• TABLE OF CONTENTS
HIDE
 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Abstract
 Introduction
 Approach and methods
 Results
 Discussion
 Management recommendations
 Summary
 Literature cited
 Appendices
 Biographical sketch
 Certification form






Group Title: Technical report - Florida Cooperative Fish and Wildlife Research Unit - no. 1
Title: Identification of feeding habitat determinants for Gulf coastal colonial birds
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Permanent Link: http://ufdc.ufl.edu/UF00073749/00001
 Material Information
Title: Identification of feeding habitat determinants for Gulf coastal colonial birds
Series Title: Technical report
Alternate Title: Winter feeding ecology of black skimmers on the Florida gulf coast
Physical Description: ix, 80 leaves : ill., maps ; 28 cm.
Language: English
Creator: Black, Barbara Buttram, 1951-
Publisher: Cooperative Fish and Wildlife Research Unit, University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1980?]
 Subjects
Subject: Black skimmer -- Habitat -- Florida   ( lcsh )
Sea birds -- Habitat -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: prepared by Barbara Black.
General Note: Title from cover.
General Note: "Submitted to: Project Officer, Cooperative Fish and Wildlife Research Unit, 117 Newins-Ziegler Hall, University of Florida, Gainesville, FL 32611, period covered: January - March 1980, contract no. 14-16-0009- 79-063."
General Note: This report was also published as the author's thesis entitled, "Winter feeding ecology of black skimmers on the Florida gulf coast."
Funding: This collection includes items related to Florida’s environments, ecosystems, and species. It includes the subcollections of Florida Cooperative Fish and Wildlife Research Unit project documents, the Sea Grant technical series, the Florida Geological Survey series, the Coastal Engineering Department series, the Howard T. Odum Center for Wetland technical reports, and other entities devoted to the study and preservation of Florida's natural resources.
 Record Information
Bibliographic ID: UF00073749
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: aleph - 001891573
oclc - 30009761
notis - AJW6801

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Table of Contents
    Title Page
        i
    Acknowledgement
        ii
    Table of Contents
        iii
        iv
    List of Tables
        v
        vi
    List of Figures
        vii
    Abstract
        viii
        ix
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
    Approach and methods
        Page 7
        Study area
            Page 7
            Page 8
            Page 9
        Variables
            Page 10
            Page 11
            Page 12
        Observation periods
            Page 13
        Phases
            Page 13
            Page 14
            Page 15
            Page 16
            Page 17
            Page 18
    Results
        Page 19
        Feeding habitat
            Page 19
            Habitat description
                Page 19
                Page 20
                Page 21
                Page 22
            Foraging zones
                Page 23
            Canals
                Page 23
                Page 24
                Page 25
            Habitat comparison
                Page 26
            Testing
                Page 26
                Page 27
                Page 28
                Page 29
                Page 30
        Prey resource
            Page 31
            Distribution and composition
                Page 31
                Page 32
            Consumption
                Page 33
                Page 34
                Page 35
                Page 36
        Foraging patterns
            Page 37
            Tidal and flurry
                Page 37
                Page 38
                Page 39
                Page 40
                Page 41
                Page 42
                Page 43
                Page 44
                Page 45
            Nocturnal
                Page 46
                Page 47
                Page 48
                Page 49
                Page 50
                Page 51
                Page 52
                Page 53
    Discussion
        Page 54
        Spatial aspects
            Page 54
            Tidal feeding habitat
                Page 54
                Page 55
                Page 56
        Dietary aspects
            Page 57
            Page 58
        Temporal aspects
            Page 59
            Page 60
        Social aspects
            Page 61
            Page 62
            Page 63
    Management recommendations
        Page 64
        Page 65
    Summary
        Page 66
        Page 67
    Literature cited
        Page 68
        Page 69
        Page 70
        Page 71
    Appendices
        Page 72
        Appendix A: Principal factor analysis
            Page 73
        Appendix B: Correlation matrix created from one feeding-specific and twelve site-specific variables
            Page 74
            Page 75
        Appendix C: Statistical analyses comparing site-specific variables in area types at Cedar Key and St. Vincent's NWR.
            Page 76
            Page 77
            Page 78
        Appendix D: Fish and shrimp specimens recovered from thirteen black skimmer stomachs
            Page 79
            Page 80
    Biographical sketch
        Page 81
    Certification form
        Page 82
        Page 83
Full Text






TECHNICAL REPORT NO. 1


Identification of Feeding Habitat

Determinants for Gulf Coastal

Colonial Birds


Prepared by:

Barbara Black, Graduate Assistant

School of Forest Resources and Conservation

University of Florida

Gainesville, FL 32611




Submitted to:

Project Officer

Cooperative Fish and Wildlife Research Unit

117 Newins-Ziegler Hall

University of Florida

Gainesville, FL 32611




Period Covered: January March 1980

Contract No.: 14-16-0009-79-063














ACKNOWLEDGMENTS

I would like to thank my committee chairman, Dr. Larry D. Harris,

for his assistance throughout this project. I also appreciate the

advice and guidance of my committee members Drs. John W. Hardy,

Richard W. Gregory and Michael W. Collopy.

I would like to thank Dr. David H. Hirth for encouragement

early in my program and Dr. Randy L. Carter for statistical advice

throughout the study. I would also like to express my gratitude

to Dr. R. Michael Erwin for both suggestions and professional

inspiration. To three persons, Dr. Carter R. Gilbert,Lourdes

Bielsa and Jeff Williams, I am grateful for assistance in identifying

fish and shrimp species. Also I would like to thank the staff of

St. Vincent's National Wildlife Refuge for their kindness and

cooperation and my fellow graduate students for their field

assistance, encouragement and friendship. To many other persons

who assisted me in this study, I extend my gratitude.

I am especially grateful to my parents for their constant

support on my endeavors and to my husband, David, whose love and

unique perspective have been invaluable.














TABLE OF CONTENTS


Page


ACKNOWLEDGMENTS.

LIST OF TABLES .

LIST OF FIGURES.

ABSTRACT .

INTRODUCTION

APPROACH AND METHODS .

Study Area.
Variables
Observation Periods
Phases


RESULTS


Feeding Habitat .
Habitat Description
Foraging Zones
Canals .
Habitat Comparison
Testing
Prey Resource
Distribution and Composition
Consumption.
Foraging Patterns
Tidal and Flurry
Nocturnal

DISCUSSION

Spatial Aspects
Tidal Feeding Habitat
Structure
Location
Wind
Canals and Channelization
Dietary Aspects
Temporal Aspects.
Social Aspects


S19
S19
S23
S23
. 26
S26
S31
S31
. 33
S37
. 37
S46


S 54

S 54
S 54
S 54
S 56
S 56
S 57
S 57
S 59
S 61


Svii

*viii


19









Page

MANAGEMENT RECOMMENDATIONS 64

SUMMARY 66

LITERATURE CITED 68

APPENDICES 72

A PRINCIPAL FACTOR ANALYSIS. 73

B CORRELATION MATRIX CREATED FROM ONE FEEDING-SPECIFIC
AND TWELVE SITE-SPECIFIC VARIABLES .75

C STATISTICAL ANALYSES COMPARING SITE-SPECIFIC
VARIABLES IN AREA TYPES AT CEDAR KEY AND AT ST.
VINCENT'S NWR. 77

D FISH AND SHRIMP SPECIMENS RECOVERED FROM THIRTEEN
BLACK SKIMMER STOMACHS 80

BIOGRAPHICAL SKETCH 81














LIST OF TABLES


Table Page

1 Discrepancies in Black Skimmer feeding times
found in the literature 5

2 Variables recorded during ten-minute observation
periods 11

3 Black Skimmer utilization of study areas during
Phases la and Ib as shown by Duncan's multiple
range test on transformed data 20

4 The first three factors, structure, distance to
mainland and wind speed, created by the factor
analysis .. 21

5 Chi-square goodness of fit test comparing Black
Skimmer utilization versus availability of
foraging zones 24

6 Chi-square goodness of fit test comparing Black
Skimmer utilization of study areas with and
without canals 25

7 Results of three 2 x 2 Analyses of Variance comparing
structure, distance to the mainland and wind speed
within location and between locations 28

8 Chi-square goodness of fit test comparing Black
Skimmer utilization of "presumed suitable" and
"presumed unsuitable" areas at St. Vincent's NWR 30

9 Means, standard errors and results of Duncan's
multiple range test for fish samples collected
in two highly utilized and two non-utilized
areas at Cedar Key 32

10 Percent distribution of weight, volume and frequency
of fish, shrimp and digested material in thirteen
Black Skimmer stomachs 36

11 Prey species described in Black Skimmer diets as
recorded in the literature 38









Table -Page

12 Means, standard errors and results of statistical
analyses comparing the nine variables recorded
during flurry and tidal feeding 40














LIST OF FIGURES

Fi aure Page

1 Locations of the study areas at Cedar Key,. Levy
County, Florida 9

2 Locations of study areas at St. Vincent's National
Wildlife Refuge, Franklin County, Florida 18

3 Frequency histograms of fish and shrimp sampled in
256 seine hauls in two highly utilized and two
non-utilized areas at Cedar Key 35

4 Foraging group sizes in tidal and flurry feeding 43

5 Percentage of total forages occurring throughout
the day for tidal and flurry feeding 45

6 Percehtage of total forages occurring at twelve
tidal stages for tidal and flurry feeding 48

7 Percentage of total forages followed by flight to
a loafing site 50

8 Percentage of total forages occurring in 500 m
increments from the mainland 52










Abstract of Thesis Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science



WINTER FEEDING ECOLOGY OF BLACK SKIMMERS
ON THE FLORIDA GULF COAST



By

Barbara Buttram Black

March 1981

Chairman: Lawrence D. Harris
Major Department: Forest Resources and Conservation

The feeding ecology of Black Skimmers (Rynchops niger) was

studied at Cedar Key and St. Vincent's National Wildlife Refuge

on the Florida Gulf coast during the winters of 1979 and 1980,

respectively. Objectives of the study were to: 1) delineate

characteristics of Black Skimmer winter feeding habitat, 2)

monitor the prey resource and prey selection by wintering Black

Skimmers, 3) describe social, temporal and spatial aspects of

winter foraging, and 4) develop recommendations for Black

Skimmer feeding habitat management.

In the first winter observations were made to identify and

characterize preferred feeding habitat. Food availability and

prey selection by skimmers were sampled. In the second winter

feeding habitat selection was tested in a second locality.

Black Skimmers at Cedar Key typically fed in study areas

with shallow water (10-20 cm) interspersed between oyster bars

or mudflat. Study areas with deep (> 30 cm), uninterrupted bodies


viii










of water typically were not used by the birds. Feeding habitat

selection was similar at St. Vincent's NWR and was predictable from

water depth, land-water interspersion and the proportions of open

water and mudflat.

Skimmers foraged 71 percent of the time within 2 m of a land-

water interface and preferred zones next to mudflat and oyster bar.

Feeding birds used areas with small canals in proportion to their

occurrence but avoided large channels. The lack of preferred

structural features (land-water interface zones) in these channelized

areas may explain the absence of skimmer feeding.

Food abundance alone did not explain the birds' preference for

feeding areas since utilized and non-utilized areas did not differ

significantly (P > 0.05) in prey abundance. Prey composition was

similar among areas sampled, but prey composition in the environment

differed from that of skimmer diets. In the diet Fundulus spp. and

Mugil sp. were predominant by weight and volume while shrimp were

most frequent. In the environment Fundulus spp. and Mugil sp. were

scarce while shrimp were abundant

Two winter foraging patterns were observed. Tidal feeding was

characterized by few birds conducting many forages over a large

area during flow tide. Flurry feeding occurred at evening ebb tide

and was spatially restricted and socially intense. In flurry feeding,

forages increased logarithmically (r2 = 0.82) with increasing bird

numbers. Evidence identifying flurry feeding as social stimulation

or a foraging tactic is inconclusive.



Chairman














INTRODUCTION

In order to survive each organism must acquire from its environ-

ment the resources necessary for its maintenance. Investigations

through theoretical, experimental and descriptive modes have focused

on social (Ward 1965, Krebs et al. 1974), temporal (Emlen 1966,

Schoener 1971), spatial (Recher 1966, MacArthur and Pianka 1966,

Bobisud and Voxman 1979, Hamilton 1971), and dietary (Ashmole 1968,

Pearson 1968) aspects of resource acquisition. Such studies of feed-

ing biology have provided insight into theoretical as well as practical

ecological aspects of avian habitat utilization.

Practical considerations of habitat availability are important

as the nation's coastal land and water resources undergo increasing

utilization by man. While approximately half of all Americans reside,

and are employed, within 80 km of a coastline (OTA 1976), this area

comprises less than 10 percent of the nation's land. In Florida, the

coastal zone contains 25 percent of the state's land area while

supporting over 75 percent of the state's population (DER 1978). In

1972 approximately 63 percent of the state's proposed developments

of regional impact (DRI's) fell within the coastal zone (DSP 1974).

In addition, the U.S. Army Corps of Engineers' National Shoreline

Study noted that 340 km of'Florida's beaches are in a state of

critical erosion. Florida's beaches annually receive 30 million

tourists (Barada.and Partington 1970). Thus, knowledge of coastal





2



species' requirements as well as coastal ecosystem mechanics is

required for future decision making.

Florida serves as a wintering ground for many North American

birds including a large number of coastal shorebirds and colonial

waterbirds. The state provides unique opportunities for biological

and ecological research on wintering species, many-of which occupy

Florida habitats for over half of every year. The present research

should contribute to knowledge of one of these species and elicit

interesting comparisons for similar studies on the species' northern

breeding grounds.

Florida's coastal development facilitates investigation regard-

ing the effects of environmental alterations on avian populations.

The feeding ecology of colonial waterbirds and the resulting manage-

ment implications involve at least two considerations. Firstly,

the effects of dredging are potentially detrimental to coastal

bird communities. Gilmore and Trent (1974) found that by volume,

macro-invertebrates were twice as' abundant in a natural marsh area

in Texas as in an adjacent marsh altered by channelization. Working

in Florida, Hall and Lindall (1974) found a reduction .in the abundance

and species of benthic organisms while Lindall et al. (1975) found a

reduction in the abundance of fishes and crustaceans in estuarine

zones altered by development canals. Thus, as a result of dredging,

bird populations may be indirectly affected by a reduction in food.

Secondly, alterations in coastal nesting habitat may cause

changes in feeding ecology. Since the initiation of the Atlantic

and Gulf Intracoastal Waterway System in the 1930's, 2000 man-made










islands have been created (Lunz et al. 1978). Studies to determine

the extent of dredge island use by colonial birds indicate an

apparent shift by coastal colonial species from historic nesting

sites to spoil islands (Landin and Soots 1977). In Florida an

estimated 70 percent of colonial seabird colonies occur on man-made

as opposed to natural sites (S. Nesbitt, H. Kale pers. comm.). The

reasons for such shifts are speculative but may involve either

increasing pressure on former nesting sites or the creation of

preferred nesting habitat in the form of spoil islands. In either

case, information concerning comparable changes in feeding habitat

is unavailable.

Inherent in the question of habitat alteration is the distance

of newly created spoil island colonies from former or suitable

feeding areas. Erwin (1977a) applied Horn's optimal spacing

model (coloniality vs. territoriality) to three colonial seabird

species and concluded that Black Skimmers (Rynchops niger) flew

shorter distances between nesting and feeding areas than did the

tern species. Erwin's results also indicate that the Black Skimmer

has a more restricted niche breadth on a habitat dimension than the

otner species studied. This apparent restriction in foraging site-

colony distance in conjunction with the more restricted feeding

habitat identifies the Black Skimmer as a likely species to be

impacted by changing environments and, thus, a valuable candidate

for study.

The.skimmer is pantropical in distribution, with two species,

Rynchops albicollis (India to Indo-China) and Rynchops flavirostris










(tropical Africa) occurring in the Eas'tern HemispKere. Three races

of Black Skimmer occur in the Western Hemisphere; these include

R. n. niqer (coastal North America), R. n. cinerescens (Brazil west

to Argentina) and R. n. intercedens (Argentina, Uruguay, Brazil).

The North American race is primarily a coastal species while the

South American subspecies also inhabit large river systems.

Rynchops n. niger breeds from New York to the Gulf coast of

Mexico with the greatest northern breeding concentrations along the

Virginia coast (2687 breeding adults) (Erwin and Korschgen 1979)

and the greatest southern breeding concentrations along the Louisiana-

Mississippi-Alabama coasts (29,980 breeding adults) (Portnoy 1978).

The birds typically leave the northern states in November (M.

Gochfeld pers. comm.) to winter in Florida, along the Gulf coast

and in Central America. Since very few skimmers seen along the north

Florida Gulf coast are banded (compared with up .to 60% of some east

coast populations, W. Robertson pers. comm.) these birds must be

either residents or migrants from states other than New York,-New

Jersey, Virginia or the Carolinas where banding is conducted.

Typical of the Charadriiformes, the Black Skimmer has-undergone

adaptive specialization in its feeding. While the morphological

adaptations of skimmer feeding have been definitively analyzed by

Zusi (1959), the species' ecological adaptations are less well

understood. In fact, the literature concerning several aspects

of the species' feeding ecology is quite varied and disparate (Table

1). For instance, six authors (Arthur, 1921, Bales 1919, Erwin 1977a,

























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Nicholson 1948, Tomkins 1951, Zusi 1959) have suggested that skimmers

are somewhat nocturnal in their feeding habits while three investi-

gators (Chapman 1908, Pettingill 1937, Zusi 1959) have suggested that

skimmers respond to diurnal influences. Chapman (1908), Tomkins

(1951) and Zusi (1959) each state that these birds are-strongly

crepuscular while Bent (1921), Erwin (1977a), Pettingill (1937)

and Tomkins (1951) suggest that tidal stage primarily governs skimmer

foraging activity. Although season, location, and moon phase may

influence perceptions of primary foraging period, the relative

importance of these factors is ambiguous. Also, discrepancies in

feeding habitat selection must be clarified to understand the

species' ecological adaptations.

Previous studies concerning the breeding and feeding biology

of the Black Skimmer have been conducted primarily in the spring

and summer (Chapman 1908, Bales 1919, Pettingill 1937, Chamberlain

1959, Zusi 1959, Erwin 1977a, 1977b, Gochfeld 1977). Only two

published works (Arthur 1921, Tomkins 1951) deal with fall

activities and only one study (Nicholson 1948) has described

ecological or biological aspects of wintering skimmers (Table 1).

The principal objective of this study is to derive information

pertaining to the feeding ecology of wintering Black Skimmers. The

specific objectives are to: 1) delineate characteristics of Black

Skimmer winter feeding habitat, 2) monitor the prey resource and

prey selection by wintering Black Skimmers, 3) describe social,

temporal and spatial aspects of winter foraging, and 4) develop

recommendations for Black Skimmer feeding habitat management.













APPROACH AND METHODS

Study Area

The Cedar Keys are a group of small islands on the west coast

of peninsular Florida at 290 080 30" N and 830 02' 30" W, roughly

midway between the Suwannee and Wacassassa Rivers. The islands are

surrounded by soft-bottomed flats, oyster bars and salt marshes

extending toward the mainland. Three vegetational zones characterize

the salt marshes. From the water's edge they are: a Spartina alter-

niflora zone, a Juncus roemerianus midzone and a third zone comprised

of Salicornia virginiana, Batis maritima and Spartina dystichum.

Tidal fluctuations in this area of the Gulf rarely exceed a meter.

Due to the low energy nature of these tides, little tidal flushing

occurs. This limited turbulence in conjunction with the detritus

from annual turtle grass (Thalassia testudinum) dieoffs results in a

highly organic sediment. Th-is organic component in proximity to fresh

water creates a rich estuarine environment.

The specific study area was comprised of a 16.0 km2 area located

within the key system (Fig. 1). Eighteen similar tidal flat areas were

selected as study sites. The 6.0 ha areas were of variable dimensions

because of particular shoreline features of the tidal flat. The

minimum distance between study areas was 100 m if separated by land

and 400 m if separated by water. Each area was investigated at some

point in the study but not all areas were observed in all phases of

the study.













APPROACH AND METHODS

Study Area

The Cedar Keys are a group of small islands on the west coast

of peninsular Florida at 290 080 30" N and 830 02' 30" W, roughly

midway between the Suwannee and Wacassassa Rivers. The islands are

surrounded by soft-bottomed flats, oyster bars and salt marshes

extending toward the mainland. Three vegetational zones characterize

the salt marshes. From the water's edge they are: a Spartina alter-

niflora zone, a Juncus roemerianus midzone and a third zone comprised

of Salicornia virginiana, Batis maritima and Spartina dystichum.

Tidal fluctuations in this area of the Gulf rarely exceed a meter.

Due to the low energy nature of these tides, little tidal flushing

occurs. This limited turbulence in conjunction with the detritus

from annual turtle grass (Thalassia testudinum) dieoffs results in a

highly organic sediment. Th-is organic component in proximity to fresh

water creates a rich estuarine environment.

The specific study area was comprised of a 16.0 km2 area located

within the key system (Fig. 1). Eighteen similar tidal flat areas were

selected as study sites. The 6.0 ha areas were of variable dimensions

because of particular shoreline features of the tidal flat. The

minimum distance between study areas was 100 m if separated by land

and 400 m if separated by water. Each area was investigated at some

point in the study but not all areas were observed in all phases of

the study.






























Figure 1. *Locations of the study areas at Cedar Key, Levy County,
Florida.













LEVY COUNTY
j .r~


s -

SFLdRIDA
CEDAR KEY


I KM


Zl


- ell









Variables

Seven feeding-specific and twenty site-specific variables (Table

2) were defined and measured in the following manner. A forage was

defined as a feeding effort made by a skimmer during which the bird

was actively skimming and did not alter the wingbeat in the manner

necessary to change direction or otherwise lift itself from the

water's surface. By this definition, the bill may be removed

briefly from the water and re-immersed without indicating the

initiation of a.new foraging effort. Due to the difficulty of.

monitoring more than one bird of a group, a single bird was chosen

and assumed to be representative of the group. The number of key

bird forages per group was obtained by recording the number of

forages made by this single bird, termed the key bird of a group.

The number of key bird forages per observation period was obtained

by summing the number of key bird forages per group for all groups

seen in an observation period. Similarly, the number of birds per

observation period was the number of birds per group summed over

groups within an observation period. Thus, whereas the number of

birds per observation period measures the individuals utilizing an

area, the number of key bird forages per observation period

measures the intensity of this utilization. The number of birds

and the number of key bird forages were multiplied by group and

summed within an observation period to derive total forages, an

approximation of total foraging effort per observation period.

The distance to the post-feeding loafing site was classified

as: 1 = loafing site in area, 2 = loafing site within 250 m of










Table 2. Variables recorded during ten-minute observation periods.

Variables Mneumonic Unit


Feeding-specific

Social
Number of birds per group
Number of birds per observation
period

Behavioral
Number of key bird forages per
group
Number of key bird forages per
observation period
Number of total forages per
observation period
Distance to loafing site

Temporal
Minutes to sunset


bird

bird


(NUF)


forage

forage


forage
classified


(MTS)


minute


Site-specific


Physical
Light intensity
Cloud cover
Wind direction
Wind speed
Air temperature


(WI D)
(WIS)


footcandle
percentage
degree
kph
degree


Social
Number of other feeders

Locational
Distance from loafing site
Distance to mainland

Physiognomic
Tidal stage
Water depth
Patchiness
Water roughness
Shelter by land
Number of obstructions
Mudflat
Sandbar
Oyster bar
Spartina
Open water
Land


(FED)


(DFL)
(DTM)


(TIS)
(WAD)
(PAT)

(SBL)





(OPW)
(LND)


bird


meter
meter


hour
centimeter
classified
percentage
meter
obstruction
percentage
percentage
percentage
percentage
percentage
percentage









area, 3 = loafing site over 250 m from area, 4 = loafing site unknown.

This is a behavioral variable and represents the distance to the

loafing site selected by the bird after feeding. Minutes to sunset

were determined using astronomical data for the local latitude and

longitude.

The 20 site-specific variables were estimated or measured as

described below. The physical variables, light intensity, wind

direction, wind speed and air temperature were measured and recorded

directly while cloud cover was est-imated in ten-percent increments.

The number of other feeders in the area was obtained by counting

only those birds in the area that were foraging. The locational

variable, distance from loafing site, represented the distance from

the center of a study area to the nearest available loafing site at

the time of observation. The variable, distance to mainland, was

classified by 500 m increments from the mainland with one representing

the least and eight representing the greatest distance from the main-

land-. Twelve physiognomic variables also were defined and measured.

The tidal stage was classified as one of 12 one-hour increments

beginning with the previous high tide. Water depth was measured in

centimeters using a water depth marker at the deepest non-channel

location in each area. Patchiness was designated by one of four

classes ranging from 1 = minimal land-water interspersion to 4 =

maximal land-water interspersion. Water roughness was estimated

by taking ten readings of the water surface through an ocular

scope (Winkworth and Goodall 1962) to estimate the percentage of

rough water as compared to smooth water surface. For each study









area a "shelter by land" classification was established for each

of the directions, N, NE, E, SE, S, SW, W, NW. Shelter by land

was classified by 50 m increments of land within 500 m of an area

in each designated direction, thus, resulting in eight readings per

area. A single classification was then assigned to an area depending

on the wind direction at the time of observation. The percentages

of mudflat, sandbar, oyster bar, spartina and open water in an area

were estimated by taking 25 point readings in a standardized pattern

with a cross-wire ocular scope and converting to percentage values.

The percentage of land was a value derived from summing the mudflat

and sandbar percentages.

Observation Periods

A ten minute interval was chosen as the basic time unit of

observation (the observation period). Such periods were assigned

randomly to the areas being sampled in a particular phase of the

study. During observation periods in which skimmers were seen

foraging, all variables (Table 2) were recorded. Only the site-

specific variables were recorded during observation periods in

non-utilized areas.

Phases

The objectives of the study were divided into a number of

components. Habitat delineation, the first objective, involved: 1)

identifying and 2) describing preferred foraging areas, 3) comparing

utilized and non-utilized feeding areas, and 4) testing these

findings in an independent location. Also, the use of topographic

features within an area and the use of areas with and without canals









area a "shelter by land" classification was established for each

of the directions, N, NE, E, SE, S, SW, W, NW. Shelter by land

was classified by 50 m increments of land within 500 m of an area

in each designated direction, thus, resulting in eight readings per

area. A single classification was then assigned to an area depending

on the wind direction at the time of observation. The percentages

of mudflat, sandbar, oyster bar, spartina and open water in an area

were estimated by taking 25 point readings in a standardized pattern

with a cross-wire ocular scope and converting to percentage values.

The percentage of land was a value derived from summing the mudflat

and sandbar percentages.

Observation Periods

A ten minute interval was chosen as the basic time unit of

observation (the observation period). Such periods were assigned

randomly to the areas being sampled in a particular phase of the

study. During observation periods in which skimmers were seen

foraging, all variables (Table 2) were recorded. Only the site-

specific variables were recorded during observation periods in

non-utilized areas.

Phases

The objectives of the study were divided into a number of

components. Habitat delineation, the first objective, involved: 1)

identifying and 2) describing preferred foraging areas, 3) comparing

utilized and non-utilized feeding areas, and 4) testing these

findings in an independent location. Also, the use of topographic

features within an area and the use of areas with and without canals









were considered as a portion of habitat delineation. The second

objective dealt with the prey resource and prey selection by

skimmers. Food abundance was sampled in two utilized and two

non-utilized areas while prey composition was compared between

areas and with skimmer diets. The third objective was to describe

feeding patterns.

To accomplish these objectives four phases of research were

outlined. During the first phase (July-October 1979) observations

to determine area use-were made according to a randomized block

design in 12 areas (Phase la, A, B, C, D, E, F, G, H, I, J, K, J,

M) during low tide. Data collection.for Phase Ib was conducted

in the same manner but differed in the addition of new areas (M,

N, 0, P) and the deletion of other areas (G, H, I, J) outside

of the birds' observed range (Fig. 1).

During the second phase of study (November 1979-March 1980)

observations were conducted to describe feeding habitat. Phase

one results revealed that skimmer foraging was not restricted

to low tide stages. Therefore, observation periods were assigned

to 6 utilized areas for 20 hours in each of 12 tidal stages. In

this manner 89 skimmer-specific observations were recorded with

accompanying environmental measurements. A principal factor

analysis was used to analyze these data (Appendix A).

In order to determine Black Skimmer response to topographic

features within an area, a number of foraging zones were defined

as: edge mudflat, edge mudflat spartina, edge mudflat oyster bar

and non-edge open water. The "edge" was defined as a 2 m zone










to either side of a land-water interface. The relative abundance

of these foraging zones was estimated by taking 25 readings with

a cross-wire ocular scope and converting to percentage values. The

number of skimmer forages in the various zones was recorded to evaluate

use. All results are reported using the standard probability levels:

n.s. P > 0.05, P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001.

The prey resource was sampled using a 3 cm delta mesh seine

(3.1 m) in a.6.0 m sweep immediately adjacent and parallel to the

land-water interface. Samples from 64 seine hauls in each of 4

areas (A, C, D, 0) were characterized by the number of individuals

per seine haul and by the number of individuals per family. Prey

selection by Black Skimmers was estimated by collecting 13 birds

during feeding in April 1980 and analyzing their stomach contents.

During the third phase of study (September-October 1980)

observations to compare utilized and non-utilized feeding habitat

were made from low tide to flow tide, the time frame identified

as the primary foraging period. Ten days of observations were

structured such that low tide occurred in each of the 10 hours

from 0700-1700. Nocturnal observations were also made during this

study phase in two highly utilized areas, A and C, and two inter-

mittently utilized areas, B and M. Three nights of observations

were conducted in each of the periods from 1900-2200, 2300-0200

and 0300-0600.

While the results of the Cedar Key study may accurately portray

skimmer feeding ecology, the results also may reflect the unique

characteristics of that area's geography. A final test phase was,









therefore, initiatedin order to account for the effects of location

while holding tides, season and time of day constant. Observations

were conducted using the same procedures described for the third

phase habitat comparison in Cedar Key. The study site, St. Vincent's

National Wildlife Refuge, was selected because it has tidal similarities

to Cedar Key (cycles (6 hrs) and fluxes (Cedar Key x = 0.8 m, St.

Vincent's x = 0.5 m)) as well as geographic similarities to the

Louisiana-Mississippi-Alabama coast, the center of Black Skimmer

breeding in North America. These geographic similarities include

barrier beaches with associated protected tidal-flats.

Candidate study sites were first judged in terms of selected

parameter values and assigned to a "presumed suitable" or "presumed

unsuitable" status (Fig. 2). Observations of skimmer use were then

conducted to ascertain if the null hypothesis of equal utilization

by feeding skimmers should be rejected.






























Figure 2. Locations of the study areas at St. Vincent's National
Wildlife Refuge, Franklin County, Florida. Areas V
and X were "presumed suitable" and areas T and U were
"presumed unsuitable."





















FRANKLIN COUNTY


INDIAN PASS LAGOON


ST. VINCENT'S


GULF OF MEXICO


ST. VINCENT


I KM


GULF COUNTY














RESULTS

Feeding Habitat

Habitat Description

The first step in identifying Black Skimmer feeding habitat

determinants in Cedar Key was the establishment of preference

classes for various feeding areas. In Phases la and Ib skimmers

utilized some study areas more frequently (ANOVA, P < 0.05) than

others: In both phases, areas A and C were used significantly

more (P < 0.05) than the other areas (Table 3). Areas D, 0, N,

H, J and I were consistently non-utilized; however, since areas

H, I, J, and N were not within the birds' observed range, these

areas were deleted from further observation. Thus, D and 0 were

the only areas within feeding range that were consistently non-

utilized. All other areas (B, E, F, G, K, L, M, P) were classified

as low utilization areas since they were intermittently used by

foraging skimmers.

Measurements of environmental variables recorded during

active skimmer feeding were used to distinguish the key factors

of intermittently and frequently used habitat (Table 4). The

first three factors created by the factor analysis accounted for

83 percent of the variation in the original data. Since the four

variables with high loadings (Appendix A) on the first factor are

variables that describe some structural feature of skimmer feeding

habitat, I refer to the first factor as structure. The variables














RESULTS

Feeding Habitat

Habitat Description

The first step in identifying Black Skimmer feeding habitat

determinants in Cedar Key was the establishment of preference

classes for various feeding areas. In Phases la and Ib skimmers

utilized some study areas more frequently (ANOVA, P < 0.05) than

others: In both phases, areas A and C were used significantly

more (P < 0.05) than the other areas (Table 3). Areas D, 0, N,

H, J and I were consistently non-utilized; however, since areas

H, I, J, and N were not within the birds' observed range, these

areas were deleted from further observation. Thus, D and 0 were

the only areas within feeding range that were consistently non-

utilized. All other areas (B, E, F, G, K, L, M, P) were classified

as low utilization areas since they were intermittently used by

foraging skimmers.

Measurements of environmental variables recorded during

active skimmer feeding were used to distinguish the key factors

of intermittently and frequently used habitat (Table 4). The

first three factors created by the factor analysis accounted for

83 percent of the variation in the original data. Since the four

variables with high loadings (Appendix A) on the first factor are

variables that describe some structural feature of skimmer feeding

habitat, I refer to the first factor as structure. The variables














RESULTS

Feeding Habitat

Habitat Description

The first step in identifying Black Skimmer feeding habitat

determinants in Cedar Key was the establishment of preference

classes for various feeding areas. In Phases la and Ib skimmers

utilized some study areas more frequently (ANOVA, P < 0.05) than

others: In both phases, areas A and C were used significantly

more (P < 0.05) than the other areas (Table 3). Areas D, 0, N,

H, J and I were consistently non-utilized; however, since areas

H, I, J, and N were not within the birds' observed range, these

areas were deleted from further observation. Thus, D and 0 were

the only areas within feeding range that were consistently non-

utilized. All other areas (B, E, F, G, K, L, M, P) were classified

as low utilization areas since they were intermittently used by

foraging skimmers.

Measurements of environmental variables recorded during

active skimmer feeding were used to distinguish the key factors

of intermittently and frequently used habitat (Table 4). The

first three factors created by the factor analysis accounted for

83 percent of the variation in the original data. Since the four

variables with high loadings (Appendix A) on the first factor are

variables that describe some structural feature of skimmer feeding

habitat, I refer to the first factor as structure. The variables
















w



c




e 1
v(,



u




















a0












.- ,













I



- -
3: i

a

i I



















C 0
C














r-CL










i- e
* ^ i-
10
F- s


o -

II yo i. tX
a U
0c5


0







9-




0
9-





0


-A






m
C4




co
uL





I-.


9 -





LL





0






lo
0
U-




0
=





0





9-
0


0
*


4.J
>1






3
'U
u




4-
C

0,
e





9.-
U


S.-
4-
4-





4-


0
e

0




a.,
C
3



I

-a
T;




3
r:~
1/1
ig
!

a


c




m
u
c


f.
<-




in


0



0
.4-












o
4-1
V,
C




'I
e








'a






0,










'iU










-a












Table 4. The first three factors, structure, distance to mainland,
and wind speed, created by the factor analysis.a These factors
accounted for 83 percent of the variation in the original data
describing skimmer feeding habitat.

Factor Pattern

Factor 1 Factor 2 Factor 3
Variablesbc "Structure" "Distance to Mainland" "Windspeed"

TIS -0.24 -0.30 -0.16
WAD 1 -0.85 -0.16 0.05
PAT 2 0.90 -0.09 0.04
DFL -0.36 0.48 0.25
DTM -0.25 5 -0.52 .-0.53
MTS 0.58 -0.38 0.09
SBL 0.24 0.46 -0.11
WID -0.10 0.45 .-0.29
WIS 0.32 -0.26 6 0.65
FED 0.05 0.49 -0.03
P 3 -0.85 -0.22 0.19
L 4 0.85 -0.06 -0.21


values represent loadings for each variable on the respective
factor and indicate relative importance. Signs indicate direction-
ality and do not indicate positive or negative status.

P represents the arcsine transformation of the percentage of open
water.

cL represents the arcsine transformation of the percentage of land
(mudflat or sandbar).









and their loadings (Table 4, first column, values 1-4, respectively)

were water depth (0.85), patchiness (0.90), amount of open water

(0.85) and amount of land including mudflat and sandbar (0.85).

Of these variables, water depth and the amount of open water were

negatively correlated with the number of forages while patchiness

and the amount of land were positively correlated with the number

of forages (Column 1, values 1-4 respectively of Appendix B). In

other words, as the water depth or amount of open water decreased,

the number of skimmer forages increased. Conversely, as the

patchiness (amount of land-water interspersion) or land (mudflat

or sandbar) increased, the number of forages increased.

The second factor had no variables with loadings greater than

0.60. However, the highest variable loading (0.52) (Table .4, value

5) was associated with the distance to the mainland and, thus, the

factor was identified as distance. The number of forages was

negatively correlated with the distance to the mainland indicating

that foraging increased closer to the mainland (Appendix B, column

1, value 5).

The third factor was designated as-wind speed since that variable

had the highest loading (0.65) (Table 4, value 6) on the third factor.

Although the number of forages was positively correlated with wind

speed (Appendix B, column 1, value 6), the interpretation that

skimmers prefer stronger winds for feeding is probably not correct.

In fact, increasing wind speed may reduce feeding success and,

thus, increase the amount of effort needed to attain a satisfactory

diet. Therefore,-increased foraging may be a bird's response to









increased wind speed, rather than a reflection of a bird's preference

for feeding in stronger winds.

Foraging Zones

In order to further evaluate the skimmer's utilization of feed-

ing habitat, several foraging zones were defined and monitored for

their availability to and utilization by foraging skimmers. These

foraging zones, edge mudflat, edge mudflat spartina, edge mudflat

oyster bar and non-edge open water, were not found to.be utilized

by feeding skimmers according to their relative occurrence within

an area (X2 = 339, P < 0.05). Thus, the birds in this study were

not only selecting areas for foraging but also preferentially

foraging near certain topographic features within an area. Specifically,

the edge mudflat (X2 = 23.8, P < 0.05) and edge mudflat oyster bar

(X2 = 187.5, P < 0.05) zones were 'utilized more frequently than

would be expected by their relative occurrence in the environment

(Table 5). Edge mudflat spartina (X2 = 172.3, P < 0.05) and non-

edge open water (X2 = 40.8, P <. 0.05) were utilized less than would

be expected if foraging were non-selective (Table 5). These results

further support the hypothesis that the structure of an area may

casually determine utilization by foraging skimmers.

Canals

A chi-square goodness of fit test comparing areas with and

without canals indicated no significant difference between their

availability and use by feeding skimmers (Table 6). While areas

with canals were used non-selectively by skimmers, some topographic

features in the areas were preferred by feeding birds. Of the









increased wind speed, rather than a reflection of a bird's preference

for feeding in stronger winds.

Foraging Zones

In order to further evaluate the skimmer's utilization of feed-

ing habitat, several foraging zones were defined and monitored for

their availability to and utilization by foraging skimmers. These

foraging zones, edge mudflat, edge mudflat spartina, edge mudflat

oyster bar and non-edge open water, were not found to.be utilized

by feeding skimmers according to their relative occurrence within

an area (X2 = 339, P < 0.05). Thus, the birds in this study were

not only selecting areas for foraging but also preferentially

foraging near certain topographic features within an area. Specifically,

the edge mudflat (X2 = 23.8, P < 0.05) and edge mudflat oyster bar

(X2 = 187.5, P < 0.05) zones were 'utilized more frequently than

would be expected by their relative occurrence in the environment

(Table 5). Edge mudflat spartina (X2 = 172.3, P < 0.05) and non-

edge open water (X2 = 40.8, P <. 0.05) were utilized less than would

be expected if foraging were non-selective (Table 5). These results

further support the hypothesis that the structure of an area may

casually determine utilization by foraging skimmers.

Canals

A chi-square goodness of fit test comparing areas with and

without canals indicated no significant difference between their

availability and use by feeding skimmers (Table 6). While areas

with canals were used non-selectively by skimmers, some topographic

features in the areas were preferred by feeding birds. Of the













Table 5. Chi-square-goodness of fit test comparing Black Skimmer
utilization versus availability of foraging zones.

Forages N = 5460

Forage Zone Observed Expecteda Chi-square

For all zones

Edge mudflat 1826 1660
Edge mudflat spartina 491 841 338.6****
Edge. mudflat oyster bar 1522 1114
Non-edge open water 1622 1845

By zone

Edge mudflat 1826 1660
Non-edge mudflat 3635 3800 23.8**

Edge mudflat spartina 491 841
Non-edge mudflat spartina 4970 4619 172.3**

Edge mudflat oyster bar 1522 1114
Non-edge mudflat oyster 3939 4346 187.5***
bar

Non-edge open water 1622 1845
Non-non-edge open water 3839 3615 40.8**


aExpected values were derived from the number of forages which should
occur in each zone based only on the zone's availability. The zone's
availability was derived in an area at the time of feeding by taking
25 readings with an ocular point sampling scope and converting to a
percentage value.















Table 6. Chi-square goodness of fit test comparing Black Skimmer
utilization of study areas with and without canals.

Forages

Feature Observed Expecteda Chi-square

Phase la
(N = 1163 forages)

With canals
N = 6 areas 605 582
n.s.
1.9
Without canals
N = 6 areas 558 582

Phase Ib
(N = 778 forages)

With canals
N = 4 areas 259 257
O.03n.s.
Without canals
N = 8 areas 519 521


aExpected values are
without canals.


based on the percentage of areas with and








total forages recorded in the second phase (N = 5460) 71 percent were

within 2 m of a land-water interface. Skimmers also preferred

interfaces next to mudflat and oyster bar. While the creation of

canals may reduce land-water interface zones in some portions of

an area, their spoil deposited nearby may result in loafing sites,

land-water interface zones, and shallow water,, features. used by

feeding skimmers. Thus, while the canal, itself, is not used for

feeding it may indirectly result in preferred habitat features in

an area.

Habitat Comparison

When utilized and non-utilized feeding areas at Cedar Key were

compared, no significant differences were found for any climatic

variables (cloud cover, wind speed, wind direction), temporal

variables (minutes to sunset, minutes from sunrise, tidal stage)

or the percentage of spartina (Appendix C1). Significant differences

were found for a number of social, locational and physiognomic

variables. Utilized areas were characterized by more feeding

birds of all species as well as proximity to loafing sites and the

mainland. Physiognomically, utilized areas were typified by

shallower, smoother water with fewer obstructions and more shelter

provided by surrounding land. There was less open water, less

oyster bar, more land-water interspersion and more mudflat in the

utilized areas.

Testing

At St. Vincent's-NWR three days of unstructured observations

indicated that the marine bird community utilized the area in a








total forages recorded in the second phase (N = 5460) 71 percent were

within 2 m of a land-water interface. Skimmers also preferred

interfaces next to mudflat and oyster bar. While the creation of

canals may reduce land-water interface zones in some portions of

an area, their spoil deposited nearby may result in loafing sites,

land-water interface zones, and shallow water,, features. used by

feeding skimmers. Thus, while the canal, itself, is not used for

feeding it may indirectly result in preferred habitat features in

an area.

Habitat Comparison

When utilized and non-utilized feeding areas at Cedar Key were

compared, no significant differences were found for any climatic

variables (cloud cover, wind speed, wind direction), temporal

variables (minutes to sunset, minutes from sunrise, tidal stage)

or the percentage of spartina (Appendix C1). Significant differences

were found for a number of social, locational and physiognomic

variables. Utilized areas were characterized by more feeding

birds of all species as well as proximity to loafing sites and the

mainland. Physiognomically, utilized areas were typified by

shallower, smoother water with fewer obstructions and more shelter

provided by surrounding land. There was less open water, less

oyster bar, more land-water interspersion and more mudflat in the

utilized areas.

Testing

At St. Vincent's-NWR three days of unstructured observations

indicated that the marine bird community utilized the area in a









manner similar to the Cedar Key avian community. Specifically, the

marine birds arrive in the study area shortly after sunrise. Loaf-

ing site utilization varies as the tides wax and wane. Typically

as the tide recedes, movement toward the mainland occurs, as birds

spread out over the tidal-flats to feed. As the tide advances and

covers these low areas the birds are again concentrated on higher

loafing sites, beaches, progressively farther from the mainland

(Cedar Key 4000 m, St. Vincent's 2200 m). In both localities the

entire community (except for Black-crowned Night Herons (Nycticorax

nycticdrax) and Great Blue Herons (Ardea herodius)) abandons these

inland sheltered areas at dusk to roost on isolated reefs (Cedar

Key Corrigan's Reef) or islands (St. Vincent's Pelican Island).

several kilometers from the mainland.

Study areas were selected such that significant differences

(P < 0.05) in structure existed between the-two sets of areas at

St. Vincent's but notbetween the Cedar Key and St. Vincent's sites

(Table 7). In other words,-two sets of two replicates were selected

at the second site such that their similarity to the Cedar Key sites

was maximized. Selection based on the second factor, distance to

the mainland, was more.difficult since the only areas with structural

features similar to the non-utilized habitat were located close to

the mainland. The third factor, wind speed, varied significantly

(P < 0.01) both between area and location (Table 7). However, since

wind speed did not vary significantly (P > 0.05) between utilized

and non-utilized areas at Cedar Key (Appendix C), it was not heavily

considered in study area selection at St. Vincent's. Thus, those















Table 7. Results of three 2 x 2 Analyses of Variance comparing
structure, distance to the mainland and wind speed within
location and between locations. Locations are Cedar Key,
Florida and St. Vincent's NWR.

Factor 1 Factor 2 Factor 3
Distance to
Effect Structure Mainland Wind speed

Within Location
(utilized & "presumed suitable" **** **** *
vs non-utilized and "presumed
unsuitable")

Between Locations
(Cedar Key vs St. Vincent's) n.s. **** ***

Interaction n.s. n.s. n.s.









variables important in the identification of structure (water depth,

patchiness, percentage of land and percentage of open water) were

the principal criteria for selection of the St. Vincent's sites.

The second major consideration in study site selection was the

distance to the mainland.

When "presumed suitable" and "presumed unsuitable" areas at

St. Vincent's were compared, no significant differences (P > 0.05)

were found in climatic variables (cloud cover, wind speed, wind

direction), temporal variables (minutes to sunset, minutes from

sunrise, tidal stage) or the percentage of spartina (Appendix C).

As expected, significant differences were found.for all structural

variables (water depth, patchiness, percentage of mudflat, percentage

of open water) by which the area types were selected. In addition,

"presumed suitable" areas had more feeders of other species, less

water roughness, more obstructions, less shelter by land, more

oyster bar, and were farther from the mainland than "presumed

unsuitable" areas. Thus, St. Vincent's "presumed suitable" sites

were farther from the mainland, had more oyster bar, less shelter

by land and more obstructions than did Cedar Key's utilized sites.

Allowing for these differences, the area types at Cedar Key and

St. Vincent's were similar for all other variables tested.

Black Skimmers used "presumed suitable" areas 2.5 times more

frequently than they utilized "presumed unsuitable"areas. A

significantly unequal distribution of forages (X2 = 15.1, P < 0.05)

was recorded in the two area types (Table 8). Two factors prevented

this difference from being even greater. First, the area most














Table 8. Chi-square goodness of fit test comparing Black Skimmer
utilization of "presumed suitable" and "presumed unsuitable" areas
at St. Vincent's NWR.

Forages N = 144

Areas Observed Expected Chi-square

Utilized 105- 72
.15.1*
Non-utilized 39 72








representative of utilized habitat was located so close to the only

"presumed unsuitable" areas that it could not be selected as a study

area. Secondly, feeding in this area resulted in some feeding in

the adjacent "presumed unsuitable" area. Considering these factors,

the results of this study indicated that feeding habitat selection

of St. Vincent's Black Skimmers was consistent with that of Cedar

Key Black Skimmers and predictable from the factor analysis of Cedar

Key habitats.

Prey Resource

Distribution and Composition

The importance of Black Skimmer feeding habitat features was

confounded by questions regarding the distribution and abundance

of the prey resource. The importance of structural features should

only be evaluated in conjunction with information regarding the

prey base. In the Cedar Key study no significant difference

(Duncan's P > 0.05) in prey abundance was found between utilized

area C and non-utilized area D (Table 9). In addition, no signi-

ficant difference was found in non-utilized area D, utilized area

A and non-utilized area 0. If the currently used index of prey

abundance were the only criterion used for discriminating between

foraging areas, then areas 0 and 0 should not differ in utilization

from areas A and C. This relation had previously been shown not

to be the case since areas A and C were utilized significantly

more (P < 0.05) than any other study areas and areas D and 0

were consistently non-utilized.








representative of utilized habitat was located so close to the only

"presumed unsuitable" areas that it could not be selected as a study

area. Secondly, feeding in this area resulted in some feeding in

the adjacent "presumed unsuitable" area. Considering these factors,

the results of this study indicated that feeding habitat selection

of St. Vincent's Black Skimmers was consistent with that of Cedar

Key Black Skimmers and predictable from the factor analysis of Cedar

Key habitats.

Prey Resource

Distribution and Composition

The importance of Black Skimmer feeding habitat features was

confounded by questions regarding the distribution and abundance

of the prey resource. The importance of structural features should

only be evaluated in conjunction with information regarding the

prey base. In the Cedar Key study no significant difference

(Duncan's P > 0.05) in prey abundance was found between utilized

area C and non-utilized area D (Table 9). In addition, no signi-

ficant difference was found in non-utilized area D, utilized area

A and non-utilized area 0. If the currently used index of prey

abundance were the only criterion used for discriminating between

foraging areas, then areas 0 and 0 should not differ in utilization

from areas A and C. This relation had previously been shown not

to be the case since areas A and C were utilized significantly

more (P < 0.05) than any other study areas and areas D and 0

were consistently non-utilized.













Table 9. Means, standard errors and results
range test for fish samples collected in two
two non-utilized areas at Cedar Key.


of Duncan's multiple
highly utilized and


Preference Duncan'sa
Area Class Mean & S.E. Test

C high 293.5 + 44.2 A
A
D non 195.2 + 73.7 A B
B
A high 124.1 + 38.6 B
B
0 non 66.4 + 8.9 B


aMeans with the same letter are not significantly different _P = .05)








# No difference in prey resource composition was apparent between

the two utilized areas, A and C, and two non-utilized areas, D and

0, (Fig. 3). lhile fish were classified by family as Sciaenidae

(including spot, drum and perch), Mugilidae (including mullet,

Mugil spp.), Cyprinodontidae (including killifish, Fundulus spp.)

Engraudidae (including bay anchovy, Anchoa spp.), Atherinidae

(including silversides, Menidia spp.) and "others", all shrimp

were grouped together. Shrimp and members of the family Sciaenidae

comprised at least 87 percent of the total catch in each of the

four sampled areas.

Consumption

In order to compare prey abundance with the prey captured by

skimmers, thirteen birds were collected and their stomach contents

analyzed (Appendix D). A total of 63 items were recovered of which

60 percent were shrimp and 40 percent were fish (Table 10). However,

by both weight and volume fish were the predominant (81% and 77%,

respectively) food acquired. In order of abundance the fish

recovered were: longnose killifish (Fundulus similis) 8; striped

mullet (Mugil cephalus) 7; Gulf killifish (F. grandis) 3; larva

(Sciaenidae) 2; diamond killifish (Adenia xenica) 1; Atlantic thread

herring (Opisthonema oglinam) 1; tidewater silvers-ide (Menidia

beryllina) 1; needlenose fish (family Belonidae) 1; larva (Clupeiformes)

1. Longnose killifish, mullet and Gulf killifish were the largest

and most frequently acquired fish species.

Although shrimp were the most abundant prey item recovered,

they represented onTy 7 percent of the weight and 9 percent of the






























Frequency histograms of fish and shrimp sampled in
256 seine hauls in two highly utilized areas, A and
C, and two non-utilized areas, D and 0. SC =
Sciaenidae, MU = Mugilidae, CY = Cyprinodontidae,
EN = Engraudidae, AT = Atherinidae, SH = Shrimp,
0 = other.


Figure 3.










UTILIZED


N = 7942


100
90
80
70
60
50
40
301
20
10


SC MU CY EN SH AT 0
CLASSES


N 18,785


SC MU CY EN SH AT 0
CLASSES


NON-UTILIZED


1001


FLcm


SC MU CY EN SH AT 0
CLASSES


100,
90
80


N 12,498


100
90
80
70
60
50
40
30
20
10


N= 4248


w

C,


-LL
0
0
LJ

z
CU


------- I -_
SC MU CY EN SH AT 0
CLASSES


L














Table 10. Percent distribution of weight, volume and-frequency
of fish, shrimp and digested material in thirteen Black Skimmer
stomachs.

Category Weight (%) Volume (%) Frequency (%)a

Fish 81 77 40

Shri-mp 7 9 60

Digested Material 12 .14


aBased on partial or whole specimens.









volume of the analyzed stomach contents. The mean length and weight

of whole specimens were 24.6 + 1.2 mm and 0.11 + 0.2 gm, respectively.

Shrimp species identified from whole specimens included Palaemonetes

pugio 4; P. intermedius 2; and P. vulgaris 1. Finely digested material

accounted for 12 percent of the weight and 14 percent of the volume

of the stomach contents analyzed.

Prey species found in the diets of Cedar Key skimmers did not

differ strikingly from those previously described (Table 11). How-

ever, 2 new fish and 3 new shrimp species were added: Adenia xenica,

Opisthonema oglinum, P. pugio, P. intermedius, and P. vulgaris.

The species composition of fish taken by foraging skimmers

differed markedly compared to the species available within the

foraging zones frequented by the birds. While Fundulus spp. were

by volume the primary prey item acquired by skimmers, they comprised

only one percent of the total sample in each of the areas seined.

Mugil spp., second in importance to skimmers, comprised.from 2 to 10

percent of the prey sampled in the four areas: Shrimp on the other

hand were the most frequent item acquired by skimmers as well as

the most frequent prey item in three of the four areas sampled.

Foraging Patterns

Tidal and Flurry

During the second phase of this study two types of feeding

were apparent. The first type was characterized by several birds

concentrating their efforts in a small area for an extended period

of time. This behavior occurred in the evening and was associated

with mid-tide stages. The second type of feeding behavior was









volume of the analyzed stomach contents. The mean length and weight

of whole specimens were 24.6 + 1.2 mm and 0.11 + 0.2 gm, respectively.

Shrimp species identified from whole specimens included Palaemonetes

pugio 4; P. intermedius 2; and P. vulgaris 1. Finely digested material

accounted for 12 percent of the weight and 14 percent of the volume

of the stomach contents analyzed.

Prey species found in the diets of Cedar Key skimmers did not

differ strikingly from those previously described (Table 11). How-

ever, 2 new fish and 3 new shrimp species were added: Adenia xenica,

Opisthonema oglinum, P. pugio, P. intermedius, and P. vulgaris.

The species composition of fish taken by foraging skimmers

differed markedly compared to the species available within the

foraging zones frequented by the birds. While Fundulus spp. were

by volume the primary prey item acquired by skimmers, they comprised

only one percent of the total sample in each of the areas seined.

Mugil spp., second in importance to skimmers, comprised.from 2 to 10

percent of the prey sampled in the four areas: Shrimp on the other

hand were the most frequent item acquired by skimmers as well as

the most frequent prey item in three of the four areas sampled.

Foraging Patterns

Tidal and Flurry

During the second phase of this study two types of feeding

were apparent. The first type was characterized by several birds

concentrating their efforts in a small area for an extended period

of time. This behavior occurred in the evening and was associated

with mid-tide stages. The second type of feeding behavior was














Table 11. Prey species described in Black Skimmer diets as
recorded in the literature.


Author


Species


Erwin (1977b)
Virginia


Arthur (1921)
Louisiana



Leavitt (1.957)
Fl ori da

Loftin (pers. comm.)
Florida


Menidia sp., Fundulus sp., Anchoa
mitchilli, Mugil sp., Leiostromus
zanthurus, Pomontomus saltatrix

Cynoscion nothus, Aterina sp., C.
nebulosus, Sciaenops ocellatus,
Trachi-notus carolinus, Carangus hiopos,
M. cephalus, Scomberomorus maculatus,
P. saltatrix

Tylosurus sp., Lutjanus sp., Fundulus
sp., Palaemonetes sp.

M. cephalus, F. heteroclitus, Brevoortia
tryannus, Paralichthys sp., Elops saurus,
Echeneis naucrates









characterized by fewer birds foraging in an area for a short period

before moving on to another feeding area. This type of feeding

occurred throughout the day and was associated with low tide. A

bimodal frequency distribution of the total forages confirmed a

temporal difference between feeding times. The frequency distri-

bution of the number of birds per observation period also was bimodal.

Based on these preliminary observations a working definition of the

first foraging type was established. Flurry feeding was defined

as seven or more groups feeding in a single area for at least 20

minutes. All other feeding was considered tidal-flat or tidal

feeding. Of the total forages recorded during the winter 1979-80,

80 percent were tidal forages and 20 percent were flurry forages.

Although the mean number of birds per group did not differ

significantly (P > 0.05) between tidal and flurry feeding, the

key bird forages per group were significantly (P < 0.05) greater

in tidal feeding than in flurry feeding (Table 12). Within an

observation period, the number of birds in tidal feeding was

significantly (P < 0.05) less than in flurry feeding. Additionally,

there were significantly more (P < 0.05) tidal key bird forages

than flurry key bird forages for the same time interval. Thus,

within an observation period tidal feeding was characterized by a

few birds conducting many forages while flurry feeding was typified

by many birds executing fewer forages.

In flurry feeding observations the number of key bird forages

increased logarithmically (r2 = 0.82) with increasing bird numbers.

No similar pattern was found in tidal feeding. Despite this difference













Table 12. Means, standard errors and results of statistical
analyses comparing the nine variables recorded during flurry
and tidal feeding. S = student's t test (homogeneous variance),
A = approximate t test (heterogeneous variance)a W = Wilcoxon's
sum rank test.

Flurry Tidal Statistical
Variable N = 30 N = 89 Test


n.s.
Number of birds pern. 2.5 + 0.2
group

Number of birds per** 11.4 + 2.7
observation period

Number of key bird **** 4.1 + 0.5
forages per group

Number of key bird* 16.5 + 2.5
forages per observation
period

Total forages pern.s. 133.4 + 37.3
observation period

Minutes to sunset**** 59.9 + 16.1

Tidal stage**** 4.8 + 0.6

Distance to loafing*b 1.5
site


2.2 + 0.2


2..3 + 0.3


24.4 + 3.5


29.2 + 4.4



87.1 + 20.2


315.5 + 16.8

8.3 + 0.2

2.5


Distance to mainland**


8.0 + 0.0


4.9 + 0.3


aApproximate t test (Stee


1 and Torrie 1960, p. 81)


Median value replaces mean









and significant differences in key bird forages and number of birds,

the total forages per observation period were not significantly

(P > 0.05) different for tidal and flurry feeding.

Flurry feeding occurred significantly (P < 0.05) closer to

sunset than did tidal feeding (Table 12). In addition, flurry

feeding occurred closer to the loafing site utilized after

feeding (Table 12). A median value of 1.5 indicated that flurry

feeding birds most often used the loafing site within the foraging

area while tidal feeding birds differed significantly (P < 0.05)

in that-they frequently used loafing sites (median 2.5) outside of

the foraging area. Also, flurry feeding occurred at significantly

greater (P < 0.05) distances from the mainland than did tidal

feeding. Thus, flurry feeding occurred closer to sunset, closer

to the utilized loafing site and farther from the mainland than did

tidal feeding.

In both foraging regimes birds fed typically alone or in

pairs with less than 10 percent of the sightings containing more

than five birds (Fig. 4). These results are consistent with

those of Erwin (1977b) who reported skimmers foraging predominantly

singly or in pairs in-Virginia.

Relative frequency histograms of total forages are shown in

Figures 5-8.. During flurry feeding 78.3 percent of the forages

occurred within 100 minutes of sunset (Fig. 5). This contrasts

with only 4.5 percent of tidal feeding during the same interval

since tidal feeding occurred primarily from midmorning until

midday. Increased sampling at preferred tidal stages occurring

at midday confirmed the lack of foraging effort during this period.






























Figure 4. Foraging group sizes in tidal and flurry feeding.















40-


30


20'


IO


50-


401


TI DAL

N- 156


in-rn,


U I


I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17
GROUP SIZE


FLURRY

N 132


I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17


GROUP SIZE


507-






























Figure 5. Percentage of total forages occurring throughout
the day for tidal and flurry feeding.











TIDAL

N=5460


NOON SUNRISE
MINUTES TO SUNSET


I Im ~


0
SUNSET


FLURRY

N= 1334


0 "
0 i
SUNSET


100 150 200 250 300 350 400 450 500 550 600
NOON SUNRISE
MINUTES TO SUNSET









The percentage of tidal forages occOrring at various tidal

stages is shown in Figure 6. The peak of tidal feeding was in

tidal state 8; 2 hours after low tide. A single long feeding

effort during the winter's lowest tide (26 February 1980) resulted

in an atypical tidal feeding peak 1 hour after high tide. If this

peak is deleted, 69.3 percent of tidal feeding is seen to occur 2

to 3 hours after low tide. Tidal feeding was typically initiated

at low tide, was most frequent during flow tide and was concluded

by high tide. Approximately 70.4 percent of flurry forages occurred

3 to 4 hours after high tide. Flurry feeding was typically initiated

at ebb tide and occurred from ebb tide to early low tide stages.

Flurry feeding and tidal feeding are not mutually exclusive and

both were recorded at evening low tide on -11 and 14 November 1979.

One hundred percent of flurry forages were recorded within

250 m of a subsequently utilized loafing site (Fig. 7). Only

57.5 percent of tidal forages occurred within this distance of the

selected loafing site. Additionally, one hundred percent of flurry

forages occurred over 3500 m from the mainland, while tidal forages

were dispersed from 1 to 4000 m from the mainland (Fig. 8).

Nocturnal

During nine nights of nocturnal observation, skimmers were

recorded utilizing diurnal feeding habitat on only one occasion.

This feeding occurred in early evening (1900-2200) during a full

moon phase and differed from the typical diurnal feeding in the

rapidity with which groups (x = 6.3 birds) moved from one study

area to another. In addition, the degree of vocalization between





























Figure 6. Percentage of total forages occurring at twelve tidal
stages for tidal and flurry feeding.' Stage 1 = high
tide, stage 6 = low tide.




48


c5 50


0 40
Li
-1
30

LL
o 20
LU





a. 0 '- O
I2 3 4 5 6 7 8
TIDAL STAGE

LUJ
o 50


o 40
Lu

-
30

Ll
20
LU


z 10

Sr
LU
0
LULr7
0


TIDAL

N=5460


9 10 II 12


FLURRY

N= 1334


TIDAL STAGE


1 2 3 4. 5 6 7 8 9 10 1 12































Figure 7. Percentage of total forages followed by flight to
a loafing site: 1) within area, 2) within 250 m
of the area, 3) over 250 m from the area, and
4) unknown.








100
90:
80


1 2 3 4


lOOr


- I


I I -f


DISTANCE TO LOAFING SITE



FLURRY
N=1334


DISTANCE TO LOAFING


TI DAL
N-5460


20
10


90
80
70
60
50
40
30,
20
10
0


SITE






























Figure 8. Percentage of total forages occurring in 500 m
increments from the mainland.






100
90
80
70
60

50

40


3 4 5. 6.
DISTANCE TO MAINLAND


7 8


FLURRY
Nx1334


I -


2 3 4
DISTANCE


5 6
TO MAINLAND


TIDAL
Nx5460


100
901

801
70
60

50
40
30

20

10
0


7 8





53



group members was noticeably greater in nocturnal feeding than in

diurnal feeding. Since nocturnal feeding, however, was recorded

on only this single occasion, evidence is lacking for typical

features of nocturnal feeding.













DISCUSSION

The feeding habits and habitat of wintering Black Skimmers on the

Florida Gulf coast were described first for one locality and then

tested in a second locality. Feeding habitat utilization was similar

in both localities and other aspects of feeding ecology were parallel.

In the following discussion spatial, dietary, temporal and social

facets of Black Skimmer feeding ecology will be discussed as they

apply to the localities studied. However, since most of the infor-

mation derives from Cedar Key that study will serve as the focal

.point.

Spatial Aspects

Tidal Feeding Habitat

Structure

A premise underlying this study is that a species having evolved

a specialized feeding behavior will demonstrate specificity rather

than plasticity in feeding habitat selection. If such specificity

exists then the identification and delineation of such feeding

habitat should be possible. The results of this study indicate

that in tidal feeding such specificity does exist.

Areas utilized most frequently by foraging skimmers had more

mudflat and more land-water interspersion than did non-utilized

areas. While a skimmer may "key into" the amount of mudflat in

an area, the amount of edge created by land-water interspersion also

54













DISCUSSION

The feeding habits and habitat of wintering Black Skimmers on the

Florida Gulf coast were described first for one locality and then

tested in a second locality. Feeding habitat utilization was similar

in both localities and other aspects of feeding ecology were parallel.

In the following discussion spatial, dietary, temporal and social

facets of Black Skimmer feeding ecology will be discussed as they

apply to the localities studied. However, since most of the infor-

mation derives from Cedar Key that study will serve as the focal

.point.

Spatial Aspects

Tidal Feeding Habitat

Structure

A premise underlying this study is that a species having evolved

a specialized feeding behavior will demonstrate specificity rather

than plasticity in feeding habitat selection. If such specificity

exists then the identification and delineation of such feeding

habitat should be possible. The results of this study indicate

that in tidal feeding such specificity does exist.

Areas utilized most frequently by foraging skimmers had more

mudflat and more land-water interspersion than did non-utilized

areas. While a skimmer may "key into" the amount of mudflat in

an area, the amount of edge created by land-water interspersion also

54













DISCUSSION

The feeding habits and habitat of wintering Black Skimmers on the

Florida Gulf coast were described first for one locality and then

tested in a second locality. Feeding habitat utilization was similar

in both localities and other aspects of feeding ecology were parallel.

In the following discussion spatial, dietary, temporal and social

facets of Black Skimmer feeding ecology will be discussed as they

apply to the localities studied. However, since most of the infor-

mation derives from Cedar Key that study will serve as the focal

.point.

Spatial Aspects

Tidal Feeding Habitat

Structure

A premise underlying this study is that a species having evolved

a specialized feeding behavior will demonstrate specificity rather

than plasticity in feeding habitat selection. If such specificity

exists then the identification and delineation of such feeding

habitat should be possible. The results of this study indicate

that in tidal feeding such specificity does exist.

Areas utilized most frequently by foraging skimmers had more

mudflat and more land-water interspersion than did non-utilized

areas. While a skimmer may "key into" the amount of mudflat in

an area, the amount of edge created by land-water interspersion also

54








may be important. Thus, the amount of mudflat in itself may or

may not be critical. At St. Vincent's, for instance, oyster bar

appeared to be a topographic substitute for mudflat. Whether or

not these two features influence a skimmer's selection of an area,

they are important in a bird's utilization of an area. Both edge

mudflat and edge mudflat oyster bar were utilized significantly

more by skimmers than would be expected by their occurrence in the

study areas. The reason for the avoidance of the edge mudflat

spartina zone is unknown.

Water depth and the amount of open water were significantly

less in highly utilized areas than in non-utilized areas. Prey

abundance must be considered with the possible importance of these

habitat features. For instance, non-utilized area D had the second

highest prey yield while at the same time having the greatest water

depth and most open water of the areas studied. While prey abundance

was relatively good the structure of the area was such that the area

was not selected for feeding by skimmers. The highly utilized

areas A and C had relatively high prey abundance, shallow water

and less open water. Finally, area 0 while having shallower water

and less open water than area D, was also non-utilized. Prey

abundance in this area was the lowest of any area.sampled. Thus,

while certain structural features (shallow water, amount of mudflat,

lack of large expanses of open water, interspersion of land and water)

of an area are important criteria for utilization by foraging skimmers,

the value of these features is not independent of prey resource

concentrations and the importance of prey concentrations is not

independent of an area's structure.









Location

Tidal feeding areas typically were located close either to the

mainland or to large land masses. The influence of location is

illustrated when considered conjointly with the speed and direction

of the prevailing winds.

Wind

At Cedar Key the water roughness was significantly less in

utilized areas although the wind speed did not differ significantly

between utilized and non-utilized areas. Two factors may account

for this discrepancy: 1) wind measurements made 2.0 m above the

water may differ from those occurring at the water's surface,

2) significantly greater patchiness in the utilized areas may

influence water roughness by creating calm microhabitats along

land-water interface zones where wind movement at the water's

surface is broken by exposed terrain.

Utilized areas are significantly more sheltered from large

bodies of water than are the non-utilized areas. This location

influences the water roughness and the water depth. Since the

non-utilized areas are unprotected from large bodies of water in

the direction of the prevailing westerly winds, water is typically

blown into these areas. This results in surface water movement,

increased water roughness and deeper water in these areas. This

deeper water covers those features (oyster bar and mudflat) that

both interrupt water movement and alter wind flow adjacent to the

water's surface. Thus, the non-utilized areas due to their location

and lack of shelter from prevailing winds had significantly deeper




57



water, more water roughness and less land-water interspersion. These

features were associated with decreased utilization by foraging

skimmers at both Cedar Key and St. Vincent's NWR.

Canals and Channelization

In this study feeding birds used areas with canals in proportion

to their occurrence but .avoided large channels (Fig. 1, No. 3 & 4

channels) (Fig. 8, distances 3, 5, 6). The lack of preferred

structural features (land-water interface zones) in large channels

may explain the. absence of skimmer feeding. Since traveling distance

between patches varies linearly with the linear dimension of the

patch and the hunting area within a patch varies as its square,

then larger patches offer smaller travel time per unit hunting

area (MacArthur and Pianka 1966). An alternative to larger patches

in reducing traveling time between areas is "connectedness" (MacArthur

1968). These concepts may apply to Cedar Key skimmers that use a

sequence of feeding areas (M, L, E, C, P, 8, A) that allows almost

continuous hunting except in large channels (Fig. 1, No..3 & 4

channels). Large channels may lower feeding efficiency by inter-

rupting the connectedness of feeding areas with preferred structural

features. Canals on the other hand, are not often used by skimmers

but may indirectly result in shallow water, loafing sites and land-

water interface zones within the same area. Canals also are not

large enough to disrupt'the connectedness of feeding areas.

Dietary Aspects

While fish were the predominant prey item by volume in the

stomachs analyzed, empirical observations indicated that shrimp








were more abundant by volume in the environment. In addition, the

fish species captured by skimmers comprised a very small percentage

of the prey resources acquired by seining. Such discrepancies may

have been caused by a number of factors. Firstly, skimmers may

select particular prey species using visual acuity during feeding

tn shallow water. However, the speed of skimmer flight while feed-

ing (26-29 kph) in conjunction with the length and straightness of

this flight, indicates that skimmers do not typically swerve and

dart to obtain prey. A highly innervated bill (Zusi 1962) implies

a tactile feeding method by which the bird could non-selectively

acquire prey as they were encountered in skimming. Also skimmers

exhibit broad food preferences as suggested by the number of prey

species listed previously. However, this lack of specificity in

prey acquisition does not preclude the possibility that skimmers

utilize visual cues in pursuing large prey while exercising tactile

skills to randomly acquire smaller, less visible prey.

Secondly, foraging skimmers are clearly biased in prey acquisition

since they sample only the population subset near the water's surface.

Thirdly, certain fish, i.e. Fundulus spp., occur near the water's

surface and are more accessible to feeding skimmers than those

species that occupy lower strata. Fourthly, seining is inadequate

for accurately sampling the prey available to skimmers because

fast swimming species may escape the seine, and the seine samples

both the surface species and the species at greater depths. Thus,

some other sampling method, e.g. Wegener ring (Wegener et al. 1974),

or a combination of methods may be preferable for sampling prey

availability for Black Skimmers.








The selective nature of the skimmer diet as compared to prey

availability in the Cedar Key study areas may result, therefore,

from predator selectivity, prey behavior and/or sampling inadequacies.

The greatest disparity probably is associated with the logistics of

accurately sampling the prey in the foraging zones used by skimmers.

Temporal Aspects

Previous studies of Black Skimmer feeding biology have indicated

diel (Arthur 1921, Zusi 1959) influences as well as tidal influences

(Erwin 1.977b, Tomkins 1951) on skimmer feeding activity. The feeding

activity of wintering skimmers at Cedar Key was influenced by both

.of these factors. Tidal-flat feeding occurred in midmorning and late

afternoon at low to incoming tide. Flurry feeding occurred typically

within one and a half hours of sunset and at ebb tide stages. Thus,

both feeding patterns are apparently governed by tidal and diel

influences.

Shifts in optimal foraging period may result from tidal and

diel changes and from seasonal and geographic changes. If the

assumption is made that animals expand their foraging time (Schoener

1971) when faced with increased energy requirements or decreased

energy resources then seasonal variation in foraging periods would

seemingly occur. In addition, Erwin (1977b) reported skimmers

foraging primarily at low tide (+ 1 hr) while the results of this

study show that feeding was initiated at low tide but occurred

primarily during the flow tide. Topographic features of the area

in conjunction with prey abundance may reconcile and explain these

differences. Erwin suggested that skimmers acquired fish trapped








in shallow mudflat pools and as the tide came in the birds shifted

to the utilization of tidal streams. Similar patterns were noted

in this study during tidal feeding but isolated tidal pools are

infrequent at Cedar Key due to the very gradual sloping of the Gulf

in this area. Additionally, areas exist which have very gentle

shoreward slopes, thus, allowing the birds up to an hour foraging

time on the tide's leading edge where fish activity is augmented.

Thus, optimal foraging periods may not onlybe tide-determined but

may be indirectly determined by the geographic features of the area.

The degree of nocturnal or crepuscular feeding performed by

Cedar Key Black Skimmers must be greater than the diurnal counter-

part. Of approximately 350 wintering birds, 30 to 40 birds will

typically leave the loafing area during low tide to feed in the

tidal flats. Observations of flight-lines to and from the loafing

site throughout the day confirmed this pattern. Thus, on any given

day the majority of the birds present are not believed to forage

diurnally. While this pattern does fluctuate in relation to moon-

phase, the primary foraging period is believed to occur between

sunset and sunrise. Further investigations will require radio and/or

luminescent tracking techniques. However, some aspects of nocturnal

feeding may be inferred from patterns of diurnal feeding.

If diurnal activity is analyzed in relation to moonchase, an

interesting pattern emerges. Since tidal feeding is during low

tide and mid to late morning (0900-1200) or mid to late afternoon

(1400-1700) (Fiq. 6), then tidal feeding must be associated with

the waxing and waning crescent moon and the waxing and waning








gibbous moon. These moon phases are associated with tides of inter-

mediate volume in the monthly tidal cycle. Conversely, the two

troughs in diurnal tidal feeding activity coincide with the full

and new moons (low tide- 0700-0800, sunrise) and both quarter moons

(low tide- 1230-1330, after noon) (Fig. 6). In other words, diurnal

feeding in the described habitats is more frequent at tides other

than neap tides (monthly low tides associated with quarter moon

phases) and spring tides (monthly high tides associated with full

and new moon phases). If the assumption is made that skimmers main-

tain a consistent dietary intake during a month, then nocturnal

feeding should increase during full moon, new moon and first and

second quarter moons.

Social Aspects

Colonial breeding and group foraging have been interpreted as

adaptations to exploit patchily distributed food resources (Ward

1965, Crook 1965, Krebs 1974). As a colonial breeding bird, however,

the Black Skimmer has been shown to utilize a more uniform food

resource. The species also exhibits less strongly the colonial

tendencies attributed to tern species (Sterna hirundo, Sterna

maxima) that exploit very patchy food resources (Erwin 1977a).

Foraging group size, one indication of social cohesion, is low

in 31ack Skimmers. In Virginia, Erwin (1977b) reported skirmners

hunting singly or in pairs while the mean group size in this study

was 2.2 + 0.2. Reduced foraging group size may be a response to a

fairly uniform prey resource and also a result of difficulties

incurred by skimming in large numbers. As an edge feeding species








(71% of observed feeding was within 2 m of a land-water interface)

skimmers are restricted to a 2-dimensional habitat, as compared to

other terns (i.e. Forster's Tern, Sterna forsterii) which feed in

large numbers and move freely in 3-dimensional space over the water's

surface. Augmented numbers of foraging skimmers in a 2-dimensional

habitat could increase the interference between feeding individuals

and result in reduced foraging efficiency.

One method by which skimmers could increase foraging efficiency

in a 2-dimensional habitat when prey is increased would be the

temporal packing of foraging groups. In flurry feeding group size

did not differ from the mean group size in tidal feeding but the

number of birds feeding per observation period increased significantly.

In addition, 83 percent of flurry forages were within 2 m of a land-

water interface. If prey concentrations are greater then flurry

feeding could provide increased foraging efficiency by allowing

more birds to feed.in an area, in a given period of time, without

violating the restrictions imposed in exploiting a 2-dimensional

habitat. Ward (1965) described the 3-dimensional "roller feeding"

or "fly over feeding" in Ouelea quelea as a mechanism to increase

foraging efficiency in response to increased food abundance. Simi-lar-

ly, feeding is a temporal "roller feeding" in a 2-dimensional habitat.

A selective advantage to gregariousness also may explain this

activity. Flurry feeding is frequently associated with increased

social behavior such as aerial flights and vocalizations. In addition,

the relationship of increased forages with increasing bird numbers,

as found in flurry but not tidal feeding, suggests social stimulation.









The identification of flurry feeding as a social phenomenon or a

foraging tactic requires further investigation concerning changes

in the prey abundance concurrent with flurry feeding.

A second method by which feeders could efficiently exploit a

2-dimensional habitat is through morphological divergence. Recher

(1966) proposed that shorebird species utilizing a 2-dimensional

habitat, the littoral zone, have occupied different segments of

the environment and diverged morphologically to use these segments

with greater efficiency. Although the Black Skimmer exhibits sexual

dimorphism (males are one quarter larger in most dimensions), the

selection pressures causing this divergence could be associated

with either breeding or feeding biology. However, the dimorphic

character of bill size may be related to feeding since some evidence

does exist that male-male and female-female foraging groups pre-

dominate over male-female groups (M. Gochfeld per. comm.). Further

study is needed to confirm or reject this hypothesis and to

investigate sexual stratification in relation to the water's

edge.













MANAGEMENT RECOMMENDATIONS

The management of habitat for coastal birds is necessary in

states such as Florida that have escalating coastal growth. Jahn

(1979) suggests a 4-step planning and evaluation approach to the

conservation of critical habitat of fish and wildlife. These are:

1).identification, 2) delineation, 3) maintenance, and 4) manage-

ment. The primary objective of this study has been the identification

and'delineationof Black Skimmer feeding habitat. I would like to

address further some implications these results have for the

maintenance and management of the species feeding habitat.

First, natural tidal-flat areas must be conserved if the species

is to persist in Florida. These tidal-flats should be characterized

by shallow water (10-20 cm at low tide) with a large degree of land-

water interspersion. Land in this case refers to mudflat, oyster

bar or sandbar. These structural features in conjunction with

shelter provided by nearby land masses can be used to identify

typical habitat. Some species, i.e., the Common Tern (Sterna

hirundo), forage both in tidal-flats and bay/inlet habitats. Because

of the Black Skimmers dependence on land-water interspersion and

shallow water, the species cannot efficiently exhibit such plasticity

in feeding habitat selection. In other words, the restricted niche

breadth described by Erwin (1977a) for Virginia Black Skimmers also

is seen in Florida Black Skimmers. This species is expected to have

limited flexibility in adapting to alternative feeding habitats.

64




65



Small canals are acceptable alterations to skimmer feeding

habitat while large channels are detrimental. Large channels

create large areas of open water with little land-water inter-

spersion. These areas are avoided by feeding skimmers. In addition,

if skimmers do rely on the connectedness of foraging areas for

efficient feeding, then channelization may interrupt this connected-

ness by making some areas unprofitable for skimming.

Natural tidal-flat areas should be maintained for other species

in addition to skimmers. In this study there were significantly

more feeders of other species in the areas characterized by shallow

water, areas of mudflat and land-water interspersion. These features

provided shallow foraging zones for many tidal-flat feeders.

Future research should investigate aspects of colony site-

feeding habitat distances. The shift by coastal colonial species

such as the skimmer td dredge deposit islands may have removed

then from proximity to traditional feeding habitats. The energy

budget of breeding birds may be stressed by these environmental

alterations. A study is needed to investigate .colony site-feeding

habitat distances, adult foraging distances and foraging time, and

colony productivity in altered and traditional habitats.













SUMMARY

Based on 599 structured and 520 unstructured hours of observation

the following findings concerning Black Skimmer winter feeding ecology

on the Florida Gulf coast were noted. The structure of feeding areas

selected by skimmers was typified by shallow water (10-20 cm) inter-

spersed between oyster bar or mudflat. Study areas with deep (> 30 cm),

uninterrupted bodies of water typically were not used by the birds.

Feeding habitat selection was similar at an independent location

and was predictable from water depth, land-water interspersion

and the proportion. of open water and mudflat.

Feeding birds used areas with small canals in proportion to their

occurrence but avoided large channels. The lack of land-water inter-

face zones in these channelized areas may explain the absence of

skimmer feeding. In the geographic and topographic setting studied,

skimmers foraged 71 percent of the time within 2 m of a land.-water

interface and preferred zones next to mudflat and oyster bar. These

preferred structural features are present in areas with small canals

but lacking in areas with large channels.

Skimmers used study areas that were close to the mainland or

other large land masses. This location provided protection from

the prevailing wind, and reduced water roughness. Non-utilized

areas had less shelter provided by surrounding land and greater

water roughness.








The skimmer's preference for particular habitat structure is

not explained by food abundance alone since utilized and non-

utilized areas did not differ significantly (P > 0.05) in prey

abundance. Prey composition was similar among the areas sampled

with shrimp and members of the family Sciaenidae comprising at

least 87 percent of the total catch in each of the four sampled

areas. Prey composition in the environment differed from that of

skimmers' diets. In the diet Fundulus spp. and Mugil sp. were pre-

dominant by weight and volume while shrimp were most frequent. In

the environment Fundulus spp. and Mugil sp. represented less than

10 percent of the prey sampled while shrimp were abundant (> 30%).

The skewed nature of the skimmer diet as compared to prey availability

in this study may be explained by predator selectivity, prey behavior,

and/or sampling inadequacies.

Two winter feeding patterns were observed. Tidal feeding was

characterized by few birds conducting many forages over a large

area during flow tide. Flurry feeding was spatially restricted

and socially intense and generally occurred at evening ebb tide.

In flurry feeding, forages increased logarithmically (r2 = 0.82)

with increasing bird numbers. While this relation suggests social

stimulation, further prey sampling is needed to identify flurry

feeding as a social phenomenon or a foraging tactic.













LITERATURE CITED


Arthur, S. 1921. The feeding habitats of the Black Skimmer. Auk
38:566-574.

Ashmole, N. P. 1968. Body size, prey size and ecological segregation
in five sympatric tropical terns (Aves:Laridae). Syst. Zool.
17:292-304.

Bales, B. R. 1919. Twenty-four hours in a Black Skimmer colony.
Wilson Bull. 31:186-193.

Barada, W., and W. M. Partington, Jr. 1970. Report of an investi-
gation of the environmental effects of private waterfront canals.
Prepared for the State of Florida. 63pp.

Bent, A. C. 1921. Life histories of North American gulls and terns.
U.S. Nat. Mus. Bull. 113. 337pp.

Bobisud, L. E., and W. L. Voxman. 1979. Predator response to
variation of prey density in a patchy environment: A
model. Am. Natur. 114:63-75.


Chamberlain, J. L. 1959. A nesting colony of
Black Skimmers in southwestern Louisiana.
283-284.

Chapman, F. M. 1908. Camps and cruises of an
Appleton and Co., New York. 432pp.


Cooley, W. W;, and P. R. Lohnes. 1971
Wiley and Sons, Inc., New York.


Forster's Terns and
Wilson Bull. 71:


ornithologist.


. Multivariate data analysis.
364pp.


Crook, J. H. 1965. The adaptive significance of avian social
organization. Symp. Zool. Soc. London 14:181-218.


Davis, L. 1951.
53:259.


Fishing-efficiency of the Black Skimmer. Condor


Department of Environmental Regulation. 1978. The Florida
zone management program. Legislative draft. Available
Florida Office of Coastal Zone Manage. 168pp.


coastal
from


Division of State Planning. 1974. Developments of regional impacts:
a summary report for the first year. DSP-BLWM-19-74. Avail-
able from Florida Dept. of Admin. 19pp.









Emlen, J. M. 1966. The role of time and energy in food preference.
Am. Natur. 100:611-617.

Erwin, R. M. 1977a. Foraging and breeding adaptations to different
food regimes in three seabirds: the Common Tern, Sterna hirundo,
Royal Tern, Sterna maxima, and Black Skimmer, Rynchops niger.
Ecology 58:389-397.

1977b. Black Skimmer breeding ecology and behavior. Auk
94:709-717.

and C. E. Korschgen. 1979. Coastal waterbird colonies:
Maine to Virginia, 1977. U.S.D.I. FWS/OBS-79-08. 647pp.

Gilmore, G., and L. Trent. 1974. Abundance of benthic macro-
invertebrates in natural and altered estuarine areas. NOAA
Tech. Rep. .NMFS-SSRF-677.

Gochfeld, M. 1977. Colony and nest site selection by Black Skimmers.
Proc. Colonial Waterbird Group 2:78-90.

Hall, J. R., and W. N. Lindall,.Jr. 1974. Benthic macroinvertebrates
and sediments from upland canals in Tampa Bay, Florida. NOAA
Data Rep. NMFS-94. 221pp.

Hamilton, W. D. 1971. Geometry for the selfish herd. J. Theor.
Biol. 31:295-311.

Jahn, L. R. 1977. Habitat data needs for managing wildlife. Pages
5-12 in Classification, inventory and analysis of fish and
wildlife habitat. U.S.D.I. FWS/OBS-78-76. 604pp.

Krebs, J. R. 1974. Colonial nesting and social feeding strategies
for exploiting food resources in the Great Blue Heron (Ardea
herodius). Behaviour 51:99-134.

J. Ryan and E. L. Charnov. 1974. Hunting by expectation
or optimal foraging? A study of patch use by chickadees.
Anim. Behav. 22:953-964.

Landin, M. C., and. R. F. Soots. 1977. Colonial bird use of dredged
material islands; a national perspective. Proc. Colonial Water-
bird Group 2:62-72.

Leavitt, B. B. 1957. Food of the Black Skimmer (Rynchops nigra).
Auk 74:394.

Lindall, W. N., W. A. Fable, and L. A. Collins. 1975. Additional
studies of the fishes, macroinvertebrates and hydrological
conditions of upland canals in Tampa Bay, Florida. Fish.
Bull. 73:81-85.








Lunz, J. D., R. J. Diaz, and R. A. Cole. 1978. Upland and wetland
habitat development with dredged material: Ecological consider-
ations. Tech. Rep. DS-78-15. U.S. Army Engineers Waterways
Exp. Sta., Vicksburg, MS.

MacArthur, R. H. 1968. The theory of the niche. Pages 159-176
in R. C. Lewontin ed. Population Biology and Evolution.
Syracuse Univ. Press, Syracuse.

and E. R. Pianka. 1966. On optimal use of a patchy
environment. Am. Natur. 100:603-609.

Nicholson, D. J. 1948. Nocturnal fresh-water wandering of the
Black Skimmer. Auk 65:299-300.

Office of the Technology Assessment. 1976. Coastal effects of
offshore energy systems. Prepared for the U.S. Congress.
278pp.

Pearson, T. H. 1968. The feeding biology of sea-bird species
breeding on the Farne Islands, Northumberland. J. Anim.
Ecol. 37:521-552.

Pettingill, 0. S. 1937. Behavior of Black Skimmers at Cardwell
Island, Virginia. Auk 54:237-244.

Portnoy, J. W. 1978. Black.Skimmer abundance on the Louisiana-
Mississippi-Alabama coast. Wilson Bull. 90:438-441.

Recher, H. F. 1966. Some aspects of the ecology of migrant shore-
birds. Ecology 47:393-407.

Schoener, T. W. 1971. Theory of feeding strategies. Ann. Rev.
Ecol. Syst. 11:369-404.

Tomkins, I. 1951. Methods of feeding of the Black Skimmer. Auk
68:236-239.

Ward, P. 1965. Feeding ecology of the Black-faced Dioch, Quelea
quelea, in Nigeria. Ibis 107:173-214.

Wegener, IV., D. Holcomb, and V. Williams. 1974. Sampling shallow
water fish populations using the Wegener ring. Proc. Annual
Conf. S.E. Assoc. Game and Fish Comm. 27:663-673.

Wilson, A. 1813. American Ornithology. Vol. 7. Philadelphia.

Winkworth and Goodall. 1962. A crosswire sighting tube for
point quadrat analysis. Ecology 43:342-343.

Zusi, R.. 1959. Fishing rates in the Black Skimmer. Condor 61:
298.




71



S1962. Structural adaptations of the head and neck in the
Black Skimmer, Rhynchops nigra. Linnaeus Publ. Nuttall Ornithol.
Club. No. 3:1-101.




























APPENDICES













APPENDIX A

Principal Factor Analysis

The principal factor procedure uses a correlation matrix of the

measured variables to create factors that are linear combinations of

the original variables and that are independent of one another. The

number of factors created.equals the number of original variables

measured. While these factors account for all of the variation in

the original data, usually the first few factors explain a large

proportion of the variation. Using a principal axis method, the

first factor is that linear combination of the original variables

that accounts for the most variance in the original data. The

second factor is that combination of the original variables that

accounts for the second greatest amount of variance and is independent

of the first factor and so on. Thus, the many variables recorded

are reduced to a manageable number of factors and a more concise

description of feeding habitat is provided.

The factor analysis results in a factor pattern which is comprised

of the loadings of each original variable on each factor. The loading

of a variable is the correlation of that variable with the factor

(Cooley and Lohnes 1971) and indicates the variable's relative im-

portance as part of the linear combination of variables comprising

that factor. Thus, variables with high loadings (e.g. > 0.60) on a

factor are considered important in the identification of that factor.






























APPENDIX B

CORRELATION MATRIX CREATED FROM ONE FEEDING-SPECIFIC AND
TWELVE SITE-SPECIFIC VARIABLES


























U 0NtOOCO O OU,(e
r NOvi00000COO
Lo -y a M 'fj 0 0 L0 CNJ MT w n
Ovi %oo oo ccioc"Lo


dd-ocd~ddoddd
0 OO -00 00 00





a- t m 3- -0- c'j 0N M- LO ,z r




S idddoodopddo
t m 0 o 9 i 0 0 r-oofM cM yM o
0 r Ln -O'









0OOr- 0000000
-I CO LO C)O:rCOD.O
% t. r Z; 0 U, W Lw LO 0 r0 0 -
C cM nnCM OO0- cM 0 I
0 00 00 00 0 00 000
I I I I I I







0 C) U, 0 CD 0 0 C -=
N- ^COO N CMOC

r. a rU, ).00 Uo o .v U, Lo CM C 4CM
r- cD ; co0 Cm U, 0M1.0 LO

00-00 C000 00
I I I I I I




M m 1cN a i
CD C 0 C, 0C 0 U a 0 0 aa
0< CD r0 CDi-naOU IO

CO00M0CNO a0CO













I I I I I I I I
O.0 C 0 U, U 1

i O MO.0C 00o0-
-- -- -- c~o m-o cct-- CM-0i












0000000000


- C LOU


CD C%.0 I C) U,- 0i 00 0
OO0 'V-- O-CO
000000o00000-
I I f I I I





rL U 0oCD' U, O CM %0 M 00 CD

a d d do a o. dV d a D a 0









LU mr %VU.0 -V CO qr~ I 0O C CO CM
Ll. CM CM M" CD 0- m 0OCM
0 orcomO oCOOCM
000000000000
I I I I I I I










n T 0M r- O C0 C -m
O 1 C ('0 C\ 1ONO (O. CUCO U

0 O-1.0 O O -

a D V 0 d VC CD CD 0 dd 0 0





-- -O O cM ni o- CI) 0 C aq
SMoCOO ooalaconc L






0 000 0 0000-000
I I I I Ia I





0 O OMLO.M Uf, M



.00000 0I00-0
I I I I I I I




Om C 0- CO-CM
U '.00U C 0 00
0 0000 00-00000


aI I I I I


'. m 'r


U- (A M U -j Z on -j t0
- a < U- M -- u .0
E 3100203211


a
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0
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c c

CL
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0 0
C C
. o




0 0

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0 0

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O 4
00





SU










Ca a
0 0
0 0


0 0
0 0-

0 0

1 4-,

C C

U (







= c
GJ 0a
Il IA
a a




*a Ca






























APPENDIX C

STATISTICAL ANALYSES COMPARING SITE-SPECIFIC VARIABLES IN
AREA TYPES AT CEDAR KEY AND AT ST. VINCENT'S NWR











Table Cl. Means, standard errors and results of statistical analyses
comparing site-specific variables in utilized and non-utilized feed-
ing habitat in the Cedar Key area. S = student's t test (homogeneous
variance), A = approximate t test (heterogeneous variance)a, W =
Wilcoxon's sum rank test.

Non-
Utilized utilized Statistical
Variable N = 49 N = 70 Test


Physical


Minutes to sunset'
Minutes to sunrisen.s.
Cloud Covern.s.
Wind directionn.s.
Wind speedn-s.


266.7
414.0
54.4
240.1
7.6


26.8
26.1
4.8
14.3
0.7


321.8
380.2
47.1
201.6
6.6


24.1
24.3
3.6
16.0
0.5


Social


Number of other feeders*


18.7 + 6.5


2.1 + 0.3


Locational


Distance from loafing site****
Distance to the mainland**


5.9 + 0.5
2.8 + 0.2


13.4 + 0.2
3.5 + 0.1


Physiognomic


Tidal stagen.s -
Water depth****
Patchiness****b
Water roughness**
Shelter by land****
Number of obstructions**
Mudflat or Land****c
Oyster bar****
Spartinan.s.
Open water****


7.8 + 0.1
13.4 + 1.1
4.0
69.6 + 3.5
5.8 + 0.5
5.0 + 0.3
43.8 + 2.8
11.6 + 0.9
17.1 + 1.6
22.7 + 2.6


7.8 + 0.1
31.9 + 1.5.
2.0
80.0 + 2.6
1.9 + 0.3
6.4 + 0.2
8.2 + 1.5
16.3 + 0.6-
13.6 0.6
62.2 + 1.6


aApproximate t test (Steel and Torrie 1960, p. 81).

bMedian value replaces mean.

cSince no sandbar was recorded, mudflat and land are synonomous.











Table C2. Means, standard errors, and results of statistical analyses
comparing site-specific variables in utilized and non-utilized feed-
ing habitat in the St. Vincent's area. S = student's t test (homo-
geneous variance), A = approximate t test (heterogeneous variance)a,
W = Wilcoxon's sum rank test.

Presumed Presumed
Suitable Unsuitable Statistical
Variable N = 41 N = 39 Test


Physical

Minutes to sunsetn.s.
Minutes from sunrisen.s"
Cloud covern.s.
Wind directionn.s.
Wind speedn.s.


293.6
339.3
36.3
104.1
8.2


22.6
22.1
6.9
15.1
0.6


310.6
322.8
53.5
108.9
7.6


20.8
20.6
7.1
17.5
0.5


S
S
S
S
S


Social


Number of other feeders****


Locational


Distance from loafing site****
Distance to the mainland****

Physiognomic
n.s.
Tidal stage
Water depth****
Patchiness****b
Water roughness****
Shelter by land**
Number of obstructions*
Mudflat or land****c
Oyster bar****
Spartinan.s.
Open water****


10.2 + 1.3



4.1 + 0.4
1.4 + 0.1



7.7 + 0.1
21.0 + 2.2
4.0
73.2 + 4.2
4.4 + 0.4
4.5 + 0.3
33.6 + 3.2
28.2 + 1.8
17.9 + 1.4
19.7 + 2.0


2.7 + 0.4



19.1 + 0.2
1.0 + 0.0



7.8 + O.T
43.6 + 2.5


92.3
7.2
3.7
0.7
17.4
16.6
65.9


aApproximate t test (Steel and Torrie 1960, p


81).


Median value replaces mean.

CSince no sandbar was recorded, mudflat and land are synonomous.




























APPENDIX D













APPENDIX D


and shrimp specimens recovered from thirteen Black
Weights and lengths of whole specimens are given.


Skimmer


Number of Whole Length Weight
Specimens Specimens (mm) (gm)


FISH
Species
Fundulus similis
Mugil cephalus
F. grandis

Adenia xenica.

Opisthonema oglinum

Menidia beryllina

.Family
Sciaenidae

Belonidae


Order
Clupeiformes


Total


69.9 + 6.9
51.3 + 6.7
60.7


S38.2

20.4


18.4


25


3.71 + 1.09
1:44 + 0.65
2.31


0.85

0.06


0.01


13


SHRIMP
Species
Palaemonetes pugio
P. intermedius
P. vulgaris
Unidentified

Total


24.6 + 1.2a 0.11 + 0.02a


aValues for whole shrimp


Fish
stomachs.













BIOGRAPHICAL SKETCH

Barbara Buttram Black was born on February 18, 1951, and was

raised in Chattanooga, Tennessee. She graduated in 1969 from

Girl's Preparatory School and entered Vanderbilt University where

she received a B.S. degree in 1973 with a major in general biology

and a minor in chemistry. Upon graduation she entered the field

of nuclear medicine and supervised two departments in the Knoxville,

Tennessee region for three years until she enrolled in supplemental

ecology courses at the University of Tennessee. In 1978 she

married David Joseph Black and in the following year moved to

Gainesville, Florida,where he joined the faculty of the College of

Veterinary Medicine at the University of Florida. She entered

the School of Forest Resources and Conservation from which she

received a Master of Science with a specialization in wildlife

ecology.




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