation matrix, bordered by hedge with adjacent hardwood, pasture, or pine

matrix, and in fields with pasture in both border and adjacent matrix (Figure 2-6).

Foraging activity in cropped fields: functional insectivory

After completing 2 h of foraging observations at each of the 60 census points each

year, I focused further sampling in each year on the 30 points with the most foraging

activity observed during the first two 1 h sessions (an additional 2 h of sampling at each of

30 points in each year for a total of 360 hours of foraging observations in cropped fields).

Of the 49 species of birds observed in or near conventionally managed crops during the

2000 breeding season, 14 species (29%) foraged in crop vegetation, and 23 of 60 (38%)

species on organic farms foraged in crop vegetation (see Appendix A). In 2001, 20 of 58

(35%) species on conventional and 36 of 66 species (55%) on organic farms actively















* Per Point
* In Crop


8-



V



a T
c


S2-






crop hardwood
crop hardwood


pineplan suburb


Field Border Type


Figure 2-5. Excluding Northern Cardinals and Northern Mockingbirds, mean densities of
all birds per point, and per crop half of point count circles, by field border type (years
combined). Error bars = 1 SE. Multiple comparisons tests (LSD) revealed the following
(P < 0.03): hardwood borders generated higher densities per point than all types except
hedge, and hedge generated higher densities per point than crop, pasture and pine
plantation. No multiple comparisons among border types for bird densities in crop half
of count circles were significant (although the main effect was).














12- Matrix Type
Scrop
11 hardwood
pasture
S 10 pineplan
,c *suburb
U 8--

17-

o 6-

5-

o 4

2-

I I


crop hardwood hedge pasture pineplan suburb

Field Border Type

Figure 2-6. Excluding Northern Cardinals and Northern Mockingbirds, mean bird
densities in crops given different combinations of field border vegetation type and
adjacent matrix vegetation type. Error bars = 1 SE.









foraged in cropped areas. In both seasons I noted that foraging activity was most common

in cropped areas with perching structures from which birds could survey for potential food

items. Densities of the ten functional insectivore species were significantly greater in the

crop half of census points that contained numerous perching structures (t = 6.13, p < 0.001,

N = 60). This was true whether the perch was manmade (e.g. an elevated sprinkler head)

or vegetative (e.g. sunflower or corn stalks) regardless of farm management type.

Of the ten functional insectivore species identified, only 4 are usually classified as

insectivores, one as a carnivore, and 5 of the ten species are normally considered

omnivores (De Graaf et al. 1985, see Appendix A), although all are known to be

insectivorous during the breeding season (Beal et al. 1941, Martin et al. 1951, Ehrlich et

al. 1988). Individuals of these species were observed to capture insects from crop

vegetation and either eat them immediately or carry them into adjacent matrix,

presumably to feed young. The two most abundant of the functional insectivores

(Northem Cardinals and Northern Mockingbirds; Figure 2-7) were also the most

abundant species overall (see above). Using a RM-ANOVA model (using the same

predictor variables and model structure as in the community structure analysis, above),

but only one response variable (mean densities of these ten species in cropped half of

count circles), no effect of year was found, and the only significant main effect was crop

diversity -mixed crop areas had more functional insectivores than monocrops (F.,29=

4.2, P = 0.051; Figure 2-8).












0.8 -



0.6

0

= 0.4 -



S0.2 -



0.0
blgr eabl inbu noca oror
brth gcfl losh nomo suta
Species

Figure 2-7. Mean densities of the ten functional insectivores observed in crop half of
census points. Species codes: blgr = Blue Grosbeak, brth = Brown Thrasher, eabl =
Eastern Bluebird, gcfl = Great Crested Flycatcher, inbu = Indigo Bunting, losh =
Loggerhead Shrike, noca = Northern Cardinal, nomo = Northern Mockingbird, oror =
Orchard Oriole, suta = Summer Tanager. Error bars = 1 SE.












A 5- I Crop Diversity
/ mixed
o0
> monocrop
15 4-


S-3-
to



4- 2

1-


I i
2000 2001
Year

Figure 2-8. Mean density often functional insectivores in fields with I (mono) or more
than 1 (mixed) type of crop planted, by year. Error bars = 1 SE.









Discussion

Avian Diversity on North-central Florida Farmlands

Avian species richness at census points (whole point and border half of count

circle) was strongly influenced by field border types, with hardwood forest and hedge

borders harboring the greatest diversity (Figure 2-3). This finding confirms the general

pattern that structurally complex windbreaks, hedgerows and field borders support more

complex farmland bird communities than conventional 'clean-farming' practices that

suppress non-crop vegetation (e.g. Osborne 1984, Green et al. 1994, Parish et al. 1994 &

1995, Chamberlain and Wilson 2000). Data analyses did not reveal any other field-scale

features or matrix types causing significant variation in the number of bird species

visiting the crop half of our point count circles. This is likely to be because the majority

of species attracted to habitats in fragmented farmscapes also utilize fields (see Appendix

A) and those few that do not utilize open fields are those that rarely come to the ground

(e.g., great homed owl, cedar waxwing, red-eyed vireo) or that have behavioral

limitations on entering open areas (e.g., Sieving et al. 1996).

Densities (species combined) of birds, however, varied significantly (among point

counts and in crop half of point counts) with border and matrix vegetation type and with

crop type. With or without Northern Cardinals and Northern Mockingbirds included in

the analysis, fields with mixed crops attracted greater numbers of individuals than mono-

crop fields (Figure 2-4), and when the two common generalist species were removed,

border and matrix habitat type also significantly affected bird densities in the crops and in

point count circles (Figure 2-5). Thus, removal of mockingbirds and cardinals was

important because as habitat generalists, their numerical dominance in our data could









have masked the responses of most species to the farmscape features we considered (see

Best et al. 1995). Hardwood and hedge field borders increased bird densities per point

(Figure 2-5; as they did number of species), and although it appears that hardwoods,

hedge, and pasture generated the highest densities in crops (Figure 2-5), the lack of

significant contrasts was probably due to: 1) the low densities of birds once the two most

abundant were removed and, 2) the significant interactions between border type and

adjacent matrix type.

Findings of this study support tentative generalizations emerging from larger scale

(landscape) analyses of bird distributions that have found blocks of hardwoods or natural

grassland adjacent to cropped areas tend to generate the highest bird diversity on

farmlands (Best et al. 1995 and 2001, Kirk et al. 2001), and that total area and

juxtaposition of vegetative cover types comprising recognizable farmscape elements

(field borders, windbreaks, etc.) largely determine bird densities in agroecosystems

(Freemark et al. 1993, Rodenhouse et al. 1993). Thus, this study emphasizes that, both,

the dominant vegetative communities in landscapes where farms and farm fields are

imbedded and the spatial configuration of habitat on farms determine bird species

diversity on farms. Farmers seeking to manage bird diversity do not have control over

landscape context (once a farm is purchased). But these results suggest that schemes to

design on-farm habitats (crops, field borders, and location of planted fields with respect

to adjacent matrix types) to influence bird diversity could be effective, very flexible, and

accommodate different classes of birds (i.e. woodland, grassland, edge, generalist

species) and, therefore, be excellent tools for avian conservation in agroecosystems (see

below).









Bird Diversity on Organic versus Conventional Farms of North-central Florida

In apparent contradiction with other studies in North America (Freemark and Kirk

2001, Beecher et al. 2002) and Europe (Christensen et al. 1996, Chamberlain et al. 1999)

that documented significantly greater bird diversity associated with organic farming

practices, I detected only slight enrichment of bird diversity in organic versus

conventional farming systems of North-central Florida. In fact, most species that could

be expected in North-central Florida during the breeding season were observed utilizing

the farmscapes I studied, regardless of farm management (Figure 2-2). This contradiction

derives from differences in cropping practices on the farms studied by others, and in the

scale at which studies were conducted. In the other studies, birds were surveyed

primarily in farms with mono-cropped fields mixed crops were uncommon and

variables similar to our 'crop type' predictor were not incorporated into analyses. As an

a prior variable in analysis models, crop diversity proved to be a very strong predictor of

bird density. Since both conventional and organic farmers in my sample employed mixed

and mono crops, differences in bird occurrence generated by chemical applications may

have been insignificant by comparison. Moreover, both organic and conventional farms

in North-central Florida are relatively small (10 out of 16 were less than 10 ha) compared

to farms used in other studies that spanned a considerable size range (from a minimum of

10 -40 ha to much larger). North-central Florida is still largely forested, and because

farms were relatively small, most farm fields were close (or adjacent) to significant areas

of hardwood forest the habitat that generated the highest farm-bird diversity in this

study. The current landscape is likely to represent a 'patch mosaic' of diverse habitat

types long recognized as essential for the maintenance of bird (and other) species on









farmlands (birds; O'Conner and Boone 1992, Best et al. 1995: plants; Freemark et al.

2002: moths; Ricketts et al. 2001: ants; Perfecto and Vandermeer 2002). Thus, I

speculate that in farming regions with larger farms (and larger farm fields), where sources

of birds are more distant and mixed cropping is less frequent, organic farm practices may

be more important in determining species diversity than in landscapes with small-scale

farms and a diverse habitat mosaic.

Functional Insectivory in Cropped Fields

I found that birds were willing to utilize cropped fields to forage at most census

points regardless of crop type or management. However, in both years, fields planted

with polycultures attracted the greatest densities of the ten functional insectivore species,

compared to monocropped fields, regardless of other factors (Figure 2-8). The most

attractive fields in this study had vegetable and cut flower intercrops, followed by

multiple vegetable crops, and monocropped systems had the fewest birds; monocropped

watermelon was the least attractive crop. These results are similar to those of Robbins et

al. (1992), Rodenhouse and Best (1994), and Stallman and Best (1996) where avian

diversity, abundance, and foraging activity were strongly associated with increased

structural complexity of vegetation in cropped fields. In general, birds can rapidly assess

within-habitat variation in food availability (Fretwell and Lucus 1970, Hutto 1985) and

will quickly recruit to feed in food-rich patches. Since insect species richness and

diversity increase with vegetation diversity in cropped fields (Elliott et al. 1998) and are

greater in polyculture verses monoculture systems (reviewed by Andow 1991), the

increased functional insectivore foraging activity 1 observed in mixed crops verses

monocultures was probably driven by variation in arthropod prey resources (though I did









not quantify this). Because organic fields tend to support greater arthropod diversity and

density (Dritschillo and Wanner 1980, Hald and Reddersen 1990, Brooks et al. 1995,

O'Leske et al. 1997, Feber et al. 1997 & 1998), and because high bird diversity in organic

fields has been linked to richer arthropod foods (Brea et al. 1988), the lack of a

significant difference in bird diversity between organic and convention fields in this study

suggests that polyculture cropping in conventional systems also results in an overall

greater arthropod diversity and abundance (Paoletti et al. 1992, Stary and Pike 1999).

One important determination I made during this study is that without watching

what birds eat when they are in fields, farmers and researchers alike may mistake the

roles that different species play. Because a few birds can be significant pests in

agroecosystems, eating sprouted plants, seed crops, and ripening fruits (Weed and

Dearborn 1935, Beal et al. 1941, Dolbeer 1990, Rodenhouse et al. 1993), this role is often

the first one ascribed to any birds observed in cropped areas. In this study I observed

abundant insectivory and only isolated instances of fruit damage (by mockingbirds on

strawberries) by birds in my study fields. But while many of the species observed to take

insects are normally classified as insectivores, several of the functional insectivores are

not. The Northern Cardinal is usually classified as an omnivore (De Graaf et al. 1985)

and popularly known as a seed-eater because it frequents backyard bird feeders. Yet the

cardinal was the most abundant functional insectivore in this study. They made longer

foraging bouts and took more insects than other species, and either immediately

consumed them or carried them into nearby field margins (presumably to feed young).

Two other species typically classified as omnivores (or popularly thought of as

granivores), blue grosbeaks and indigo buntings, were also among the functional









insectivores (top ten most common species in cropped fields taking insect prey; see

Appendix A, Figure 2-7) and caused no crop damage during our observations. Clearly,

these species are omnivores when the diet is summarized over an entire year. But

because many omnivores and primarily granivorous species become highly insectivorous

during the breeding season to support their energetic needs and those of their nestlings

(Beal et al. 1941, Martin et al. 1951, Ehrlich et al. 1988), I advocate the utility of

'functional insectivore' in the context of farm birds. If the seasonality of bird diets is

emphasized, then farmers and conservationists alike can make more careful, and more

accurate, assessments of the potential positive and negative interactions birds can have

with cropping systems.

In conclusion, I found a large number of insectivorous bird species utilize cropped

fields of North-central Florida (see Appendix A), and direct observations during foraging

bouts indicated that most of these species were actively capturing insect prey from crop

vegetation. Insectivorous birds exhibit numerical and functional responses to insect

outbreaks in North American forest systems, potentially decreasing pest outbreak

frequency and severity (Holling 1988, Dahlston et al. 1990, Holmes 1990). This work

supports the general assessment that the ecological role of birds, as insect predators in

agroecosystems, is likely to realize enhanced production and economic values to farmers.

Moreover this work, in light of the current dearth of studies attempting to document

economic and production benefits of natural pest control agents, begs for further

investigation of avian insectivory as a component of pest management schemes that are

consistent with ecologically sound agriculture (Jackson 1979, McFarlane 1986 and Kirk

et al. 1996).









Conservation Implications

Increased awareness of the functional role that insectivorous species may have in

cropping systems could further encourage producers to engage in avian conservation

efforts on their lands. Recent surveys of farmers in North-central Florida indicated they

were supportive of increasing populations of certain bird species if it would benefit their

production efforts (i.e. insectivorous birds that may eat insect crop pests; Jacobson et al.

2003). Encouragingly, an overwhelming majority of farmers surveyed believed birds

could help lower insect populations on their farms (91%). Most farmers also indicated

that they would like to attract such birds to their farms (85%), and over a third of these

farmers were already engaged in attracting birds to their farms (Jacobson et al. 2003).

Additionally, since farmers in Florida have expressed great interest in conservation of

birds if they can aid in control of insect pests (without causing crop damage; Jacobson et

al. 2003), the potential for integrating bird conservation with farm production is

encouraging, particularly if more research is devoted to assessing realized benefits to

farmers. This work suggests that functional insectivory in fields can be encouraged at the

farm scale (by land-owners) by planting polycultures in fields adjacent to blocks (matrix)

of hardwood and pine forest with structurally complex field borders (hardwood, hedge)

between the matrix and the crop. It was also observed that insect eating birds heavily

utilized elevated perch structures (irrigation pipes, sprinkler heads, wire fence posts,

trellises, and natural structures such as sunflowers, cornstalks, bushes, and trees).

Though I did not characterize these effects, perches to enhance bird activity in disturbed

areas appears to be effective in many systems (Holl 1998). My next steps are to pursue









an understanding of economic benefits of on-farm manipulations of functional

insectivores.

While farmers cannot readily manipulate the relative abundance of land cover and

land use at the landscape scale surrounding their farms, it is quite clear that farms in

landscapes with greater proportions of their original native habitats will be able to attract

more birds, in part because larger pools of species and individuals are supported in such

landscapes. It is also apparent that such landscapes generate complex mosaics at the farm

scale, unlike regions with large (corporate) conventional fanning operations adjacent to

one another. Because most recent studies of bird diversity on farms in the U.S. have

occurred in expansive conventional systems of the Midwest (see Best et al. 1995, Best et

al. 1997, Beecher et al. 2002) and California (see Elphick and Oring 1998, Bird et al.

2000), where there is little habitat (and impoverished avifaunas that often cause crop

damage), and because such conventional corporate farms comprise most acreage in

agricultural use, the current view of integrating birds and agriculture is somewhat

pessimistic (Peterjohn 2003). Numerically, mostfarms in the US are small to medium

sized traditional operations occurring in landscapes with a mosaic of crop and non-crop

habitat elements (ERS-USDA 2003), like the farms in this study. A recent national study

found the average small farm devotes 17% of its land to forest patches compared to 5%

on large farms, and allocates nearly twice the acreage to soil improvement efforts such as

cover crops (D'Souza and Ikerd 1996). Additionally, non-cropped acreage or acreage set

aside for conservation purposes is substantial among small farms in the U.S. For

example small family farm operators controlled 85% of acres enrolled in the

Conservation Reserve Program as of 1998 (USDA 2001b). Given that many of the small









farms surveyed in North-central Florida appear to provide suitable habitat for a diversity

of species, and that these farmers' attitudes toward avian conservation are positive, I

argue that the prevailing negative view of agriculture as a partner in biodiversity

conservation is counter-productive. Large-scale conventional farming operations that

dominate large regions and comprise the majority of farmed areas in the US are, indeed,

devastating to birds and native biodiversity in general. But studies, including mine,

indicate that most farms (the smaller operations in diverse landscapes) already support

significant avian (and other) biodiversity, in part, because most farmers are open to

fostering such conservation goals. Therefore, I am encouraged that the potential to alter

agriculture in positive ways is tremendous. Policies are in place that provide monetary

and other incentives (i.e. 2002 Farm Bill conservation programs), and most stakeholders

are apparently open to possibilities (Jacobson et al. 2003), and the kind of research

needed to establish an economic basis for more ecologically sound agriculture is known

(McNeely and Scheer 2003).















CHAPTER 3
INTERCROPPING WITH SUNFLOWERS TO CREATE LOCAL
REFUGIA FOR AVIAN PREDATORS OF ARTHROPOD PESTS

Introduction

Innovative crop protection, through enhancement of predator-prey

relationships characteristic of natural systems, has a pivotal role to play in the

evolution of agriculture towards environmentally sustainable systems (Atkinson and

McKinlay 1997). Methodologies that promote pest insect predators (e.g., birds, bats,

wasps, beetles) on farms can augment both non-chemical crop protection and

conservation of biological diversity in agricultural landscapes. Although the value of

native insectivorous animals as predators in agroecosystems was once widely

recognized and promoted by scientists and farmers, research on potentially beneficial

species inhabiting agroecosystems was largely abandoned in 20"h Century North

America due to the pervasive use of pesticides and related technologies. As sectors

of the agricultural industry explore lower input systems (e.g., organic farming, natural

systems agriculture; Colby 1990) to reduce destructive impacts on human health

(www.epa.gov/pesticides/citizens/riskassess.htm) and ecosystem functions (Altieri

1994), research focused on designing farming systems that emulate more complex

ecosystems is urgently needed. Efficient and sustainable agro-ecosystems will

support ecosystem functions and species composition that reflect local biotic and

abiotic conditions (Soule and Piper 1992, McNeely and Scherr 2003). Thus, research









on sustainable and ecologically sophisticated agriculture should develop designs

appropriate for local conditions and sets of species, in addition to general principles

of agroecosystem function and management (Lewis et al. 1997).

Biological control by natural enemies has been the most successful and

promising alternative to unilateral reliance on chemical pesticides (Hoy 1992, Zalom

et al. 1992), and is considered to be the 'backbone' of integrated pest management

schemes (Rosen et al. 1996). The economic value of biological control methods

included in integrated pest management (IPM) programs may be considerable over

long time periods. For example, a study of citrus production in the San Joaquin

Valley of California indicated substantial savings of pesticide and energy costs could

be realized by growers utilizing IPM methodologies (Flint 1992). Biological control

methods that promote native pest insect predators for non-chemical crop protection,

by their nature, also contribute to conservation of biological diversity in agricultural

landscapes (The Soil Association 2000).

Habitat Management for Predators in Agroecosystems

Habitat management to enhance biological control refers to the establishment

of environmental conditions amenable to natural enemies that increase and sustain

their populations and improve their effectiveness in controlling pests (Pickett and

Bugg 1998). Population processes such as colonization / dispersal and foraging

movements of predators can be influenced by habitat modifications (Helenius 1998).

On farms, such dynamics of natural enemy populations can be altered through

management of within-field strips, cover crops, field margins, hedgerows, fencerows,

windbreaks, irrigation and drainage ditches, and roadside margins. For example,









Nentwig (1998) found that sown weed strips within cropped areas increased

arthropod enemy abundance and activity in crops, via greater effective dispersal into

the interior of expansive fields. Moreover, predation rates on pest species were

higher near the sown strips. Others have recognized the potential importance of

predator refugia within farmed areas for pest control and call for better understanding

of the mechanisms underlying refugium design and function for managing natural

enemies (Schoenig et al. 1998, Wratten et al. 1998).

Clearly, agroecological infrastructure (e.g., the landscape context and within-

field structure of cropped areas) affects the maintenance and activity of predators at

the scale of individual fields, and the conservation of predator diversity (richness and

abundance) requires consideration of both favorable and unfavorable habitat aspects

when designing predator-friendly agroecosystems (Booij and Noorlander 1992,

Wratten et al. 1998). For example, studies of abundances and foraging activities of

insectivorous birds in cropped systems (reviewed by Kirk et al. 1996) suggest that

bird use of crops for foraging depends not only on food abundance, but also upon

vegetation cover and microclimate in the field (Rodenhouse and Best 1994) and upon

habitat composition in the surrounding landscape (see Chapter 2).

Objectives

This study investigates the effect of within-field habitat structure upon the

abundance and foraging activity of insectivorous birds in cropping systems where all

features are under the direct control of farmers. The occurrence, densities, and

foraging activities of insectivorous birds in cropped fields are significantly higher in

those having the greatest diversity of vegetation (polycultures vs. monocultures; see









Chapter 2). Therefore, the overall objective of this study was to examine the effect of

sunflowers (Helianthus annuus) within cropped fields as refugia for birds. I tested

the hypothesis that sunflower rows included in a cropping system would increase the

occurrence, density, and foraging activity of insectivorous birds in cropped fields.

Additionally, I varied the density of sunflower rows per unit-area to determine its

influence on bird behavior and distribution in cropped fields. I conducted

observational assessments of foraging activity budgets of insectivorous bird species

utilizing cropped fields with sunflower rows compared to control plots. Using visual

observations I attempted to verify if birds were consuming economically important

pest insects. Forced regurgitation gut samples were collected from a few birds

captured in mist nets after they foraged in crop vegetation to aid in this verification.

Insects found within regurgitate samples were identified to order and family.

The addition of sunflowers to attract beneficial insects into cropping systems

has been described in several extension fact sheets (Univ. of Florida Extension

Circular 563, Univ. of Rhode Island Landscape Horticulture Factsheet, Univ. of

Maine Coop Extension Bulletin # 7150) and gardening publications (Long 1993,

Starcher 1995, Turton 1998). However, one concern with adding non-crop vegetation

strips within cropped fields is that this treatment may attract and increase the

abundance of pest insects to the crops (Bugg and Pickett 1998). Therefore, I also

performed a limited survey of the insect fauna found in sunflower treatment plots to

establish a partial listing and the relative occurrences of both beneficial and pest

arthropods found on sunflower and nearby crop vegetation (sensu Henn et al. 1997

and the UF Coop. Ext. Service Insect Identification Sheets SPSET 5 1997).









Methods

Research Site Selection

Growers were identified in North-central Florida during the fall of 2001 and

permission was obtained to conduct research activities on their properties. All

participating farms were under certified organic management as designated by the

Florida Organic Growers Association (Florida Certified Organic Growers and

Consumers, Inc., PO Box 12311 Gainesville, FL 32604) and most are now USDA

Organic certified.

Experimental Design

Four organic growers were asked to incorporate rows of multi-branched open-

pollinating varieties of sunflowers into their cropped acreage at the earliest planting

dates during their spring summer growing seasons 2002 and 2003. These multi-

branched sunflowers have been observed to provide foraging, roosting, and even

nesting micro-habitat for many species of insectivorous birds in two organic farms

that already incorporate them extensively for cut flower production (Jones

unpublished data). Vegetable crops grown in the experimental blocks chosen for the

study included polycultures of kale, collard greens, yellow and zucchini squash,

tomatoes, green beans, cucumbers, and sweet corn. Only two of the farm sites had

entire fields dedicated to a single crop type (sweet corn).

A total of 18, 4-hectare blocks were available for the study 8 of which

received sunflower row treatment while the other 10 served as controls within the

farm sites. This unbalanced arrangement of 8 treatment and 10 control blocks was

necessary to ensure that each farm contained at least 1 control and treatment block, to









pair crop types in treatment and control blocks as much as possible, and to allow the

incorporation of sunflower rows into blocks in such a way as to minimize their impact

on each farmer's production regime. Treatment blocks were divided among farms

that ranged in size from 8 ha to 80 ha in size with 2 blocks in the smallest farm, 4

blocks in each of 2 farms that were 20 ha in size, and 8 blocks in the largest farm. A

randomized block design was incorporated into the 4-hectare plots with sunflower

row treatments at varying densities of 0, 1, or 2 rows per 0.4 ha. All sunflower rows

consisted of Im-wide rows of plants at a density of 9 plants per square meter and

were interspersed between, and parallel with, production rows (Figure 3-1). In all

blocks that had sunflower rows placed in them the rows were centered in roughly

rectangular fields, planted in strips that would not otherwise have had crop

vegetation, and were approximately 100 m in length (Figure 3-2).

Sunflower rows were maintained throughout the spring growing season as other crops

were planted, harvested, and rotated through each farm's production area. Treatment

blocks were assigned different treatments during the second field season (either 1, 2

or no rows/0.4 ha of sunflowers) to control for differences in the border habitat types

that were adjacent to each treatment block. This was important since border habitat

types significantly affect the numbers of birds available to venture into cropped

fields. Avian occurrence and abundance in field borders varied significantly from site

to site being greatly influenced by the vegetation composition of the field border (see

Chapter 2).
















































Figure 3-1. Multi-branching sunflower varieties were planted at 1 or 2 rows per 0.4
ha between vegetable rows to attract birds and beneficial insects into cropped fields.
A row of sunflowers is shown here planted in a non-production strip containing
irrigation sprinklers between rows of tomatoes.















































100 m


Figure 3-2. Typical layout of treatment and control blocks at a 20 ha farm site. A
randomized block design was incorporated into the 4-hectare plots with sunflower
row treatments at varying densities of 0, 1, or 2 rows per 0.4 ha. All sunflower rows
consisted of Im-wide rows of plants at a density of 9 plants per square meter and
were interspersed between, and parallel with, production rows. In all blocks that had
sunflower rows placed in them the rows were centered in roughly rectangular fields,
planted in strips that would not otherwise have had crop vegetation, and were
approximately 100 m in length.









Bird Sampling

Birds were censused and their foraging activities quantified throughout the 2

growing periods from 1 April 15 June 2002 and 2003. Birds were censused 6 times

in each treatment and control block utilizing standard point count methods (Bibby et

al. 1992) modified as described by Freemark and Rogers (1995) for censusing in

croplands. All census points were located at least 200 m from each other when

occurring within the same farm management unit. Point counts were conducted

between dawn and 1000 EST on fair weather days. All birds seen or heard within a

50 m fixed-radius from each census point during a ten-minute period were recorded.

Observations began 2-3 minutes after 1 arrived at each point count station. Birds

flying over sample areas were excluded, except swallows or martins if they were

feeding on aerial invertebrates directly over crop vegetation (see Boutin et al. 1999).

Utilizing mapping data sheets (marking exact locations of individuals and their

movements) minimized duplicate records. Both species numbers and bird densities

were averaged across samples at each point. Univariate analyses were performed to

compare bird densities within the treatment and control blocks to determine

sunflower row treatment effects upon bird response variables among experimental

plots for the study (Zar 1999).

Point count circles used to assess bird species occurrence and density were

located on the edges of fields centered to the ends (1 sunflower row plots) or between

(2 sunflower row plots) sunflower rows in treatment blocks, V2 in the field and /2 in

the field border vegetation (Figure 3-2). For comparisons among treatments and

control blocks, only birds detected in the crop half of count circles were used in









assessing species occurrence and density. Count circle radii extended V2 the length of

the sunflower rows, and were therefore sufficient to detect sunflower effects on birds.

Half of each count circle was located in the field border vegetation for two reasons.

First, standing in the border provided some cover to reduce the conspicuousness of

the observer (and minimize effects on bird behavior in the crop). Second, all census

points in this study were censused in the 2 years previous to this study and those data

were used to assess variation in bird abundances in cropped field blocks among years

and treatments.

Foraging Surveys

Observations of foraging behavior were made during six, I-hour scan

sampling sessions (Martin and Bateson 1993) at each treatment plot spread over the

study period. Avian species observed to forage in crop vegetation and the time spent

in foraging bouts were noted. Birds were considered foraging if they were observed

to be making their way through or on crop vegetation and actively scanning or

probing that vegetation for prey items (as opposed to being perched and resting,

singing, or grooming etc.). Any successful capture of an insect prey item was noted

and an attempt was made to visually identify those insects being consumed by

foraging birds. Use of sunflower plants by foraging species was described. The

degree that inclusion of sunflower rows increased foraging activity in surrounding

crop vegetation was determined by univariate analysis of variance comparing

differences in mean numbers of birds and duration of foraging bouts among treatment

blocks. Regression analysis was used to examine the relationship between foraging

activity and growth of sunflower plants through each growing season (Zar 1999).









Gut Content Surveys

An attempt was made to identify insects eaten by insectivorous birds within

the test plots through gut content analysis. Birds were captured directly after foraging

in crop vegetation utilizing mist-netting techniques within treatment plots. A partial

sample of each bird's stomach contents was collected via a non-lethal forced

regurgitation (Prys-Jones et al. 1974). After capture, birds were administered an oral

emetic consisting of a 0.1 cm3 of 1% solution of antimony potassium tartrate per 10 g

of body mass and placed in a darkened holding cage lined with wax paper. Within 2

- 3 minutes, most birds regurgitated pellets of partially digested insects that were then

collected and preserved in alcohol for identification. Birds were then released at

point of capture after a short rest period and an examination for any signs of stress.

Samples obtained in this way are highly correlated with total crop and stomach

contents of collected birds (Rosenburg and Cooper 1990).

Insect Surveys

Insects were sampled a minimum of 3 times in 10 randomly chosen 1 m2

quadrats within sunflower rows and in 10 randomly chosen locations in crop

vegetation a minimum of 10 m distant from the sunflower rows within treatment

blocks during the growing season 2002. During 2003 insects were again sampled a

minimum of 3 times in 10 randomly chosen 1 m2 quadrats within sunflower rows, 10

quadrats in crop vegetation at 1 m, and 10 quadrats at 10 m distant from the

sunflower rows. Insects were sampled utilizing a standard scouting technique in each

quadrat counting the numbers of individuals found per 1 m2 of crop vegetation (after

Morris 1960, Southwood 1978). Insects observed were identified to family level and









relative abundances noted. Using Henn et al. (1997) and the UF Coop. Ext. Service

Insect Identification Sheets SPSET 5 (1997), I classified insects as beneficiall" or as

crop pests. Then, I compared the occurrence and number of individuals per m2

beneficial and pest insects found upon sunflower plants and crop vegetation (at 2

distances away from sunflowers in year 2) during the two growing periods (Zar

1999).



Results

Bird Species Occurrence and Densities

A total of 68 species were observed utilizing cropped areas of the treatment

and control blocks or their bordering habitats (within 50 m of field edges; see

Appendix B). Of these 68 species observed within the blocks, 62 species (91%) were

observed in the border habitat while 49 species (72%) were observed in the cropped

areas themselves; 5 of which were only observed in the cropped fields. Mean

densities of birds occurring in the cropped areas of the treatment and control blocks

varied significantly from year to year during the study and from the two years (2000

and 2001) previous to the study (2.9 birds/ha in 2003, 3.3 birds/ha in 2002, 4.3

birds/ha in 2001, and 1.8 birds/ha in 2000; F,3.34 = 2.74, p = 0.04). During the study

cropped areas with sunflower treatments of one row and two rows per 0.4 ha

exhibited significantly greater mean densities of birds than did control plots (3.5 3.5,

5.8 4.5, and 0.9 1.8 birds/ha respectively; F2.20 = 43.33, p< 0.001). This difference

was apparent with the addition of just a single row of sunflowers per 0.4 ha (Figure 3-

3). Differences in bird densities between treatment and control blocks were greatest









in 2003 (2-way ANOVA Year x treatment F,2, = 4.41, p = 0.013) during which

blocks having 2 sunflower rows per 0.4 ha exhibited a 206% greater mean density of

birds than did 1 row and a 1500% greater mean density of birds than did control plots

(Figure 3-3). Mean bird densities occurring in cropped areas were not significantly

different among these same blocks in the two years previous to this study (2000: F.5,

=.843, p = 0.436; 2001: F253 = 1.41, p = 0.254).

Foraging Behavior

Foraging observations during the 2 growing seasons indicated that the presence of

sunflower rows significantly increased the presence and activity of insectivorous

birds in vegetable or row-crops compared to control blocks. Mean number of

individual birds foraging per hour in cropped areas was significantly greater in those

blocks with sunflower rows versus control blocks, 0.7 0.1 and 1.7 0.1 individuals

per hour respectively (Fj.1 = 59.84, p < 0.001; Figure 3-4). Mean foraging activity

per hour in cropped areas was also significantly greater in those blocks with

sunflower rows versus controls, 0.06 1.01 hr and 0.24 .02 hr respectively (F1.i =

51.93, p < 0.001; Figure 3-5). This difference in foraging activity was consistent

each year as treatment plots were rotated among the 18 experimental plots. Mean

time birds spent foraging in crop vegetation significantly increased over the course of

each growing season as both sunflowers and crop vegetation matured (F,. = 9.13, p =

0.003). Birds were found to be attracted to and utilize sunflower plants as perches by

the time they were 0.6 m tall. As sunflowers increased in stature through the growing

season, birds were observed to increasingly utilize sunflower plants as cover and

perch sites from which they would forage into crop vegetation (Figure 3-6).















: ar
8.00 2002
2003
.5
*E 6.00


4.00 -
r &
c 2.00


0.00 -


Control


I
Sunflower
(1 row / acre)


I
Sunflower
(2 row / acre)


Figure 3-3. Sunflower treatment plots exhibited significantly greater mean densities
of birds in the cropped fields than control plots during both spring growing seasons
(F2.o = 43.33, p< 0.001), and especially in 2003 (2-way ANOVA Year x treatment
F2,20 = 4.41, p= 0.013). This difference was apparent with the addition of just a
single row of sunflowers per 0.4 ha increasing mean density nearly 4 times that of
control plots. Error bars = 1 SE.












year
SU 2002
'i*r 2003
S1.50 -
o







S o0.50 -



0.00 -
Control Sunflower




Figure 3-4. Mean number of individual birds foraging in cropped areas was
significantly greater in those plots with sunflower treatments in both growing seasons
2002 and 2003 (FI.t96 = 59.84, p < 0.001). Error bars = 1 SE.













ear
2002
2003

0.20"
I..


I-

". 0.10-
C




0.00 0 ......--...-

Control Sunflower



Figure 3-5. Mean foraging time (proportion of 1 hour observation session) in cropped
areas was significantly greater in those plots with sunflower treatments in both
growing seasons 2002 and 2003 (F,,x = 51.93, p < 0.001). Error bars = 1 SE.
















































Figure 3-6. As sunflowers increased in stature, birds were observed to increasingly
utilize sunflower plants as cover and perch sites from which they would forage into
crop vegetation. An Eastern Kingbird (Tyrannus tyrannus) surveys crop vegetation
from a sunflower perch looking for prey.









During the 216 hours of foraging observations made during the study period a

total of 428 foraging bouts were observed. The species most often observed to forage

in crops for insects included 2 resident species Northern Cardinals (Cardinalis

cardinalis) and Eastern Bluebirds (Sialia sialis), and two migrants, Blue Grosbeaks

(Guiraca caerulea), and Indigo Buntings (Passerina cyanea)(see Appendix B).

These four species accounted for 63% of the foraging bouts observed and 65% of the

time birds were observed to forage in the treatment and control blocks during the

study (Figure 3-7). Northern Cardinals were the most prevalent foragers throughout

each growing season accounting for more than 1/3 of the foraging bouts observed.

Eastern Bluebirds were also common foragers accounting for 8.6% of the foraging

bouts observed. Blue Grosbeaks and Indigo Buntings became common foragers (7%

and 9% of foraging bouts observed respectively) as they returned from wintering

grounds several weeks into the two growing seasons. Small flocks of species that

winter in North-central Florida such as Western Palm Warblers (Dendroica

palmarum) and Yellow-rumped Warblers (Dendroica coronata) were observed

foraging in cropped areas during the first few weeks of each growing season.

In approximately 10% of the foraging bouts I was able to identify an insect

prey item that had been captured. Two of the most common prey identified were

lepidopteran larvae and grasshoppers. Inspections of crop vegetation after bouts, in

spots where birds had foraged, allowed further confirmation of likely prey species

being consumed. Insects most prevalent in inspected foraging sites included Green

Stink Bugs (Acrosternum hilare), Imported Cabbageworm (Pieris rapae Linnaeus),

and numerous Dipterans (Figure 3-8).











a. Foraging bouts


BLGR
70%
COGD



I -







" : : ,


b. Foraging time


BLGR










INBU
8.7%


Figure 3-7. Species-specific proportion of foraging bouts (a.) and time spent foraging
per hour (b.) of birds observed during 216 hours of observation in sunflower and
control blocks during the 2002 and 2003 spring growing seasons. Northern Cardinals
(Cardinalis cardinalis), Eastern Bluebirds (Sialia sialis), Blue Grosbeaks (Guiraca
caerulea), and Indigo Buntings (Passerina cyanea) accounted for 63% of the foraging
bouts observed and 65% of the time birds were observed to forage in the treatment
and control blocks during the study. See Appendix B for complete list of those
species observed foraging in crops.


YRWA
47%
WPWA
68%






NOCA
38.3%


Other














NOCA
35.7%















































Figure 3-8. Birds foraging in crop vegetation were observed to consume numerous
lepidopteran larvae as well as grasshoppers and beetles. Insects consumed by birds
included Green Stink Bugs (Acrosternum hilare), Imported Cabbageworm (Pieris
rapae Linnaeus), and numerous Dipterans.









Insects were taken directly from crop vegetation and either consumed on the spot or

carried into nearby field border habitat (presumably to be consumed there or to feed

to young). A total of 20 birds observed to forage for insects in crop vegetation (10

Northern Cardinals, 3 Blue Grosbeaks, 6 Indigo Buntings, and 1 Summer Tanager)

were captured immediately after foraging. Regurgitated gut samples obtained from

12 of these captured birds confirmed that economically important pest insects were

consumed such as leaf-chewing caterpillars and grasshoppers (Figures 3-9). Remains

of beneficial insects were not evident in these gut samples.

Beneficial and Pest Insect Occurrence

Beneficial insects were attracted to sunflower plants by the time they reached

0.15 m in height. Beneficial insects observed on sunflowers and nearby crop

vegetation (within 1m of sunflowers) included arthropod predators, parasitic wasps,

and important pollinators representing 30 different families (Appendix C). The most

commonly occurring beneficial insects observed on sunflowers were Big-eyed Bugs

(Geocoris ssp.), Honey Bees (Apis mellifera), Green Lynx Spiders (Peucetia

viridans), Ants (Formicidae), and Sphecid Wasps (Sphecidae). The most commonly

occurring beneficial insects observed on nearby crop vegetation were Green Lynx

Spiders (Peucetia viridans), Lady Beetles (Coccinellidae), Big-eyed Bugs (Geocoris

ssp.), Predatory Stink Bugs (Pentatomidae), and Assassin Bugs (Reduviidae). The

occurrence of beneficial insects was significantly greater on sunflower vegetation

than on crop vegetation greater than 10 m distant from sunflowers in both 2002 (Fl.16

= 11.78, p = 0.003; Figure 3-10) and 2003 (Fi.6 = 12.94, p = 0.002; Figure 3-11).

While crop vegetation 10 m distant from sunflowers harbored significantly fewer





















































Figure 3-9. Gut content samples obtained from birds captured after foraging in crop
vegetation confirmed that economically important pest insects were consumed such
as leaf-chewing caterpillars. The intestinal tracts and other internal organs of
numerous caterpillars were identifiable in most stomach samples.









While crop vegetation 10 m distant from sunflowers harbored significantly fewer

beneficial insects, this difference in occurrence in sunflower and crop vegetation was

not seen in crop vegetation directly adjacent to sunflowers (within Im) when this was

assessed during the 2003 growing period (F,22 = 2.29, p = 0.144; Figure 3-11).

Pest insects representing 12 different arthropod families were found on

sunflowers and nearby crop vegetation. The most commonly occurring pest insects

were Green Stink Bugs (Acrosternum hilare), Corn Flea Beetles (Chaetocnema

pulicaria, Chrysomelidae) and Imported Cabbageworm larvae (Pieris rapae -

Linnaeus) respectively. The occurrence of pest insects on sunflower and crop

vegetation greater than 10 m distant from sunflowers did not significantly differ in

2002 (F1,16 = 0.12, p = 0.74; Figure 3-12) but did significantly differ in 2003 (F,16 =

14.7, p = 0.001; Figure 3-13). Greater mean numbers of pest insects per meter were

observed on sunflower vegetation than on crop vegetation greater than 10 m distant

from sunflowers (2.5 individuals / m2 vs. 0.2 individuals / m2 respectively). This

same difference was found on crop vegetation within 1 m of sunflowers as well in

2003 (2.5 individuals / m2 vs. 0.5 individuals / m2 respectively, F1,22 = 13.4, p =

0.001; Figure 3-13).













6.0-


4.0-


0.0--


Crop Vegetation


Sunflowers


Figure 3-10. Occurrence of beneficial insects was significantly greater on sunflower
vegetation than on crop vegetation during the 2002 growing
season (F,.,, = 11.78, p = 0.003). Error bars = 1 SE.

















M 3.0"
CE

2.0-

Eo

1.0-



Distant Adjacent Sunflowers






Figure 3-11. The occurrence of beneficial insects was significantly greater on
sunflower vegetation than on crop vegetation more than 10 m distant from
sunflowers in 2003 (F1.,6 = 12.94, p = 0.002). Occurrence of beneficial insects on
crop vegetation directly adjacent to sunflowers (within Im) did not significantly
differ from that found on sunflower vegetation (F,2, = 2.29, p = 0.144).
Error bars = 1 SE.















2.50-



2.00-



2 1.50-



O0 1.00-
E


0.50-




Crop Vegetation Sunflowers



Figure 3-12. Occurrence of pest insects on sunflower and crop vegetation greater
than 10 m distant from sunflowers did not significantly differ in 2002 (F.6 = 0.12,
p = 0.74). Error bars = 1 SE.











3.00 -




S 2.00 -

c E
-0


E 1.00-




0.00-
Distant Adjacent Sunflowers



Figure 3-13. Occurrence of pest insects on sunflower and crop vegetation greater
than 10 m distant from sunflowers significantly differed in 2003 (F,,, = 14.7, p =
0.001). Greater mean numbers of pest insects per meter were observed on sunflower
vegetation than on crop vegetation greater than 10 m distant from sunflowers (2.5
individuals / m2 vs. 0.2 individuals / m2 respectively). This same difference was
found on crop vegetation within I m of sunflowers as well (2.5 individuals / m2 vs.
0.5 individuals / m2 respectively, F,,, = 13.4, p = 0.001)









Discussion

Avian Abundance and Foraging Activity

In this study 1 tested the hypothesis that cropped fields with sunflower rows

incorporated into the cropping system would exhibit greater bird densities. My

results support this hypothesis. Those fields with even one row of sunflowers per 0.4

ha exhibited significantly greater bird densities than those without, regardless of crop

type or crop diversity. While an additional increase in density was seen with an

additional row of sunflowers, it appears that a single row may be enough to make

cropped areas more attractive for bird use. A single row of sunflowers added to a

field increased bird densities and foraging time spent by those birds nearly 4 times

that seen in control blocks. Therefore the addition of a single sunflower row may

provide the added structural vegetation to make a cropped field attractive for bird use

in those systems where their presence could possibly provide a benefit. However,

additional work needs to document and quantify the impact this increase in bird

density has on insect populations in crops and crop production.

In this study I also tested the hypothesis that foraging activity would be

increased in crop vegetation with the presence of sunflower rows. Results of my

foraging observations support this hypothesis since foraging activity was 4 times

greater in crops with sunflower rows. Previous studies suggest foraging activities of

insectivorous birds in cropped systems depends upon vegetation cover and

microclimate in the field (Rodenhouse and Best 1994, and reviewed by Kirk et al.

1996). Birds were found to begin to utilize sunflower vegetation as soon as the plants

were able to support perching and provide some cover (Figure 3-14).
















































Figure 3-14. Birds were found to begin to utilize sunflower vegetation as soon as the
plants were able to support them as a perch and begin to provide some cover. Once
sunflowers reached a height of at least 24", birds were observed to fly in to the fields
and first land on the sunflowers before venturing into nearby crop vegetation. A
Palm Warbler (Dendroica palmarum) is shown perched on a sunflower while
foraging for insects in nearby rows of kale.









Once sunflowers reached a height of at least 0.6 m, birds were observed to fly in to

the fields and, first, land on the sunflowers before venturing into nearby crop

vegetation. Several studies have confirmed the strong relationship between hedgerow

presence and composition, and avian presence and community structure in

agricultural landscapes (see O' Connor 1984, MacDonald and Johnson 1995).

Therefore in those fields in which birds may provide a benefit as insect predators, the

addition of sunflowers into the cropping system may be an effective and temporary

habitat modification.

I observed birds actively pursuing and consuming economically important

pest insects gleaned from crop vegetation. The value of utilizing naturally occurring

enemies cannot be overemphasized within organic farming systems and IPM

programs (Rosen et al. 1996). Insectivorous birds are naturally occurring components

of agroecosystems and their feeding activities in and around cropped areas may be of

great economic value. Birds are both mobile enough to recruit readily to high-density

food patches in their home ranges, and are capable of complex prey-switching and

specialization behaviors (McFarlane 1976, Kirk et al. 1996). Due to these

characteristics birds are potentially important components of biological control

regimes, provided they increase the natural mortality of agricultural arthropod pests

without adversely affecting other natural enemies and the crops themselves

(McFarlane 1976, Kirk et al. 1996).

As pest predators, birds may provide both numerical and functional responses

to prey availability over short time periods and large areas (Holling 1988, Dahlston et

al. 1990, Holmes 1990) potentially stabilizing pest communities in agroecosystems,









augmenting the activities of other classes of predators with different characteristics

(Price 1987, Rosen et al. 1996, Helenius 1998). Since birds responded to the

presence of sunflower rows after they reached a certain height, timing of planting of

these rows will be critical to maximize the benefit of attracted insect predators to

crops. Sunflower plantings should proceed that of other crop vegetation by several

weeks to allow their establishment and potential attraction of beneficial predators

before crops, and any associated pests, reach critical growth stages. Optimally,

potential suppression of pest insects will occur if an adequate predator base is present

before pests colonize crop vegetation and their populations grow to economically

damaging levels (Price 1987, Rosen et al. 1996, Helenius 1998).

Most bird damage to crops in the U.S. occurs to grain and small sized fruit

crops appear to be worse in certain regional locations, certain cropping system

designs, and in crops bred for very early or late season harvests (reviewed by

Rodenhouse et al. 1995). Several bird species are known to cause considerable

damage to crops, especially flocking species such as Red-winged Blackbirds

(Agelaiusphoeniceus) and Cedar Waxwings (Bombycilla cedrorum). During my 4

years of observations of birds in cropping systems I observed very little damage to

vegetable crops by birds. During the spring growing season of 2001, North-central

Florida experienced severe drought conditions. In this season I observed watermelon

damage cause by American Crows (Corvus brachyrhyncos) presumably to obtain

water. In all 4 years, 2000 2003, I also observed a limited amount of strawberry

damage caused by Northern Mockingbirds (Mimuspolyglottos). During this study

participating farmers reported that they did not experience any increase in bird









damage due to attracting more birds into their cropping systems with sunflower

plantings. I did not observe any of the 3 most problematic species mentioned above

utilizing sunflowers (blackbirds, crows, or waxwings) or being attracted to plots with

sunflower rows over the study period.

In a recent survey of Florida farmers, bird damage to crops was reported by

32.9% of the survey participants primarily indicating damage to watermelon or corn

by crows (Jacobsen et al. 2003). However only 11.8% reported the need to utilize

bird control methods to limit damage. In some cases proper "farmscaping" cannot

only increase the presence of beneficial organisms, but may reduce the presence or

abundance of problematic species in cropping systems as well. Farmscaping is

defined as a whole-farm, ecological approach to pest management through selective

placement of hedgerows, insectiary plants, cover crops, and water reservoirs to attract

and support populations of beneficial organisms such as insects, bats, and birds of

prey (http://attra.ncat.org/attra-pub/PDF/farmscaping.pdf). Research in farmscaping

to maximize beneficial organisms and limit pests is ongoing to identify and develop

such management strategies (Pickett and Bugg 1988, Bommarco and Ekbom 2000).

Beneficial and Pest Insect Occurrence

Insect sampling efforts revealed that sunflowers did indeed attract and play

host to numerous beneficial insects as has been described in numerous publications

(Henn et al. 1997, UF Coop. Ext. Service Insect Identification Sheets SPSET 5 1997).

Sunflower plants were found to attract predaceous insects almost immediately after

establishment. Parasitoids and pollinators were attracted as soon as these plants

began to produce flowers. These same beneficial insects were found to also occur on








crop vegetation but in lower numbers. It has been found in several studies that

providing predator refugia within cropping systems via strip crops or uncultivated

corridors can result in the migration of predatory insects into adjacent crops (see

Johanowicz and Mitchell 2000, Mensah 1999, Nentwig 1998, Schoenig et al. 1998,

Wratten et al. 1998, Rodenhouse et al. 1992). In the 2003 growing season I modified

the sampling methodology in an attempt to determine whether beneficial insects

attracted to the sunflowers may have been moving out from the sunflowers into

adjacent crop vegetation. Results indicated that crop vegetation 10 m distant from

sunflowers harbored significantly fewer beneficial insects than did that within 1 m.

Moreover, crop vegetation within 1 m of sunflowers exhibited nearly the same

abundance and diversity of beneficial insects as did the sunflowers themselves.

Further study is required to fully describe the distances key beneficial insects move

from sunflowers and the impact these beneficial insects have on crop pests.



Conclusion

Bird populations and avian community structure are known to respond

differently to the distribution of cropped and non-cropped landscape elements and the

distribution, relative cover classes, and juxtaposition of agricultural landscape

elements in agroecosystems (Freemark et al. 1993, Rodenhouse et al. 1993). Intrinsic

habitat qualities such as food resources or shelter availability play important roles in

habitat selection by birds (Bairlein 1983, Martin and Karr 1986, Moore et al. 1995).

Moreover, habitat complexity resulting from a mix of different plant species,

percentages of vegetative cover and variations in the size, distribution, and









juxtaposition of plant assemblages will influence the local diversity of bird species

(James 1971). The addition of structurally diverse vegetation strips within cropped

fields appears to attract and provide cover for birds utilizing adjacent non-crop

habitats. In so doing the probability that these highly insectivorous animals may

provide an economic benefit to producers is greatly increased. In return, the creation

of suitable habitat within cropping systems may aid in the conservation of all avian

species within agroecosystems. Within the discipline of conservation biology there is

increasing recognition that protected reserves alone will not be sufficient to conserve

biodiversity in the long term; therefore, methods of integrating conservation and

productive use must be achieved (Hobbs and Norton 1996). This study contributes to

a better understanding of the effects of vegetative structure and crop species

composition on farm-bird community structure, with more general applications to

implementation of environmentally sensitive agriculture.















CHAPTER 4
PARASITIZED AND NON-PARASITIZED PREY SELECTIVITY OF
INSECTIVOROUS BIRDS: POTENTIAL FOR AUGMENTATION OF
CLASSICAL BIOCONTROL


Introduction

Biological control by natural enemies is the most successful and promising

alternative to unilateral reliance on chemical pesticides in low input cropping systems

(Rosen et al. 1996). Classical biological control programs often rely on releasing

introduced (non-native) parasitoids to reduce exotic pest populations (DeBach and

Rosenl991), where host specificity is emphasized using parasitoids or predators of

targeted pest arthropods. While a majority of biological control research has focused

upon "specialist" enemies for individual agricultural pests, the strategy of enhancing

these efforts by increasing "background mortality" (see Beddington et al. 1978) through

assemblages of native generalist predators also shows promise in crop management

schemes (Helenius 1998). Such augmentation of classical biological control programs

will require sustained availability of large numbers of inexpensive, high quality, naturally

occurring predators (Hoy 1992). Multiple natural enemies in a system are understood to

provide a shifting temporal and spatial mosaic of predation rates across multiple prey,

dampening variability in the systemic predator-prey dynamic (Rabb 1971). Thus

augmentation of classical biological control measures involves efforts to enhance the

presence of naturally occurring enemies of pest arthropods in agroecosystems.









Over the past 2 decades, field entomologists and agronomists have increasingly

recognized that the conservation of natural enemies via the management of non-cropped

habitats that support them is important to effective and successful biological control in

agricultural systems (Rosen et al. 1996). However, little work has been done looking at

avian insect predators in modem cropping systems to fill this role of augmenting other

control measures. One particularly important potential mechanism whereby birds might

stabilize and augment pest control is consumption of individual prey that escape mortality

from other agents of biological control. In systems where introduced or native

parasitoids are supported via provision of critical habitat (e.g., insectiary plantings) rather

than through repeated releases onto fields, parasitism rates undergo fluctuations due to

parasitoid population lags (Bugg and Pickett 1998). In such systems birds could function

to stabilize and maintain sufficient pest mortality rates given their abilities to respond

functionally to changes in prey abundance (McFarlane 1976). While this scenario

reasonably explains how birds could effectively augment arthropod pest mortality

induced by parasitoids typically employed in classical biological control regimes

(McFarlane 1976, Kirk et al. 1996), its generality, practicality, and economic efficiency

have not been assessed for any agroecosystem.

Bruns (1959) stated that birds would be of value as insect predators in a system

only if they increase the effectiveness of control by taking insects over and above those

that would normally have been destroyed by other agents. Several studies have

demonstrated that birds select and consume non-parasitized insects suggesting that bird

predation may be additive to the mortality caused by parasitoids (Sloan and Simmons

1973, Schlichter 1978). Sloan and Simmons (1973) reported that hymenopterous









parasitized jack pine budworm (Choristoneura pinus Bechstein) larvae and pupae were

unanimously rejected by foraging chipping sparrows (Spizella passerina). Similarly,

Schlicter (1978) reported that black-capped chickadees (Parus atricapillus) largely

avoided foraging upon galls on Canada goldenrod (Solidago canadensis) that had been

parasitized by mordellid beetle (Mordellistena unicolor) larvae to extract gall fly

(Eurosta solidaginis) larvae. Therefore it appears that birds have the ability to

distinguish prey that have been damaged or may be compromised by a parasite and avoid

such prey.

Previous observations have confirmed that many birds occurring in cropped fields

of North-central Florida actively forage for and consume caterpillars in crop vegetation

(see Chapters 2 and 3). Fall armyworms [Lepidoptera: Noctuidae, Spodopterafrugiperda

(J. E. Smith)] are important pests in vegetable and row crops (Johnson and Sprenkel

1996) and are often subjected to biological control using cultured parasitoids (R.

Meagher, USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology

(CMAVE), Gainesville, FL, pers. comm., Johnson and Sprenkel 1996). Parasitoids are

insects whose eggs are deposited on another arthropod (usually an insect) host, its larvae,

or in the host's egg. The resultant larvae develop by feeding upon the bodies of the host

resulting in the host's death (Godfray 1994).

In this study I addressed whether birds would consume armyworms that had been

parasitized or avoid such prey. I tested the hypothesis that birds prefer to forage upon

non-parasitized armyworm prey via captive feeding trials where birds were also offered

prey parasitized by Euplectrus wasp larvae. In both studies where birds avoided prey, it

was suggested that visual cues were utilized to distinguish between prey types (Sloan and









Simmons 1973, Schlichter 1978). Parasitoids can be divided into two classes by the

feeding behavior of their larvae. Endoparasitoid larvae feed from, and develop within,

the body of their host. Ectoparasitoid larvae develop while externally attached to the host

feeding with mouthparts buried into the host's body (Godfray 1994). Larvae of the genus

Euplectrus are gregarious (more than one parasitoid larvae per host) external parasites of

lepidopteran larvae. Euplectrus larvae remain attached to the exoskeleton and feed on the

dorsum of their host, which is often still able to move freely about (Figure 4-1). Once the

Euplectrus larvae mature they move below the emaciated host to pupate, spinning silk

from the host's Malpighian tubes which hold the host down and separate the larvae from

each other (Grissell and Schauff 1997). Therefore, Euplectrus served as a good

representative of commonly occurring ectoparasitoids whose larvae develop on the

external surface of their host that could be visually identified by a bird.



Methods

Research Facilities and Test Species

Feeding trials were conducted in an aviary at the USDA National Wildlife

Research Center's Florida Field Station, Gainesville, Florida. Red-winged blackbirds

(Agelaius phoeniceus) captured in agricultural settings and housed at the field station

were utilized as a test insectivorous species. This species was chosen due to the fact that

individuals of this species commonly occur in agricultural landscapes (Ehrlich et al.

1988, Dolbeer 1990) and have been previously examined for their predatory impact on

insect pest populations in crops (Bendell et al. 1981). Birds were presented parasitized

and non-parasitized fall armyworms provided by the USDA- ARS CMAVE, Gainesville,









FL. Parasitized armyworm larvae were those that had been exposed to and carried larvae

of the Eulophid parasitoid species Euplectrus plathypenae (Howard). This

Hymenopteran species commonly occurs in Florida and has been investigated for its

biological control value (R. Meagher, USDA-ARS, Center for Medical, Agricultural and

Veterinary Entomology (CMAVE), Gainesville, FL, pers. comm.).

Paired Feeding Trials With Non-parasitized Larvae

The first set of feeding trials performed with non-parasitized prey test if the

captive birds would feed upon fall armyworms, and I determined their baseline

consumption given this food item. Only those birds willing to readily eat armyworms

were utilized for subsequent tests. Additionally, since birds have exhibited prey size

selectivity when presented a choice (Krebs et al.1977, Davies 1977, Zach 1979) an

assessment was made whether birds exhibited a feeding preference for different instar

sizes of these caterpillars. Maintenance food was removed by 0700 EST and 1-2 hrs later

birds were presented with a plastic cup divided into two chambers (Figure 4-2). In the

first protests, 10 armyworms of equal size were simultaneously presented in the cup's

chambers and birds were allowed to forage undisturbed for '/2 hour (Figure 4-3). The

propensity of each bird to eat the armyworms, the chamber location (left or right side of

cup) the larvae were chosen from, and the time it took for the bird to consume all 10

larvae were noted. In these tests, as well as all that followed in this study, a bird would

not be given a subsequent test presentation until at least 1 hour had passed.

In the second set of tests, those birds that had exhibited a willingness to eat

armyworms in the first tests were simultaneously presented 10 larvae of two different

instar sizes, 5 large (5th instar, 26.1 + 3.0 SD mm, n = 28) vs. 5 small (2"d or 3rd instar,

















































Figure 4-1. Euplectrus plathypenae Howard (Hymenoptera: Eulophidae) larvae attached
to an armyworm (Spodoptera ssp.) larvae host.















































Figure 4-2. Prey item presentation cup placed in test cage with a red-winged blackbird
(Agelaius Phoeniceus) foraging for a food item. The presentation cup contained a center
divider partitioning the cup into two chambers. A red line painted on the exterior of the
cup allowed observers to easily determine which chamber a food item was taken from.





















-4,:


v
:i4:



1 J
S,. .r. ~." 4 '
i' .. ..,






I'.

..,. : .:..


Figure 4-3. In multiple trials, birds were offered fall armyworms [Spodopterafrugiperda
(J. E. Smith)] of similar body size in each of the presentation cup's chambers.




Full Text
25
Figure 2-1. Aerial view of a farm site in Alachua Co. illustrating 50 m radius point count
circle positioned on the edge of a cropped field where cropped field and field border
habitat type were characterized. Matrix type adjacent to each field was characterized
within a 200 m radius semicircle at each census point (after Freemark and Kirk 2001).

69
Figure 3-8. Birds foraging in crop vegetation were observed to consume numerous
lepidopteran larvae as well as grasshoppers and beetles. Insects consumed by birds
included Green Stink Bugs (Acrosternum hilare), Imported Cabbageworm (Pieris
rapae - Linnaeus), and numerous Dipterans.

ASSESSMENT OF THE POTENTIAL FOR INTEGRATION OF AVIAN
CONSERVATION WITH MODERN AGRICULTURAL PRODUCTION
BY
GREGORY ALAN JONES
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
2003

r
Copyright 2003
by
Gregory Alan Jones

ACKNOWLEDGMENTS
Funding for my research was provided by the Florida FIRST initiative of
the University of Florida’s Institute of Food and Agricultural Sciences, the
Organic Farming Research Foundation, The Eastern Bird Banding Association,
The North American Bluebird Society, and the University of Florida’s
Department of Wildlife Ecology and Conservation.
I am truly grateful for the collaborative assistance of the following
researchers: Dr. Kathryn Sieving, Dr. Michael Avery, Dr. Robert Meagher, Dr.
Kenneth Buhr, and Dr. Jennifer Gillett. I thank Dr. Avery, Kandy Rocca, and all
of the staff members at the USDA Denver Wildlife Research Center’s Florida
Field Station, Gainesville, Florida, for use of their facilities, birds and their help in
conducting experiments. I also thank Dr. Meagher, Charlie Dillard and all of the
staff members at the USDA-ARS Insect Behavior & Biocontrol Unit, Gainesville,
Florida, for the help and provision of experimental materials. I thank the
following research assistants: Matt Reetz, Leonard Santisteban, and Kat Smith. I
thank the WEC staff members Caprice McRea, Monica Lindberg, Delores
Tillman, Laura Hayes, and Sam Jones for their kind help and friendship over the
past years.
A very special thank you goes to the members of my supervisory
committee for their guidance and support during pursuit of my degree: Dr.

Kathryn Sieving (Chair), Dr. George Tanner, Dr. Michael Avery, Dr. Douglas
Levey, and Dr. E. Jane Luzar. I will always be grateful for Dr. Sieving’s
commitment, encouragement, and patience as I struggled through the process of
developing a research program and seeing it through to completion. I appreciate
the special attention and help provided to me by all of these people, each in their
own way over the years. I have very much enjoyed working with each of these
fine individuals.
I wish to relate my appreciation to Dean Jimmy Cheek and Associate
Dean E. Jane Luzar for providing me the opportunity to work with the students
and faculty in the College of Agricultural and Life Science’s Honors Program. It
has been a great privilege and learning experience to be able to interact with the
brightest and the best of the college’s students. I have been very fortunate to be
able to work and learn from some of the top teaching staff in the college as well in
this program. I am very grateful for these people’s support over the past few
years.
I greatly appreciate the logistic cooperation of the following extension
agents Gary Brinen, Austin Tilton, David Denkins, Jacque Bremen, Marvin,
Anthony Drew, and David Holmes. I would also like to thank Marty Mesh and
the Florida Certified Organic Growers and Consumers, Inc. for their assistance.
The cooperation and participation of the following producers is gratefully
acknowledged as well: Larry and Greg Rogers, the Hauffler Brothers, Don King,
Andy Mulberry, W. K. Bagwell, Dennis Short, Kathy and Marvin Graham, Lois
Milton, Tommy Simmons, Bill Ogle, Bill Allen, Rosalie Koenig, Charles
IV

Lybrand, Donald Appelbaum, Ed Parker, Charles Andrews, Joe Durando, Paul
Morris, Archer Christian, Cynthia Conolly, and Bikram Singh.
I would especially like to thank my fellow colleagues in Dr. Sieving’s lab
for their fellowship over the years. Their reviews, sharing of ideas, and guidance
has truly been an important factor in the success of my graduate program. I have
enjoyed their friendship while I have been at the university and hope to continue
to be close to them in the future. Thanks Tom, Marcela, John, Traci, Matt, Mike
and Ivan.
Finally, I thank my wife Leigh and my two sons Ben and Zach for their
love, support and patience. I know I have not always been easy to live with,
especially at times when I was frustrated or stressed during the past few years. I
could not have achieved my academic or career goals without them. I love you
all. I also appreciate the love and support provided to me and my family by my
parents and especially my mother-in-law Jamie Schnabel.
v

TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS ni
ABSTRACT viii
CHAPTERS
1 INTRODUCTION 1
Economic Ornithology - The First Attempt to Integrate Bird
Conservation and Agricultural Production 2
Effects of Agricultural Practices on Avian Populations 4
Birds as Predators in Agroecosystems S
Examples of Experimental Work Investigating the Impact of
Birds on Insect Populations in Modem Agroecosystems 10
Natural Systems Agriculture or Ecoagriculture 12
Research Needs 16
Conclusion 17
2 AVIAN BIODIVERSITY AND FUNCTIONAL INSECTIVORY
ON NORTH-CENTRAL FLORIDA FARMLANDS 19
Introduction 19
Methods 23
Results 30
Discussion 40
3 INTERCROPPING WITH SUNFLOWERS TO CREATE LOCAL
REFUGIA FOR AVIAN PREDATORS OF ARTHROPOD PESTS 50
Introduction 50
Methods 54
Results 61
Discussion 76
Conclusion 82
vi

4 PARASITIZED AND NON-PARASITIZED PREY SELECTIVITY
OF INSECTIVOROUS BIRDS: POTENTIAL FOR
AUGMENTATION OF CLASSICAL BIOCONTROL 84
Introduction 84
Methods 87
Results 95
Discussion 96
Conclusion 100
5 SUMMARY AND FUTURE RESEARCH NEEDS 102
Summary 102
Future Research Needs 106
Conclusion 107
LITERATURE CITED 109
APPENDICES
A BIRD SPECIES OBSERVED DURING CENSUS SURVEYS
IN NORTH-CENTRAL FLORIDA FARMLANDS 128
B BIRD SPECIES OBSERVED ON ORGANIC FARMLANDS
OF NORTH-CENTRAL FLORIDA 133
C BENEFICIAL INSECTS OCCURING ON SUNFLOWER
AND CROP VEGETATION 138
BIOGRAPHICAL SKETCH 140
vii

Abstract of Dissertation Presented to the Graduate School
Of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
ASSESSMENT OF THE POTENTIAL FOR INTEGRATION OF AVIAN
CONSERVATION WITH MODERN AGRICULTURAL PRODUCTION
By
Gregory Alan Jones
December 2003
Chair: Kathryn E. Sieving, Associate Professor
Major Department: Wildlife Ecology and Conservation
The overall goal of my research was to assess the potential for integrating
bird conservation on farmlands while enhancing production goals through
augmentation of insect pest control. Working on selected conventional and
organic farms in North-central Florida my study objectives were to: 1) assess
habitat characteristics on and adjacent to farms influencing avian species diversity
and insect-foraging activity, and to identify ‘functional insectivores’ on these
farms, 2) determine the effectiveness of sunflower intercrops as refugia for both
insectivorous birds and beneficial insects in cropped fields, and as tools to
enhance insect-foraging by birds in cropped areas, and 3) test the hypothesis that
insectivorous birds can potentially augment pest control programs involving
hymenopteran parasitoid predators, via preference for unparasitized over
parasitized prey.
viii

Using a combination of bird surveys and focal foraging observations over
2 years, I determined that bird diversity in cropped and non-cropped habitats on
farms varied in the following ways: a) vegetation type in field borders
significantly influenced species richness per census point (Fs,3o = 3.5, P = 0.013)
and in field borders (Fsjo = 3.8, P = 0.009), b) mixed crops generated
significantly greater bird densities per point (Fi,30 = 7.4, P = 0.011) and in cropped
fields (F1,30 = 8.2, P = 0.008), and c) foraging activity and abundance of
functional insectivores were greatest in mixed crops (Fi,29 = 4.2, P = 0.051). In a
replicated, controlled field experiment I determined that intercropping rows of
sunflowers significantly increased densities of birds (F2JOo = 43.33, p< 0.001),
numbers of individuals (FU96 = 59.84, p < 0.001), and foraging time by individual
insectivores in crops (Fl l% = 51.93, p < 0.001). Visual observations and stomach
samples confirmed that birds consumed economically important pest insects. In
experimental feeding trials, blackbirds exhibited no preference between
parasitized and non-parasitized lepidopteran larvae of similar body size (W0 =
139, p = 0.69) but a significant preference for larger non-parasitized prey (W0 =
248, p < 0.001). My study suggests that farmlands can be managed to enhance
wild bird populations and the potential that birds could augment pest control
programs in modem agricultural operations.
IX

CHAPTER 1
INTRODUCTION
The relationship of birds to agricultural activities in the temperate zones of the
Northern Hemisphere has long been of interest to ornithologists both in the United
States and in Europe. Early naturalists published numerous papers describing careful
observations and thoughtful consideration of the relation of birds to crop production.
During its existence, multiple reports produced by the Section for Economic
Ornithology within the federal Department of Agriculture confirmed the utility of
birds as destroyers of pest insects, often recommending their classification as highly
beneficial to agriculture. However, with the advent of farm mechanization, synthetic
chemical pesticides, and the intensification of agricultural production, focus upon the
positive impact birds may have on agriculture waned and research interest regarding
the detrimental effect agriculture has on avian populations increased. Currently
ornithologists have suggested that change in agricultural practices and landscape
structure over the past few decades have reduced the occurrence of farmland habitat
elements many farmland species had traditionally utilized (O’Conner and Boone
1990, Freemark 1995, McLaughlin and Mineau 1995).
Rodenhouse et al. (1995) believe that agriculture has had a greater impact on
the status of Neotropical migratory birds than any other human activity. Additionally,
their review also shows that conservation measures benefiting avian species in
1

2
agricultural landscapes will be acceptable to farmers if management
recommendations have neutral or positive effects on food production. Sufficient
evidence has accumulated from studies in forest, grassland, orchard, and row
cropping systems that offers sufficient evidence that insectivorous birds may be of
economic value by enhancing production through predation of pest insects. Due to
this potential ecological role of birds in agroecosystems, several reviewers of past
work, including McFarlane (1976), Jackson (1979), and Kirk et al. (1996), suggest
birds should be considered as components of modem biological pest management
schemes. However, despite potential values of birds on farms, the theory and practice
of enhancing these native natural enemies by providing habitat for them within
cropping systems has been relatively neglected.
Ornithologists have an opportunity to propose management recommendations
favoring avian conservation within agricultural production systems by working within
interdisciplinary teams developing modem sustainable or natural systems agriculture
(Rodenhouse et al. 1995). As agricultural producers recognize the importance of a
structurally and biologically diverse farmed environment, ornithologists can institute
the resurrection of quality avian habitat within agroecosystems. Enlightened
management of farmlands can satisfy the needs of agriculture and numerous avian
species while providing mutual benefits (Rodenhouse et al. 1995).
Economic Ornithology - The First Attempt to Integrate Bird Conservation
and Agricultural Production
Early naturalists in this country, such as Alexander Wilson, James Audubon,
and even Benjamin Franklin, became interested in bird behavior and made references

3
to the purely economic phases of bird life. Their writings repeatedly relate the value
of different species as destroyers of insects. After 1850, various researchers
interested in agriculture published numerous papers in agricultural journals and in
reports of agricultural and horticultural societies that described careful observations
and thoughtful considerations of the relation of birds to crop production (reviewed by
Weed and Dearborn 1935). Needless to say, these publications generated a great deal
of discussion as to the true utility of birds, because some bird species had long been
considered agricultural pests.
One of the results of the organization of the American Ornithologist’s Union
(AOU; circa 1883) was the impetus it gave to the study of bird’s food habits to
resolve questions of their utility as pest predators and the desirability of legislation
permitting the destruction of species popularly considered pests. At the request of the
AOU and researchers within the Department of Agriculture, congress appropriated
monies to establish a Section for Economic Ornithology (SEO) within the Division of
Entomology of the federal Department of Agriculture (McAtee 1933). The section
was responsible for the promotion of economic ornithology (or the study of the
interrelation of birds and agriculture), the investigation of avian food habits, the
investigation of both resident and migratory birds in relation to both insects and
plants, and publish reports thereon (McAtee, 1933, Weed and Dearborn 1935).
Research emphasis at this time consisted of the examination of the contents of
bird stomachs, together with observations of birds in the field. Multiple reports
produced by the SEO confirmed the utility of birds as destroyers of pest insects and
as important weed seed predators. Reports of this nature submitted to the USDA's

4
administrators often concluded that birds feed largely upon pest insects and should be
classified among the species highly beneficial to agriculture. The section later
developed into the original Biological Survey, and research of this kind continued
until the early 1930s (Weed and Dearborn 1935, Kirk et al. 1996). However, with the
advent of synthetic chemical pesticides in the 1940’s, little work in this field has been
done (Kirk et al. 1996). Currently, avian research performed by the USDA focuses,
for the most part, upon control of crop damage by birds. While focus upon the
positive impact birds may have upon agriculture waned, research interest regarding
the detrimental effects agriculture has had on birds has increased since the 1940s.
Effects of Agricultural Practices on Avian Populations
Agricultural development since the 1700s has dramatically altered or
eliminated the natural landscape of the continental United States. Forests originally
covered about one-half of this region of North America, 40% was covered in
grasslands, and the remaining area was arid and barren (Cochrane 1993). Between
1790 and 1890, 300 million acres of virgin forests were cleared and an equal amount
of grasslands were plowed. Agriculture today comprises the largest landuse class
encompassing over 50% of the arable land area of the contiguous 48 states (USDA
1998). Currently, of the 1.9 billion acres of land in the U. S., some 350 - 400 million
acres are under intensive crop cultivation with approximately another 200 million
acres of marginal land at the ready to be put into this practice should prices warrant
its use (Cochrane 1993). While the conversion of natural landscapes to
agroecosystems in Europe occurred much earlier in history, this alteration took place

5
steadily across several centuries, and agricultural lands now comprise 41% of the land
area of the 15 countries of the European Union (Pain and Dixon 1997).
Agricultural practices on farmlands have changed drastically over the past 150
years. The concept of farm mechanization was widely accepted in the 1850s,
characterized by the use of cultivators, mowing machines, and reapers (Cochrane
1993). From this point farm machines evolved rapidly; increasing in size and
efficiency and incorporating both steam and then internal combustion power.
Increased size and efficiency of farm machinery in the post World War 2 years
allowed for the expansion of field size and homogenization in farmland structure.
During the period from 1935 to 1970, while the acreage of land under cultivation did
not change the number of farms declined from 6.8 million to 3 million via corporate
consolidation concomitantly with an intensification of production per unit area
(Cochrane 1993). This same phenomenon occurred in post World War 2 Europe
including increased field sizes, reductions or elimination of boundary features, and an
overall change in agricultural landscape structure (Pain and Dixon 1997).
Many researchers here in the U.S. have suggested that changes in agricultural
practices over the past few decades have reduced the favorability of agricultural
landscapes for foraging and nesting by many native and migrant species (Best 1986,
O’Conner and Boone 1990, Warner 1992, Bollinger and Gavin 1992). The once
heterogeneous landscape found in agroecosystems composed of woodlots, ponds,
shelterbelts, wooded hedgerows and fencerows, and other such landscape elements
provided for an abundance and diversity of bird species. However, these landscapes
have become increasingly homogenized through the removal, fragmentation, and

6
isolation of these elements upon which many species had come to depend (O’Conner
and Boone 1990). For example, Gawlick and Bildstein (1990) attribute the decline of
Loggerhead Shrikes to loss of their preferred edge habitat in farm landscapes. This
same sentiment has been voiced by researchers in Europe relating that increased
specialization has reduced the prevalence of mixed farming and the habitat mosaics
inherent to traditional types of farming (O’Conner and Shrubb 1986, Baillie et al.
1997). Groppali (1993) related the percentage of eradication of tree rows and hedges
to expand cultivated parcels within his study area near Cremona, Italy, was 33% and
36% respectively over a 9-year period, 1980-1989. In these parcels where tree rows
and hedges had been removed, species diversity and numbers of nesting pairs of birds
were significantly reduced. In Britain, Baillie et al. (1997) found that more farmland
birds are declining than increasing, and more importantly, specialist farmland species
are declining more than generalists due to loss of preferred farmland habitat.
Within the U.S., resident and migratory landbird passerines, represented by
over 200 different species, constitute over 70% of the bird species that feed, roost, or
breed on agricultural lands (Rodenhouse et al. 1993). Most landbirds utilizing crop
fields and edges are Neotropical migrants, and agricultural practices have been
implicated in the decline of at least nine of these species currently listed as threatened
or endangered. Studies in U.S. farm landscapes have found the majority of bird
species utilizing agricultural lands are found in uncultivated areas. Highest species
richness and abundance have been documented in those areas with greatest vegetative
structure, including woody shrubs and trees. Avian richness and abundance are often
lower in grassed edge, and lowest in row cropped fields (Shalaway 1985, Best et al.

7
1990, Camp 1990). Therefore there appears to be a strong correlation between
decreasing species richness and abundance and decreasing structural diversity in farm
systems. Similar results have been obtained in European studies (Baillie et al. 1997).
Production practices associated with agricultural intensification are also
problematic for birds utilizing agricultural landscapes. Intensive agricultural
practices include greater working of the land with quick rotations or relay cropping,
cover crops replacing fallow rotations, increased livestock densities, and use of high
yielding cultivars requiring greater or more frequent fertilization and irrigation
(O’Connor and Boone 1990). Rodenhouse et al. (1993) indicated that Breeding Bird
Survey abundances of many bird species in agricultural landscapes have exhibited
significant negative associations with specific crops between 1973-1989, suggesting
detrimental cropping practices are being employed. Multiple quick crop rotations
within a year, or relay cropping, increases the frequency of disturbance during avian
breeding potentially causing direct injury to adults and nestlings. Injury and nest
destruction by farm machinery can occur during field preparation, planting, crop
management, and harvest operations. Individuals can also be harmed indirectly
through the application of herbicides and insecticides that alter vegetation structure
and the insect food base within and immediately surrounding cultivated parcels
(O’Conner and Boone 1990, Rodenhouse et al. 1993). In their publication Birds in
Europe, Tucker and Heath’s (1994) analysis of the major threats to birds listed as
species of conservation concern showed that agricultural intensification affects more
species than any other threat.

Birds as Predators in Agroecosystems
While the detrimental effects of modem agriculture on birds has received
much attention, the importance of wild bird management to enhance the productivity
and sustainability of agriculture, or to maintain ecological integrity and biodiversity
in agroecosystems, has not been thoroughly investigated (Rodenhouse et al. 1993,
Kirk et al. 1996). Rodenhouse et al. (1993) suggest that the development of lower
input sustainable agriculture and acceptance of integrated pest management (IPM)
programs may offer opportunities for greater avian conservation in agroecosystems.
Most importantly, management of uncultivated habitats (where birds may thrive) to
preserve natural enemies of agricultural pests will become a central part of pest
management planning in IPM (Rosen et al. 1996). The conservation value for bird
species utilizing low-input agricultural landscapes will be realized through the
reestablishment of habitat (i.e. Woodlots, windbreaks, complex hedgerows, etc.) and
an increase in food resources enhancing both their survival and reproductive success.
Rodenhouse et al. (1995) believe that the key to acceptance of conservation measures
that benefit avian species in agricultural landscapes is that management
recommendations do not interfere with, and hopefully enhance, production. Here lies
an important opportunity for ornithologists. By illustrating that birds may be of
economic value by enhancing production through predation of pest insects, farmers
could be encouraged to consider providing habitat for these species in their cropping
systems and farm landscapes.
Studies relating individual pest species to individual bird species or groups of
species offer sufficient evidence that birds can and should be considered as an

9
important component of modem biological pest management schemes (Jackson
1979). Birds are important predators of many destructive forest insects and play an
important role in suppressing phytophagous insect populations in forest ecosystems
(reviewed by Takekawa et al. 1982, McFarlane 1986, Price 1987). Moreover, via
numerical and functional responses to insect outbreaks in North America birds are
potentially decreasing insect outbreak frequency and severity (Holling 1988, Dahlston
et al. 1990, Holmes 1990). Limitation of phytophagous insect biomass in these
systems may have an important effect upon primary productivity within forest
systems. For example, Marquis and Whelan (1994) have demonstrated that exclusion
of insectivorous birds from foraging on phytophagous pests of white oak in Missouri
significantly reduces long-term primary productivity of individual trees. Over several
years, trees harboring insectivorous birds had greater leaf area and stem elongation
than did trees where birds were excluded or in trees that were sprayed with
insecticide. Conceivably, birds utilizing agricultural areas could provide similar
biomass reduction and productivity benefits, which could be realized through
appropriate management practices (Rodenhouse et al. 1995, Kirk et al. 1996).
Over the past 10 years, field entomologists and agronomists have increasingly
recognized that conservation of natural enemies via management of non-cropped
habitats that support them is important to effective and successful biological control
in agricultural systems (Rosen et al. 1996). However, despite its demonstrated value,
the theory and practice of enhancing native natural enemies as integral components of
agroecosystems has been relatively neglected (Picket and Bugg 1998). If a low-input
productive balance is to be restored within agroecosystems, farmers must recognize

10
and make use of natural control of insect pests by providing for the needs of all
potential predators of pest insect within these systems. As was recognized long ago
by economic ornithologists, most birds that traditionally utilize agricultural areas may
be of great economic value by providing biological stability in agroecosystems.
Conservation of beneficial insectivorous birds through habitat enhancement on farms
could result in significant economic benefits to agricultural production by reducing
pest control costs and improve sustainability through reduced reliance upon persistent
toxic agrochemicals.
Examples of Experimental Work Investigating the Impact of Birds
on Insect Populations in Modern Agroecosystems
Since 1950, several studies have focused upon 2 pests of field crops, com
borers and grasshoppers, utilizing exclosures to compare insect populations protected
from bird predation (Kirk et al. 1996). Both Floyd et al. (1971, 1969) and Black et al.
(1970) reported significantly lower survival of overwintering com borer larvae found
in com stalks exposed to bird predation compared to those present within exclosures.
As overwinter losses were normally low due to other factors, they concluded these
were destroyed via predation by birds [such as Northern Flickers (Colaptes auratus)]
observed feeding on com stalks. Numbers of larvae removed compared with the
numbers remaining in infested stalks where birds had been excluded ranged from
45% to over 80% in these studies. Quiring and Timmins (1988) found similar results
of reduced com borer larvae overwinter survival due to predation by American Crows
(Corvus brachyrhynchos) in southwestern Ontario, Canada. Additionally, com borer

11
larvae removal was found to be greatest in those fields nearest one of the largest
known crow roosts in the region.
Exclusion studies of bird predation impact upon grasshoppers in rangeland
systems (frequently grasslands are interspersed with row cropping fields) have
produced mixed results. While Belovsky et al. (1990) determined birds had a minor
impact on grasshopper populations, other studies indicated that birds do affect
grasshopper densities and species richness. Joem (1986) concluded that avian
predation can have a significant impact on grasshopper populations through biomass
reduction and reduction of species diversity. Modeling this, Kirk et al. (1996)
estimated that a grasshopper-eating passerine family unit could consume 3.7 kg of
grasshopper biomass, or approximately 149,000 individuals per breeding season. In a
grassland system of Northwest China, numbers of breeding Rosy Starlings (Sturnus
roseus) were increased after human made nesting sites with shrubby cover and water
were added (Olkowski and Zhang 1998). Researchers determined grasshopper
numbers were reduced from 42 to 2.3 per m2 within a 500 m radius around artificial
nesting structures by the end of the birds’ breeding season (Chen 1986, Olkowski and
Zhang 1998).
Two recent exclosure studies have evaluated the impact of bird predation on
foliage arthropods in coffee plantations and lepidopteran pests in an orchard system.
Greenberg et al. (2000) found birds reduced the abundance of large arthropods on
coffee plants by 64-80%, compared to that those found on plants where birds were
excluded, depending on the coffee system type (shade or sun coffee). A significant
reduction in leaf damage to coffee plants was associated with this reduction in

12
arthropod biomass in both coffee systems. Mols and Visser (2002) found that
caterpillar damage levels to apples in orchards decreased with increased periods of
foraging by great tits (Pams major). Overall damage to apples by caterpillars was
reduced by measurable amounts improving yield, number of apples per tree,
compared to trees where great tits were excluded.
Both McFarlane (1976) and Kirk et al. (1996) conclude that strong
experimental evidence in forest and grassland systems suggests avian predation could
suppress crop insect pest populations at medium or low infestation levels,
representing an important ecological in agroecosystems would compliment integrated
pest management plans. While birds alone may not “regulate” insect pest
populations, combined with other forms of pest management, they promise to play an
important ecological role in agroecosystems (Kirk et al. 1996). Sympathetic
management is needed to stem the decline of farmland birds and enable them to
assume a mutualistic role with agricultural production.
Natural Systems Agriculture or Ecoagriculture
Agricultural modernization largely contradicts ecological principles.
Consequently modem, or “conventional”, agroecosystems are inherently unstable,
plagued by recurrent pest outbreaks, pollution of water systems, soil erosion,
salinization, and other undesirable environmental and social costs (Altieri 1994).
Modem agriculture emphasizes artificial single species monocultures, requiring
constant human intervention to suppress ecological succession and maintain
productivity (Swift and Anderson 1993). Additionally, simplification of species

13
composition of biological communities both reduces their stability and results in
increased susceptibility of that community to invasion by undesirable species (Elton
1958, Crawley 1987). Therefore, conventional agriculture exists in a metastable
equilibrium regulated by enormous inputs of energy (Harwood 1990) and human
activity (Gliessman 1987). The inherent self-regulation of populations within natural
biotic communities is lost when humans modify community interactions and disrupt
coevolutionary processes (Turnbull 1969). Inherent limitations of species populations
within natural communities is a desirable attribute to incorporate into synthetic
agroecosystems (Turnbull 1969) and, in particular, enhancement of predator-prey
relationships characteristic of natural systems has a pivotal role to play in the
evolution of agriculture towards more environmentally sustainable systems in this
century (Atkinson and McKinlay 1997).
An ecosystem approach to agriculture emphasizes management of
agroecosystems in such a manner that sufficient food production will be sustainable
and of high quality with minimal environmental disturbance (Colby 1990, McNeely
and Scherr 2003). Utilizing this approach, it is believed that a multitude of beneficial
ecological processes can be incorporated into agroecosystems (Soule and Piper 1992).
The central idea for “ecological agriculture” is that the structures of native biological
communities are the most appropriate structural models for agriculture. Such
communities have developed and endured in particular environments as a result of
centuries of evolutionary selection for ecosystem function (The Land Institute 1999,
McNeely and Scherr 2003). Agricultural systems that are modeled after natural
ecosystems should exhibit many functional attributes and processes that stabilize

14
natural systems, including vegetation adapted to the local climate, closed nutrient
cycling, effective resource partitioning, soil preservation, and biological methods of
crop protection (Soule and Piper 1992). Therefore, by mimicking the local natural
vegetation structure of native biological communities, farmers can emulate a whole
package of patterns and processes that have developed over an evolutionary time
frame exhibited by these ecological systems. Additionally, rather than perfecting one
crop at a time, this holistic ecological perspective to agricultural production suggests
seeking out a collection of plants and animals that work well together. It is this
perspective of natural systems agriculture that provides a great opportunity for avian
conservation.
The potential exists to manage farm habitats to attract selected desirable
species in greater numbers in order to create a stable guild of insect predators, capable
of rapid aggregation to high density “hot spots” of colonizing pests, and capable of
switching to pest species from alternative foods (Helenius 1998). Methodologies that
promote the abundance and diversity of pest insect predators will not only
significantly contribute to non-chemical based crop protection but also provide
beneficial consequences in conserving biological diversity in agricultural landscapes.
Habitat management to enhance biological control of arthropod pests can provide
various environmental requisites to pest insect enemies (such as birds) including
modified climate, protective cover, nesting habitat, and supplementary foods (Pickett
and Bugg 1998). Colonization, dispersal by diffusion, and foraging movements of
beneficial predators can be influenced through habitat modifications within cropping
systems (Helenius 1998). For example, weedy vegetation strips within fields could

15
be arranged in such a way as to provide refuge and increase interspersion of foraging
predators within large cropped areas (Nentwig 1998). Modifying agricultural
landscapes, or “farmscaping,” by adding features such as hedgerows, field margins,
shelterbelts, and roadside and watercourse plantings using native trees, shrubs,
perennial grasses, and herbaceous and annual broadleaf species can attract and sustain
beneficial arthropod pest predators (Bugg et al. 1998).
Ornithologists have an opportunity to propose management recommendations
favoring avian conservation within agricultural production systems by working within
interdisciplinary teams developing modem sustainable or ecoagriculture. The largely
unexplored diversity of avian insect predators that could be included in natural
biological regimes offers numerous possibilities for their use in cropping systems.
Birds of conservation concern, both resident and migratory, can benefit from
cropping systems and farmland habitat structure created to enhance insectivorous bird
use of agroecosystems. Through this effort, many habitat features and the structural
complexity once found within agricultural landscapes supporting avian species in the
past would be reintroduced. As agricultural producers recognize the importance of a
structurally and biologically diverse farmed environment, ornithologists can institute
the resurrection of quality avian habitat within agroecosystems. With enlightened
management of farmlands both the needs of agriculture and numerous avian species,
as well as other wildlife, can be satisfied and mutually beneficial (Rodenhouse et al.
1995).

16
Research Needs
Before we can propose that agricultural producers can truly employ birds in
pest management schemes we must not only know the relationship between insect
pests and avian species, we must have an understanding of the functional role birds
currently play in modem agroecosystems. With this understanding, management
recommendations for biological control enhancement can be developed by
manipulating populations of avian species identified as potentially beneficial
currently existing in, or that could be attracted to, these systems. Rodenhouse et al.
(1995) state that future research should focus upon identifying farmland structures
and agricultural practices that create and sustain avian populations. They explain that
studies of annual breeding productivity and survival of birds nesting in fields and
edges are few, potential source areas that may require protection or expansion have
not been identified, and the values of specific landscape elements and combinations
of elements have not been determined for agroecosystems. Therefore, they believe
that both field-scale and landscape scale studies need to be performed and integrated.
Kirk et al. (1996) believe that a consideration of birds should be part of any
economic cost/benefit assessment related to pest control programs and farm
landscapes should be managed with them in mind. They state that more
multidisciplinary studies are needed to examine: (1) the abundance and availability of
birds relative to various insect pest species, (2) avian diets and foraging habits to
determine quantitatively the site-specific level of predation on invertebrate pest
species compared to other arthropods, (3) integration of birds with other natural insect
enemies, and (4) management of farmland landscapes in ways that best augment

17
natural control of insect pests. Wratten et al. (1998) indicate the potential for the
expansion of research exploiting ecological knowledge in farmland management is
promising. They suggest that a better understanding is needed of 3 related processes:
(1) the spatial scale dynamics of beneficial insect predators on farmland, (2) the
potential negative effects of insect predator refugia, and (3) the mechanisms involved
in the functioning of within-field and border refugia for the enhancement of natural
enemies of insect pests in agroecosystems.
Conclusion
Ornithologists have suggested that change in agricultural practices and
landscape structure over the past few decades have reduced the favorability of
farmland habitat elements many farmland species had traditionally utilized.
Agricultural landscapes have become increasingly homogeneous through the
removal, fragmentation, and isolation of these elements upon which many species had
come to depend. Intensification of agriculture, resulting in changes in production
practices, has also been cited as being problematic for birds utilizing agricultural
landscapes. Direct injury to individuals and nest destruction can be caused by farm
machinery during cropping operations. Individuals may also be harmed indirectly
through the application of agrochemicals. Holistic ecological perspectives to
agricultural production of both sustainable and natural systems agriculture provide an
opportunity to promote the inclusion of suitable habitat in agricultural lands for avian
species. Farm habitats can be managed to attract desirable insect pest predator
species in greater numbers contributing to non-chemical based crop protection as well

18
as improve conservation of biological diversity in agricultural landscapes. Migratory
and resident species of conservation concern will also benefit from farm structure and
management created to enhance avian presence in agroecosystems.
Recommendations developed by the ornithological community integrating the
body of information defining the problems faced by farmland birds with research
illuminating the functional role birds play in these systems, can potentially reverse
agricultural practice-induced avian population declines. Aldo Leopold stated,
In its extreme form it [agriculture] is humanly desolate and economically
unstable. These extremes will someday die of their own too much, not
because they are bad for wildlife, but because they are bad for farmers.
When that day comes, the farmer will be asking us how to enrich the wildlife
of his community. (Leopold 1945, page 168)
As imperatives for agricultural shift from the single goal of increasing production per
acre to environmentally sustainable systems, an excellent opportunity exists to match
the aspirations of farmers with needs of birds of conservation concern.

CHAPTER 2
AVIAN BIODIVERSITY AND FUNCTIONAL INSECTIVORY ON NORTH-
CENTRAL FLORIDA FARMLANDS
Introduction
Although agroecosystems do not support the biodiversity of natural landscapes
they replace, under the right circumstances they can provide diverse ecological functions
in addition to habitat for wild species. In regions where urbanization is rampant (e.g.,
Florida) farmlands are often the only ecological buffer between natural ecosystems and
suburban sprawl (Evans and McGuire 1996, McNeeley and Scherr 2002). Reflecting
growing public concerns over scientific reports of agriculture’s negative effects on
human and ecosystem health (e.g., Parsons et al. 2000) during the past decades, policy
makers have been responding with incentives to modify grower operations to reduce
negative environmental impacts and increase ecological values of farmlands (Ikard 1996,
D’Souza and Ikerd 1996). For example, USDA programs like SARE (Sustainable
Agriculture Research and Education) promote development of sustainable agricultural
practices through research partnerships between farmers and scientists
(http://www.sare.org/htdocs/sare/about.html). Additionally, the Farm Bill of 2002
provides farmers monetary incentives for conservation of soil, water, air, and biodiversity
(Farm Security and Rural Investment Act of 2002). Signs of change toward ecological
agriculture include an increase of 10% per year in US farmland acreage under certified
organic management (USDA 1996, 2000, 2001a). With the public, policy makers, and
19

20
farmers increasingly involved in exploring alternative agriculture, the need for research to
integrate production of ecological services, native biodiversity, and healthy foods is also
intensifying (Rodenhouse et al. 1995, McNeeley and Scherr 2002).
Wildlife conservation is a natural partner in cultivating ecological agriculture
(Vandermeer and Perfecto 1997, McNeeley and Scherr 2002), yet this partnership is
weak because conventional food production practices that are detrimental to biodiversity
still dominate, and because research has not been satisfying demands for information for
ecologically-oriented farm operations (Hess 1991, Alston and Reding 1998, Jacobson et
al. 2003). Habitat destruction for agricultural expansion remains the single most
important cause of biodiversity impoverishment the world over (Vitousek et al. 1997),
and if native biotas are to survive the coming decades of human population expansion,
agricultural production lands must improve their biodiversity-holding capacity (Pimental
et al. 1992, Hobbs and Norton 1996). Indications are that alternative agriculture practices
encourage native wildlife and protect ecosystem services better than conventional
production agriculture (Warburton and Klimstra 1984, Pimental et al. 1992, Uri et al.
1999, McNeely and Scheer 2002), in part because sustainable farming generates
heterogeneous vegetative environments with features (hedge rows, shelter belts, mixed
cropping systems, and plantings that host natural enemies of pest species; O’Conner and
Boone 1992) that encompass many recognized values for both wildlife and people (e.g.,
wild flowers, pollinators, and game; Daily 1997a). Conventional agriculture, however,
still dominates human landscapes in the developed world, to the detriment of native
biodiversity. For example in the U.S., over 200 native species of resident and migratory
birds feed, roost, or breed on agricultural lands (Rodenhouse et al. 1993), but many of

21
their populations decline by 50% or more where expansive monocropping systems with
short rotation periods, heavy chemical inputs, and intensive mechanization reign
(O’Conner and Shrubb 1986, Rodenhouse et al 1993, Freemark 1995, McLaughlin and
Mineau 1995; bird declines in Europe - see, Pain and Dixon 1997, Pain and Pienkowski
1997, Ormerod and Watkinson 2000).
Ecological research on farmlands would help the shift to ecologically sustainable
agriculture, but research to foster ecological integrity on farms is scarce (Cochrane 1993,
McNeely and Scheer 2002), despite numerous encouraging factors: 1) considerable
public interest, 2) diverse ecological values of farmlands, 3) an enormous area on the
earth’s surface in which to work (950 million acres in the U.S.; USDA 1999), 4) global
biodiversity conservation needs to prioritize farmlands, because current parks and
reserves are insufficient and, 5) farmlands are relatively easy to restore to native
ecosystems (Askins 2000, McNeely and Scheer 2002). One reason for lack of interest in
conservation research in agroecosystems is that agriculture is a business and ecologists
have largely failed to show how biodiversity conservation and ecological functionality
can realize economic benefits for growers (Daily 1997b, McNeely and Scheer 2002). A
priority area of interest to growers has always been pest control. Whereas bio-control
programs focus primarily on invertebrate predators on pests, little work has been done to
integrate vertebrate species into row crop agricultural systems. In this study I assessed
the potential that native bird species could serve as effective predators of pests. I
examined factors influencing avian species diversity on North-central Florida farmlands
and, in particular, factors that increased insect-eating activity by wild birds in cropped
fields. Goals for this study were two-fold: 1) to assess overall avian biodiversity (species

22
richness and densities) on a selection of conventional and certified organic farms, and
identify farm characteristics (management and vegetative structural features) correlated
with bird diversity, and 2) to identify ‘functional insectivores’ among the bird species
utilizing farmlands (or, those species that we observed to feed frequently on insect prey
in cropped fields), and to identify farm characteristics (management and vegetative
structural features) correlated with the densities of functional insectivores in cropped
fields.
Study Design
Certified organic farming is defined as crop production without the use of most
conventional pesticides, synthetic fertilizers, sewage sludge, or bio-engineered food
plants (USDA 2002). Other works have shown that both birds and insect biomass can be
higher on organic, or low input, than conventional farms (birds: Christensen et al. 1996,
Chamberlain et al. 1999, Freemark and Kirk 2001, Beecher et al. 2002; insects:
Dritschillo and Wanner 1980, Hald and Reddersen 1990, Brooks et al. 1995, O’Leske et
al. 1997, Feber et al. 1997 & 1998). Therefore, in this investigation of factors affecting
bird diversity, abundance, and insect foraging paired sampling sites were selected on both
organic and conventional farms. In addition to censusing the bird community over 2
years (2000 and 2001), extensive foraging observations were conducted on individual
birds in cropped areas, and both field scale features (crop type, field border vegetation)
and type of matrix adjacent to each sampled field were characterized as predictors of both
bird diversity and foraging activity on the two farm types. I define functional
insectivores as bird species that were observed most commonly feeding on insect prey
taken from crop vegetation. All of my study species have been classified in the literature

23
according to well-established foraging guilds (e.g., frugivore, insectivore, omnivore)
based on their most typical or average annual diet composition across the US (De Graaf
et al. 1985). However, many birds’ diets vary with season, and both typical frugivores
and omnivores can be highly insectivorous during breeding efforts (Beal et al. 1941,
Martin et al. 1951, Ehrlich et al. 1988). Therefore, rather than using ‘typical’ dietary
guilds to classify how birds might be interacting with insect pests, I wanted to know
which species were frequently out in fields eating insects during the spring growing
seasons on the farms studied. The most abundant of these insect-foraging species were
designated as functional insectivores - or those most likely to consume insect biomass
with positive economic outcomes for farming operations.
Methods
Research Site Selection
With the aid of University of Florida Cooperative Extension agents, and following
farmer participation in surveys (see Jacobsen et al. 2003), local producers were contacted
to obtain permission for conducting research on their properties. A total of 30 census
points were established on certified organic farms during April of 2000, and a paired
reference site for each of these points on a nearby conventional farm was established (n =
60 total points, 10 organic and 10 conventional farm properties) in an effort to match crop
types, habitat structure, field border types, and matrix vegetation where possible (after
Rogers and Freemark 1991, Christensen et al. 1996, Chamberlain 1999). In 2001, one of
the organic farms sampled in 2000 was not planted, thus 5 fewer points were used in the
second year of the study. The 20 farm properties ranged in size from 4 to 104 ha located
within Alachua, Gilchrist, Marion, and Jefferson Counties of North-central Florida.

24
Patterns of Bird Diversity
Census surveys
Surveys were used to estimate bird species richness and density in cropped and
non-cropped habitats on farms. Birds were censused utilizing point count methods
described in Bibby et al. (1992) with modifications recommended by Freemark and
Rogers (1995) to suit agricultural landscapes. Sampling points of 50 m radius (fixed)
were situated on the border of cropped fields with non-cropped areas (Figure 2-1).
Census points were at least 200 m apart if they occurred on any single farm management
unit. All points were sampled a minimum of 4 times between 25 April and June 30 in
both 2000 and 2001, and order of visitation to sites in the pair (organic vs. conventional)
and the order of points visited on each farm management unit were reversed each visit.
Censuses were conducted between dawn and 1100 EST on fair weather days. All birds
seen or heard within the 50 m fixed-radius during a 10 min period were recorded.
Registrations were recorded and mapped onto two 180° semi-circles (in the cropped field
and the un-cropped area - after Freemark and Rogers 1995; Figure 2-1). By marking the
locations of individuals and noting their movements on maps this minimized the potential
of double counting individuals during counts. By censusing in this manner, I quantified
bird occurrences, both within cropped areas close to field edges and in adjacent non-
cropped habitats.
I began counting 2-3 minutes after arriving at each station. Birds occurring
outside of the circles or flying overhead were noted (see below) but excluded from point
count data, with one exception; I considered swallows or purple martins flying low (< 10
m above vegetation) over fields to be ‘using’ them (since they are likely to be foraging on

25
Figure 2-1. Aerial view of a farm site in Alachua Co. illustrating 50 m radius point count
circle positioned on the edge of a cropped field where cropped field and field border
habitat type were characterized. Matrix type adjacent to each field was characterized
within a 200 m radius semicircle at each census point (after Freemark and Kirk 2001).

26
insects; see Boutin et al. 1999). Birds flushed within a count circle as an observer
approached or left a station were counted if they were not otherwise recorded during the
count period. If a flock was encountered, it was followed after the end of the sampling
period (if needed) to determine its composition and size. Because sampling occurred
during the breeding seasons only, singing males observed repeatedly during counts were
assumed to be paired breeders and were counted as two individuals (after Bibby et al.
1992). Walk-abouts were conducted in cropped and non-cropped areas on each farm unit
following point counts (Freemark and Rogers 1995). Only species not noted during the
formal point counts were recorded during walk-abouts.
Habitat classification: field-scale features and adjacent matrix type
Habitat characteristics associated with each census point were assessed at field
edges and in surrounding matrix (Figure 2-1; refer to Table 2-1). Field scale
characteristics of the farms were classified within each 50 m census point and included
whole-farm management type (certified organic or conventional), crop diversity (mixed
or mono crops), and field border habitat types (see Table 2-1). Matrix types that
dominated the immediate area adjacent to fields sampled were characterized within a 200
m (6.3 ha) radius semi-circle adjacent to the cropped field edge (see Freemark and Kirk
2001, Figure 2-1, Table 2-1). The dominant matrix type was identified as the one habitat
type covering the largest area within the 200 m semi-circle. Area of each matrix type
was measured within the semicircle plot utilizing ESRI ArcView software and the Xtools
extension package (Oregon Dept, of Forestry 2001) and 1999 digital ortho quarter-quad
aerial photos obtained from the Florida Department of Environmental Protection. Of the

27
Table 2-1. Predictor and response variables used in analyses. The representative scale of
measurement for each predictor variable is indicated in column 3. See text for clarification.
Variable Categories Scale Definition
Predictor Variables
Year
2000
2001
Farm type
Conventional
Organic
Crop
Mono
Diversity
Mixed
Border type
Crop
Hardwood
Hedge
Pasture
Suburb
Pine
plantation
Matrix type
Crop
Hardwood
Pasture
Suburb
Pine
plantation
Response Variables
Density *
Species richness *
Insect-foraging observed **
Whole Farm
Whole farm
50 m radius census plot
50 m radius census plot
50 m radius census plot
50 m radius census plot
50 m radius census plot
50 m radius census plot
50 m radius census plot
50 m radius census plot
200 m radius semicircle
200 m radius semicircle
200 m radius semicircle
200 m radius semicircle
200 m radius semicircle
50 m radius census plot
50 m radius census plot
50 m radius census plot
Time (2 levels) included as
repeated measure in analyses
Conventional management
Certified organic management
Single crop species in field
2 or more crop species in field
Cultivated field in production
Broad-leaved trees > 5 m tall
Linear strip of woody
vegetation
Improved grassland: grazed
Residential development
Slash pine trees > 5 m tall
Cultivated field in production
Broad-leaved trees > 5 m tall
Improved grassland: grazed
Residential development
Slash pine trees > 5 m tall
Mean # of birds / ha
Total # of species counted
Categorical (yes / no)
3 measures taken: whole point count circle, crop half, and field border half of circle.
Only in crop half of point count circle.

28
five matrix types (Table 2-1), the mean coverage for each primary matrix type was never
less than 62% (max 90%) of the 200 m radius semi-circle.
Determination of functional insectivores
In order to identify those species exhibiting the greatest potential as arthropod
pest predators in cropping systems a minimum of two 1-hour ad libitum foraging
observation sessions per census point were conducted during each of the two breeding
seasons (Robinson and Holmes 1982, Rodenhouse and Best 1994). Observations were
taken within the cropped portions of the 50 m fixed-radius point count circles. Foraging
data included identification of species observed to take invertebrate prey from crop
vegetation. Birds were determined to be insect foragers if they perched on, or flew low
over, crop vegetation while taking insect prey - at least one successful prey capture had
to be observed for a bird to be designated as a forager. I then selected functional
insectivores, or those species most likely to have an impact on insect pests in cropped
areas, in the following manner - from among the species documented to be taking insects
in cropped fields the ten species were picked that also occurred in the greatest densities in
the cropped areas (from point counts). The factors (field and matrix characteristics;
Table 2-1) associated with the highest recorded densities of the ten functional
insectivores were then assessed in cropped fields that were sampled (see Data Analysis).
Data Analysis
Bird diversity
Because of my initial expectation that farm management would influence avian
biodiversity, avifaunal differences between the organic and conventional farm sites
sampled was broadly assessed, including species lists, comparisons of total species

29
counts with Breeding Bird Survey data and Audubon Society occurrence data from
Alachua County (where most of the farms were located). Total species counts for each
farm were determined by totaling the number of species detected on point counts, species
noted inside cropped areas but outside the fixed radius during point counts, and species
detected during search surveys (walk-abouts for 30 min).
In order to determine how field and matrix characteristics influenced bird species
richness and density only point count data was used and analyzed in the following way.
The number of individuals and species counted in each circle was averaged over all
counts done in each circle in each year. Count data by crop versus field border portions
of each count circle were also separated out. Thus, for each count circle the following 6
response variables were derived: mean number of species per count circle, mean number
of species in the field border vegetation, mean number of species in crop vegetation;
mean density of birds per count circle (standardized to # of birds / ha), mean density of
birds / ha of field border, and mean density of birds / ha of crop. The three density
variables and the three richness variables were submitted to two separate repeated
measures multivariate analysis of variance (RM-MANOVA) with the following predictor
variables: year (as the repeated measure), farm type, crop diversity, border type, and
matrix type (Table 2-1).
Functional insectivory
Finally, to understand what farm-scale habitat features might influence
insectivory in cropped fields a univariate repeated measures analysis of variance
(RMANOVA) model was applied with the same predictor variables as above, and density
of birds (ten functional insectivore species only) detected only in the crop half of count

30
circles as the response variable.
Results
Bird Species Richness on Organic versus Conventional Farms
In statistical models of factors influencing species richness, farm management
(organic versus conventional) was never a significant predictor. However, on average,
more bird species were observed on (and unique to) organic than conventionally managed
farms (Figure 2-2, see Appendix A). A total of 64 different bird species were recorded in
point count censuses during the first field season (1 May - 30 June 2000). Sixty species
were observed in or near organic crops, 49 in or near conventional fields, 45 were
common to both farm types, 4 were unique to conventional and 15 to organic systems.
Seventy-four species were counted in 2001 (25 April - 30 June). Sixty-six of these
species were observed in or near organic and 58 in or near conventionally managed
fields, 52 species were common to both farm types, and 6 were unique to conventional
systems, and 14 to organic systems (see Appendix A). Together, the species observed
using farmscapes of North-central Florida represented 82 % of resident and migratory
landbird species listed as breeders in Alachua County (where most of our samples were
taken; Alachua Audubon Society 2003) and nearly all of those species noted in recent
Breeding Bird Surveys along the two routes monitored in the same county (USGS 2001a,
USGS 2001b; FFWCC 2003; Figure 2-2). I observed 24 listed species on organic farms
(18 state listed, 6 federally listed), and 18 listed species on conventional farms (14 state, 4
federal; see Appendix A). Of the five farms with the most bird species, 3 were organic
and 2 conventional. Finally, all 10 of the functional insectivore species (abundant insect-

31
100-
Figure 2-2. Number of landbird species known to breed in Alachua County, FL (Alachua
County Audubon Society 2003) and species documented on the two Breeding Bird
Survey routes (# 25013 and 25113; USGS 2001a, USGS b, Florida Fish and Wildlife
Conservation Commission 2003) compared to the number of species observed in organic
and conventionally managed farmlands of north-central Florida during the breeding
seasons of2000 and 2001 (1 May- 30 June, 25 April - 30 June, respectively).

32
eating species observed in cropped areas) were observed in both organic and
conventional fields (see below).
Factors Influencing Bird Community Structure
Species richness
A RM-MANOVA model was constructed in the following way: year (2 levels) as
the repeated measure; mean number of species per point, per crop half, and per border
half of point count circles as response variables; farm type, crop diversity, field border
type, adjacent matrix type as categorical predictors; all main effects and 2-way
interactions were specified using Type III sum of squares. No within-subjects contrasts
(year effects) were significant (at alpha = 0.05), and only field border type had a
significant influence on species richness (per point; Fsjo = 3.5, P = 0.013, and field
border half of the count circle; Fsjo = 3.8, P = 0.009; see Figure 2-3 caption for multiple
comparison tests).
Bird density variation
Using the same RM-MANOVA model as above, with three different response
variables (mean densities of birds per point, per crop, and per border half of count
circles), again no effects of year were found, and only crop diversity significantly
influenced bird densities (per point; Fijo = 7.4, P = 0.011, and per crop half of the count
circle; Fijo = 8.2, P = 0.008); fields with more than one crop type had higher bird
densities (Figure 2-4). All other factors and interaction terms were non-significant. I
noted that the two most abundant species sampled were Northern Cardinal and Northern
Mockingbird. Since these two species numerically dominated the data, and both are
known to be edge and disturbance associated (Ehrlich et al. 1988, Derrickson and

33
Figure 2-3. Mean number of species detected per point, and in crop half of point count
circles (both years averaged). Error bars = 1 SE. Multiple comparisons tests (LSD)
indicate the following: hardwood and hedge borders generated significantly more species
per point than crop, pasture, or pine plantation borders (P < 0.03); hardwood borders
generated more species in crops than all other border types except hedges (P < 0.05), and
hedge borders generated more species in crops than pasture and pine plantation (P <
0.03).

Mean Density (Birds / ha)
34
mix mono
Crop Diversity
Figure 2-4. Mean densities of birds (all species) detected per point, and per crop half of
point (years combined) in mono-cropped and poly-cropped fields. Error bars = 1 SE.

35
Breitwisch 1992, Halkin and Linville 1999), I decided to re-run this analysis without
them to get insights about abundance variation of species with other kinds of habitat
associations. The same RM-MANOVA model was re-applied and again found no effects
of year but significant effects of crop diversity on densities of birds in crops (Fi^ = 10.5,
P = 0.003; higher densities in mixed crops). Border vegetation type was also found to
significantly affect densities per point (Fs,29 = 3.8, P = 0.01) and in the crop (Fs,29 = 4.1, P
= 0.006; see Figure 2-5 caption for multiple comparison tests), and there was a significant
interaction between adjacent matrix and field border vegetation types on bird densities in
the crop (F6,29 = 2.5, P = 0.044; Figure 2-6). Given that I did not have all combinations of
border and matrix types represented in my point count sampling, multiple comparisons
could not be run on the interaction. However, of the combinations sampled, the greatest
numbers of birds were observed in crops that were bordered by hardwood with adjacent
pine plantation matrix, bordered by hedge with adjacent hardwood, pasture, or pine
matrix, and in fields with pasture in both border and adjacent matrix (Figure 2-6).
Foraging activity in cropped fields: functional insectivory
After completing 2 h of foraging observations at each of the 60 census points each
year, I focused further sampling in each year on the 30 points with the most foraging
activity observed during the first two 1 h sessions (an additional 2 h of sampling at each of
30 points in each year for a total of 360 hours of foraging observations in cropped fields).
Of the 49 species of birds observed in or near conventionally managed crops during the
2000 breeding season, 14 species (29%) foraged in crop vegetation, and 23 of 60 (38%)
species on organic farms foraged in crop vegetation (see Appendix A). In 2001, 20 of 58
(35%) species on conventional and 36 of 66 species (55%) on organic farms actively

36
Field Border Type
Figure 2-5. Excluding Northern Cardinals and Northern Mockingbirds, mean densities of
all birds per point, and per crop half of point count circles, by field border type (years
combined). Error bars = 1 SE. Multiple comparisons tests (LSD) revealed the following
(P < 0.03): hardwood borders generated higher densities per point than all types except
hedge, and hedge generated higher densities per point than crop, pasture and pine
plantation. No multiple comparisons among border types for bird densities in crop half
of count circles were significant (although the main effect was).

Bird Density in Crop (Birds / ha)
37
12 '
11 -
10 ‘
8-
T
6‘
5'
4‘
2"
1 "
4
Matrix Type
â–  crop
H hardwood
â–  pasture
Slpineplan
â–  suburb
i* D,.l
crop hardwood
hedge
pasture pineplan
Field Border Type
Figure 2-6. Excluding Northern Cardinals and Northern Mockingbirds, mean bird
densities in crops given different combinations of field border vegetation type and
adjacent matrix vegetation type. Error bars = 1 SE.

38
foraged in cropped areas. In both seasons I noted that foraging activity was most common
in cropped areas with perching structures from which birds could survey for potential food
items. Densities of the ten functional insectivore species were significantly greater in the
crop half of census points that contained numerous perching structures (t = 6.13, p < 0.001,
N = 60). This was true whether the perch was manmade (e.g. an elevated sprinkler head)
or vegetative (e.g. sunflower or com stalks) regardless of farm management type.
Of the ten functional insectivore species identified, only 4 are usually classified as
insectivores, one as a carnivore, and 5 of the ten species are normally considered
omnivores (De Graaf et al. 1985, see Appendix A), although all are known to be
insectivorous during the breeding season (Beal et al. 1941, Martin et al. 1951, Ehrlich et
al. 1988). Individuals of these species were observed to capture insects from crop
vegetation and either eat them immediately or carry them into adjacent matrix,
presumably to feed young. The two most abundant of the functional insectivores
(Northern Cardinals and Northern Mockingbirds; Figure 2-7) were also the most
abundant species overall (see above). Using a RM-ANOVA model (using the same
predictor variables and model structure as in the community structure analysis, above),
but only one response variable (mean densities of these ten species in cropped half of
count circles), no effect of year was found, and the only significant main effect was crop
diversity - mixed crop areas had more functional insectivores than monocrops (Fi¿9=
4.2, P = 0.051; Figure 2-8).

Mean Density in Crop (Birds / ha)
39
0.8 -
blgr eabl inbu noca oror
brth gcfl losh nomo suta
Species
Figure 2-7. Mean densities of the ten functional insectivores observed in crop half of
census points. Species codes: blgr = Blue Grosbeak, brth = Brown Thrasher, eabl =
Eastern Bluebird, gcfl = Great Crested Flycatcher, inbu = Indigo Bunting, losh =
Loggerhead Shrike, noca = Northern Cardinal, nomo = Northern Mockingbird, oror =
Orchard Oriole, suta = Summer Tanager. Error bars = 1 SE.

Density of Functional Insectivores
(Birds / ha)
40
5-
4-
2000
Year
Figure 2-8. Mean density often functional insectivores in fields with 1 (mono) or more
than 1 (mixed) type of crop planted, by year. Error bars = 1 SE.

41
Discussion
Avian Diversity on North-central Florida Farmlands
Avian species richness at census points (whole point and border half of count
circle) was strongly influenced by field border types, with hardwood forest and hedge
borders harboring the greatest diversity (Figure 2-3). This finding confirms the general
pattern that structurally complex windbreaks, hedgerows and field borders support more
complex farmland bird communities than conventional ‘clean-farming’ practices that
suppress non-crop vegetation (e.g. Osbome 1984, Green et al. 1994, Parish et al. 1994 &
1995, Chamberlain and Wilson 2000). Data analyses did not reveal any other field-scale
features or matrix types causing significant variation in the number of bird species
visiting the crop half of our point count circles. This is likely to be because the majority
of species attracted to habitats in fragmented farmscapes also utilize fields (see Appendix
A) and those few that do not utilize open fields are those that rarely come to the ground
(e.g., great homed owl, cedar waxwing, red-eyed vireo) or that have behavioral
limitations on entering open areas (e.g., Sieving et al. 1996).
Densities (species combined) of birds, however, varied significantly (among point
counts and in crop half of point counts) with border and matrix vegetation type and with
crop type. With or without Northern Cardinals and Northern Mockingbirds included in
the analysis, fields with mixed crops attracted greater numbers of individuals than mono¬
crop fields (Figure 2-4), and when the two common generalist species were removed,
border and matrix habitat type also significantly affected bird densities in the crops and in
point count circles (Figure 2-5). Thus, removal of mockingbirds and cardinals was
important because as habitat generalists, their numerical dominance in our data could

42
have masked the responses of most species to the farmscape features we considered (see
Best et al. 1995). Hardwood and hedge field borders increased bird densities per point
(Figure 2-5; as they did number of species), and although it appears that hardwoods,
hedge, and pasture generated the highest densities in crops (Figure 2-5), the lack of
significant contrasts was probably due to: 1) the low densities of birds once the two most
abundant were removed and, 2) the significant interactions between border type and
adjacent matrix type.
Findings of this study support tentative generalizations emerging from larger scale
(landscape) analyses of bird distributions that have found blocks of hardwoods or natural
grassland adjacent to cropped areas tend to generate the highest bird diversity on
farmlands (Best et al. 1995 and 2001, Kirk et al. 2001), and that total area and
juxtaposition of vegetative cover types comprising recognizable farmscape elements
(field borders, windbreaks, etc.) largely determine bird densities in agroecosystems
(Freemark et al. 1993, Rodenhouse et al. 1993). Thus, this study emphasizes that, both,
the dominant vegetative communities in landscapes where farms and farm fields are
imbedded and the spatial configuration of habitat on farms determine bird species
diversity on farms. Farmers seeking to manage bird diversity do not have control over
landscape context (once a farm is purchased). But these results suggest that schemes to
design on-farm habitats (crops, field borders, and location of planted fields with respect
to adjacent matrix types) to influence bird diversity could be effective, very flexible, and
accommodate different classes of birds (i.e. woodland, grassland, edge, generalist
species) and, therefore, be excellent tools for avian conservation in agroecosystems (see
below).

43
Bird Diversity on Organic versus Conventional Farms of North-central Florida
In apparent contradiction with other studies in North America (Freemark and Kirk
2001, Beecher et al. 2002) and Europe (Christensen et al. 1996, Chamberlain et al. 1999)
that documented significantly greater bird diversity associated with organic farming
practices, I detected only slight enrichment of bird diversity in organic versus
conventional farming systems of North-central Florida. In fact, most species that could
be expected in North-central Florida during the breeding season were observed utilizing
the farmscapes I studied, regardless of farm management (Figure 2-2). This contradiction
derives from differences in cropping practices on the farms studied by others, and in the
scale at which studies were conducted. In the other studies, birds were surveyed
primarily in farms with mono-cropped fields - mixed crops were uncommon and
variables similar to our ‘crop type’ predictor were not incorporated into analyses. As an
a priori variable in analysis models, crop diversity proved to be a very strong predictor of
bird density. Since both conventional and organic farmers in my sample employed mixed
and mono crops, differences in bird occurrence generated by chemical applications may
have been insignificant by comparison. Moreover, both organic and conventional farms
in North-central Florida are relatively small (10 out of 16 were less than 10 ha) compared
to farms used in other studies that spanned a considerable size range (from a minimum of
10 - 40 ha to much larger). North-central Florida is still largely forested, and because
farms were relatively small, most farm fields were close (or adjacent) to significant areas
of hardwood forest - the habitat that generated the highest farm-bird diversity in this
study. The current landscape is likely to represent a ‘patch mosaic’ of diverse habitat
types long recognized as essential for the maintenance of bird (and other) species on

44
farmlands (birds; O’Conner and Boone 1992, Best et al. 1995: plants; Freemark et al.
2002: moths; Ricketts et al. 2001: ants; Perfecto and Vandermeer 2002). Thus, I
speculate that in farming regions with larger farms (and larger farm fields), where sources
of birds are more distant and mixed cropping is less frequent, organic farm practices may
be more important in determining species diversity than in landscapes with small-scale
farms and a diverse habitat mosaic.
Functional Insectivory in Cropped Fields
I found that birds were willing to utilize cropped fields to forage at most census
points regardless of crop type or management. However, in both years, fields planted
with polycultures attracted the greatest densities of the ten functional insectivore species,
compared to monocropped fields, regardless of other factors (Figure 2-8). The most
attractive fields in this study had vegetable and cut flower intercrops, followed by
multiple vegetable crops, and monocropped systems had the fewest birds; monocropped
watermelon was the least attractive crop. These results are similar to those of Robbins et
al. (1992), Rodenhouse and Best (1994), and Stallman and Best (1996) where avian
diversity, abundance, and foraging activity were strongly associated with increased
structural complexity of vegetation in cropped fields. In general, birds can rapidly assess
within-habitat variation in food availability (Fretwell and Lucus 1970, Hutto 1985) and
will quickly recruit to feed in food-rich patches. Since insect species richness and
diversity increase with vegetation diversity in cropped fields (Elliott et al. 1998) and are
greater in polyculture verses monoculture systems (reviewed by Andow 1991), the
increased functional insectivore foraging activity I observed in mixed crops verses
monocultures was probably driven by variation in arthropod prey resources (though 1 did

45
not quantify this). Because organic fields tend to support greater arthropod diversity and
density (Dritschillo and Wanner 1980, Hald and Reddersen 1990, Brooks et al. 1995,
O’Leske et al. 1997, Feber et al. 1997 & 1998), and because high bird diversity in organic
fields has been linked to richer arthropod foods (Brea et al. 1988), the lack of a
significant difference in bird diversity between organic and convention fields in this study
suggests that polyculture cropping in conventional systems also results in an overall
greater arthropod diversity and abundance (Paoletti et al. 1992, Stary and Pike 1999).
One important determination I made during this study is that without watching
what birds eat when they are in fields, farmers and researchers alike may mistake the
roles that different species play. Because a few birds can be significant pests in
agroecosystems, eating sprouted plants, seed crops, and ripening fruits (Weed and
Dearborn 1935, Beal et al. 1941, Dolbeer 1990, Rodenhouse et al. 1993), this role is often
the first one ascribed to any birds observed in cropped areas. In this study I observed
abundant insectivory and only isolated instances of fruit damage (by mockingbirds on
strawberries) by birds in my study fields. But while many of the species observed to take
insects are normally classified as insectivores, several of the functional insectivores are
not. The Northern Cardinal is usually classified as an omnivore (De Graaf et al. 1985)
and popularly known as a seed-eater because it frequents backyard bird feeders. Yet the
cardinal was the most abundant functional insectivore in this study. They made longer
foraging bouts and took more insects than other species, and either immediately
consumed them or carried them into nearby field margins (presumably to feed young).
Two other species typically classified as omnivores (or popularly thought of as
granivores), blue grosbeaks and indigo buntings, were also among the functional

46
insectívoras (top ten most common species in cropped fields taking insect prey; see
Appendix A, Figure 2-7) and caused no crop damage during our observations. Clearly,
these species are omnivores when the diet is summarized over an entire year. But
because many omnivores and primarily granivorous species become highly insectivorous
during the breeding season to support their energetic needs and those of their nestlings
(Beal et al. 1941, Martin et al. 1951, Ehrlich et al. 1988), I advocate the utility of
‘functional insectivore’ in the context of farm birds. If the seasonality of bird diets is
emphasized, then farmers and conservationists alike can make more careful, and more
accurate, assessments of the potential positive and negative interactions birds can have
with cropping systems.
In conclusion, I found a large number of insectivorous bird species utilize cropped
fields of North-central Florida (see Appendix A), and direct observations during foraging
bouts indicated that most of these species were actively capturing insect prey from crop
vegetation. Insectivorous birds exhibit numerical and functional responses to insect
outbreaks in North American forest systems, potentially decreasing pest outbreak
frequency and severity (Holling 1988, Dahlston et al. 1990, Holmes 1990). This work
supports the general assessment that the ecological role of birds, as insect predators in
agroecosystems, is likely to realize enhanced production and economic values to farmers.
Moreover this work, in light of the current dearth of studies attempting to document
economic and production benefits of natural pest control agents, begs for further
investigation of avian insectivory as a component of pest management schemes that are
consistent with ecologically sound agriculture (Jackson 1979, McFarlane 1986 and Kirk
et al. 1996).

47
Conservation Implications
Increased awareness of the functional role that insectivorous species may have in
cropping systems could further encourage producers to engage in avian conservation
efforts on their lands. Recent surveys of farmers in North-central Florida indicated they
were supportive of increasing populations of certain bird species if it would benefit their
production efforts (i.e. insectivorous birds that may eat insect crop pests; Jacobson et al.
2003). Encouragingly, an overwhelming majority of farmers surveyed believed birds
could help lower insect populations on their farms (91%). Most farmers also indicated
that they would like to attract such birds to their farms (85%), and over a third of these
farmers were already engaged in attracting birds to their farms (Jacobson et al. 2003).
Additionally, since farmers in Florida have expressed great interest in conservation of
birds if they can aid in control of insect pests (without causing crop damage; Jacobson et
al. 2003), the potential for integrating bird conservation with farm production is
encouraging, particularly if more research is devoted to assessing realized benefits to
farmers. This work suggests that functional insectivory in fields can be encouraged at the
farm scale (by land-owners) by planting polycultures in fields adjacent to blocks (matrix)
of hardwood and pine forest with structurally complex field borders (hardwood, hedge)
between the matrix and the crop. It was also observed that insect eating birds heavily
utilized elevated perch structures (irrigation pipes, sprinkler heads, wire fence posts,
trellises, and natural structures such as sunflowers, cornstalks, bushes, and trees).
Though I did not characterize these effects, perches to enhance bird activity in disturbed
areas appears to be effective in many systems (Holl 1998). My next steps are to pursue

48
an understanding of economic benefits of on-farm manipulations of functional
insectivores.
While farmers cannot readily manipulate the relative abundance of land cover and
land use at the landscape scale surrounding their farms, it is quite clear that farms in
landscapes with greater proportions of their original native habitats will be able to attract
more birds, in part because larger pools of species and individuals are supported in such
landscapes. It is also apparent that such landscapes generate complex mosaics at the farm
scale, unlike regions with large (corporate) conventional farming operations adjacent to
one another. Because most recent studies of bird diversity on farms in the U.S. have
occurred in expansive conventional systems of the Midwest (see Best et al. 1995, Best et
al. 1997, Beecher et al. 2002) and California (see Elphick and Oring 1998, Bird et al.
2000), where there is little habitat (and impoverished avifaunas that often cause crop
damage), and because such conventional corporate farms comprise most acreage in
agricultural use, the current view of integrating birds and agriculture is somewhat
pessimistic (Peteijohn 2003). Numerically, most farms in the US are small to medium
sized traditional operations occurring in landscapes with a mosaic of crop and non-crop
habitat elements (ERS-USDA 2003), like the farms in this study. A recent national study
found the average small farm devotes 17% of its land to forest patches compared to 5%
on large farms, and allocates nearly twice the acreage to soil improvement efforts such as
cover crops (D’Souza and Ikerd 1996). Additionally, non-cropped acreage or acreage set
aside for conservation purposes is substantial among small farms in the U.S. For
example small family farm operators controlled 85% of acres enrolled in the
Conservation Reserve Program as of 1998 (USDA 2001b). Given that many of the small

49
farms surveyed in North-central Florida appear to provide suitable habitat for a diversity
of species, and that these farmers’ attitudes toward avian conservation are positive, I
argue that the prevailing negative view of agriculture as a partner in biodiversity
conservation is counter-productive. Large-scale conventional farming operations that
dominate large regions and comprise the majority of farmed areas in the US are, indeed,
devastating to birds and native biodiversity in general. But studies, including mine,
indicate that most farms (the smaller operations in diverse landscapes) already support
significant avian (and other) biodiversity, in part, because most farmers are open to
fostering such conservation goals. Therefore, I am encouraged that the potential to alter
agriculture in positive ways is tremendous. Policies are in place that provide monetary
and other incentives (i.e. 2002 Farm Bill conservation programs), and most stakeholders
are apparently open to possibilities (Jacobson et al. 2003), and the kind of research
needed to establish an economic basis for more ecologically sound agriculture is known
(McNeely and Scheer 2003).

CHAPTER 3
INTERCROPPING WITH SUNFLOWERS TO CREATE LOCAL
REFUGIA FOR AVIAN PREDATORS OF ARTHROPOD PESTS
Introduction
Innovative crop protection, through enhancement of predator-prey
relationships characteristic of natural systems, has a pivotal role to play in the
evolution of agriculture towards environmentally sustainable systems (Atkinson and
McKinlay 1997). Methodologies that promote pest insect predators (e.g., birds, bats,
wasps, beetles) on farms can augment both non-chemical crop protection and
conservation of biological diversity in agricultural landscapes. Although the value of
native insectivorous animals as predators in agroecosystems was once widely
recognized and promoted by scientists and farmers, research on potentially beneficial
species inhabiting agroecosystems was largely abandoned in 20lh Century North
America due to the pervasive use of pesticides and related technologies. As sectors
of the agricultural industry explore lower input systems (e.g., organic farming, natural
systems agriculture; Colby 1990) to reduce destructive impacts on human health
(www.epa.gov/pesticides/citizens/riskassess.htm) and ecosystem functions (Altieri
1994), research focused on designing farming systems that emulate more complex
ecosystems is urgently needed. Efficient and sustainable agro-ecosystems will
support ecosystem functions and species composition that reflect local biotic and
abiotic conditions (Soule and Piper 1992, McNeely and Scherr 2003). Thus, research
50

51
on sustainable and ecologically sophisticated agriculture should develop designs
appropriate for local conditions and sets of species, in addition to general principles
of agroecosystem function and management (Lewis et al. 1997).
Biological control by natural enemies has been the most successful and
promising alternative to unilateral reliance on chemical pesticides (Hoy 1992, Zalom
et al. 1992), and is considered to be the ‘backbone’ of integrated pest management
schemes (Rosen et al. 1996). The economic value of biological control methods
included in integrated pest management (IPM) programs may be considerable over
long time periods. For example, a study of citrus production in the San Joaquin
Valley of California indicated substantial savings of pesticide and energy costs could
be realized by growers utilizing IPM methodologies (Flint 1992). Biological control
methods that promote native pest insect predators for non-chemical crop protection,
by their nature, also contribute to conservation of biological diversity in agricultural
landscapes (The Soil Association 2000).
Habitat Management for Predators in Agroecosystems
Habitat management to enhance biological control refers to the establishment
of environmental conditions amenable to natural enemies that increase and sustain
their populations and improve their effectiveness in controlling pests (Pickett and
Bugg 1998). Population processes such as colonization / dispersal and foraging
movements of predators can be influenced by habitat modifications (Helenius 1998).
On farms, such dynamics of natural enemy populations can be altered through
management of within-field strips, cover crops, field margins, hedgerows, fencerows,
windbreaks, irrigation and drainage ditches, and roadside margins. For example,

52
Nentwig (1998) found that sown weed strips within cropped areas increased
arthropod enemy abundance and activity in crops, via greater effective dispersal into
the interior of expansive fields. Moreover, predation rates on pest species were
higher near the sown strips. Others have recognized the potential importance of
predator refugia within farmed areas for pest control and call for better understanding
of the mechanisms underlying refugium design and function for managing natural
enemies (Schoenig et al. 1998, Wratten et al. 1998).
Clearly, agroecological infrastructure (e.g., the landscape context and within-
field structure of cropped areas) affects the maintenance and activity of predators at
the scale of individual fields, and the conservation of predator diversity (richness and
abundance) requires consideration of both favorable and unfavorable habitat aspects
when designing predator-friendly agroecosystems (Booij and Noorlander 1992,
Wratten et al. 1998). For example, studies of abundances and foraging activities of
insectivorous birds in cropped systems (reviewed by Kirk et al. 1996) suggest that
bird use of crops for foraging depends not only on food abundance, but also upon
vegetation cover and microclimate in the field (Rodenhouse and Best 1994) and upon
habitat composition in the surrounding landscape (see Chapter 2).
Objectives
This study investigates the effect of within-field habitat structure upon the
abundance and foraging activity of insectivorous birds in cropping systems where all
features are under the direct control of farmers. The occurrence, densities, and
foraging activities of insectivorous birds in cropped fields are significantly higher in
those having the greatest diversity of vegetation (polycultures vs. monocultures; see

53
Chapter 2). Therefore, the overall objective of this study was to examine the effect of
sunflowers (Helianthus annuus) within cropped fields as refugia for birds. I tested
the hypothesis that sunflower rows included in a cropping system would increase the
occurrence, density, and foraging activity of insectivorous birds in cropped fields.
Additionally, I varied the density of sunflower rows per unit-area to determine its
influence on bird behavior and distribution in cropped fields. I conducted
observational assessments of foraging activity budgets of insectivorous bird species
utilizing cropped fields with sunflower rows compared to control plots. Using visual
observations I attempted to verify if birds were consuming economically important
pest insects. Forced regurgitation gut samples were collected from a few birds
captured in mist nets after they foraged in crop vegetation to aid in this verification.
Insects found within regurgitate samples were identified to order and family.
The addition of sunflowers to attract beneficial insects into cropping systems
has been described in several extension fact sheets (Univ. of Florida Extension
Circular 563, Univ. of Rhode Island Landscape Horticulture Factsheet, Univ. of
Maine Coop Extension Bulletin # 7150) and gardening publications (Long 1993,
Starcher 1995, Turton 1998). However, one concern with adding non-crop vegetation
strips within cropped fields is that this treatment may attract and increase the
abundance of pest insects to the crops (Bugg and Pickett 1998). Therefore, I also
performed a limited survey of the insect fauna found in sunflower treatment plots to
establish a partial listing and the relative occurrences of both beneficial and pest
arthropods found on sunflower and nearby crop vegetation (sensu Henn et al. 1997
and the UF Coop. Ext. Service Insect Identification Sheets SPSET 5 1997).

54
Methods
Research Site Selection
Growers were identified in North-central Florida during the fall of 2001 and
permission was obtained to conduct research activities on their properties. All
participating farms were under certified organic management as designated by the
Florida Organic Growers Association (Florida Certified Organic Growers and
Consumers, Inc., PO Box 12311 Gainesville, FL 32604) and most are now USDA
Organic certified.
Experimental Design
Four organic growers were asked to incorporate rows of multi-branched open-
pollinating varieties of sunflowers into their cropped acreage at the earliest planting
dates during their spring - summer growing seasons 2002 and 2003. These multi-
branched sunflowers have been observed to provide foraging, roosting, and even
nesting micro-habitat for many species of insectivorous birds in two organic farms
that already incorporate them extensively for cut flower production (Jones
unpublished data). Vegetable crops grown in the experimental blocks chosen for the
study included polycultures of kale, collard greens, yellow and zucchini squash,
tomatoes, green beans, cucumbers, and sweet com. Only two of the farm sites had
entire fields dedicated to a single crop type (sweet com).
A total of 18, 4-hectare blocks were available for the study 8 of which
received sunflower row treatment while the other 10 served as controls within the
farm sites. This unbalanced arrangement of 8 treatment and 10 control blocks was
necessary to ensure that each farm contained at least 1 control and treatment block, to

55
pair crop types in treatment and control blocks as much as possible, and to allow the
incorporation of sunflower rows into blocks in such a way as to minimize their impact
on each farmer’s production regime. Treatment blocks were divided among farms
that ranged in size from 8 ha to 80 ha in size with 2 blocks in the smallest farm, 4
blocks in each of 2 farms that were 20 ha in size, and 8 blocks in the largest farm. A
randomized block design was incorporated into the 4-hectare plots with sunflower
row treatments at varying densities of 0, 1, or 2 rows per 0.4 ha. All sunflower rows
consisted of lm-wide rows of plants at a density of 9 plants per square meter and
were interspersed between, and parallel with, production rows (Figure 3-1). In all
blocks that had sunflower rows placed in them the rows were centered in roughly
rectangular fields, planted in strips that would not otherwise have had crop
vegetation, and were approximately 100 m in length (Figure 3-2).
Sunflower rows were maintained throughout the spring growing season as other crops
were planted, harvested, and rotated through each farm’s production area. Treatment
blocks were assigned different treatments during the second field season (either 1, 2
or no rows/0.4 ha of sunflowers) to control for differences in the border habitat types
that were adjacent to each treatment block. This was important since border habitat
types significantly affect the numbers of birds available to venture into cropped
fields. Avian occurrence and abundance in field borders varied significantly from site
to site being greatly influenced by the vegetation composition of the field border (see
Chapter 2).

56
Figure 3-1. Multi-branching sunflower varieties were planted at 1 or 2 rows per 0.4
ha between vegetable rows to attract birds and beneficial insects into cropped fields.
A row of sunflowers is shown here planted in a non-production strip containing
irrigation sprinklers between rows of tomatoes.

57
Sunflower block
Control block
census
point
census
point
Sunflower row
census
point
census
point
Sunflower block
Control block
Field border habitat
100 m
Figure 3-2. Typical layout of treatment and control blocks at a 20 ha farm site. A
randomized block design was incorporated into the 4-hectare plots with sunflower
row treatments at varying densities of 0, 1, or 2 rows per 0.4 ha. All sunflower rows
consisted of lm-wide rows of plants at a density of 9 plants per square meter and
were interspersed between, and parallel with, production rows. In all blocks that had
sunflower rows placed in them the rows were centered in roughly rectangular fields,
planted in strips that would not otherwise have had crop vegetation, and were
approximately 100 m in length.

58
Bird Sampling
Birds were censused and their foraging activities quantified throughout the 2
growing periods from 1 April - 15 June 2002 and 2003. Birds were censused 6 times
in each treatment and control block utilizing standard point count methods (Bibby et
al. 1992) modified as described by Freemark and Rogers (1995) for censusing in
croplands. All census points were located at least 200 m from each other when
occurring within the same farm management unit. Point counts were conducted
between dawn and 1000 EST on fair weather days. All birds seen or heard within a
50 m fixed-radius from each census point during a ten-minute period were recorded.
Observations began 2-3 minutes after I arrived at each point count station. Birds
flying over sample areas were excluded, except swallows or martins if they were
feeding on aerial invertebrates directly over crop vegetation (see Boutin et al. 1999).
Utilizing mapping data sheets (marking exact locations of individuals and their
movements) minimized duplicate records. Both species numbers and bird densities
were averaged across samples at each point. Univariate analyses were performed to
compare bird densities within the treatment and control blocks to determine
sunflower row treatment effects upon bird response variables among experimental
plots for the study (Zar 1999).
Point count circles used to assess bird species occurrence and density were
located on the edges of fields centered to the ends (1 sunflower row plots) or between
(2 sunflower row plots) sunflower rows in treatment blocks, Zz in the field and Zz in
the field border vegetation (Figure 3-2). For comparisons among treatments and
control blocks, only birds detected in the crop half of count circles were used in

59
assessing species occurrence and density. Count circle radii extended 'A the length of
the sunflower rows, and were therefore sufficient to detect sunflower effects on birds.
Half of each count circle was located in the field border vegetation for two reasons.
First, standing in the border provided some cover to reduce the conspicuousness of
the observer (and minimize effects on bird behavior in the crop). Second, all census
points in this study were censused in the 2 years previous to this study and those data
were used to assess variation in bird abundances in cropped field blocks among years
and treatments.
Foraging Surveys
Observations of foraging behavior were made during six, 1-hour scan
sampling sessions (Martin and Bateson 1993) at each treatment plot spread over the
study period. Avian species observed to forage in crop vegetation and the time spent
in foraging bouts were noted. Birds were considered foraging if they were observed
to be making their way through or on crop vegetation and actively scanning or
probing that vegetation for prey items (as opposed to being perched and resting,
singing, or grooming etc.). Any successful capture of an insect prey item was noted
and an attempt was made to visually identify those insects being consumed by
foraging birds. Use of sunflower plants by foraging species was described. The
degree that inclusion of sunflower rows increased foraging activity in surrounding
crop vegetation was determined by univariate analysis of variance comparing
differences in mean numbers of birds and duration of foraging bouts among treatment
blocks. Regression analysis was used to examine the relationship between foraging
activity and growth of sunflower plants through each growing season (Zar 1999).

60
Gut Content Surveys
An attempt was made to identify insects eaten by insectivorous birds within
the test plots through gut content analysis. Birds were captured directly after foraging
in crop vegetation utilizing mist-netting techniques within treatment plots. A partial
sample of each bird’s stomach contents was collected via a non-lethal forced
regurgitation (Prys-Jones et al. 1974). After capture, birds were administered an oral
emetic consisting of a 0.1cm3 of 1% solution of antimony potassium tartrate per 10 g
of body mass and placed in a darkened holding cage lined with wax paper. Within 2
- 3 minutes, most birds regurgitated pellets of partially digested insects that were then
collected and preserved in alcohol for identification. Birds were then released at
point of capture after a short rest period and an examination for any signs of stress.
Samples obtained in this way are highly correlated with total crop and stomach
contents of collected birds (Rosenburg and Cooper 1990).
Insect Surveys
Insects were sampled a minimum of 3 times in 10 randomly chosen 1 m2
quadrats within sunflower rows and in 10 randomly chosen locations in crop
vegetation a minimum of 10 m distant from the sunflower rows within treatment
blocks during the growing season 2002. During 2003 insects were again sampled a
minimum of 3 times in 10 randomly chosen 1 m2 quadrats within sunflower rows, 10
quadrats in crop vegetation at 1 m, and 10 quadrats at 10 m distant from the
sunflower rows. Insects were sampled utilizing a standard scouting technique in each
quadrat counting the numbers of individuals found per 1 m2 of crop vegetation (after
Morris 1960, Southwood 1978). Insects observed were identified to family level and

61
relative abundances noted. Using Henn et ai. (1997) and the UF Coop. Ext. Service
Insect Identification Sheets SPSET 5 (1997), I classified insects as “beneficiáis” or as
crop pests. Then, I compared the occurrence and number of individuals per m2
beneficial and pest insects found upon sunflower plants and crop vegetation (at 2
distances away from sunflowers in year 2) during the two growing periods (Zar
1999).
Results
Bird Species Occurrence and Densities
A total of 68 species were observed utilizing cropped areas of the treatment
and control blocks or their bordering habitats (within 50 m of field edges; see
Appendix B). Of these 68 species observed within the blocks, 62 species (91%) were
observed in the border habitat while 49 species (72%) were observed in the cropped
areas themselves; 5 of which were only observed in the cropped fields. Mean
densities of birds occurring in the cropped areas of the treatment and control blocks
varied significantly from year to year during the study and from the two years (2000
and 2001) previous to the study (2.9 birds/ha in 2003, 3.3 birds/ha in 2002, 4.3
birds/ha in 2001, and 1.8 birds/ha in 2000; Fj,!M = 2.74, p = 0.04). During the study
cropped areas with sunflower treatments of one row and two rows per 0.4 ha
exhibited significantly greater mean densities of birds than did control plots (3.5 1 3.5,
5.8 14.5, and 0.9 J 1.8 birds/ha respectively; F2.20o = 43.33, p< 0.001). This difference
was apparent with the addition of just a single row of sunflowers per 0.4 ha (Figure 3-
3). Differences in bird densities between treatment and control blocks were greatest

62
in 2003 (2-way ANOVA Year x treatment F2.200 = 4.41, p = 0.013) during which
blocks having 2 sunflower rows per 0.4 ha exhibited a 206% greater mean density of
birds than did 1 row and a 1500% greater mean density of birds than did control plots
(Figure 3-3). Mean bird densities occurring in cropped areas were not significantly
different among these same blocks in the two years previous to this study (2000: F2.53
= .843, p = 0.436; 2001: F2,53 = 1.41, p = 0.254).
Foraging Behavior
Foraging observations during the 2 growing seasons indicated that the presence of
sunflower rows significantly increased the presence and activity of insectivorous
birds in vegetable or row-crops compared to control blocks. Mean number of
individual birds foraging per hour in cropped areas was significantly greater in those
blocks with sunflower rows versus control blocks, 0.710.1 and 1.710.1 individuals
per hour respectively (F,i196 = 59.84, p < 0.001; Figure 3-4). Mean foraging activity
per hour in cropped areas was also significantly greater in those blocks with
sunflower rows versus controls, 0.061.01 hr and 0.241.02 hr respectively (FU96 =
51.93, p < 0.001; Figure 3-5). This difference in foraging activity was consistent
each year as treatment plots were rotated among the 18 experimental plots. Mean
time birds spent foraging in crop vegetation significantly increased over the course of
each growing season as both sunflowers and crop vegetation matured (F,. = 9.13, p =
0.003). Birds were found to be attracted to and utilize sunflower plants as perches by
the time they were 0.6 m tall. As sunflowers increased in stature through the growing
season, birds were observed to increasingly utilize sunflower plants as cover and
perch sites from which they would forage into crop vegetation (Figure 3-6).

63
(1 row/acre) (2 row/acre)
Figure 3-3. Sunflower treatment plots exhibited significantly greater mean densities
of birds in the cropped fields than control plots during both spring growing seasons
(F2,200 = 43.33, p< 0.001), and especially in 2003 (2-way ANOVA Year x treatment
F2.200 = 4.41, p = 0.013). This difference was apparent with the addition of just a
single row of sunflowers per 0.4 ha increasing mean density nearly 4 times that of
control plots. Error bars = 1 SE.

Mean No. Individuals Foraging
(birds / hr)
64
1.50
1.00
0.50
0.00
Control Sunflower
Figure 3-4. Mean number of individual birds foraging in cropped areas was
significantly greater in those plots with sunflower treatments in both growing seasons
2002 and 2003 (FM96 = 59.84, p < 0.001). Error bars = 1 SE.

Mean Foraging Time
65
Figure 3-5. Mean foraging time (proportion of 1 hour observation session) in cropped
areas was significantly greater in those plots with sunflower treatments in both
growing seasons 2002 and 2003 (FM96 = 51.93, p < 0.001). Error bars = 1 SE.

66
Figure 3-6. As sunflowers increased in stature, birds were observed to increasingly
utilize sunflower plants as cover and perch sites from which they would forage into
crop vegetation. An Eastern Kingbird (Tyrannus tyrannus) surveys crop vegetation
from a sunflower perch looking for prey.

67
During the 216 hours of foraging observations made during the study period a
total of 428 foraging bouts were observed. The species most often observed to forage
in crops for insects included 2 resident species Northern Cardinals (Cardinalis
cardinalis) and Eastern Bluebirds (Sialia sialis), and two migrants, Blue Grosbeaks
(Guiraca caerulea), and Indigo Buntings (Passerina cyanea)(see Appendix B).
These four species accounted for 63% of the foraging bouts observed and 65% of the
time birds were observed to forage in the treatment and control blocks during the
study (Figure 3-7). Northern Cardinals were the most prevalent foragers throughout
each growing season accounting for more than 1/3 of the foraging bouts observed.
Eastern Bluebirds were also common foragers accounting for 8.6% of the foraging
bouts observed. Blue Grosbeaks and Indigo Buntings became common foragers (7%
and 9% of foraging bouts observed respectively) as they returned from wintering
grounds several weeks into the two growing seasons. Small flocks of species that
winter in North-central Florida such as Western Palm Warblers (Dendroica
palmarum) and Yellow-rumped Warblers (Dendroica coronata) were observed
foraging in cropped areas during the first few weeks of each growing season.
In approximately 10% of the foraging bouts I was able to identify an insect
prey item that had been captured. Two of the most common prey identified were
lepidopteran larvae and grasshoppers. Inspections of crop vegetation after bouts, in
spots where birds had foraged, allowed further confirmation of likely prey species
being consumed. Insects most prevalent in inspected foraging sites included Green
Stink Bugs (Acrosternum hilaré), Imported Cabbageworm (Pieris rapae - Linnaeus),
and numerous Dipterans (Figure 3-8).

68
a. Foraging bouts
Other
16.4%
YRWA
4.7%
WPWA
6.8%
BLGR
7.0%
COGD
5.4%
EABL
8.6%
GCFL
3.7%
INBU
9.1%
NOCA
38.3%
b. Foraging time
Figure 3-7. Species-specific proportion of foraging bouts (a.) and time spent foraging
per hour (b.) of birds observed during 216 hours of observation in sunflower and
control blocks during the 2002 and 2003 spring growing seasons. Northern Cardinals
(Cardinalis cardinalis), Eastern Bluebirds (Sicilia sialis), Blue Grosbeaks (Guiraca
caerulea), and Indigo Buntings (Passerina cyanea) accounted for 63% of the foraging
bouts observed and 65% of the time birds were observed to forage in the treatment
and control blocks during the study. See Appendix B for complete list of those
species observed foraging in crops.

69
Figure 3-8. Birds foraging in crop vegetation were observed to consume numerous
lepidopteran larvae as well as grasshoppers and beetles. Insects consumed by birds
included Green Stink Bugs (Acrosternum hilare), Imported Cabbageworm (Pieris
rapae - Linnaeus), and numerous Dipterans.

70
Insects were taken directly from crop vegetation and either consumed on the spot or
carried into nearby field border habitat (presumably to be consumed there or to feed
to young). A total of 20 birds observed to forage for insects in crop vegetation (10
Northern Cardinals, 3 Blue Grosbeaks, 6 Indigo Buntings, and 1 Summer Tanager)
were captured immediately after foraging. Regurgitated gut samples obtained from
12 of these captured birds confirmed that economically important pest insects were
consumed such as leaf-chewing caterpillars and grasshoppers (Figures 3-9). Remains
of beneficial insects were not evident in these gut samples.
Beneficial and Pest Insect Occurrence
Beneficial insects were attracted to sunflower plants by the time they reached
0.15 m in height. Beneficial insects observed on sunflowers and nearby crop
vegetation (within lm of sunflowers) included arthropod predators, parasitic wasps,
and important pollinators representing 30 different families (Appendix C). The most
commonly occurring beneficial insects observed on sunflowers were Big-eyed Bugs
(Geocoris ssp.), Honey Bees (Apis mellifera), Green Lynx Spiders (Peucelia
viridans), Ants (Formicidae), and Sphecid Wasps (Sphecidae). The most commonly
occurring beneficial insects observed on nearby crop vegetation were Green Lynx
Spiders (Peucetia viridans), Lady Beetles (Coccinellidae), Big-eyed Bugs (Geocoris
ssp.), Predatory Stink Bugs (Pentatomidae), and Assassin Bugs (Reduviidae). The
occurrence of beneficial insects was significantly greater on sunflower vegetation
than on crop vegetation greater than 10 m distant from sunflowers in both 2002 (FU6
= 11.78, p = 0.003; Figure 3-10) and 2003 (FU6 = 12.94, p = 0.002; Figure 3-11).
While crop vegetation 10 m distant from sunflowers harbored significantly fewer

71
Figure 3-9. Gut content samples obtained from birds captured after foraging in crop
vegetation confirmed that economically important pest insects were consumed such
as leaf-chewing caterpillars. The intestinal tracts and other internal organs of
numerous caterpillars were identifiable in most stomach samples.

72
While crop vegetation 10 m distant from sunflowers harbored significantly fewer
beneficial insects, this difference in occurrence in sunflower and crop vegetation was
not seen in crop vegetation directly adjacent to sunflowers (within lm) when this was
assessed during the 2003 growing period (Fi,22 = 2.29, p = 0.144; Figure 3-11).
Pest insects representing 12 different arthropod families were found on
sunflowers and nearby crop vegetation. The most commonly occurring pest insects
were Green Stink Bugs (Acrosternum hilare), Com Flea Beetles (Chaetocnema
pulicaria, Chrysomelidae) and Imported Cabbageworm larvae (Pieris rapae -
Linnaeus) respectively. The occurrence of pest insects on sunflower and crop
vegetation greater than 10 m distant from sunflowers did not significantly differ in
2002 (Fi,i6 = 0.12, p = 0.74; Figure 3-12) but did significantly differ in 2003 (Fi_i6 =
14.7, p = 0.001; Figure 3-13). Greater mean numbers of pest insects per meter were
observed on sunflower vegetation than on crop vegetation greater than 10 m distant
from sunflowers (2.5 individuals / m2 vs. 0.2 individuals / m2 respectively). This
same difference was found on crop vegetation within 1 m of sunflowers as well in
2003 (2.5 individuals / m2 vs. 0.5 individuals / m2 respectively, F]¿2 = 13.4, p =
0.001; Figure 3-13).

Occurrance
( mean no. / m. sq.)
73
Crop Vegetation Sunflowers
Figure 3-10. Occurrence of beneficial insects was significantly greater on sunflower
vegetation than on crop vegetation during the 2002 growing
season (FU6 = 11.78, p = 0.003). Error bars = 1 SE.

74
OI
O
c
cr
É
3
O
u
O
o
c
c
ra
0)
E
Distant Adjacent Sunflowers
Figure 3-11. The occurrence of beneficial insects was significantly greater on
sunflower vegetation than on crop vegetation more than 10 m distant from
sunflowers in 2003 (FM6 = 12.94, p = 0.002). Occurrence of beneficial insects on
crop vegetation directly adjacent to sunflowers (within lm) did not significantly
differ from that found on sunflower vegetation (F,^ = 2.29, p = 0.144).
Error bars = 1 SE.

Occurrence
nean no. I m. sq.)
75
2.50
2.00
1.50
1.00
0.50
Crop Vegetation Sunflowers
Figure 3-12. Occurrence of pest insects on sunflower and crop vegetation greater
than 10 m distant from sunflowers did not significantly differ in 2002 (FU6 = 0.12,
p = 0.74). Error bars = 1 SE.

76
3.00 “
Distant Adjacent Sunflowers
Figure 3-13. Occurrence of pest insects on sunflower and crop vegetation greater
than 10 m distant from sunflowers significantly differed in 2003 (Fu6 = 14.7, p =
0.001). Greater mean numbers of pest insects per meter were observed on sunflower
vegetation than on crop vegetation greater than 10 m distant from sunflowers (2.5
individuals / m2 vs. 0.2 individuals / m2 respectively). This same difference was
found on crop vegetation within 1 m of sunflowers as well (2.5 individuals / m2 vs.
0.5 individuals / m2 respectively, FU2 = 13.4, p = 0.001)

77
Discussion
Avian Abundance and Foraging Activity
In this study I tested the hypothesis that cropped fields with sunflower rows
incorporated into the cropping system would exhibit greater bird densities. My
results support this hypothesis. Those fields with even one row of sunflowers per 0.4
ha exhibited significantly greater bird densities than those without, regardless of crop
type or crop diversity. While an additional increase in density was seen with an
additional row of sunflowers, it appears that a single row may be enough to make
cropped areas more attractive for bird use. A single row of sunflowers added to a
field increased bird densities and foraging time spent by those birds nearly 4 times
that seen in control blocks. Therefore the addition of a single sunflower row may
provide the added structural vegetation to make a cropped field attractive for bird use
in those systems where their presence could possibly provide a benefit. However,
additional work needs to document and quantify the impact this increase in bird
density has on insect populations in crops and crop production.
In this study I also tested the hypothesis that foraging activity would be
increased in crop vegetation with the presence of sunflower rows. Results of my
foraging observations support this hypothesis since foraging activity was 4 times
greater in crops with sunflower rows. Previous studies suggest foraging activities of
insectivorous birds in cropped systems depends upon vegetation cover and
microclimate in the field (Rodenhouse and Best 1994, and reviewed by Kirk et al.
1996). Birds were found to begin to utilize sunflower vegetation as soon as the plants
were able to support perching and provide some cover (Figure 3-14).

78
Figure 3-14. Birds were found to begin to utilize sunflower vegetation as soon as the
plants were able to support them as a perch and begin to provide some cover. Once
sunflowers reached a height of at least 24”, birds were observed to fly in to the fields
and first land on the sunflowers before venturing into nearby crop vegetation. A
Palm Warbler (Dendroica palmarum) is shown perched on a sunflower while
foraging for insects in nearby rows of kale.

79
Once sunflowers reached a height of at least 0.6 m, birds were observed to fly in to
the fields and, first, land on the sunflowers before venturing into nearby crop
vegetation. Several studies have confirmed the strong relationship between hedgerow
presence and composition, and avian presence and community structure in
agricultural landscapes (see O’ Connor 1984, MacDonald and Johnson 1995).
Therefore in those fields in which birds may provide a benefit as insect predators, the
addition of sunflowers into the cropping system may be an effective and temporary
habitat modification.
I observed birds actively pursuing and consuming economically important
pest insects gleaned from crop vegetation. The value of utilizing naturally occurring
enemies cannot be overemphasized within organic farming systems and IPM
programs (Rosen et al. 1996). Insectivorous birds are naturally occurring components
of agroecosystems and their feeding activities in and around cropped areas may be of
great economic value. Birds are both mobile enough to recruit readily to high-density
food patches in their home ranges, and are capable of complex prey-switching and
specialization behaviors (McFarlane 1976, Kirk et al. 1996). Due to these
characteristics birds are potentially important components of biological control
regimes, provided they increase the natural mortality of agricultural arthropod pests
without adversely affecting other natural enemies and the crops themselves
(McFarlane 1976, Kirk et al. 1996).
As pest predators, birds may provide both numerical and functional responses
to prey availability over short time periods and large areas (Holling 1988, Dahlston et
al. 1990, Flolmes 1990) - potentially stabilizing pest communities in agroecosystems,

80
augmenting the activities of other classes of predators with different characteristics
(Price 1987, Rosen et al. 1996, Helenius 1998). Since birds responded to the
presence of sunflower rows after they reached a certain height, timing of planting of
these rows will be critical to maximize the benefit of attracted insect predators to
crops. Sunflower plantings should proceed that of other crop vegetation by several
weeks to allow their establishment and potential attraction of beneficial predators
before crops, and any associated pests, reach critical growth stages. Optimally,
potential suppression of pest insects will occur if an adequate predator base is present
before pests colonize crop vegetation and their populations grow to economically
damaging levels (Price 1987, Rosen et al. 1996, Helenius 1998).
Most bird damage to crops in the U.S. occurs to grain and small sized fruit
crops appear to be worse in certain regional locations, certain cropping system
designs, and in crops bred for very early or late season harvests (reviewed by
Rodenhouse et al. 1995). Several bird species are known to cause considerable
damage to crops, especially flocking species such as Red-winged Blackbirds
(Agelaius phoeniceus) and Cedar Waxwings (Bombycilla cedrorum). During my 4
years of observations of birds in cropping systems I observed very little damage to
vegetable crops by birds. During the spring growing season of 2001, North-central
Florida experienced severe drought conditions. In this season I observed watermelon
damage cause by American Crows (Corvus brachyrhyncos) presumably to obtain
water. In all 4 years, 2000 - 2003,1 also observed a limited amount of strawberry
damage caused by Northern Mockingbirds (Mimus polyglottos). During this study
participating farmers reported that they did not experience any increase in bird

81
damage due to attracting more birds into their cropping systems with sunflower
plantings. I did not observe any of the 3 most problematic species mentioned above
utilizing sunflowers (blackbirds, crows, or waxwings) or being attracted to plots with
sunflower rows over the study period.
In a recent survey of Florida farmers, bird damage to crops was reported by
32.9% of the survey participants primarily indicating damage to watermelon or com
by crows (Jacobsen et al. 2003). However only 11.8% reported the need to utilize
bird control methods to limit damage. In some cases proper “farmscaping” cannot
only increase the presence of beneficial organisms, but may reduce the presence or
abundance of problematic species in cropping systems as well. Farmscaping is
defined as a whole-farm, ecological approach to pest management through selective
placement of hedgerows, insectiary plants, cover crops, and water reservoirs to attract
and support populations of beneficial organisms such as insects, bats, and birds of
prey (http://attra.ncat.org/attra-pub/PDF/farmscaping.pdf). Research in farmscaping
to maximize beneficial organisms and limit pests is ongoing to identify and develop
such management strategies (Pickett and Bugg 1988, Bommarco and Ekbom 2000).
Beneficial and Pest Insect Occurrence
Insect sampling efforts revealed that sunflowers did indeed attract and play
host to numerous beneficial insects as has been described in numerous publications
(Henn et al. 1997, UF Coop. Ext. Service Insect Identification Sheets SPSET 5 1997).
Sunflower plants were found to attract predaceous insects almost immediately after
establishment. Parasitoids and pollinators were attracted as soon as these plants
began to produce flowers. These same beneficial insects were found to also occur on

82
crop vegetation but in lower numbers. It has been found in several studies that
providing predator refugia within cropping systems via strip crops or uncultivated
corridors can result in the migration of predatory insects into adjacent crops (see
Johanowicz and Mitchell 2000, Mensah 1999, Nentwig 1998, Schoenig et al. 1998,
Wratten et al. 1998, Rodenhouse et al. 1992). In the 2003 growing season I modified
the sampling methodology in an attempt to determine whether beneficial insects
attracted to the sunflowers may have been moving out from the sunflowers into
adjacent crop vegetation. Results indicated that crop vegetation 10 m distant from
sunflowers harbored significantly fewer beneficial insects than did that within 1 m.
Moreover, crop vegetation within 1 m of sunflowers exhibited nearly the same
abundance and diversity of beneficial insects as did the sunflowers themselves.
Further study is required to fully describe the distances key beneficial insects move
from sunflowers and the impact these beneficial insects have on crop pests.
Conclusion
Bird populations and avian community structure are known to respond
differently to the distribution of cropped and non-cropped landscape elements and the
distribution, relative cover classes, and juxtaposition of agricultural landscape
elements in agroecosystems (Freemark et al. 1993, Rodenhouse et al. 1993). Intrinsic
habitat qualities such as food resources or shelter availability play important roles in
habitat selection by birds (Bairlein 1983, Martin and Karr 1986, Moore et al. 1995).
Moreover, habitat complexity resulting from a mix of different plant species,
percentages of vegetative cover and variations in the size, distribution, and

83
juxtaposition of plant assemblages will influence the local diversity of bird species
(James 1971). The addition of structurally diverse vegetation strips within cropped
fields appears to attract and provide cover for birds utilizing adjacent non-crop
habitats. In so doing the probability that these highly insectivorous animals may
provide an economic benefit to producers is greatly increased. In return, the creation
of suitable habitat within cropping systems may aid in the conservation of all avian
species within agroecosystems. Within the discipline of conservation biology there is
increasing recognition that protected reserves alone will not be sufficient to conserve
biodiversity in the long term; therefore, methods of integrating conservation and
productive use must be achieved (Hobbs and Norton 1996). This study contributes to
a better understanding of the effects of vegetative structure and crop species
composition on farm-bird community structure, with more general applications to
implementation of environmentally sensitive agriculture.

CHAPTER 4
PARASITIZED AND NON-PARASITIZED PREY SELECTIVITY OF
INSECTIVOROUS BIRDS: POTENTIAL FOR AUGMENTATION OF
CLASSICAL BIOCONTROL
Introduction
Biological control by natural enemies is the most successful and promising
alternative to unilateral reliance on chemical pesticides in low input cropping systems
(Rosen et al. 1996). Classical biological control programs often rely on releasing
introduced (non-native) parasitoids to reduce exotic pest populations (DeBach and
Rosenl991), where host specificity is emphasized using parasitoids or predators of
targeted pest arthropods. While a majority of biological control research has focused
upon “specialist” enemies for individual agricultural pests, the strategy of enhancing
these efforts by increasing “background mortality” (see Beddington et al. 1978) through
assemblages of native generalist predators also shows promise in crop management
schemes (Helenius 1998). Such augmentation of classical biological control programs
will require sustained availability of large numbers of inexpensive, high quality, naturally
occurring predators (Hoy 1992). Multiple natural enemies in a system are understood to
provide a shifting temporal and spatial mosaic of predation rates across multiple prey,
dampening variability in the systemic predator-prey dynamic (Rabb 1971). Thus
augmentation of classical biological control measures involves efforts to enhance the
presence of naturally occurring enemies of pest arthropods in agroecosystems.
84

85
Over the past 2 decades, field entomologists and agronomists have increasingly
recognized that the conservation of natural enemies via the management of non-cropped
habitats that support them is important to effective and successful biological control in
agricultural systems (Rosen et al. 1996). However, little work has been done looking at
avian insect predators in modem cropping systems to fill this role of augmenting other
control measures. One particularly important potential mechanism whereby birds might
stabilize and augment pest control is consumption of individual prey that escape mortality
from other agents of biological control. In systems where introduced or native
parasitoids are supported via provision of critical habitat (e.g., insectiary plantings) rather
than through repeated releases onto fields, parasitism rates undergo fluctuations due to
parasitoid population lags (Bugg and Pickett 1998). In such systems birds could function
to stabilize and maintain sufficient pest mortality rates given their abilities to respond
functionally to changes in prey abundance (McFarlane 1976). While this scenario
reasonably explains how birds could effectively augment arthropod pest mortality
induced by parasitoids typically employed in classical biological control regimes
(McFarlane 1976, Kirk et al. 1996), its generality, practicality, and economic efficiency
have not been assessed for any agroecosystem.
Bruns (1959) stated that birds would be of value as insect predators in a system
only if they increase the effectiveness of control by taking insects over and above those
that would normally have been destroyed by other agents. Several studies have
demonstrated that birds select and consume non-parasitized insects suggesting that bird
predation may be additive to the mortality caused by parasitoids (Sloan and Simmons
1973, Schlichter 1978). Sloan and Simmons (1973) reported that hymenopterous

86
parasitized jack pine budworm (Choristoneura pinus Bechstein) larvae and pupae were
unanimously rejected by foraging chipping sparrows (Spizella passerina). Similarly,
Schlicter (1978) reported that black-capped chickadees (Parus atricapillus) largely
avoided foraging upon galls on Canada goldenrod (Solidago canadensis) that had been
parasitized by mordellid beetle (Mordellistena unicolor) larvae to extract gall fly
(Eurosta solidaginis) larvae. Therefore it appears that birds have the ability to
distinguish prey that have been damaged or may be compromised by a parasite and avoid
such prey.
Previous observations have confirmed that many birds occurring in cropped fields
of North-central Florida actively forage for and consume caterpillars in crop vegetation
(see Chapters 2 and 3). Fall armyworms [Lepidoptera: Noctuidae, Spodoptera frugiperda
(J. E. Smith)] are important pests in vegetable and row crops (Johnson and Sprenkel
1996) and are often subjected to biological control using cultured parasitoids (R.
Meagher, USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology
(CMAVE), Gainesville, FL, pers. comm., Johnson and Sprenkel 1996). Parasitoids are
insects whose eggs are deposited on another arthropod (usually an insect) host, its larvae,
or in the host’s egg. The resultant larvae develop by feeding upon the bodies of the host
resulting in the host’s death (Godfrey 1994).
In this study I addressed whether birds would consume armyworms that had been
parasitized or avoid such prey. I tested the hypothesis that birds prefer to forage upon
non-parasitized armyworm prey via captive feeding trials where birds were also offered
prey parasitized by Euplectrus wasp larvae. In both studies where birds avoided prey, it
was suggested that visual cues were utilized to distinguish between prey types (Sloan and

87
Simmons 1973, Schlichter 1978). Parasitoids can be divided into two classes by the
feeding behavior of their larvae. Endoparasitoid larvae feed from, and develop within,
the body of their host. Ectoparasitoid larvae develop while externally attached to the host
feeding with mouthparts buried into the host’s body (Godfray 1994). Larvae of the genus
Euplectrus are gregarious (more than one parasitoid larvae per host) external parasites of
lepidopteran larvae. Euplectrus larvae remain attached to the exoskeleton and feed on the
dorsum of their host, which is often still able to move freely about (Figure 4-1). Once the
Euplectrus larvae mature they move below the emaciated host to pupate, spinning silk
from the host’s Malpighian tubes which hold the host down and separate the larvae from
each other (Grissell and Schauff 1997). Therefore, Euplectrus served as a good
representative of commonly occurring ectoparasitoids whose larvae develop on the
external surface of their host that could be visually identified by a bird.
Methods
Research Facilities and Test Species
Feeding trials were conducted in an aviary at the USDA National Wildlife
Research Center’s Florida Field Station, Gainesville, Florida. Red-winged blackbirds
(Agelaius phoeniceus) captured in agricultural settings and housed at the field station
were utilized as a test insectivorous species. This species was chosen due to the fact that
individuals of this species commonly occur in agricultural landscapes (Ehrlich et al.
1988, Dolbeer 1990) and have been previously examined for their predatory impact on
insect pest populations in crops (Bendell et al. 1981). Birds were presented parasitized
and non-parasitized fall armyworms provided by the USDA- ARS CMAVE, Gainesville,

88
FL. Parasitized armyworm larvae were those that had been exposed to and carried larvae
of the Eulophid parasitoid species Euplectrus plathypenae (Howard). This
Hymenopteran species commonly occurs in Florida and has been investigated for its
biological control value (R. Meagher, USDA-ARS, Center for Medical, Agricultural and
Veterinary Entomology (CMAVE), Gainesville, FL, pers. comm.).
Paired Feeding Trials With Non-parasitized Larvae
The first set of feeding trials performed with non-parasitized prey test if the
captive birds would feed upon fall armyworms, and I determined their baseline
consumption given this food item. Only those birds willing to readily eat armyworms
were utilized for subsequent tests. Additionally, since birds have exhibited prey size
selectivity when presented a choice (Krebs et al.1977, Davies 1977, Zach 1979) an
assessment was made whether birds exhibited a feeding preference for different instar
sizes of these caterpillars. Maintenance food was removed by 0700 EST and 1-2 hrs later
birds were presented with a plastic cup divided into two chambers (Figure 4-2). In the
first pretests, 10 armyworms of equal size were simultaneously presented in the cup’s
chambers and birds were allowed to forage undisturbed for Vi hour (Figure 4-3). The
propensity of each bird to eat the armyworms, the chamber location (left or right side of
cup) the larvae were chosen from, and the time it took for the bird to consume all 10
larvae were noted. In these tests, as well as all that followed in this study, a bird would
not be given a subsequent test presentation until at least 1 hour had passed.
In the second set of tests, those birds that had exhibited a willingness to eat
armyworms in the first tests were simultaneously presented 10 larvae of two different
instar sizes, 5 large (5th instar, 26.113.0 SD mm, n = 28) vs. 5 small (2nd or 3rd instar,

89
Figure 4-1. Euplectrus plathypenae Howard (Hymenoptera: Eulophidae) larvae attached
to an armyworm (Spodoptera ssp.) larvae host.

90
Figure 4-2. Prey item presentation cup placed in test cage with a red-winged blackbird
(Agelaius Phoeniceus) foraging for a food item. The presentation cup contained a center
divider partitioning the cup into two chambers. A red line painted on the exterior of the
cup allowed observers to easily determine which chamber a food item was taken from.

91
Figure 4-3. In multiple trials, birds were offered fall armyworms [Spodoptera frugiperda
(J. E. Smith)] of similar body size in each of the presentation cup’s chambers.

92
14.5 12.4 SD mm, n = 28), presented in a plastic cup divided into two separate chambers
(Figure 4-4). Birds were allowed to forage until 5 armyworms were consumed or 'A hour
had elapsed, which ever occurred first. Choice of prey size and order of prey taken was
recorded each time a bird chose to consume a larva and choices ranked first to last taken.
Prey Recognition Trials
In prey recognition trials, birds were simultaneously offered a paired choice of
parasitized and non-parasitized fall armyworms (following methods described by Avery
et al. 1994 & 1999). Maintenance food was removed by 0700 EST and 1-2 hrs later birds
were presented with a plastic cup divided into two chambers, one containing 5 parasitized
armyworms the other containing 5 non-parasitized armyworms. Birds were allowed to
forage undisturbed for 15 minutes or until 5 caterpillars were selected. Position of prey
type in the cup’s 2 chambers (left side or right side) was alternated for each trial. In each
trial the order and number of each prey item taken was noted and choices ranked first to
last taken. The objective of these paired trials was to document immediate prey
preference response and overall preference of individual birds to parasitized and non-
parasitized prey choices.
In the first set of these prey recognition-feeding trials, birds were presented
parasitized and non-parasitized armyworms of equal body size. Therefore birds were
presented a choice of prey differing only in the appearance of having attached parasitoid
larvae or not. The second set of prey recognition trials presented parasitized and non-
parasitized armyworms of equal age. Host larvae that have had a Euplectrus female
oviposit or attempt to oviposit an egg in them exhibit arrested growth thereafter. This is a
typical host response to venom of Euplectrus injected during oviposition (Coudron and

93
typical host response to venom of Euplectrus injected during oviposition (Coudron and
Puttier 1988). The resultant arrested growth causes a substantial size difference to
develop between parasitized and non-parasitized armyworms within 24 - 48 hours
(Figure 4-4).
Data Analysis
Initial preference for choosing the first prey item from 1 of the 2 cup chambers
(right vs. left), size (large vs. small), or parasitized vs. non-parasitized prey was
determined in the paired trials using Chi-square tests of the null hypothesis that birds
chose from each side of the cup or prey type with equal frequency. Overall prey
preference was determined utilizing stratified Wilcoxon rank sum tests of the null
hypothesis that birds show no preference for feeding upon the paired prey types. Of the
five bird selections, the first food selected by the bird receives rank 5, the second rank
four, etc. and the fifth receives rank 1. All ranks assigned to a particular food are then
summed over the many birds in the trial. A preferred food would receive higher ranks
and more ranks than a food that was less preferred. The null hypothesis for the rank sum
is derived by assuming that each bird randomly selects its next food item, so that
selections are made as though an honest coin (having probability of 1/2 of selecting each
of the two foods) is tossed each time a food item is selected by the bird. Thus each rank
is randomly assigned to one of the foods based on an independent coin toss. Violations
of this assumption causing one of the foods to receive higher rank totals can then be
assessed via a p-value computed under this null distribution. A small p-value thus
indicates a strong preference for one of the two foods (R. H. Randles and M. Capanu,
IF AS Statistics, University of Florida, FL, Pers. Comm.)

94
Figure 4-4. In multiple trials, birds were offered fall armyworms [Spodoptera frugiperda
(J. E. Smith)] of significantly different body size in each of the presentation cup’s
chambers.

95
Results
Tests with non-parasitized larvae found that most birds (14 out of 18 individuals)
would quickly consume the 10 larvae presented to them. In 80% of the trails, birds
consumed all 10 larvae presented to them within 15 minutes, regardless of instar size.
Typically, each bird would mandibulate the larvae up and down its entire length before
swallowing (especially so for the largest larvae). This handling often caused the larvae to
exude a gut secretion, which was allowed to fall to the cage floor. Sloan and Simmons
(1973) observed similar behavior and suggested that lepidopteran gut secretions may be
distasteful to birds, leading to this behavior.
Birds showed no initial preference for feeding from a particular chamber (right or
left side) of the presentation cup (j? = 0.05, p> 0.05, n = 19). Birds did exhibit a
significant initial preference for larger armyworms when presented a size difference in
Prey Of2 = 28.30, p> 0.001, n = 20). Birds also showed a significant overall preference
for larger prey even while this prey item became increasingly less numerous in the cup
during each trial (Z = -3.63, p < 0.001, n = 20).
In prey-recognition trials, birds were readily willing to eat both parasitized and
non-parasitized prey offered to them. Interestingly, some of the Euplectrus larvae
became detached from their host when birds handled the caterpillars and often remained
behind in the presentation cup. When the cup was left in the cage, birds often consumed
the free Euplectrus larvae. Birds did not exhibit an initial preference between
simultaneously presented parasitized and non-parasitized armyworms of the same size
= 1.0, p> 0.05, n = 20). Likewise, birds did not exhibit an overall preference between
these prey types in the cup during each trial (W0 = 139, p = 0.69, n = 20). However as

96
expected, birds did exhibit a significant initial preference for larger non-parasitized
armyworms versus the smaller parasitized prey of the same age (x 2 = 38.44, p> 0.001, n
= 21). Birds also showed a significant overall preference for the larger non-parasitized
prey (W0 = 248, p < 0.001, n = 21) even while this prey item became increasingly less
numerous in the cup during each trial (Figure 4-5).
Discussion
Birds will augment pest control programs if they consume individual prey that
have escaped mortality from other agents of biological control in the cropping system. In
this study, the hypothesis that birds prefer to forage upon non-parasitized prey was tested
and found to be functionally valid although via a different mechanism than I expected.
Red-winged blackbirds were equally willing to eat both parasitized and non-parasitized
fall armyworm prey of the same body size. However, in the case examined in this study,
birds showed a strong preference for the larger lepidopteran prey confirming findings by
Krebs et al. (1977). Fall armyworm larvae that have escaped parasitism quickly become
larger in body size compared to those parasitized by Euplectrus wasps. Birds
overwhelmingly preferred these larger caterpillars when they were given a choice
between the 2 prey types and subsequently avoided parasitized prey. This supports
previous work indicating that birds avoid prey that have been damaged or compromised
by a parasite.
Sloan and Simmons (1973) observed that the avoidance of parasitized prey items
by chipping sparrows appeared to be related to a size difference between parasitized and
non-parasitized jack pine budworms. Similar to larvae stung by ovipositing Euplectrus

97
Choice Available
np = larger non-parasitized armyworm
p = smaller parasitized armyworm
Figure 4-5. Birds showed a significant overall preference for the larger non-parasitized
prey (W0 = 248, p < 0.001, n = 21) even while this prey item became increasingly less
numerous in the cup during each trial. Birds overwhelmingly chose a larger larvae in
each case of choice pairings from 5 larger non-parasitized with 5 smaller parasitized to
pairings of only 1 non-parasitized with 5 smaller parasitized fall armyworms [Spodoptera
frugiperda (J. E. Smith)].

98
wasps, those jack pine budworms that had been parasitized by Aponíales fumiferanae
Viereck (Hymenoptera: Braconidae) are comparatively small. Since many parasitoid
wasps, such as those in the genus Euplectrus, cause a significant difference in body size
to develop between hosts and those lepidopteran larvae missed by these parasitoids, birds
preferentially foraging for larger caterpillars could indeed increase overall mortality of
these pests in cropping systems. Difference in size occurs between those caterpillars that
are parasitized and those that have not been attacked by Euplectrus and similar wasps,
regardless if the caterpillar actually carries wasp larvae or not. Continued molting for
growth to larger instars is arrested in caterpillars that have been stung by these wasps in
attempts to oviposit even if eggs where not actually deposited or develop successfully
(Coudron and Puttier 1988, Coudron et al. 1990).
Foraging upon leaf-eating caterpillars that have escaped control by parasitoid
wasps, such as Euplectrus ssp., could indeed be of great value to a producer. Parkman
and Shepard (1981) measured the difference in foliage consumption between parasitized
(by E. plathypenae) and non-parasitized yellowstriped armyworms (Spodoptera
ornithogalli) and found parasitized larvae consumed significantly less foliage (1.23 vs.
8.85 cm2 / d / larvae). Additionally, Coudron et al. (1990) found that in most cases
parasitized caterpillars cease to feed altogether due to this arrested growth condition.
Therefore, it is very important in an integrated pest management system to include an
additional predator that exhibits a preference for feeding on those lepidopteran larvae that
have escaped attack by parasitoids of this kind.
In this study most red-winged blackbirds were more than willing to eat fall
armyworms and were capable of consuming a number of these prey in short time periods.

99
In cropped fields where armyworms are problematic, insectivorous birds may provide a
benefit by consuming this prey item. For example, Bendell et al. (1981) found that
predation by red-winged blackbirds was responsible for lowering overwintering
European com borer [Ostrinia nubilalis (Hübner), Lepidoptera: Pyralidae] populations in
standing com of the following year. Unfortunately, red-winged blackbirds can also cause
damage to many fall ripening row crops. This damage can be especially high in fields
nearest to their favored roost habitats (wetlands), where large flocks congregate (Dolbeer
1990).
Results of this study suggest that birds may indeed augment biological control
programs when those arthropod pests that escape control become distinctly different in
body size and subsequently a favored prey item. However, feeding behavior of birds in
the field may be substantially different than that in a laboratory setting. Krebs et al.
(1977) found that when prey items were scarce, birds chose to eat large and small food
items equally. Birds began to exhibit a preference for large prey when large and small
food items were in abundance. Additionally, the behavior of parasitized verses non-
parasitized prey may affect the vulnerability of parasitized lepidopteran larvae to avian
predation in a field setting. The fitness of an organism that parasitizes another is not only
a function of its own survival and reproduction but also upon the survival of its host (May
and Anderson 1983). There is growing evidence that parasitoids may manipulate the
behavior of their hosts to their advantage (reviewed by Godfray 1994). More?
Therefore, these aspects of the interaction of avian predators and arthropod pest prey
subject to biocontrol need further investigation within cropping systems.

100
Conclusion
In the U.S., resident and migratory passerines (over 200 different species)
constitute more than 70% of the bird species that feed, roost, or breed on agricultural
lands (Rodenhouse et al. 1993). Fortunately, few landbird species indigenous to the U.S.
are pests to crops, and less than 10 are known to cause significant damage to any crop
(Dolbeer 1990). Many species occurring in the U.S. are wholly or partly insectivorous
(Freemark et al. 1991) and as such have great potential for stabilizing insect populations
including crop pests thus enhancing plant growth via insectivory.
Biotic diversity is a vital and irreplaceable component of our natural resources
providing ecosystem services that are essential to agriculture (Ehrlich et al. 1995, Daily
1997a). In a recent survey of farmers in Florida, 80% of conventional farmers (non-
organic) indicated that they considered leaf-eating insects a serious pest problem
(Jacobsen et al. 2003). In another survey, leaf-eating caterpillars were the most
frequently mentioned type of insect pest by Florida organic farmers; armyworms were
specifically mentioned (Swisher et al. 1994). Observations of birds foraging in cropping
systems have confirmed that birds actively seek out and consume crop pest lepidopteran
larvae (see Chapter 3). While numerous researchers in the past purported the value of
bird predation, few modem studies have quantified their potential as agents of biocontrol
in cropping systems (see Kirk et al. 1996, McFarlane 1976). This study aids in the
determination of the pest control potential avian insect predators have in agroecosystems
and increases our understanding of the functional role of insectivorous birds in modem
agricultural systems. Information obtained from captive feeding trials can be
incorporated into estimates of overall pest regulation potential and sets the stage for

101
future field research to investigate actual arthropod biomass reductions due to foraging by
insectivorous birds in cropping systems (i.e. exclosure studies etc.).

CHAPTER 5
SUMMARY AND FUTURE RESEARCH NEEDS
Summary
I examined factors influencing avian species diversity on North-central
Florida farmlands and, in particular, focused upon factors that increased the
presence and abundance of insectivorous birds and their foraging activity in
cropped fields. I assessed overall avian biodiversity on a selection of
conventional and certified organic farms, and identified farm characteristics
correlated with bird diversity. I also identified ‘functional insectivores’ among
the bird species utilizing farmlands and identified farm characteristics correlated
with densities of these species in cropped fields. I found that many birds,
including several listed as species of conservation concern by both the Federal
Fish and Wildlife Service and the Florida Fish and Wildlife Conservation
Commission, utilize croplands. Encouragingly, a large percentage of species that
might be expected to occur in North-central Florida croplands, based upon the
Audubon of Alachua County checklist of birds and BBS census data from the
county, were observed utilizing these landscapes. This would suggest that the
agricultural landscape composed of the small- to medium-size farmsteads typical
of this region offer suitable habitats for a large number of species.
102

103
Avian species abundances and diversity on farms was strongly influenced
by the presence of complex hedgerows and windbreaks of natural vegetation
bordering cropped fields. Likewise, abundances of functional insectivores were
also strongly influenced by the presence of these farmscape elements. Moreover,
the landscape matrix adjacent to cropped fields, which serves as source areas of
birds to the farm, in combination with complex hedgerows and windbreaks was
found to be very important in determining bird densities in cropped fields. These
results emphasize that the dominant vegetative communities in landscapes where
farms and farm fields are embedded, as well as the composition and spatial
configuration of habitat, determine bird species diversity on farms. These results
also suggest that schemes to design on-farm habitats (crops, field borders, and
location of planted fields with respect to adjacent matrix types) to influence bird
diversity could be effective, very flexible, accommodate different classes of birds
(i.e. woodland, grassland, edge, generalist species), and therefore, could be
excellent tools for avian conservation in agroecosystems.
In apparent contradiction with other studies in North America (Freemark
and Kirk 2001, Beecher et al. 2002) and Europe (Christensen et al. 1996,
Chamberlain et al. 1999) that documented significantly greater bird diversity
associated with organic farming practices, I detected only slight enrichment of
bird diversity in organic versus conventional farming systems of North-central
Florida. This could be a factor of the smaller size of the farms surveyed in the
study and the heterogeneity of the North-central Florida landscape compared to
other studies. Crop diversity proved to be a very strong predictor of bird density

104
on the farms. Since many conventional farms surveyed in this study employ
polyculture management, this factor appeared to out weigh the differences in bird
occurrence that may have been generated by chemical applications to crops.
Therefore avian conservation efforts in farmlands should emphasize the value of
polyculture cropping systems.
I found a large number of insectivorous bird species utilizing cropped
fields of North-central Florida to forage in. Direct observations during foraging
bouts indicated that most of these species were actively capturing insect prey from
crop vegetation. One important determination I made during this study is that
without determining what birds eat when they are in fields, farmers may assume
that all species are detrimental to crops since a few species can be significant
pests in agroecosystems. Because many birds species are insectivores, or are
insectivorous to some degree, and most become highly insectivorous during the
breeding season to support their energetic needs and those of their nestlings, I
advocate the utility of these ‘functional insectivores’ on farms. This work
supports the general assessment that the ecological role of birds, as insect
predators in agroecosystems, is likely to realize enhanced production and
economic value to farmers. Therefore, through an increased awareness of the
functional role that insectivorous species may have in cropping systems,
producers should be encouraged to engage in avian conservation efforts on their
lands.
I found that the occurrence, density, and especially foraging activity of
insectivorous birds in polyculture cropping systems I surveyed were highest in

105
those having sunflowers (Helianthus annuus) and other decorative cut flowers
intercropped between vegetable rows. I tested the hypothesis that cropped fields
with sunflower rows incorporated into the cropping system would exhibit greater
bird densities and found in those fields with even one row of sunflowers
intercropped within it exhibited significantly greater bird densities than those with
no sunflowers. The addition of even a single sunflower row per acre may provide
the added structural vegetation to make a cropped field attractive for bird use in
those systems where their presence can provide a benefit. Foraging activity by
functional insectivores also was greatly enhanced by this sunflower treatment.
Additionally, intercropped sunflowers attracted and played host to numerous
beneficial insects, and these insects attracted to the sunflowers appeared to move
from them into nearby crop vegetation. Therefore, in those fields in which birds
(and predatory insects) may provide a benefit as insect predators, the addition of
sunflowers into cropping systems may be an effective, and temporary habitat
modification.
Birds can be of value as insect predators in a cropping system only if they
increase the effectiveness of control by taking insects over and above those that
would normally have been destroyed by other agents (Bruns 1959). My foraging
observations of birds in cropping systems have confirmed that birds actively seek
out and consume crop pests. Birds will augment pest control programs such as
those that utilize parasitoids of the crop pests if they consume individual prey that
have escaped mortality from such agents of biological control. I observed that
birds exhibit a strong preference for larger prey when given a choice, even when

106
that prey item is not the most numerous available. Since many parasitoid wasps
often utilized in biological control cause a significant difference in body size to
develop between hosts and those prey missed by these parasitoids, birds
preferentially foraging for larger prey could indeed increase overall mortality of
many pests in cropping systems.
Future Research Needs
Biotic diversity is a vital and irreplaceable component of our natural
resources providing ecosystem services that are essential to agriculture (Ehrlich et
al. 1995, Daily 1997). While numerous researchers in the past purported the
value of bird predation, few modem studies have quantified their potential as
agents ofbiocontrol in cropping systems (see Kirk et al. 1996, McFarlane 1976).
My work aids in the determination of the pest control potential avian insect
predators have in agroecosystems and increases our understanding of the
functional role of insectivorous birds in modem agricultural systems. However,
many questions remain that need to be addressed before biological control
enhancement can be developed manipulating populations of avian species
identified as potentially beneficial currently existing in, or that could be attracted
to these systems. Further, investigations of avian insectivory as a component of
pest management schemes that are consistent with ecologically sound agriculture
are needed, and the actual impact avian insectivory has in these systems needs to
be quantified.

107
While landscape matrix and farm-scale habitat characteristics that appear
to support avian populations are identified, annual breeding productivity and
survival of birds nesting in North-central Florida agroecosystems needs to be
assessed. If avian conservation and agricultural production are to be truly
integrated, these systems must not only attract birds but also be capable of
sustaining species populations that have been attracted. Management that creates
farmland structure that attracts birds, when combined with harmful agricultural
practices (those that cause adult or nestling mortality), or with an over abundance
of avian predators, can become ecological traps functioning as population sinks
for avian species (reviewed by Rodenhouse et al. 1995). Therefore, farmland
management to provide suitable habitat for birds must be such that optimize
survivability and nesting success for those species attracted to such systems.
Evaluation of farmscapes in regard to breeding success must be performed in
differing agroecosystems to aid in the development of systems that will sustain
the greatest avian diversity and abundance.
Conclusion
Ornithologists have suggested that changes in agricultural practices and
landscape structure over the past few decades have reduced the favorability of
farmland habitat elements many farmland species had traditionally utilized. The
current landscape of North-central Florida appears to represent a ‘patch mosaic’
of diverse habitat types long recognized as essential for the maintenance of bird
(and other) species on farmlands (birds; O’Conner and Boone 1992, Best et al.

108
1995: plants; Freemark et al. 2002: moths; Ricketts et al. 2001: ants; Perfecto and
Vandermeer 2002). Farms of all sizes in Florida agroecosystems represent a
diversity of soil types, climatic conditions, cropping systems, landscapes,
biological organization, culture, and traditions. This diversity mirrors and
compliments that of Florida’s many different natural ecosystems. The potential
for responsible management of soil, water, and wildlife encompassed by Florida’s
farms produces an opportunity for significant environmental sensitivity by our
agricultural producers. As imperatives for agricultural shift from the single goal
of increasing unit-area production to environmentally sustainable systems, an
excellent opportunity exists to match the aspirations of Florida’s farmers with
needs of native birds.

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126

APPENDIX A
BIRD SPECIES OBSERVED DURING CENSUS SURVEYS
IN NORTH-CENTRAL FLORIDA FARMLANDS

Table A-l. Species observed during census surveys in cropped fields (F) or within 50 in
of cropped fields (M) of organic (O) and conventionally (C) managed farmlands (or both;
B) of North-central Florida during breeding seasons 1 May through 30 June 2000 and 25
April through 30 June 2001. Species observed foraging within crop vegetation are
indicated with an asterisk and the 10 most common of those (i.e., functional insectivores)
are in bold face type. Conservation status of species is indicated in the right column,
according to the US Fish and Wildlife Service (FWS) and Florida Fish and Wildlife
Conservation Commission (FWC; CC = conservation concern (after Millsap 1990,
revised), T = threatened, SSC = species of special concern).
Common Name
Scientific Name
Farm
Habitat
Status
Acadian Flycatcher
Empidonax virescens
O
M
CC - FWC
American Bald Eagle
Haliaeetus leucocephalus
C
M
T-FWS
American Crow *
Corvus brachyrhynchos
B
FM
American Kestrel
Falco sparverius
O
F
SSC - FWS
American Redstart *
Setophaga ruticilla
O
FM
CC - FWC
Bam Swallow
Hirundo rustica
C
FM
Bay-breasted Warbler *
Dendroica castanea
O
FM
CC - FWC
Black Vulture
Coragyps atratus
C
FM
Black-and-white Warbler *
Mniotilta varia
C
FM
CC - FWC
Blackpoll Warbler *
Dendroica striata
B
FM
CC - FWC
Blue Grosbeak *
Guiraca caerulea
B
FM
Blue Jay *
Cyanocitta cristata
B
FM
Blue-gray Gnatcatcher *
Polioptila caerulea
B
FM
Blue-headed Vireo
Vireo solitarius
O
M
Boat-tailed Grackle *
Quiscalus major
O
F
Bobolink *
Dolichonyx oryzivorus
O
FM
CC - FWC
Brown Thrasher *
Toxostoma rufum
B
FM
128

Table A-l. Continued.
Common Name
Scientific Name
Farm
Habitat
Status
Brown-headed Cowbird *
Molothrus ater
B
FM
Carolina Chickadee *
Parus carolinensis
B
FM
Carolina Wren *
Thryothorus ludovicianus
B
FM
Cattle Egret *
Bubulcus ibis
B
F
Cedar Waxwing
Bombycilla cedrorum
B
M
Chimney Swift
Chaetura pelágica
B
FM
Common Grackle
Quiscalus quiscula
B
F
Common Ground Dove *
Columbina passerina
B
FM
SSC-FWS
Common Yellowthroat *
Geothlypis trichas
B
FM
Downy Woodpecker *
Picoides pubescens
B
FM
Eastern Bluebird *
Sialia sialis
B
FM
CC-FWC
Eastern Kingbird *
Tyrannus tyrannus
B
F
CC - FWC
Eastern Meadowlark *
Sturnella magna
B
FM
CC - FWC
Eastern Towhee
Pipilo erythrophthalmus
B
M
Eastern Tufted Titmouse
Parus bicolor
B
M
Eastern Wood-pewee
Contopus virens
0
M
European Starling
Sturnus vulgaris
B
FM
Fish Crow
Corvus ossifragus
B
FM
Gray Catbird *
Dumetella carolinensis
B
FM
Great Crested Flycatcher *
Myiarchus crinitus
B
FM
Great Homed Owl
Bubo virginianus
0
M
129

Table A-l. Continued.
Common Name
Scientific Name
Farm Habitat
Status
Green Heron
House Finch *
Indigo Bunting *
Killdeer
Loggerhead Shrike *
Mississippi Kite
Mourning Dove *
Northern Bobwhite *
Northern Cardinal *
Northern Mockingbird *
Northern Parula *
Orchard Oriole *
Ovenbird
Pileated Woodpecker
Pine Warbler
Purple Martin
Red-bellied Woodpecker *
Red-eyed Vireo
Red-headed Woodpecker *
Red-shouldered Hawk *
Red-winged Blackbird *
Butorides striatus
Carpodacus mexicanus
Passerina cyanea
Charadrius vociferus
Lanins ludovicianus
Ictinia mississippiensis
Zenaida macroura
Colinus virginianus
Cardinalis cardinalis
Mimus polyglottos
Parula americana
Icterus spurius
Seiurus aurocapillus
Dryocopus pileatus
Dendroica pinus
Progne subis
Melanerpes carolinus
Vireo olivaceus
Melanerpes erythrocephalus
Buteo lineatus
Agelaius phoeniceus
0
F
B
F
B
FM
CC-FWC
C
FM
B
FM
SSC - FWS
B
M
CC - FWC
B
FM
B
FM
CC - FWC
B
FM
B
FM
B
FM
B
FM
0
M
CC - FWC
B
M
B
M
CC - FWC
B
FM
CC - FWC
B
FM
B
M
CC - FWC
O
F
SSC - FWS
B
FM
B
FM
130

Table A-l. Continued.
Common Name
Scientific Name
Farm
Habitat
Status
Rock Dove *
Columba livia
C
F
Rough-winged Swallow
Stelgidopteryx ruficollis
B
FM
Rudy-throated Hummingbird *
Archilochus colubris
B
FM
CC - FWC
Sandhill Crane *
Grus canadensis
0
FM
T-FWS
Summer Tanager *
Piranga rubra
B
FM
Turkey Vulture
Cathartes aura
C
FM
Western Palm Warbler *
Dendroica palmarum
B
FM
CC - FWC
White Ibis
Eudocimus albus
B
FM
SSC - FWC
White-eyed Vireo
Vireo griseus
B
M
Wild Turkey *
Meleagris gallopavo
B
FM
CC - FWC
Yellow-billed Cuckoo
Coccyzus americanus
B
M
CC - FWC
Yellow-shafted Flicker
Colaptes auratus
B
M
Yellow-throated Vireo
Vireo flavifrons
B
F
131

APPENDIX B
BIRD SPECIES OBSERVED ON ORGANIC FARMLANDS
OF NORTH-CENTRAL FLORIDA

Table B-l. Species observed within cropped fields or within 50 m of
cropped fields of organic farmlands in North-central Florida during the
spring growing seasons 1 April through 15 June 2002 and 2003. Those
species observed foraging within crop vegetation are indicated with an
asterisk.
Common Name
Forager
Scientific Name
Acadian Flycatcher
Empidonax virescens
American Crow
*
Corvus brachyrhynchos
American Goldfinch
Carduelis tristis
American Kestrel
*
Falco sparverius
Barred Owl
Strix varia
Bay-breasted Warbler
Dendroica castanea
Blackpoll Warbler
Dendroica striata
Blue-gray Gnatcatcher
Polioptila caeruiea
Blue-headed Vireo
Vireo solitarius
Blue Grosbeak
*
Guiraca caeruiea
Blue Jay
*
Cyanocitta cristata
Bobolink
Dotichonyx oryzivorus
Brown-headed Cowbird
Molothrus ater
Brown Thrasher
*
Toxostoma rufum
Boat-tailed Grackle
Quiscalus major
Cape May Warbler
Dendroica tigrina
Carolina Chickadee
Parus carolinensis
133

Table B-l. Continued.
Common Name Forager Scientific Name
Cattle Egret
Carolina Wren
Cedar Waxwing
Chimney Swift
Common Grackle
Common Ground Dove
Common Yellowthroat
Downy Woodpecker
Eastern Bluebird
Eastern Kingbird
Eastern Towhee
Eastern Tufted Titmouse
European Starling
Eastern Wood-pewee
Fish Crow
Gray Catbird
Great Crested Flycatcher
Great Horned Owl
Green Heron
Bubulcus ibis
Thryothorus ludovicianus
Bombycilla cedrorum
Chaetura pelágica
Quiscalus quiscula
Columbina passerina
Geothlypis trichas
Picoides pubescens
Sialia sialis
Tyrannus tyrannus
Pipilo erythrophthalmus
Parus bicolor
Sturnus vulgaris
Contopus virens
Corvus ossifragus
Dumetella caroiinensis
Myiarchus crinitus
Bubo virginianus
Butorides striatus
134

Table B-l. Continued.
Common Name Forager Scientific Name
House Finch
Indigo Bunting
Loggerhead Shrike
Mississippi Kite
Mourning Dove
Northern Bobwhite
Northern Cardinal
Northern Flicker
Northern Mockingbird
Northern Parula
Orchard Oriole
Ovenbird
Pine Warbler
Pileated Woodpecker
Purple Martin
Red-bellied Woodpecker
Red-eyed Vireo
Red-headed Woodpecker
Red-shouldered Hawk
Rudy-throated Hummingbird
Carpodacus mexicanus
Passerina cyanea
Lanius ludoviclanus
Ictinia mississippiensis
Zenaida macroura
Colinus virginianus
Cardinalis cardinalis
Cotaptes auratus
Mimus polyglottos
Parula americana
Icterus spurius
Seiurus aurocapillus
Dendroica pinus
Dryocopus pileatus
Progne subis
Melanerpes carolinus
Vireo olivaceus
Melanerpes erythrocephalus
Buteo lineatus
Archilochus colubris
135

Table B-l. Continued.
Common Name Forager Scientific Name
Red-winged Blackbird
Rough-winged Swallow
Sandhill Crane
Summer Tanager
Western Palm Warbler
White-eyed Vireo
White Ibis
Wild Turkey
Yellow-billed Cuckoo
Yellow-rumped Warbler
Yellow-throated Vireo
Agelaius phoeniceus
Stelgidopteryx ruficollis
Grus canadensis
Piranga rubra
Dendroica palmarum
Vireo griseus
Eudocimus albus
Meleagris gallopavo
Coccyzus americanus
Dendroica coronata
Vireo flavifrons
136

APPENDIX C
BENEFICIAL INSECTS OCCURING ON SUNFLOWER
AND CROP VEGETATION

Table C-l. Beneficial insects that were observed to occur in randomly placed lm
scouting plots on sunflower and nearby crop vegetation (within lm of
sunflowers) during spring growing seasons 2002 and 2003. Beneficial insects
included arthropod predators, parasitic wasps, and important pollinators
representing 30 different families.
Family
Common Name
Benefit
Anthocoridae
Pirate Bugs
predator
Apidae
Honey Bees
pollinator
Asilidae
Robber Flies
predator
Cantharidae
Soldier Beetles
predator
Chrysididae
Cuckoo Wasps
predator
Coccinellidae
Lady Beetles
predator
Danaidae
Milkweed Butterflies
pollinator
Dermaptera
Earwigs
predator
Eulophidae
Eulophid Wasps
parasite
Formicidae
Ants
predator
Gelastocoridae
Big-eyed Bugs
predator
Halictidae
Green Metallic Bees
pollinator
Hesperiidae
Skippers
pollinator
Ichneumonidae
Parasitic Wasps
parasite
Lycaenidae
Gossamer-winged Butterflies
pollinator
Mordellidae
Tumbling Flower Beetles
predator
Mutillidae
Velvet-ants
predator
Mymaridae
Mymarid Wasps
parasite
138

Table C-1. Continued.
Family
Common Name
Benefit
Oxyopidae
Lynx Spiders
predator
Papilionoidae
Swallowtail Butterflies
pollinator
Pentatomidae
Predatory Stink Bugs
predator
Plutellidae
Diamond-backed Moths
pollinator
Reduviidae
Assassin Bugs
predator
Scarabaeidae
Scarab Beetles
predator
Sphecidae
Sphecid Wasps
parasite
Tenebrionidae
Darkling Beetles
predator
Thomisidae
Crab Spiders
predator
Tiphiidae
Tiphiid Wasps
parasite
T richogrammatidae
Trichogrammatid Wasps
parasite
Vespidae
Vespid Wasps
parasite
139

BIOGRAPHICAL SKETCH
Gregory Alan Jones was bom in North Platte, Nebraska, and raised in
Rochester, New York. He attended the University of Miami in Miami, Florida,
where he received a B.A. in music, with a concentration in audio engineering, in
1984. In this same year Gregory married and over the next few years began a
family while working in the restaurant and entertainment industry. After
Gregory’s youngest of two sons began school, he enrolled at the State University
of New York’s College at Brockport where he received a B.S. magna cum laude
in biology in 1995. He continued at SUNY Brockport and received an M.S. in
biology, with a concentration in avian and terrestrial ecology, in 1997. During
this time he served as a research associate at the Braddock Bay Bird Observatory
in Rochester, New York.
In the summer of 1996 Gregory moved his family to Gainesville, Florida,
and took a teaching position in the Natural Sciences Department of Santa Fe
Community College and served as a research assistant to a good friend, Karl
Miller, at the University of Florida. Gregory was admitted to the University of
Florida’s Department of Wildlife Ecology and Conservation in the fall of 1997.
He gained tenure at Santa Fe Community College in the summer of 2002. He
graduated from the University of Florida with his doctorate in December 2003.
Gregory has conducted research in avian community ecology and behavior of
140

birds in agroecosystems as well as monitoring projects on Neotropical and long
distance migratory birds, cavity-nesting birds, and resident birds in New York and
Florida.
141

I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation fir the degree of Doctor of Philosophy
ovpiiy a
hryn E. Sieving, Ch;
S:
Kathryn E. Sieving, Chair
Associate Professor of Wildlife Ecology
and Conservation
1 certify that 1 have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation fir the degree of Doctor of Philosojjhy
jSeorge WfTanner
Professor of Wildlife Ecology
and Conservation
I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation fir the degree of Doctor of Philosophy
Michael L. Avery (j
Courtesy Associate Professor of
Wildlife Ecology and Conservation
1 certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation fir the degree of Doctor of Philosojj
"7U
Douglas I. Lev^
Professor of Zoology

I certify that I have read this study and that in my opinion it conforms to
acceptable standards of scholarly presentation and is fully adequate, in scope and quality,
as a dissertation fir the degree of Doctor of Philosophy
E. Jane Lu
Professor of Food and 1
Economics
This dissertation was submitted to the Graduate Faculty of the College of
Agricultural and Life Sciences and to the Graduate School and was accepted as partial
fulfillment of the requirements for the degree of Doctor of Philosophy.
Dean, College of Agricultural and Life)
Sciences
Dean, Graduate School

UNIVERSITY OF FLORIDA
3 1262 08556 6205



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