• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Executive summary
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Introduction
 Overview of bird damage in planted...
 Migratory and nonmigratory components...
 Roost dynamics from late winter...
 Foraging flock dynamics
 Summary and recommendation
 Literature cited






Group Title: Florida Cooperative Fish and Wildlife Research Unit Technical report no. 36
Title: Population analysis and roosting- and feeding-flock behavior of blackbirds damaging sprouting rice in Southeastern Louisiana
CITATION PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00073792/00001
 Material Information
Title: Population analysis and roosting- and feeding-flock behavior of blackbirds damaging sprouting rice in Southeastern Louisiana final report
Series Title: Technical report (Florida Cooperative Fish and Wildlife Research Unit)
Physical Description: 77 leaves : ill. ; 28 cm.
Language: English
Creator: Labisky, Ronald F
Brugger, Kristin E., 1955-
Denver Wildlife Research Center
Florida Cooperative Fish and Wildlife Research Unit
Publisher: Florida Cooperative Fish and Wildlife Research Unit
Place of Publication: Tallahassee Fla.?
Publication Date: [1989]
 Subjects
Subject: Blackbirds -- Behavior   ( lcsh )
Blackbirds -- Feeding and feeds   ( lcsh )
Rice -- Diseases and pests -- Louisiana   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (leaves 73-77)
Statement of Responsibility: Ronald F. Lubisky, principal investigator and Kristin E. Brugger, associate investigator.
General Note: "Supported by U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Denver Wildlife Research Center and U.S. Department of the Interior, Fish and Wildlife Service, Florida Cooperative Fish and Wildlife Research Unit, Cooperative Agreement no. 14-16-0009-1544, Research Work Order no. 23."
General Note: "June 30, 1989."
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: UF00073792
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 - 001566133
oclc - 22762138
notis - AHH9895

Table of Contents
    Front Cover
        Front cover
    Title Page
        Title page
    Executive summary
        i
        ii
        iii
    Acknowledgement
        iv
        v
    Table of Contents
        vi
        vii
    List of Tables
        viii
        ix
    List of Figures
        x
    Introduction
        Page 1
        Page 2
    Overview of bird damage in planted rice in Louisiana
        Page 3
        Rice farming
            Page 3
            Annual sequence of rice production
                Page 3
                Page 4
            Rice planting
                Page 5
            Damage to sprouting rice and seedling protection
                Page 6
                Page 7
        Blackbird roosts
            Page 8
        The study area: Millers Lake as an area of special concern
            Page 9)
            The study area
                Page 9)
                Page 10
                Page 11
            Millers Lake blackbird roost
                Page 12
            Grain production
                Page 12
                Page 13
                Page 14
                Page 15
    Migratory and nonmigratory components of the red-winged blackbird population
        Page 16
        Introduction
            Page 16
            Page 17
        Methods
            Page 18
            Banding data
                Page 18
            Morphology
                Page 19
                Page 20
        Results
            Page 21
            Banding data
                Page 21
            Morphology
                Page 22
                Page 23
                Page 24
                Page 25
                Page 26
                Page 27
                Page 28
                Page 29
                Page 30
                Page 31
                Page 32
                Page 33
                Page 34
        Discussion
            Page 35
            Page 36
            Page 37
            Page 38
    Roost dynamics from late winter through spring
        Page 39
        Introduction
            Page 39
        Methods
            Page 40
            Weather
                Page 40
            Roost size and composition
                Page 40
                Page 41
                Page 42
            Spatial patterns of roosting
                Page 43
        Results
            Page 43
            Spring weather patterns
                Page 43
            Roost size and composition
                Page 44
                Page 45
                Page 46
                Page 47
            Spatial pattern of roosting
                Page 48
            Other roosts
                Page 48
                Page 49
        Discussion
            Page 50
            Page 51
            Page 52
            Page 53
    Foraging flock dynamics
        Page 54
        Introduction
            Page 54
        Methods
            Page 54
            Flock size, composition, and distribution
                Page 54
            Land-use patterns
                Page 55
            Individual movements
                Page 55
            Statistical analyses
                Page 56
        Results
            Page 56
            Flock size, composition, and distribution
                Page 56
                Page 57
                Page 58
                Page 59
                Page 60
                Page 61
            Land-use patterns
                Page 62
            Individual movements
                Page 62
                Page 63
                Page 64
                Page 65
        Discussion
            Page 66
            Page 67
            Page 68
    Summary and recommendation
        Page 69
        Page 70
        Page 71
        Page 72
    Literature cited
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
Full Text

POPULATION ANALYSIS AND ROOSTING- AND
FEEDING-FLOCK BEHAVIOR OF BLACKBIRDS
DAMAGING SPROUTING RICE IN
SOUTHWESTERN LOUISIANA


I*4jL 1


RONALD
KRISTIN


F. LABISKY
E. BRUGGER


FLORIDA COOPERATIVE FISH AND WILDLIFE RESEARCH UNIT
TECHNICAL REPORT NO. 36
JUNE 1989


040pk









FINAL REPORT


Population Analysis and Roosting- and Feeding-flock Behavior
of Blackbirds Damaging Sprouting Rice
in Southwestern Louisiana



Ronald F. Labisky, Principal Investigator

and

Kristin E. Brugger, Associate Investigator

Department of Wildlife and Range Sciences
118 Newins Ziegler Hall
University of Florida
Gainesville, FL 32611-0304



Supported by

U. S. Department of Agriculture
Animal and Plant Health Inspection Service
Denver Wildlife Research Center

and

U. S. Department of the Interior
Fish and Wildlife Service
Florida Cooperative Fish and Wildlife Research Unit
Cooperative Agreement No. 14-16-0009-1544
Research Work Order No. 23


June 30, 1989



Citation:

R. F. Labisky, and K. E. Brugger. 1989. Population analysis and roosting- and
feeding-flock behavior of blackbirds damaging sprouting rice in
southwestern Louisiana. Florida Coop. Fish Wildl. Res. Unit, Tech. Rep.
No. 36. 77 pp.








EXECUTIVE SUMMARY

1. Rice is planted annually in southwestern Louisiana from mid-March

through late May. Blackbirds, primarily female red-winged blackbirds

(Aqelaius phoeniceus), cause localized damage to early-planted fields by

eating seed and pulling sprouts, possibly reducing or destroying stand

establishment. Financial losses ensue due to decreased yield, reduced grade

or price at the mill, and increased costs for replanting. There are no

studies that objectively quantify losses of the rice crop caused by blackbird

damage.

2. A 3-year field study, 1986-1988, was conducted during the early

planting season near one large blackbird roost, Millers Lake, Evangeline

Parish, Louisiana. The 3 objectives of the study were to: (1) identify the

geographic origin of red-winged blackbirds responsible for damage to rice

crops; (2) estimate size, composition, and stability of the Millers Lake

roost; and (3) describe feeding and movement patterns of flocks during the

damage period (planting season).

3. Migrant and nonmigrant redwings from across North America winter at

roosts in southwestern Louisiana. Northward migration begins in mid-February.

However, banding analyses revealed that some migrants (from as far away as

Michigan) may occur in southwestern Louisiana during planting season.

Morphometric data from a sample of approximately 500 red-winged blackbirds

collected at and surrounding Millers Lake during the spring season of 1986,

1987, and 1988 suggested that, after March 20 each year, >80% of adult males

and variable proportions (42-53% in 1986, 25-50% in 1987, and >80% in 1988) of

females were resident Louisiana birds.

4. The roost at Millers Lake declined in a negative exponential pattern

from about 15 million birds in mid-February to 20,000 in late April each year.








Female redwings were proportionally more abundant in March and April than were

cowbirds (Molothrus after starlings (Sturnus vulgaris), or common grackles

(Quiscalus quiscula). Two patterns of decline in roost size occurred during 6

years for which data were available: the roost, as of April 1, contained

either 500,000 or <100,000 birds. Turnover at the roost appeared to be high

during the planting season because of continued migration of females

throughout April.

5. The number of flocking birds observed feeding in fields declined with

advancing season, and was correlated with roost size. Mean flock size and

number of flocks observed per road survey also declined with season. Female

redwings were the most abundant group observed during road surveys. Sex

ratios of red-winged blackbirds observed per route were female-dominated in 24

of 28 surveys conducted during the 3 spring seasons of study. However,

second-year males were observed in male-dominated flocks, and thus, may

contribute to rice damage. There was no evidence of stability in flock

membership and only weak evidence of fidelity to feeding site.

6. Recommendations for mitigation of blackbird damage to spring-planted

rice depend on the severity and locations of damage. The lethal control of

blackbirds, although expensive, may be justified in specific rice fields

located near roosts. If large-scale population reduction is deemed necessary,

control efforts must focus on resident birds. The best recommendations are

those of the Louisiana State Agricultural Center (1987): delay rice planting

until after March 24 (or after April 1 for fields near large roosts); drill-

plant or water-plant only if a continuous water-flood of 2 to 6 inches can be

maintained; simultaneously plant as many fields as possible; and clear farms

of brush--a practice not conducive to the enhancement of many other wildlife








species. A critical need exists for a current cost-benefit analysis of crop

losses and damage control alternatives.








ACKNOWLEDGMENTS


Many people contributed to the work performed under this contract. Drs.

N. R. Holler and H. F. Percival, who developed the Cooperative Education

Agreement and research contract between the Denver Wildlife Research Center

(formerly under the U. S. Fish and Wildlife Service, now with U. S. Department

of Agriculture, Animal and Plant Health Inspection Service) and the Department

of Wildlife and Range Sciences, University of Florida, contributed time and

energy to the project. The Florida Cooperative Fish and Wildlife Research

Unit provided clerical and logistical support.

In Louisiana, E. A. Wilson (Louisiana State University Rice Research

Station, Crowley), E. A. LeBoeuf, and D. J. Leblanc (USDA/APHIS/ADC State

Office, Crowley and Baton Rouge) provided valuable advice and assisted with

logistical support throughout the project. The rice farmers of Evangeline

Parish, especially Mssrs. C. Fruge, and C. Veillon, both of Ville Platte,

allowed access not only to their fields, camps, docks, and homes, but also

provided information about blackbird damage to sprouting rice. Mr. G. Miller

(President, Millers Lake Association) and Mr. J. Shipp permitted access to

Millers Lake for collection of birds. Mr. A. Mire (LSU Agricultural Extension

Service, Ville Platte) provided background information about rice culture

practices and other agricultural activities in the Parish.

Assistance in field work and in collecting birds was provided by D.

Daneke and his retriever, Miss Kitty, and N. Dwyer, (Department of Wildlife

and Range Sciences, University of Florida), and C. Nelms and his retriever,

Jake, P. Lefebvre, R. Matteson, D. Decker, and J. Glahn (USDA/APHIS Denver

Wildlife Research Center). L. Whitehead typed drafts of the final report.








Jo Ann Monaco produced the final copy on the Word-Processor. Advice on

statistical analyses and software applications were provided by

S. Colbert, S. deSouza, W. Hubbard, J. Smallwood, H. Tiebout III, and E.

Warrag. M. L. Avery, R. A. Dolbeer, C. 0. Nelms, H. M. Tiebout III, and E. A.

Wilson reviewed drafts of the manuscript.

Sincere appreciation is extended to Drs. R. A. Dolbeer and M. L. Avery,

USDA/APHIS Denver Wildlife Research Center, for encouragement, support, and

technical advice.








TABLE OF CONTENTS



Executive summary


Acknowledgments . .

List of tables . .

List of figures . .

Chapter 1. Introduction .

Chapter 2. Overview of bird d

Rice farming .

Economy .
Annual sequence
Rice planting
Damage to sprout

Blackbird roosts


Chapter 3.














Chapter 4.


The study area: Mi

The study area
Millers Lake bla
Grain production

Migratory and nonn
blackbird populati

Introduction .

Methods . .
Banding data
Morphology .

Results . .
Banding data
Morphology .

Discussion .

Roost dynamics frc

Introduction .

Methods . .
Weather .
Roost size and
Spatial pattern


. . . . . iv


amage in planted rice in Louisiana .




of rice production . . .

ing rice and seedling protection .

. . . . . .

llers Lake as an area of special concern


Lckbird roost . . . .


migratory components of the red-winged
on . . . . .












m late winter through spring . .





position . . . .
of ro sting . . . .
s of roosting . . . .


Page


viii

. x

. 1

S3

S3

S3
S3
S5
S6

S8

9

S9
. 12
. 12


. 16

. 16

. 18
S18
. 19

. 21
. 21
. 22

S35

. 39

. 39

. 40
S40
40
S43








Page

Results . . . ... ....... 43
Spring weather patterns . . . .... 43
Roost size and composition . . . .... 44
Spatial pattern of roosting . . . .... 48
Other roosts . . . . .. ..... 48

Discussion . . . . ... .. ... . 50

Chapter 5. Foraging flock dynamics . . . .... 54

Introduction . . . . ... .... 54

Methods . . . . . . 54
Flock size, composition, and distribution . ... .54
Land-use patterns . . . . ... .. 55
Individual movements . . . .... 55
Statistical analyses . . . .... 56

Results . .. . ... . . 56
Flock size, composition, and distribution . ... .56
Land-use patterns . . . . ... .. 62
Individual movements . . . .... 62

Discussion . . . . . .. 66

Chapter 6. Summary and recommendations . . . ... 69

Literature Cited . . . . .. . . . 73








LIST OF TABLES


Page


Table 2-1.


Table 2-2.



Table 2-3.



Table 3-1.



Table 3-2.



Table 3-3.



Table 3-4.



Table 3-5.



Table 3-6.



Table 3-7.



Table 3-8.


Summary of results of 5 National Roost Surveys conducted
in winter by the U. S. Fish & Wildlife Service between
1962-63 and 1979-80 . . . . .

Summary of blackbirds and starlings estimated in annual
Christmas Bird Counts (CBC) conducted from Pine Prairie,
Louisiana, between 1974 and 1987 . . . .

Seasonal change in bird numbers and species composition
of blackbirds and starlings roosting at Millers Lake,
Evangeline Parish, Louisiana, during (1) winter 1974-75,
(2) spring 1979, and (3) fall 1979-spring 1980 . .

State of origin of red-winged blackbirds banded in North
America between May 1-September 30, 1924-85, and recovered
(banding station data excluded) in southwestern Louisiana
during 6 rice culture periods . . . .

State of origin of red-winged blackbirds banded in North
America between May 1-September 30, 1924-85, and recovered
(banding station data included) in southwestern Louisiana
during 6 rice culture periods . . . .

Yearly collections of red-winged blackbirds by age/sex
class and 10-day intervals, Evangeline Parish, Louisiana,
1986-1988 . . . . . . .

Means ( SD) of 10 traits of body size in second-year male
(SYM) red-winged blackbirds collected by shooting in
Evangeline Parish, Louisiana, during 6, 10-day collection
intervals, 1986-1988 . . . . .


. 10



. 13



S. 14



. 23



. 24


. 25



. 31


Means ( SD) of 10 traits of body size in second-year
female(SYF) red-winged blackbirds collected by shooting
in Evangeline Parish, Louisiana, during 6, 10-day
collection intervals, 1986-1988. . .... .. ..... 32


Means ( SD) of 10 traits of body size in after-second year
(ASY) male red-winged blackbirds collected by shooting in
Evangeline Parish, Louisiana, during 6, 10-day collection
intervals, 1986-1988 . . . . .

Means ( SD) of 10 traits of body size in after hatching-
year (AHY) female red-winged blackbirds collected by shooting
in Evangeline Parish, Louisiana, during 6, 10-day collection
intervals, 1986-1988 . . . . .

Percentage of nonresident red-winged blackbirds in the
Millers Lake area of Evangeline Parish, Louisiana, during 6,
10-day collection intervals in spring, 1986-1988 . .


. 33



. 34


. 36


viii










Table 4-1.

Table 4-2.





Table 4-3.


Table 5-1.



Table 5-2.



Table 5-3.


Table 5-4.


Table 5-5.



Table 5-6.


Table 5-7.


Estimates of roost size at Millers Lake, Evangeline Parish,
Louisiana, mid-February to late-April, 1986-88 . .

Multiple linear regression analyses relating log-
transformed roost size to Julian calendar date and 2 weather
variables (mean 3-day maximum air temperature [max] and
summed 3-day rainfall [rain]) at Millers Lake, Evangeline
Parish, Louisiana, for the period February 15-April 30,
1986-88 . . . . . .

Weekly estimates of percentage composition of starlings and
blackbirds in the Millers Lake roost, Evangeline Parish,
Louisiana, 1986-88 . . . . .

Total number of birds and flocks, and mean (SD) number of
birds per 3-min stop and flock, recorded along north and
south survey-routes, Evangeline Parish, Louisiana, 1986-
1988 . . . . . . .

Temporal distribution of flock sizes observed along north
and south survey-routes, Evangeline Parish, Louisiana, 1986-
1988. Percentage of total is given only for flocks with
<25 birds . . . . . .

Percentage species composition of birds observed along north
and south survey-routes, Evangeline Parish, Louisiana, 1986-
1988 . . . . . . .

Sex ratios of red-winged blackbirds observed along north
and south survey-routes, Evangeline Parish, Louisiana, 1986-
1988 . . . . . . .

Percentage of red-winged blackbird flocks engaged in
different activities (when first observed) in relation to
habitat types along north and south survey-routes, Evangeline
Parish, Louisiana, 1986-88 . . . .

Area (ha) of cropland by stage of rice production along the
north and south survey-routes, Evangeline Parish, Louisiana,
1987 . . . . . . .

Summary of movements of 6 radio-instrumented red-winged
blackbirds that were monitored between 17 and 28 March 1986
in Evangeline Parish, Louisiana . . . .


Page

. 45





. 47


. 49



. 57



. 59


. 60


. 61



. 63


. 64


. 65








LIST OF FIGURES


Page


Figure 2-1.

Figure 3-1.



Figure 3-2.



Figure 3-3.



Figure 3-4.



Figure 4-1.


The 8-parish region of southwestern Louisiana in which 75%
of the state's rice crop is produced annually. . . 4

Box-and-whisker plot of the measurement for wing chord by
year and 10-day collection interval for second-year male
(SYM) red-winged blackbirds collected near Millers Lake,
Evangeline Parish, Louisiana, 1986-88. . . ... 26

Box-and-whisker plot of the measurement for wing chord by
year and 10-day collection interval for second-year female
(SYF) red-winged blackbirds collected near Millers Lake,
Evangeline Parish, Louisiana, 1986-88. . . ... 27

Box-and-whisker plot of the measurement for wing chord by
year and 10-day collection interval for after second-year
male (ASY) red-winged blackbirds collected near Millers Lake,
Evangeline Parish, Louisiana, 1986-88. . . ... 28

Box-and-whisker plot of the measurement for wing chord by
year and 10-day collection interval for after hatching-year
female (AHY) red-winged blackbirds collected near Millers
Lake, Evangeline Parish, Louisiana, 1986-88. . ... 30

Negative exponential decline in size of the blackbird roost
during the period February 15-April 24, Millers Lake,
Evangeline Parish, Louisiana, 1986-1988. . . ... 46















CHAPTER 1: INTRODUCTION


Flocking blackbirds, primarily red-winged blackbirds (Aqelaius

phoeniceus), damage sprouting and ripening rice in the southern United States

by pulling new sprouts or removing ripening grains (Meanley 1971). Damage,

which is often localized in regions near blackbird roosts (Neff and Meanley

1957, Pierce 1970), may result in heavy financial losses (Holler et al. 1982).

Damage to spouting rice is particularly severe in early-planted rice in

southwestern Louisiana and east Texas (Kalmbach 1937, Besser 1973); hence,

there is a strong regional interest in development of techniques for

mitigation of bird damage during the early weeks of spring planting. Scare

devices, repellents, and toxicants have been used to reduce numbers of birds

in rice fields temporarily; however, a long-term solution is desired.

Blackbird population reduction has been proposed as a long-term method for

reducing damage to agricultural crops (Wright et al. 1980, Dolbeer 1986, Stehn

1989), and also has been suggested as a solution by local rice growers'

associations, but the information needed to develop a long-term bird

management program is sparse.

Before the effectiveness of alternative management strategies for reducing

damage to spring-planted rice by blackbirds southwestern Louisiana can be

evaluated, those components of the population responsible for damage--as well

as their patterns of roosting and flocking--must be identified. Answers to

the following questions would provide a strong foundation for development of a







blackbird management program in the region: (1) Are birds that damage rice in

spring of local or migratory origin, and if migratory, from what region do

birds that cause damage derive? (2) Are roosts stable in numbers and species

composition preceding and during the damage period? (3) Are feeding flocks

stable with respect to membership (individual birds)? (4) Are feeding flocks

consistent in their selection of feeding locations?

These questions provided the rationale for conducting a 3-year field study

of blackbird depredations on planted rice in southwestern Louisiana. The

study, conducted during the late winter and spring seasons of 1986, 1987, and

1988, had 3 major objectives:

(1) To determine the geographic source of populations of red-winged

blackbirds damaging sprouting rice in southwestern Louisiana;

(2) To determine the stability of roosting populations of blackbirds in

southwestern Louisiana preceding and during the period that sprouting

rice is susceptible to damage; and

(3) To determine the stability of feeding flocks of blackbirds damaging

sprouting rice.

This report is designed to (1) present an overview of rice farming

techniques and blackbird roost locations in southwestern Louisiana, focusing

specifically on one large winter blackbird roost in Evangeline Parish (Millers

Lake), (2) identify the component of the spring blackbird population in

southwestern Louisiana that causes damage to newly planted rice, (3)

characterize the size and composition of roosting blackbird populations in the

region, (4) describe the spatial and temporal distribution of flocks in rice

fields near Millers Lake in relation to rice farming practices, and (5) to

provide recommendations for mitigation of damage to newly planted rice by

blackbirds.















CHAPTER 2: OVERVIEW OF BIRD DAMAGE TO PLANTED RICE IN LOUISIANA


RICE FARMING

Economy

Rice production is a major industry in Louisiana. In 1987, approximately

100,000 t of rice (15% of the United States' production), valued at $200

million (Louisiana State University 1988), were produced on 210,000 ha. The

land area planted to rice and value of rice production in Louisiana peaked in

1981 at about 303,000 ha and $254 million, respectively (Fielder and Nelson

1984). Approximately 75% of the state's annual rice harvest is produced in 8

parishes (counties) of southwestern Louisiana (Fig. 2-1).


Annual Sequence of Rice Production

Planting dates are largely weather-dependent and can range from late

February through May; most fields, however, are planted between mid-March and

mid-April (P. Seilhan, Louisiana Coop. Ext. Serv., Crowley, pers. commun.).

Germination and seedling stand establishment require 1 to 4 weeks, depending

on environmental conditions; growth rates are notably depressed by cool

weather. Most varieties of medium- and long-grain rice planted in

southwestern Louisiana reach harvest maturity within 120 to 135 days from

planting; accordingly, the first harvest usually peaks in August. Regrowth

sometimes produces a second crop, called ratoon rice, which is harvested in















CHAPTER 2: OVERVIEW OF BIRD DAMAGE TO PLANTED RICE IN LOUISIANA


RICE FARMING

Economy

Rice production is a major industry in Louisiana. In 1987, approximately

100,000 t of rice (15% of the United States' production), valued at $200

million (Louisiana State University 1988), were produced on 210,000 ha. The

land area planted to rice and value of rice production in Louisiana peaked in

1981 at about 303,000 ha and $254 million, respectively (Fielder and Nelson

1984). Approximately 75% of the state's annual rice harvest is produced in 8

parishes (counties) of southwestern Louisiana (Fig. 2-1).


Annual Sequence of Rice Production

Planting dates are largely weather-dependent and can range from late

February through May; most fields, however, are planted between mid-March and

mid-April (P. Seilhan, Louisiana Coop. Ext. Serv., Crowley, pers. commun.).

Germination and seedling stand establishment require 1 to 4 weeks, depending

on environmental conditions; growth rates are notably depressed by cool

weather. Most varieties of medium- and long-grain rice planted in

southwestern Louisiana reach harvest maturity within 120 to 135 days from

planting; accordingly, the first harvest usually peaks in August. Regrowth

sometimes produces a second crop, called ratoon rice, which is harvested in















CHAPTER 2: OVERVIEW OF BIRD DAMAGE TO PLANTED RICE IN LOUISIANA


RICE FARMING

Economy

Rice production is a major industry in Louisiana. In 1987, approximately

100,000 t of rice (15% of the United States' production), valued at $200

million (Louisiana State University 1988), were produced on 210,000 ha. The

land area planted to rice and value of rice production in Louisiana peaked in

1981 at about 303,000 ha and $254 million, respectively (Fielder and Nelson

1984). Approximately 75% of the state's annual rice harvest is produced in 8

parishes (counties) of southwestern Louisiana (Fig. 2-1).


Annual Sequence of Rice Production

Planting dates are largely weather-dependent and can range from late

February through May; most fields, however, are planted between mid-March and

mid-April (P. Seilhan, Louisiana Coop. Ext. Serv., Crowley, pers. commun.).

Germination and seedling stand establishment require 1 to 4 weeks, depending

on environmental conditions; growth rates are notably depressed by cool

weather. Most varieties of medium- and long-grain rice planted in

southwestern Louisiana reach harvest maturity within 120 to 135 days from

planting; accordingly, the first harvest usually peaks in August. Regrowth

sometimes produces a second crop, called ratoon rice, which is harvested in

















LOUISIANA


S : ;


US DOmntm o Cmmdre


I a*MU O Tr CNSUS


AD-400.16 (6/85)


Figure 2-1. The 8-parish region of southwestern Louisiana in which 75% of the
state's rice crop is produced annually. Millers Lake is located in the center
of Evangeline Parish.


U C f


or or f I 7 1 I 9W* W


I


--------








October. Many farmers believe that early planting results in early first

harvest, which, in turn increases the likelihood of a successful ratoon crop.

Recent research at the Louisiana State University Rice Experiment Station

has examined the potential for double cropping rice, by planting a second crop

in early August after first harvest, rather than allowing ratoon growth

(Dunand et al. 1985, Bollich et al. 1987). If this cropping

procedure proves successful with respect to yield/profitability, early spring

planting may be promoted in the future in order to facilitate the growing of a

successful second crop.


Rice Planting

Rice is planted either by water-seeding or dry-seeding, each with

variations. Rice may be sown aerially into flooded fields at rates of 100 to

170 kg/ha, or it may either be drilled in 18- to 25-cm rows or broadcast dry

at rates of 100 to 125 kg/ha. Water-seeded fields usually are drained

immediately after germination to promote "pegging" or root establishment.

Dry-seeded fields are flooded after seeding to promote germination, and then

drained for pegging. Some fields are "pin-point" flooded once seedlings have

rooted, i. e., after pegging, water is applied and the level is increased

slowly to match seedling growth. All fields, irrespective of planting method,

are usually flooded after stand establishment. Many farmers prefer water-

seeding to dry-seeding because the typically wet conditions of soil during

spring can delay field preparation required for dry-seeding. Also, the

preparation of the seed bed is less intensive and less costly for water- than

for dry-seeding. As an additional benefit, water-seeding suppresses weed

growth, especially that of red rice.








Damage to Sprouting Rice and Seedling Protection

After the water is drained from planted fields, the germinating seeds lie

on or near the soil surface, making them readily available to birds. Drilled

seed is less vulnerable than broadcast seed because a layer of soil covers the

grain. Stand establishment is affected by many factors, including weather

(temperature, wind, rain), disease, invertebrate pests, and vertebrate pests

--particularly blackbirds. Blackbirds damage rice plantings principally by

pulling the weakly rooted seedlings to obtain the grain. Seedlings are

vulnerable to blackbirds until the kernel is absorbed, which occurs when the

plant is about 8-cm tall or approximately 2-4 weeks of age (Wilson 1986).

Early planting exacerbates the bird-damage problem because, in addition to

resident blackbirds, large numbers of wintering migrant birds still remain in

the region, thus augmenting the abundance of blackbirds that feed in planted

rice. Goodloe (1983) reported that farmers who planted prior to mid-March

lost an average of 25% of the seed to birds. Seed losses >99% have been

reported in fields planted in mid-March, whereas fields planted during mid-

April may suffer less than 5% seed loss (Holler et al. 1986; Wilson et al.

1986, 1987, 1989).

Intensive efforts may be needed for field protection throughout the period

of stand establishment. Several methods are used to varying degrees to

prevent or reduce bird damage: gas-powered exploders are set in field edges;

field hands shoot "shell crackers" and live ammunition at flocks; scarecrows

are placed in fields; and chemical repellents are applied to seed or bait.

Toxic chemicals, such as Aldrin@, were once used on seed or bait as the

primary means to reduce blackbird damage in rice fields because of their low

cost and high effectiveness. However, the Environmental Protection Agency

(EPA) rescinded registration of such chemicals in 1975. Subsequent research








into toxicants and repellents has focused on Avitrol@ (Mott et al. 1982) and

Mesurol* (Mott et al. 1976, Holler et al. 1982). Effective repellency was

obtained with Methiocarb, but, currently, it is not registered for use on rice

seed. Since the mid-1970s, farmers primarily have used exploders and shooting

to attempt to protect fields from bird damage.

The loss of seedlings represents a potential for financial loss due to

reduced yield, and, if losses are severe, the need for replanting. Also if

stands of planted rice are thinned significantly by bird damage, openings that

allow weed growth often develop. Weed seeds (foreign material) may

contaminate harvested rice, thereby resulting in lower grades and prices at

the mill. If replanting is necessary, the harvest may be delayed, which may

result in a lower market price and a reduced probability for a ratoon crop.

The cost of replanting fields is estimated to be $100/ha for water-seeded

crops (Zacharias and McManus 1987). This value is lower than those presented

by Holler et al. (1982), who reported costs to replant fields heavily damaged

by blackbirds were $100-112/ha ($40-45/acre) for both water-planted and

drilled fields if no tilling were required, $125-137/ha ($50-55/acre) if light

tilling were required, and $150-162/ha ($60-65/acre) if heavy tilling were

required. These costs were based on estimates for owner-operated farms, with

basic costs of seed at $70/ha ($35/acre), and did not include possible costs

associated with losses in yield or grade due to late planting.

Unfortunately, little information is available to estimate overall

financial losses resulting from blackbird damage in southwestern Louisiana,

which is, in part, due to the lack of a cost-effective method to assess damage

in fields (Otis et al. 1983). However, based on crop insurance statistics for

1983, loss of seed rice to wildlife was minimal when compared with other








annual causes of rice loss, i. e., <2% of the total dollar amount of claims

(U. S. Dep. Agric., Fed. Crop Insurance Progr., unpubl. data).

Mail-questionnaires directed to local farmers have been used to estimate

losses of rice seed to blackbirds in Louisiana. In 1981, 63 of 71 (89%)

farmers responding to a survey in southwestern Louisiana reported that birds

were responsible for some damage to rice at one or more stages of development

(Goodloe 1983). Farmers reported losses of the newly planted seed that ranged

as high as 75% of the crop. Seed loss to birds was highest in Allen Parish,

averaging 27%; losses averaged <15% per parish in other parishes (Goodloe

1983). In a 1983 survey, 92% of 146 respondents from Vermillion Parish

reported blackbird depredation in the rice crop, and approximately 50%

reported that they suffered losses of sprouting rice to blackbirds severe

enough to require replanting (Linscombe 1983). Although losses were not

quantified, damage was localized and unevenly distributed among farms as

determined in a 1979 survey of 66 farmers in Acadia Parish (Naquin 1979).

These data are only suggestive inasmuch as responses may have been biased

towards those farmers receiving damage. However, if the pattern of localized

and uneven damage is valid, the cost of bird damage is unequally distributed

among farms/producers. Thus, differential spatial patterns of damage must be

considered in the development of effective control measures for reducing

blackbird damage to rice.


BLACKBIRD ROOSTS

In autumn, blackbirds and starlings across North America migrate south and

congregate in roosts, most of which form south of 38 N. latitude (Meanley

1971). Four species prevail in these roosts: common grackle (Quiscalus

quiscula); red-winged blackbird; brown-headed cowbird (Molothrus after ; and








European starling (Sturnus vulgaris). Seven National Roost Surveys (NRS) were

conducted by the U. S. Fish & Wildlife Service between 1958 and 1980 for the

purpose of mapping the locations and estimating the sizes of winter blackbird

and starling roosts. Although the data are difficult to compare among years

and locations, due to inconsistent observer efforts, the surveys provide

information on the location, size, and species composition of many roosts in

the eastern United States, and specifically in the Louisiana-Texas rice belt

(Table 2-1).

Common grackles and red-winged blackbirds are typically most abundant in

the eastern U. S., each comprising slightly less than 1/3 of individuals

identified to species (Table 2-1). Major roosts (> 1 million) were

concentrated along the lower Mississippi River, south of the confluence of the

Ohio and Missouri Rivers. Major roosts in the rice belt of southwestern

Louisiana and east Texas were found along coastal marshes of the Gulf of

Mexico and inland along the Mississippi River.


THE STUDY AREA: MILLERS LAKE AS AN AREA OF SPECIAL CONCERN

One roost, Millers Lake, near Ville Platte in Evangeline Parish (Fig. 2-

1), was chosen as an exemplar study roost because it is large, accessible,

close to rice fields, and is used year-round by roosting blackbirds. Hence,

birds are in the region throughout the rice-growing season. Bird damage to

rice fields has been reported from the region since the early 1970s.


The Study Area

The study area comprises Millers Lake and adjacent farmlands, principally

those to the south. Millers Lake is a 2,500 ha shallow, man-made impoundment,

with a maximum axis of 5 km. The lake is located at the boundary of the








European starling (Sturnus vulgaris). Seven National Roost Surveys (NRS) were

conducted by the U. S. Fish & Wildlife Service between 1958 and 1980 for the

purpose of mapping the locations and estimating the sizes of winter blackbird

and starling roosts. Although the data are difficult to compare among years

and locations, due to inconsistent observer efforts, the surveys provide

information on the location, size, and species composition of many roosts in

the eastern United States, and specifically in the Louisiana-Texas rice belt

(Table 2-1).

Common grackles and red-winged blackbirds are typically most abundant in

the eastern U. S., each comprising slightly less than 1/3 of individuals

identified to species (Table 2-1). Major roosts (> 1 million) were

concentrated along the lower Mississippi River, south of the confluence of the

Ohio and Missouri Rivers. Major roosts in the rice belt of southwestern

Louisiana and east Texas were found along coastal marshes of the Gulf of

Mexico and inland along the Mississippi River.


THE STUDY AREA: MILLERS LAKE AS AN AREA OF SPECIAL CONCERN

One roost, Millers Lake, near Ville Platte in Evangeline Parish (Fig. 2-

1), was chosen as an exemplar study roost because it is large, accessible,

close to rice fields, and is used year-round by roosting blackbirds. Hence,

birds are in the region throughout the rice-growing season. Bird damage to

rice fields has been reported from the region since the early 1970s.


The Study Area

The study area comprises Millers Lake and adjacent farmlands, principally

those to the south. Millers Lake is a 2,500 ha shallow, man-made impoundment,

with a maximum axis of 5 km. The lake is located at the boundary of the













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piedmont and coastal plain. Pine forests lie north, and agricultural fields

south of the lake. Lake water is derived from rainfall, seepage from the

rolling hills to the north, drainage from bayous to the west, and 2 wells.

Millers Lake originated as a shallow marsh that collected runoff from

rolling country to the north. The following history of the lake is reported

as described by Mr. and Mrs. Clifton Fruge, and Mr. Charles Veillon, residents

adjacent to the lake and members of the LaHaye and Miller families,

respectively. By the turn of the century, a levee was constructed in a joint

effort by the Miller and LaHaye families to retain water for flooding over a

large area for the production of rice, a crop introduced to the region in the

late 1800s. The lake was enlarged in the 1930s. And, in 1957, the U. S. Army

Corps of Engineers constructed a 2-m fortified levee to contain the lake

subsequent to hurricane-caused flooding. Two water wells were constructed on

the east shore of the lake after a drought in 1976, and have been used

occasionally to resupply water to the lake. Millers Lake provides irrigation

water to approximately 3,000 ha of rice fields south of the lake.

The lake is deepest at the southwest. Water depths are variable during

the year. In winter, water depths in the southwest portion of the lake range

from 2 to 3.5 m; in late spring, after rice fields are flooded, water depth

may be < 2 m. During drought periods, water depths have dropped to 1.5 m,

leaving exposed land inside the levees.

Millers Lake is in advanced stages of succession. Approximately 70% of

the lake is covered with woody vegetation, such as buttonbush (Cephalanthus

occidentalis) and tupelo (Nvssa aquatica). Thick mats of aquatic weeds grow

throughout the open water in the southwest portion of the lake. The Millers

Lake Association, the administrative body that oversees business related to

the lake, does not control woody vegetation in the lake--believing that it








reduces wave action, thereby controlling erosion and stabilizing the levees.

A detailed description of lake vegetation is provided by Ortego (1976).


Millers Lake Blackbird Roost

Millers Lake hosts a large winter blackbird and starling roost annually.

The roost first was included in National Roost Surveys in 1974-75 (Meanley

1976). Since 1974, the roost also has been included in the Pine Prairie Route

of the Audubon Christmas Bird Count; these counts yielded >100 million

blackbirds in 1986 and 1987 (Table 2-2), most of which were found at Millers

Lake (B. Ortego, Texas Parks and Wildlife, Jasmine, pers. commun).

Inconsistent observer effort or duplicate counting of birds may have

contributed to the high estimates reported in these Christmas Bird Counts.

Individual-observer censuses at Millers Lake, however, revealed that peak

winter populations of blackbirds, which occurred during January and February,

numbered about 15 million (Table 2-3). The species composition of the roost

changes during the winter, with red-winged blackbirds being relatively most

abundant early and late in the season, and cowbirds being relatively most

abundant in mid-winter (Table 2-3).


Grain Production

Historically, Evangeline Parish was a cotton-growing region. By the

1930s, rice had become a major cash crop. Five grains are currently produced

in Evangeline Parish: soybeans, rice, corn, sorghum, and wheat. Land area

planted to grains has decreased in the last decade from approximately 90,000

ha in the late 1970s-early 1980s to about 50,000 ha in 1987. This reduction

in cropland was due largely to a decreasing number of active farmers in the

parish and to the increasing participation by farmers in land conservation








reduces wave action, thereby controlling erosion and stabilizing the levees.

A detailed description of lake vegetation is provided by Ortego (1976).


Millers Lake Blackbird Roost

Millers Lake hosts a large winter blackbird and starling roost annually.

The roost first was included in National Roost Surveys in 1974-75 (Meanley

1976). Since 1974, the roost also has been included in the Pine Prairie Route

of the Audubon Christmas Bird Count; these counts yielded >100 million

blackbirds in 1986 and 1987 (Table 2-2), most of which were found at Millers

Lake (B. Ortego, Texas Parks and Wildlife, Jasmine, pers. commun).

Inconsistent observer effort or duplicate counting of birds may have

contributed to the high estimates reported in these Christmas Bird Counts.

Individual-observer censuses at Millers Lake, however, revealed that peak

winter populations of blackbirds, which occurred during January and February,

numbered about 15 million (Table 2-3). The species composition of the roost

changes during the winter, with red-winged blackbirds being relatively most

abundant early and late in the season, and cowbirds being relatively most

abundant in mid-winter (Table 2-3).


Grain Production

Historically, Evangeline Parish was a cotton-growing region. By the

1930s, rice had become a major cash crop. Five grains are currently produced

in Evangeline Parish: soybeans, rice, corn, sorghum, and wheat. Land area

planted to grains has decreased in the last decade from approximately 90,000

ha in the late 1970s-early 1980s to about 50,000 ha in 1987. This reduction

in cropland was due largely to a decreasing number of active farmers in the

parish and to the increasing participation by farmers in land conservation










Table 2-2. Summary of blackbirds and starlings estimated in annual Christmas
Bird Counts (CBC) conducted from Pine Prairie, Louisiana, between 1974 and
1987 (data from annual issues of American Birds). A single asterisk (*)
indicates the highest count per species in all CBC routes run in a given year
in the United States and Canada, as compiled by Burt L. Monroe, Jr., and
reported in annual issues of American Birds. Two asterisks (**) indicate the
all-time highest number of a species ever recorded in one count among all
counts since 1900 (Monroe 1986).

Total number
(millions)
Starlings Birds
No. of Number (millions) and in
Year observers Starlings Grackles Redwings Cowbirds blackbirds count


1974 9 0.024 0.023 0.060 0.353 0.460 0.467
1975 11 0.003 0.064 0.377 5.019* 9.563a 9.582
1976 11 0.007 0.018 1.120 4.022* 5.167 5.189
1977 10 0.001 0.015 0.123 0.363* 0.502 0.534
1978 17 0.027 0.036 0.259 2.303* 2.625 2.652
1979 12 0.025 0.028 5.655 16.610 22.318 22.352
1980 15 0.162 0.011 0.081 0.038 0.292 0.160
1981 14 0.031 0.011 2.331 5.950* 8.323 8.354
1982 14 2.395* 0.588 14.907" 19.806* 37.696 37.726
1983 8 0.256* 1.101* 16.032 30.031* 47.400 47.426
1984 18 0.312 0.096 24.520* 10.113* 35.041 35.078
1985 12 1.625 2.095 39.800 19.600 63.120 63.142
1986 9 10.010* 10.032 50.403 38.201* 108.646 108.687
1987 12 3.000" 27.509*" 53.148" 20.005* 103.662 103.697


'In 1975, 4.1 million unidentified blackbirds
Prairie Christmas Bird Count.


were included in the Pine










Table 2-3. Seasonal change in bird numbers and species composition of
blackbirds and starlings roosting at Millers Lake, Evangeline Parish,
Louisiana, during (1) winter 1974-75 (Ortego 1976), (2) spring 1979, and (3)
fall 1979-spring 1980 (Wilson 1986). Trace numbers of birds are indicated by
the letter T.


Percentage composition
Date Roost size Starlings Grackles Redwings Cowbirds

Winter 1974-75

Oct 12 45,000 10 0 90 0
Nov 25 550,000 5 10 20 65
Dec 18 1,000,000 T 15 20 65
Jan 18 15,000,000 T 5 20 75
Feb 08 15,000,000 T 5 20 75
Mar 26 500,000 T 5 40 55

Spring 1979

Feb 15 7,200,000 T 5 30 65
Feb 28 8,700,000 T 5 30 65
Mar 13 2,800,000 0 T 60 40
Mar 27 200,000 0 0 90 10
Apr 10 50,000 0 0 90 10
Apr 25 25,000 0 0 90 10
May 07 2,000 0 0 100 T

Fall 1979-Spring 1980

Aug 27 5,000 0 0 95 5
Sep 11 35,000 0 T 75 25
Sep 24 52,000 0 T 75 25
Oct 16 75,000 T T 80 20
Oct 30 100,000 T T 80 20
Nov 15 400,000 5 T 60 35
Nov 27 450,000 5 T 60 35
Dec 08 1,700,000 10 T 40 50
Dec 21 5,500,000 10 5 30 55
Jan 07 8,600,000 15 5 25 55
Jan 23 11,200,000 15 5 25 55
Feb 06 13,800,000 10 5 20 65
Feb 20 15,400,000 10 5 20 65
Mar 03 9,000,000 5 5 25 65
Mar 17 2,900,000 T T 60 40
Mar 30 1,100,000 T T 80 20
Apr 14 250,000 0 T 90 10
Apr 28 15,000 0 T 99 T
May 14 2,000 0 0 99 T








programs. The relative proportion of land planted to each grain crop changed

during the last decade; notably, the acreage of soybeans decreased from 78% to

48%, whereas that of rice increased from 20% to 40%. In 1987, the gross gate

value of the rice crop in Evangeline Parish was estimated to be $24.8 million

(Louisiana State University 1988).















CHAPTER 3: MIGRATORY AND NONMIGRATORY COMPONENTS OF THE RED-WINGED
BLACKBIRD POPULATION AT MILLERS LAKE: WINTER AND SPRING

INTRODUCTION

Winter and spring roosts in the Gulf coastal region of Louisiana and Texas

attract blackbirds that originate in breeding populations from Alberta to

Maine, as well as birds that are summer residents of states bordering the Gulf

of Mexico (Meanley et al. 1966). Roosts dissolve at the onset of breeding

season. Resident birds of Louisiana begin territory establishment in early to

mid-April (Kalmbach 1937, Wilson 1986); the breeding season in northern North

America begins in late April (Ohio: 20 April, Dolbeer 1976; Quebec: early May,

Greenwood and Weatherhead 1982). Hence, some birds that breed north of

Louisiana might remain in the Gulf-coastal region through April, joining

resident birds at roosts and in feeding flocks in newly planted rice fields.

Consequently, the blackbirds that are responsible for damage to planted rice

in southwestern Louisiana during March and April are probably a mixture of

residents from the Louisiana-Texas Gulf coast and nonresidents from northern

breeding localities. To design and assess effectiveness of blackbird

management programs, the components) of the mixed northern and southern

populations responsible for damage in the region must be identified. This

information also would add to the understanding of population dynamics, extent

of geographic mixing among populations, and general population movements by

red-winged blackbirds.















CHAPTER 3: MIGRATORY AND NONMIGRATORY COMPONENTS OF THE RED-WINGED
BLACKBIRD POPULATION AT MILLERS LAKE: WINTER AND SPRING

INTRODUCTION

Winter and spring roosts in the Gulf coastal region of Louisiana and Texas

attract blackbirds that originate in breeding populations from Alberta to

Maine, as well as birds that are summer residents of states bordering the Gulf

of Mexico (Meanley et al. 1966). Roosts dissolve at the onset of breeding

season. Resident birds of Louisiana begin territory establishment in early to

mid-April (Kalmbach 1937, Wilson 1986); the breeding season in northern North

America begins in late April (Ohio: 20 April, Dolbeer 1976; Quebec: early May,

Greenwood and Weatherhead 1982). Hence, some birds that breed north of

Louisiana might remain in the Gulf-coastal region through April, joining

resident birds at roosts and in feeding flocks in newly planted rice fields.

Consequently, the blackbirds that are responsible for damage to planted rice

in southwestern Louisiana during March and April are probably a mixture of

residents from the Louisiana-Texas Gulf coast and nonresidents from northern

breeding localities. To design and assess effectiveness of blackbird

management programs, the components) of the mixed northern and southern

populations responsible for damage in the region must be identified. This

information also would add to the understanding of population dynamics, extent

of geographic mixing among populations, and general population movements by

red-winged blackbirds.








Several methods can be used to infer geographic origin of a mixed

population of wintering birds. Banding data can reveal broad patterns in

wintering and breeding regions, although small sample sizes and limitations of

the data base constrain estimates of movement patterns by individuals and/or

populations within short time intervals. Support for identification of

geographic origin derived from banding data can be obtained by more detailed

methods that focus on traits that vary geographically among individuals. One

potential method is a study of geographic variation in endoparasite loads,

which previously has been employed to identify (1) geographic origins of

different populations of Canada goose (Branta canadensis) (Hanson et al. 1957)

and (2) migratory and nonmigratory populations of wood ducks (Aix sponsa)

(Thul et al. 1985). However, because of low rates of infection by

endoparasites in red-winged blackbirds during winter, the method was judged

inappropriate for this study (Brugger 1989).

A morphometric study appeared to be the most promising means to obtain a

second line of evidence, as a supplement to banding analyses, to estimate

geographic origin of redwings; this approach is characterized by a strong

empirical basis, relatively small sample size required for inferences, and low

cost. Redwings in the eastern and central United States have a gradual, but

regular dine of increasing size northward and westward from Florida (Power

1970, James et al. 1984). Morphometrics have been applied to a comparative

data base from redwings collected in central and southeastern U. S. for

analysis of general migratory movements of populations (James et al. 1984).

Additionally, the method has been applied to monthly collections of redwings

from southwestern Louisiana to identify components of the population

responsible for damage to planted rice. Using discriminant analyses, Wilson

(1986) found that the proportion of large-bodied redwings (assumed to be








migrants to Louisiana) obtained from monthly collections declined from

approximately 80% in January to 22% and 4% in March and April, respectively.

Wilson (1986) inferred from morphometric data and road surveys of flocks that

resident female redwings were responsible for most damage to planted rice.

Although Wilson (1986) identified resident redwings as the primary cause

of bird damage to rice, his sample sizes were small and his collections were

not repeated among years. Thus, there was no accounting for spatial and

temporal variation in sex- and age-related migration patterns that had been

documented from banding data, i.e., adult males moved shorter distances from

their breeding areas and stayed at wintering sites for a shorter time than did

adult females or birds of the year (Dolbeer 1978, 1982). Hence, the dynamics

of interpopulation mixing by redwings in southwestern Louisiana during spring

might be more complex than that described by Wilson (1986). The objective of

the current investigation was to refine the identification of geographic

source areas of redwings in southwestern Louisiana by a comparison of 2

independent methods: (1) analysis of banding data to define source populations

by ascertaining the summering (assumed to be breeding) areas of redwings found

in the rice growing region in Louisiana throughout all cultural phases of the

crop production; and (2) identification of general geographic source areas

from morphometric measurements of birds collected in Millers Lake roost and in

rice fields during 3 spring seasons, 1986-88.


METHODS

Banding Data

A copy of the entire 62-year (1924-1985) recovery-retrieval file for red-

winged blackbirds was provided by the U. S. Fish & Wildlife Service Bird

Banding Laboratory (BBL). The file was tabulated by dates and states where








migrants to Louisiana) obtained from monthly collections declined from

approximately 80% in January to 22% and 4% in March and April, respectively.

Wilson (1986) inferred from morphometric data and road surveys of flocks that

resident female redwings were responsible for most damage to planted rice.

Although Wilson (1986) identified resident redwings as the primary cause

of bird damage to rice, his sample sizes were small and his collections were

not repeated among years. Thus, there was no accounting for spatial and

temporal variation in sex- and age-related migration patterns that had been

documented from banding data, i.e., adult males moved shorter distances from

their breeding areas and stayed at wintering sites for a shorter time than did

adult females or birds of the year (Dolbeer 1978, 1982). Hence, the dynamics

of interpopulation mixing by redwings in southwestern Louisiana during spring

might be more complex than that described by Wilson (1986). The objective of

the current investigation was to refine the identification of geographic

source areas of redwings in southwestern Louisiana by a comparison of 2

independent methods: (1) analysis of banding data to define source populations

by ascertaining the summering (assumed to be breeding) areas of redwings found

in the rice growing region in Louisiana throughout all cultural phases of the

crop production; and (2) identification of general geographic source areas

from morphometric measurements of birds collected in Millers Lake roost and in

rice fields during 3 spring seasons, 1986-88.


METHODS

Banding Data

A copy of the entire 62-year (1924-1985) recovery-retrieval file for red-

winged blackbirds was provided by the U. S. Fish & Wildlife Service Bird

Banding Laboratory (BBL). The file was tabulated by dates and states where








recovered or banded, How Obtained and Status codes, and sex for birds banded

or recovered in (1) Louisiana and (2) southwestern Louisiana (the

area bounded by 29* and 31" N. latitude and 91 and 94 W. longitude) (Brugger

and Dolbeer, in press).


Morphology

Collections. Red-winged blackbirds were collected in and surrounding

Millers Lake during 10-day sampling intervals in March and April 1986 and

1987, and February, March, and April 1988. Three methods of collection were

used: (1) shotgun; (2) mist-nets; and (3) baited decoy traps, dove traps and

cannon nets. Live birds were weighed, measured, color marked for a study of

local movements, and released at the site of capture. Carcasses were weighed,

injected with 1 cc 70% ethanol in the esophagus to preserve gut contents, and

frozen for later measurement. Exact location, activity, and time of

collection were recorded for each bird collected.

Measurements. Nine parameters of external morphology were measured with

dial calipers (0.1 mm resolution): (1) bill length; (2) bill depth at center

of nostril; (3) lower bill width; (4) upper bill width; (5) wing chord; (6)

length of secondaries; (7) tail length; (8) tarsus length; and (9) central toe

length (Baldwin et al. 1931). Reliability of measurements was evaluated by

the repeated measuring of 10 individuals at 4 intervals during the collection

season; differences in measurements due to changes in technique over time were

not significant (P > 0.05).

Assumptions. Although the ages associated with the full sequence of molts

and plumages of redwings have not been established with certainty (James et

al. 1984), the assumption was made that all redwings collected from February

to April could be classified into 1 of 4 age/sex classes based on plumage








color: (1) second-year male (SYM), (2) second-year female (SYF), (3) after

second-year male (ASY), and (4) after hatching-year female (AHY). Also, it

was assumed that age and/or wear of feathers was identical on birds within

age/sex classes at this time of year, and that inter-year variation in body

sizes of local populations of birds was negligible.

Statistics and sampling. All statistical tests were performed at the a

priori alpha of 0.05. A one-way ANOVA of measurements by method of capture

was performed for birds collected in 1986 to determine if method of capture

resulted in bias of the collections by body size. Adult males that were

collected by shooting had longer bills and shorter tarsi than those captured

in mist-nets. AHY females collected from baited traps had shorter bills and

longer wings than those that were either shot or mist-netted. Thus, to avoid

biases associated with method of collection, only data for birds collected by

shooting were included in the analyses of morphometric measurements.

Data were tabulated by year, age/sex class, and 10-day interval of

collection (February 11-20, March 1-10, March 11-20, March 21-31, April 1-10,

and April 11-20). No collections were made the period February 21-28/29 in

any year. An exploratory analysis was performed by examining box-and-whisker-

plots (Tukey 1977, James et al. 1984) for each measurement within age/sex

class and 10-day collection interval; these plots present the median, middle

half, and range of the distribution of measures.

A 1-way ANOVA was used to test for differences in body mass and in each of

9 external measures within age/sex class and 10-day collection interval among

years. It was followed, where appropriate, by a Waller-Duncan multiple

comparison (Carmer and Swanson 1973).

The discriminant analysis performed by Wilson (1986) to distinguish

northern migrants (termed nonresidents) from residents of southwestern








Louisiana yielded classification equations that were estimated to be highly

efficient in categorizing adult redwings. These equations were used to

estimate percentage of nonresidents by age/sex class and 10-day interval. A

second method of classification was based on the measure of wing chord, a

characteristic that Wilson (1986) found to be the singlemost important

discriminating variable. Birds were categorized as nonresidents when wing

chord exceeded 120, 115, and 97 mm, for ASY, SYM, and AHY birds, respectively

(Wilson 1986, Howell and van Rossem 1928). Second-year females, i.e., females

without color on the epaulets, were omitted from the analysis because no

comparable morphometric data from this age/sex class are available for

Lousiania--a result of poorly documented plumage characteristics for SYF.


RESULTS

Banding Data

[Note: This section contains only a summary of the analyses of the

banding data. A thorough treatise of the topic is available in Brugger and

Dolbeer (in press).]


Of 12,020 cases in the 62-year (1924-1985) recovery-retrieval file, 688

were either banded or recovered in Louisiana (610 banded in Louisiana and

recovered anywhere, and 655 recovered in Louisiana and banded anywhere). Of

these, 597 (86.7%) were year-round residents. Most records were obtained

prior to 1945.

Only 58 cases were randomly recovered (i.e., not biased by recovery at

banding operations) in southwestern Louisiana. In relation to rice-growing

seasons, resident birds comprised 34% (13 of 38) of records in winter, 67% (4








Louisiana yielded classification equations that were estimated to be highly

efficient in categorizing adult redwings. These equations were used to

estimate percentage of nonresidents by age/sex class and 10-day interval. A

second method of classification was based on the measure of wing chord, a

characteristic that Wilson (1986) found to be the singlemost important

discriminating variable. Birds were categorized as nonresidents when wing

chord exceeded 120, 115, and 97 mm, for ASY, SYM, and AHY birds, respectively

(Wilson 1986, Howell and van Rossem 1928). Second-year females, i.e., females

without color on the epaulets, were omitted from the analysis because no

comparable morphometric data from this age/sex class are available for

Lousiania--a result of poorly documented plumage characteristics for SYF.


RESULTS

Banding Data

[Note: This section contains only a summary of the analyses of the

banding data. A thorough treatise of the topic is available in Brugger and

Dolbeer (in press).]


Of 12,020 cases in the 62-year (1924-1985) recovery-retrieval file, 688

were either banded or recovered in Louisiana (610 banded in Louisiana and

recovered anywhere, and 655 recovered in Louisiana and banded anywhere). Of

these, 597 (86.7%) were year-round residents. Most records were obtained

prior to 1945.

Only 58 cases were randomly recovered (i.e., not biased by recovery at

banding operations) in southwestern Louisiana. In relation to rice-growing

seasons, resident birds comprised 34% (13 of 38) of records in winter, 67% (4








of 6) in planting, 100% (5 of 5) in growth, harvest, and ratoon crop, and 78%

(7 of 9) in ratoon harvest (Table 3-1).

Resident redwings comprised all of the 104 nonrandom recoveries (i.e.,

taken by banding operations) beyond the 58 recovered at banding stations. In

relation to rice-growing seasons, nonrandom recoveries suggested that resident

birds comprised 60% (37 of 62) of records in winter, 94% (31 of 33) in

planting, 100% (34 of 34) in first growth and harvest, and 94% (31 of 33) in

ratoon harvest (Table 3-2).

Migrant red-winged blackbirds that were recovered in Louisiana originated

in breeding populations from North and South Dakota, Minnesota, Iowa,

Missouri, Illinois, Michigan, New York south to Texas and Arkansas. Only 2

recoveries of migrants (1 female from Michigan and 1 male from Texas) were

made during the planting season.


Morphology

Exploratory analysis. Measurements were obtained from 488, 521, and 592

birds in 1986, 1987, and 1988, respectively (Table 3-3). A trend of

decreasing median wing-chord length with increasing collection date was

observed among years in SYM and SYF (Figs. 3-1 and 3-2), indicating a decline

in nonresident birds with seasonal advance. However, each year of study

yielded different patterns in median wing-chord length among collection

intervals for ASY and AHY. Median wing chord of ASY increased slightly from

mid-March to April in 1986, was relatively stable across all collection

intervals in 1987, and decreased from February to April in 1988, all evidence

suggesting a decline in the proportion of nonresidents after February (Fig. 3-

3). In 1986 and 1987, median wing chord of AHY decreased through March,

indicating a decline in proportion of nonresident birds; in 1987, it then

















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Table 3-3. Yearly collections of red-winged blackbirds by age/sex class and
10-day intervals, Evangeline Parish, Louisiana, 1986-1988. All birds were
collected by shooting.


Age/sex Collection Year
class interval 1986 1987 1988


Second-year
male (SYM)




After second-
year male (ASY)




Second-year
female (SYF)




After hatching-
year female (AHY)


Feb 11-20
Mar 01-10
Mar 11-20
Mar 21-31
Apr 01-10
Apr 11-20

Feb 11-20
Mar 01-10
Mar 11-20
Mar 21-31
Apr 01-10
Apr 11-20

Feb 11-20
Mar 01-10
Mar 11-20
Mar 21-31
Apr 01-10
Apr 11-20

Feb 11-20
Mar 01-10
Mar 11-20
Mar 21-31
Apr 01-10
Apr 11-20


Total


0
3
37
26
8
2

0
2
39
42
19
6

0
0
16
17
0
0

0
1
141
93
24
18

488


0
7
9
7
16
1

0
3
42
17
65
6

0
10
28
26
9
5

0
29
101
79
55
6

521



















130 t


120


S 110 n


a 100


90



1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6

1986 1987 1988


Collection Interval

Figure 3-1. Box-and-whisker plot of the measurement for wing chord by year
and 10-day collection interval for second-year male (SYM) red-winged
blackbirds collected near Millers Lake, Evangeline Parish, Louisiana, 1986-88.
Dotted horizontal line represents the separation point for migrants (above)
and residents (below). Collection intervals were: (1) February 10-20; (2)
March 1-10; (3) March 11-20; (4) March 21-31; (5) April 1-10; and (6) April
11-20. No collections were made during February 21-28/29 in any year.

















110

100

90


1 2 3 4 5 6


1987


1 2 3 4


1988


Collection Interval


Figure 3-2. Box-and-whisker plot of the measurement for wing chord by year
and 10-day collection interval for second-year female (SYF) red-winged
blackbirds collected near Millers Lake, Evangeline Parish, Louisiana, 1986-88.
Collection intervals were: (1) February 10-20; (2) March 1-10; (3) March 11-
20; (4) March 21-31; (5) April 1-10; and (6) April 11-20. No collections were
made during February 21-28/29 in any year.


5 6


I i l i I


^I


"~b!e






















120 ......... ..... ........... ..... ... ..... ... .......

S 110


0
Io
. 100
0M

90



1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6

1986 1987 1988


Collection Interval



Figure 3-3. Box-and-whisker plot of the measurement for wing chord by year
and 10-day collection interval for after second-year male (ASY) red-winged
blackbirds collected near Millers Lake, Evangeline Parish, Louisiana, 1986-88.
Dotted horizontal line represents the separation point for migrants (above)
and residents (below).Collection intervals were: (1) February 10-20; (2) March
1-10; (3) March 11-20; (4) March 21-31; (5) April 1-10; and (6) April 11-20.
No collections were made during February 21-28/29 in any year.








increased in mid-April, suggesting a temporary increase in the proportion of

nonresident AHY (Fig. 3-4). In 1988, median wing chord of AHY was relatively

stable during all collection intervals, suggesting constant proportions of

resident and nonresident birds throughout the spring planting season.

Analysis of variance. Few temporal trends in body size were detected by

ANOVA, coupled with multiple comparisons. Among SYM, mean body mass decreased

significantly with seasonal advance in 1987 (Table 3-4). Also, the mean

tarsus length of SYM increased with seasonal advance in 1986 (Table 3-4);

inasmuch as birds from more northerly regions of the continent are

characterized by longer tarsi, the latter suggested the presence of

nonresident SYM in the area during the late spring season of 1986.

Among SYF, mean body mass decreased from early March to early April in

1987, but then increased from early to mid-April; the increase in body mass of

birds in April suggested the probable influx of large-bodied nonresident SYF

(Table 3-5). Similarly, mean measures of bill depth at nares, wing chord,

length of secondaries, and length of tail among SYF in 1988 decreased in March

and increased in April (Table 3-5).

Among ASY males, mean body mass declined with advance of season each year

(Table 3-6). Mean bill length increased with seasonal advance in 1986 and

1987, wing chord decreased from February to March in 1988, and tarsus length

peaked in mid-March in 1986, all of which suggested a decline in the

proportion of nonresident adult males from late February through March (Table

3-6).

Among AHY females, all characters except tail length and tarsus length

varied among collection intervals in at least 1 year (Table 3-7). However,

only body mass varied significantly among collection intervals in each of the

3 years, decreasing significantly from February to April.



























E

100
0 ..... ............. . .. ... .
o

90
C 90




1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6

1986 1987 1988


Collection Interval


Figure 3-4. Box-and-whisker plot of the measurement for wing chord by year
and 10-day collection interval for after hatching-year female (AHY) red-winged
blackbirds collected near Millers Lake, Evangeline Parish, Louisiana, 1986-88.
Dotted horizontal line represents the separation point for migrants (above)
and residents (below). Collection intervals were: (1) February 10-20; (2)
March 1-10; (3) March 11-20; (4) March 21-31; (5) April 1-10; and (6) April
11-20. No collections were made during February 21-28/29 in any year.










Table 3-4. Means ( SO) of 10 traits of body size in second-year male (SYM) red-winged blackbirds collected
by shooting in Evangeline Parish, Louisiana, during 6, 10-day collection intervals, 1986-1988. Traits are
body mass (MASS), bill length (BILL), bill depth at nares (BDN), bill width at gonys (WGON), bill width at
nares (WNAR), wing chord (CRD), length of secondary feathers (SEC), tail length (TAIL), tarsus length
(TARS), and length of central toe (CTOE). A dash (-) indicates that no birds were collected during the
interval.

Collection interval
Feb Mar Mar Mar Apr Apr
Trait Year 10-20 1-10 11-20 21-31 1-10 11-20

MASS (g) 1986 -66.0(1.0) 62.4(3.6) 61.4(3.6 62.1(2.7) 61.5(3.5)
1987 67.7(3.2) 62.7(4.5) 60.0(3.9) 58.5(3.3) 61.5 *
1988 61.7(7.4) 61.0(5.0) 56.4(2.6) 59.4(6.6) 59.0(2.6) 59.7(0.3)

BILL (mm) 1986 24.8(1.2) 23.8(0.6) 23.6(0.8) 24.3(0.9) 24.0(0.5)
1987 23.7(1.1) 23.6(1.0) 24.2(0.8) 24.0(0.8)
1988 23.4(1.1) 23.8(0.3) 24.0(0.5) 23.7(0.7) 23.5(1.2) 23.9(0.2)
BON (mm) 1986 10.9(0.3) 10.9(0.2) 11.0(0.4) 11.8(0.3) 11.2(0.7)
1987 11.9(0.8) 12.4(0.4) 11.8(0.5) 11.5(0.3)
1988 10.5(0.5) 10.4(0.4) 10.3(0.6) 10.2(0.5) 9.9(0.2) 10.0(0.1)
WGON (mm) 1986 10.0(0.4) 9.6(0.4) 9.4(0.4) 9.4(0.2) 9.4(0.1)
1987 9.6(0.3) 9.7(0.3) 9.5(0.1) 9.7(0.4) 0.2
1988 9.7(0.5) 9.6(0.3) 9.6(0.2) 9.6(0.4) 9.7(0.4) 9.4(0.1)

WNAR (mm) 1986 7.7(0.4) 7.7(0.3) 7.7(0.4) 7.6(0.1) 8.0(0.4)
1987 6.5(0.2) 6.6(0.3) 6.7(0.2) 6.6(0.2)
1988 6.7(0.3) 6.6(0.1) 6.6(0.3) 6.6(0.2) 6.5(0.4) 6.5(0.1)
CRD (mm) 1986 114.3(3.3) 111.9(3.5) 111.9(1.8) 109.7(5.4) 109.2(4.8)
1987 115.3(2.8) 113.0(3.2) 113.5(2.9) 111.7(3.2) 112.1
1988 114.4(4.7) 116.1(2.5) 112.7(3.3) 112.6(2.7) 112.6(1.9) 112.1(0.5)

SEC (mm) 1987 88.3(2.4) 89.4(4.0) 87.8(3.5) 87.2(3.7) 89.9
1988 87.8(3.6) 89.3(3.8) 89.2(4.2) 87.9(2.8) 86.8(2.4) 87.2(1.6)
TAIL (mm) 1986 86.5(1.3) 84.8(2.4) 87.5(3.6) 84.8(5.2) 86.6(2.9)
1987 85.6(2.8) 84.7(3.5) 84.5(2.8) 85.2(4.6)
1988 89.6(4.0) 90.0(3.1) 90.5(4.7) 88.3(4.1) 87.9(3.1) 92.0(8.6)
TARS (mm) 1986 27.5(0.5) 27.7(0.7) 27.8(1.6) 27.9(0.6) 28.2(0.7) *
1987 27.3(1.2) 27.5(1.2) 28.1(0.5) 27.5(0.9) 27.5
1988 28.1(1.1) 28.5(0.7) 28.0(0.8) 28.7(0.6) 27.9(0.4) 27.8(1.7)
CTOE (mm) 1987 19.0(0.4) 18.9(0.9) 19.4(0.6) 18.5(2.7) 19.5
1988 18.7(0.9) 18.7(0.8) 19.1(1.2) 19.1(0.7) 18.8(0.9) 19.0(0.4)
Significant differences among means within year, P < 0.05.








Table 3-5. Means ( SO) of 10 traits of body size in second year-female (SYF) red-winged blackbirds
collected by shooting in Evangeline Parish, Louisiana, during 6, 10-day collection intervals, 1986-1988.
Traits are body mass (MASS), bill length (BILL), bill depth at nares (BON), bill width at gonys (WGON), bill
width at nares (WNAR), wing chord (CRD), length of secondary feathers (SEC), tail length (TAIL), tarsus
length (TARS), and length of central toe (CTOE). A dash (-) indicates that no birds were collected during
the interval.

Collection interval
Feb Mar Mar Mar Apr Apr
Trait Year 10-20 1-10 11-20 21-31 1-10 11-20

MASS (g) 1987 44.7(5.8) 44.3(4.8) 40.5(3.3) 38.7(3.2) 46.8(6.9) *
1988 44.2(2.9) 41.2(3.8) 38.5(1.2) 40.3(3.9) 41.8(3.7) 41.5(5.4)

BILL (mn) 1987 20.2(0.5) 20.3(0.4) 20.3(0.5) 20.6(0.6) 20.4(0.6)
1988 20.4(0.9) 20.4(0.7) 20.2(0.7) 20.4(0.7) 20.4(0.8) 20.2(0.5)
BDN (mm) 1987 10.4(0.5) 10.5(0.5) 10.2(0.6) 10.0(0.6) 10.2(0.2)
1988 8.9(0.4) 9.0(0.3) 9.0(0.4) 8.6(0.3) 8.7(0.3) 8.8(0.3) *
WGON (mm) 1987 8.4(0.6) 8.6(0.5) 8.4(0.3) 8.2(0.4) 8.5(0.2)
1988 8.5(0.4) 8.5(0.3) 8.5(0.1) 8.4(0.3) 8.3(0.3) 8.4(0.3)
WNAR (mm) 1987 5.9(0.3) 5.9(0.2) 5.8(0.3) 6.0(0.3) 5.9(0.1)
1988 6.1(0.3) 5.9(0.2) 6.0(0.2) 5.9(0.1) 5.9(0.2) 5.9(0.1)
CRD (mm) 1987 98.3(4.1) 97.1(4.0) 96.1(3.0) 95.0(3.7) 94.2(3.1)
1988 96.5(2.9) 98.0(3.4) 95.9(2.9) 94.6(3.1) 95.6(2.9) 94.5(4.1) *
SEC (mn) 1987 73.7(3.5) 74.8(3.7) 74.2(2.5) 72.8(2.1) 73.0(1.9)
1988 75.1(2.3) 75.7(2.8) 75.0(2.5) 75.5(2.7) 73.4(2.1) 72.8(4.0) *
TAIL (mm) 1987 72.0(4.1) 72.0(3.6) 71.6(4.0) 70.3(2.7) 69.4(1.0)
1988 74.9(3.3) 75.7(3.5) 76.0(4.2) 73.7(3.3) 73.0(2.9) 74.3(2.0) *
TARS (mm) 1987 24.8(0.7) 24.9(0.8) 24.9(0.6) 24.9(0.8) 24.7(0.8)
1988 24.8(0.8) 25.3(1.0) 25.0(0.6) 25.1(0.7) 24.9(0.6) 24.6(0.4)

CTOE (mm) 1987 16.9(0.7) 17.0(0.4) 17.0(0.5) 16.7(0.7) 17.0(0.3)
1988 16.4(0.5) 16.5(0.5) 16.3(0.6) 16.7(0.5) 16.6(0.5) 16.7(0.1)
* Significant differences among means within year, P < 0.05.








Table 3-6. Means (+ SD) of 10 traits of body size in after second-year (ASY) male red-winged blackbirds
collected by shooting in Evangeline Parish, Louisiana, during 6, 10-day collection intervals, 1986-1988.
Traits are body mass (MASS), bill length (BILL), bill depth at nares (BDN), bill width at gonys (WGON), bill
width at nares (WNAR), wing chord (CRD), length of secondary feathers (SEC), tail length (TAIL), tarsus
length (TARS), and length of central toe (CTOE). A dash (-) indicates that no birds were collected during
the interval.

Collection interval
Feb Mar Mar Mar Apr Apr
Trait Year 10-20 1-10 11-20 21-31 1-10 11-20

MASS (g) 1986 68.0(2.8) 61.3(3.5) 61.2(3.0) 62.7(2.7) 62.0(0.0) *
1987 68.3(4.6) 61.6(4.5) 61.2(1.8) 60.4(3.1) 62.0(3.7) *
1988 69.2(8.0) 60.5(2.1) 60.4(5.8) 60.1(3.6)
BILL (mm) 1986 24.3(0.1) 23.8(0.9) 24.9(1.0) 25.0(0.8) 25.1(0.5) *
1987 24.4(0.6) 24.3(1.3) 25.0(1.0) 24.9(0.8) 25.9(1.0) *
1988 23.7(0.8) 24.5(0.1) 24.4(0.9) 24.4(0.8)
BDN (mn) 1986 10.2(0.6) 10.1(0.4) 9.9(0.4) 9.9(0.5) 9.5(0.1)
1987 12.3(0.8) 11.7(0.5) 11.8(0.6) 11.6(0.5) 11.8(0.7)
1988 10.4(0.5) 10.1(0.4) 10.1(0.3) 10.0(0.4)
WGON (mm) 1986 9.7(0.1) 9.4(0.6) 9.4(0.4) 9.5(0.4) 9.7(0.3)
1987 9.6(0.5) 9.3(0.3) 9.4(0.2) 9.4(0.3) 9.5(0.4)
1988 9.8(0.4) 9.5(0.6) 9.5(0.3) 9.5(0.3)
WNAR (mm) 1986 7.3(0.4) 7.5(0.4) 7.7(0.5) 7.6(0.3) 7.9(0.4)
1987 6.4(0.3) 6.6(0.2) 6.5(0.3) 6.4(0.8) 6.3(0.1)
1988 6.7(0.3) 6.6(0.2) 6.5(0.1) 6.6(0.2)
CRD (mm) 1986 119.8(1.3) 112.6(10.6) 115.9(2.7) 116.8(5.3) 116.1(3.4)
1987 119.6(1.1) 117.7(4.3) 119.4(3.6) 117.8(3.3) 118.2(3.5)
1988 120.4(3.9) 117.3(3.8) 114.3(2.0) 116.6(2.2) *
SEC (mm) 1987 92.0(1.2) 93.6(4.0) 92.6(3.4) 91.8(2.6) 91.5(4.4)
1988 93.8(3.1) 91.7(1.5) 92.1(1.6) 90.4(2.4)
TAIL (mm) 1986 92.0(5.3) 92.2(4.5) 92.6(3.7) 92.8(1.9) 92.1(4.4)
1987 91.0(2.9) 90.6(4.5) 91.9(2.8) 91.7(3.6) 91.8(4.0)
1988 94.6(3.4) 96.6(3.4) 93.1(2.5) 93.9(3.4)
TARS (mm) 1986 25.5(4.0) 28.4(1.0) 27.9(0.9) 27.7(1.1) 27.0(0.6)*
1987 27.0(1.3) 28.2(1.2) 28.2(0.6) 27.9(0.8) 28.1(0.6)
1988 28.0(1.0) 27.7(0.4) 28.2(0.9) 28.2(0.8)

CTOE (mm) 1987 18.7(0.4) 19.0(0.9) 19.1(0.6) 19.1(0.7) 19.9(0.2)
1988 18.9(0.7) 17.9(0.4) 19.0(0.6) 18.8(0.8)
Significant differences among means within year, P < 0.05.









Table 3-7. Means (+ SD) of 10 traits of body size in after hatching-year (AHY) female red-winged blackbirds
collected by shooting in Evangeline Parish, Louisiana, during 6, 10-day collection intervals, 1986-1988.
Traits are body mass (MASS), bill length (BILL), bill depth at nares (BDN), bill width at gonys (WGON), bill
width at nares (WNAR), wing chord (CRD), length of secondary feathers (SEC), tail length (TAIL), tarsus
length (TARS), and length of central toe (CTOE). A dash (-) indicates that no birds were collected during
the interval.


Collection interval
Feb Mar Mar Mar Apr Apr
Trait Year 10-20 1-10 11-20 21-31 1-10 11-20

MASS (g) 1986 52.0 44.6(4.4) 42.0(3.7) 46.5(4.4) 43.7(5.5) *
1987 47.8(3.2) 45.3(3.9) 42.6(4.0) 40.8(3.7) 44.0(5.8) *
1988 46.0(3.6) 42.1(2.6) 40.3(3.3) 43.3(3.6) 42.6(5.8) 44.3(4.1) *
BILL (mm) 1986 21.1 20.4(0.7) 20.6(0.7) 20.8(0.6) 20.7(0.7)
1987 20.5(0.6) 20.5(0.5) 20.5(0.6) 20.7(0.7) 21.7(0.6) *
1988 20.3(0.7) 20.4(0.7) 20.5(0.6) 20.6(0.7) 20.7(0.6) 20.9(0.5)
BON (mm) 1986 9.0 8.8(0.3) 8.7(0.2) 8.6(0.3) 8.6(0.4)
1987 10.1(0.4) 10.4(0.5) 10.3(0.5) 10.1(0.3) 10.5(0.4) *
1988 9.1(0.9) 8.9(0.3) 9.0(0.3) 8.8(0.3) 9.0(0.4) 8.8(0.3)
WGON (mm) 1986 8.6 8.6(0.4) 8.4(0.4) 8.5(0.3) 8.5(0.5)
1987 8.4(0.2) 8.6(0.4) 8.4(0.3) 8.3(0.3) 8.4(0.3) *
1988 8.4(0.4) 8.4(0.3) 8.3(0.3) 8.5(0.3) 8.7(0.4) 8.4(0.3) *
WNAR (mm) 1986 6.9 6.9(0.4) 7.0(0.3) 7.2(0.4) 7.2(0.5)
1987 6.0(0.2) 6.0(0.2) 5.9(0.2) 5.9(0.2) 5.8(0.3)
1988 6.0(0.2) 5.9(0.2) 5.8(0.2) 6.0(0.3) 6.1(0.2) 6.0(0.3) *
CRD (mn) 1986 91.6 98.4(3.1) 97.4(4.0) 96.4(3.7) 96.6(3.8) *
1987 100.9(2.7) 99.4(3.0) 98.4(3.5) 98.7(3.2) 100.6(3.0) *
1988 99.1(2.8) 99.0(2.7) 99.8(3.1) 99.0(3.1) 99.5(3.1) 99.8(4.6)
SEC (mn) 1987 76.3(2.0) 76.9(2.3) 76.1(2.4) 75.6(2.6) 77.2(1.9) *
1988 76.3(3.2) 77.5(2.1) 77.3(2.9) 78.4(2.1) 76.1(2.0) 76.8(2.9) *
TAIL (mm) 1986 -76.2 75.6(3.7) 75.5(3.1) 74.5(3.7) 73.4(3.1)
1987 76.0(2.9) 75.4(2.4) 75.0(2.9) 75.3(2.4) 76.4(2.1)
1988 78.1(2.5) 78.3(2.6) 78.7(2.8) 78.1(2.9) 77.3(2.8) 80.1(3.6)
TARS (mm) 1986 -22.7 24.8(1.0) 24.5(1.2) 24.7(0.7) 24.4(0.6)
1987 24.8(0.9) 24.8(0.9) 24.7(0.9) 24.8(0.6) 25.1(0.7)
1988 25.0(0.7) 25.2(0.8) 25.2(0.8) 25.2(0.9) 25.4(0.8) 25.0(0.7)
CTOE (mm) 1987 -16.5(0.6) 17.1(0.5) 16.8(0.6) 17.0(0.6) 16.5(1.1)
1988 16.5(0.6) 16.3(0.6) 16.5(0.5) 16.6(0.6) 16.7(0.6) 17.0(0.7) *

Significant differences among means within year, P < 0.05.








Classification functions. As determined by Wilson's (1986) classification

equations, nonresident adult birds were present after the beginning of early

planting season each year (Table 3-8). However, there was great variation

among years and age/sex classes in the estimated percentages of nonresident

birds found near Millers Lake. During the main planting season (March 21

April 10), 0-17% of ASY and 15%-76% of AHY were classified as nonresidents.

Wing-chord data suggested that nonresident SYM left the region by April 10

each year, whereas some nonresident ASY remained through April. By wing chord

data, 40%-100% of AHY collected after March 20 were classified as nonresidents

(Table 3-8).


DISCUSSION

Two lines of evidence show that most redwings found in southwestern

Louisiana after mid-March were resident birds. Recoveries of banded birds,

compiled from 1924-1985, suggested that 67%-94% found in southwestern

Louisiana during March and April were resident birds. However, banding data

were insufficient to estimate age and sex-related patterns of migration.

Discriminant analysis of morphometric data suggested that >80% of adult male

redwings in the region were residents, and from 25%->80% of adult females

(42%-53% in 1986, 25%-50% in 1987, and >80% in 1988) were residents during

early planting season.

The estimates of the resident and nonresident components of the population

calculated from banding and morphometric data are in general agreement with

those of Wilson (1986), who reported that proportionally more residents were

present in April than in March. However, the current morphometric data

suggest a greater representation of nonresident birds, especially female

redwings, during the planting season than previously identified. The











Table 3-8. Percentage of nonresident red-winged blackbirds in the Millers
Lake area of Evangeline Parish, Louisiana, during 6, 10-day collection
intervals in spring, 1986-1988. Two methods for estimating migratory status
were used-- classification functions from discriminant analyses for adult
birds only (Wilson 1986), and simple wing-chord measurements for second-year
males and adult birds. A dash (-) indicates that no birds of an age/sex class
were collected during the interval. No classification function exists for
second-year males.


Age/sex Collection Classification function Wing chord

class interval 1986 1987 1988 1986 1987 1988


Second- Feb 10-20 57
year Mar 01-10 33 62 55
male Mar 11-20 22 22 16
(SYM) Mar 21-31 12 28 20
Apr 01-10 16 7 0
Apr 11-20 0 0 0

After Feb 10-20 0 59
second- Mar 01-10 4 0 0 50 50 0
year Mar 11-20 3 0 13 36 -
male Mar 21-31 17 0 0 12 50 0
(ASY) Apr 01-10 17 2 0 16 25 5
Apr 11-20 0 0 0 31 -

After Feb 10-20 32 78
hatching- Mar 01-10 81 23 0 93 79
year Mar 11-20 58 76 35 66 79 81
female Mar 21-31 38 76 15 46 70 71
(AHY) Apr 01-10 47 52 17 40 67 74
Apr 11-20 39 50 11 40 100 75








estimates also provide support for the observation of age- and sex-specific

migration patterns by red-winged blackbirds from wintering to breeding sites

(Dolbeer 1978, 1982). The among-year variation in the proportion of

nonresident female redwings in the area during the planting season suggests a

dynamic pattern of migration by females in southwestern Louisiana in late

winter and early spring.

Female redwings are implicated in causing the greatest damage to seeded

rice in the Millers Lake region of Evangeline Parish, as well as in other

parishes of southwestern Louisiana. Because of inter-year variation in the

proportion of nonresident female redwings, the component of the blackbird

population responsible for damage is dynamic. To illustrate, in 1986 and

1988, resident females primarily were responsible for damage, whereas, in

1987, migratory females principally were responsible for damage. Efforts to

mitigate bird damage to early planted rice are thus complicated by annual

change in the component of the population responsible for damage. The

lingering presence of migrant birds during some spring planting seasons, but

not others, also may result in increased seed loss during those years. A

conservative recommendation to avoid or reduce seed loss in either situation

is to delay planting until after migration is over.

The differences in estimates of the proportions of resident and

nonresident red-winged blackbirds derived both from banding data (biased

toward residents) and from morphometric data may reflect changes in

distribution patterns that are related to changes in agricultural practices

that occurred after World War II. Is it possible that prior to 1945, the

period in which most band recoveries were reported, there were not as many

migrant red-winged blackbirds remaining in Louisiana during spring. The

availability of food resources resulting from increased rice production in








recent decades may be the attractant that has precipitated an increase in the

numbers of migrant blackbirds that remain in the region after winter--or

during the planting season. Thus, the presence of these nonresident

blackbirds during the planting season, due to "delayed" migration, increases

the damage to spring-planted rice beyond the level normally caused by resident

blackbirds.















CHAPTER 4: ROOST DYNAMICS FROM LATE WINTER THROUGH SPRING


INTRODUCTION

The winter roost at Millers Lake has attracted large numbers of blackbirds

and starlings for several decades (Ortego 1976, Wilson 1986). Because of its

large size and close proximity to rice fields, the roost facilitates bird

damage to newly planted rice during spring. To develop a biologically-based

bird population management program for mitigating bird damage in the rice-

growing region, data that quantified roost dynamics--the changes in size and

species composition over time--at the Millers Lake roost in spring were

needed.

Factors that have influenced the size and stability of other blackbird and

starling roosts in the eastern United States offer some insight into the roost

dynamics at Millers Lake. Long-term variation in roost size simply may be

related to timing of migration or differential migratory patterns (White 1980,

Greenleaf 1982). Long-term stability in numbers and species in roosts may be

related to persistent mild air temperatures (Crebbs 1960, Meanley 1965, 1971,

Martin 1977, Cutright 1973). Short-term abundance of birds in roosts may be

related to (1) fluctuations in air temperature and precipitation (White 1980),

(2) food resource abundance (Coon 1974, Morrison and Caccamise 1985, Maccarone

1987), (3) roosting substrate availability (Weatherhead and Hoysack 1984), (4)

human intrusion (Greenleaf 1982), or (5) estimation techniques (White 1980).















CHAPTER 4: ROOST DYNAMICS FROM LATE WINTER THROUGH SPRING


INTRODUCTION

The winter roost at Millers Lake has attracted large numbers of blackbirds

and starlings for several decades (Ortego 1976, Wilson 1986). Because of its

large size and close proximity to rice fields, the roost facilitates bird

damage to newly planted rice during spring. To develop a biologically-based

bird population management program for mitigating bird damage in the rice-

growing region, data that quantified roost dynamics--the changes in size and

species composition over time--at the Millers Lake roost in spring were

needed.

Factors that have influenced the size and stability of other blackbird and

starling roosts in the eastern United States offer some insight into the roost

dynamics at Millers Lake. Long-term variation in roost size simply may be

related to timing of migration or differential migratory patterns (White 1980,

Greenleaf 1982). Long-term stability in numbers and species in roosts may be

related to persistent mild air temperatures (Crebbs 1960, Meanley 1965, 1971,

Martin 1977, Cutright 1973). Short-term abundance of birds in roosts may be

related to (1) fluctuations in air temperature and precipitation (White 1980),

(2) food resource abundance (Coon 1974, Morrison and Caccamise 1985, Maccarone

1987), (3) roosting substrate availability (Weatherhead and Hoysack 1984), (4)

human intrusion (Greenleaf 1982), or (5) estimation techniques (White 1980).








Time, weather, and resource abundance emerged as the factors most likely

to affect roost size, composition, and stability at Millers Lake as there is

little human intrusion in the lake after waterfowl season closes (mid-January)

and before fishing season begins (mid-March) and little change in roosting

substrate in the lake because of a laissez-faire management policy. Food

resource abundance could not be assessed in this study because of the large

area (5-6,000 km2) over which birds from Millers Lake might feed (Brugger

1988). Therefore, objectives of this facet of the investigation, conducted at

Millers Lake from late winter through the rice-planting season in the 3 years,

1986-88, were to: (1) enumerate roost size and species composition; (2)

develop a predictive model for bird abundance based on time and weather

variables; and (3) estimate stability of the roost immediately preceding and

during the damage period.


METHODS

Weather

Records of daily minimum and maximum air temperatures and precipitation

were obtained from the Louisiana State University Weather Service Station at

Eunice (30 km south of Millers Lake) for the dates, February 1-April 30, 1986-

1988. Daily air temperatures and precipitation were plotted against time

(Julian date) to depict seasonal weather patterns.


Roost Size and Composition

Estimates of abundance and composition of birds roosting at Miller Lake

were made 1 evening per 7 days from mid-February to late-April, 1986, and 1

evening per 5 days from mid-February to April, 1987 and 1988. Because








Time, weather, and resource abundance emerged as the factors most likely

to affect roost size, composition, and stability at Millers Lake as there is

little human intrusion in the lake after waterfowl season closes (mid-January)

and before fishing season begins (mid-March) and little change in roosting

substrate in the lake because of a laissez-faire management policy. Food

resource abundance could not be assessed in this study because of the large

area (5-6,000 km2) over which birds from Millers Lake might feed (Brugger

1988). Therefore, objectives of this facet of the investigation, conducted at

Millers Lake from late winter through the rice-planting season in the 3 years,

1986-88, were to: (1) enumerate roost size and species composition; (2)

develop a predictive model for bird abundance based on time and weather

variables; and (3) estimate stability of the roost immediately preceding and

during the damage period.


METHODS

Weather

Records of daily minimum and maximum air temperatures and precipitation

were obtained from the Louisiana State University Weather Service Station at

Eunice (30 km south of Millers Lake) for the dates, February 1-April 30, 1986-

1988. Daily air temperatures and precipitation were plotted against time

(Julian date) to depict seasonal weather patterns.


Roost Size and Composition

Estimates of abundance and composition of birds roosting at Miller Lake

were made 1 evening per 7 days from mid-February to late-April, 1986, and 1

evening per 5 days from mid-February to April, 1987 and 1988. Because








Time, weather, and resource abundance emerged as the factors most likely

to affect roost size, composition, and stability at Millers Lake as there is

little human intrusion in the lake after waterfowl season closes (mid-January)

and before fishing season begins (mid-March) and little change in roosting

substrate in the lake because of a laissez-faire management policy. Food

resource abundance could not be assessed in this study because of the large

area (5-6,000 km2) over which birds from Millers Lake might feed (Brugger

1988). Therefore, objectives of this facet of the investigation, conducted at

Millers Lake from late winter through the rice-planting season in the 3 years,

1986-88, were to: (1) enumerate roost size and species composition; (2)

develop a predictive model for bird abundance based on time and weather

variables; and (3) estimate stability of the roost immediately preceding and

during the damage period.


METHODS

Weather

Records of daily minimum and maximum air temperatures and precipitation

were obtained from the Louisiana State University Weather Service Station at

Eunice (30 km south of Millers Lake) for the dates, February 1-April 30, 1986-

1988. Daily air temperatures and precipitation were plotted against time

(Julian date) to depict seasonal weather patterns.


Roost Size and Composition

Estimates of abundance and composition of birds roosting at Miller Lake

were made 1 evening per 7 days from mid-February to late-April, 1986, and 1

evening per 5 days from mid-February to April, 1987 and 1988. Because








relatively few birds were reported to return to the roost from the pinelands

lying north of the lake (Ortego 1976, Wilson 1986), only flightlines on the

southern fringe of the lake were censused. Two procedures for counting

blackbirds were used to estimate roost size.

Stationary count. Between 1630 and 1830 h, 1 or 2 observers, stationed

either at the south levee and/or on Rt. 376, estimated the number of birds

entering the lake from the south and southwest by means of block-count

methodology (Meanley 1965, Arbib 1972, Dolbeer et al. 1978). Counts were

conducted in 5-min segments. The first minute in five, birds flying to the

lake between the Lake road and the west treeline were estimated; the second

minute, the number of birds between the road and east treeline were estimated;

the third minute, species and sex of birds west of the road were estimated;

and the fourth minute, species and sex of birds east of the road were

estimated. No data were taken in the fifth minute. If 2 observers were

present at the same count site, each observer estimated birds in only one

compass direction (east or west). Estimates of number of birds per 5-min

segment were summed over the evening's counts and then multiplied by 5

(abundance recorded for only 1 min in each of two compass-direction counts per

5-min segment) to obtain an overall estimate of roost size. The total number

of 5-min segments per evening varied among counts depending on weather, time

of sunset, and flight patterns of birds.

Drive-and-count. In March and April 1988, the numbers of blackbirds

entering the roost in evening were estimated from counts taken along

standardized road transects (Ortego 1976, Wilson 1986). An observer drove the

8 km length of Rt. 376 at 48 km/h (30 mph) and block-counted numbers of birds

flying to the lake within a zone that extended 0.5 km on either side of the

road for each of 5, 1.6 km segments of the route. Each 1.6 km segment of the








route was driven in 2 min, once every 10 min. The total number of 10-min

segments driven per evening varied among evenings depending on weather, time

of sunset, and flight patterns of birds. Estimates were summed per 1.6 km

interval of road, and then multiplied by 5 to obtain an estimate of roost

size. Composition by sex and species could not be determined by this count

technique.

Assumptions inherent to both methods were: (1) equal competency among

observers in identifying and counting birds; (2) equal visibility of birds

throughout the sampling region; (3) equal numbers of birds in the sampling

space during each minute of the sampled and nonsampled times; and (4) equal

volumes of airspace sampled on each side of the road.

Species composition. In clear weather, evening flights of birds to the

roost occurred principally from 30 min pre-sunset to 30 min post-sunset.

During inclement weather (cold, rainy, cloudy), evening flights began as early

as 2 h before sunset. Under the latter conditions, usually due to the low

intensity of light, species and sex composition of birds entering the roost

could not be determined consistently by identifying individual birds in

flightlines, as recommended by Dolbeer et al. (1978). Female red-winged

blackbirds were especially difficult to distinguish from brown-headed cowbirds

in poor light. Information on the species and sex composition of blackbirds

at the roost derived from stationary counts was supplemented by 2 additional

methods. In 1986, species and sex composition of roosting birds were derived

from weekly samples collected in the northeast horn of Millers Lake. In 1987

and 1988, flocks, rather than individuals, entering the lake from the south

were identified to species and sex for 1 min of each 5 min-interval of the

stationary counts. In both cases, the spatial and temporal distributions of

species and sexes in the roost and in flightlines were assumed to be random.








Statistical analyses. Estimates of roost size compiled during 3 spring

planting seasons, 1986-1988, were combined for analysis. The subsequent decay

curve was fitted to polynomial and exponential equations (Rafferty and Norling

1985). A best fit was found by r2, the coefficient of determination. A logo,

transformation was then applied to estimates of roost size to linearize

values. Relationships among roost sizes, and date, air temperatures (mean

minimum and mean maximum for 3 days preceding the count), and precipitation

(sum of rainfall for 3 days preceding the count) were estimated with Pearson

correlation coefficients and multiple linear regressions at alpha=0.05. An

estimate of reliability of stationary-count and drive-and-count methods for

quantifying roost size was obtained by Spearman rank correlation.


Spatial Patterns of Roosting

Weekly surveys of Millers lake were made by boat during the interval

extending from 2 h pre-sunset to 0.5 h post-sunset to determine the

approximate locations of roosting birds. Early in 1986, it was determined

that birds roosted primarily in the northeastern portion of the lake during

March and April. Hence, after mid-March in subsequent years, only the

northeastern portion of the lake was surveyed by boat for locations of

roosting birds.


RESULTS

Spring Weather Patterns

Air temperatures and precipitation were different in each of the 3 spring

seasons in southwestern Louisiana. Freezes occurred approximately 4 days/mo

in February and 2 days/mo in March of each year. Dates of last freezes in

spring at Eunice, Louisiana, were: March 21-22, 1986; April 2-5, 1987; and








Statistical analyses. Estimates of roost size compiled during 3 spring

planting seasons, 1986-1988, were combined for analysis. The subsequent decay

curve was fitted to polynomial and exponential equations (Rafferty and Norling

1985). A best fit was found by r2, the coefficient of determination. A logo,

transformation was then applied to estimates of roost size to linearize

values. Relationships among roost sizes, and date, air temperatures (mean

minimum and mean maximum for 3 days preceding the count), and precipitation

(sum of rainfall for 3 days preceding the count) were estimated with Pearson

correlation coefficients and multiple linear regressions at alpha=0.05. An

estimate of reliability of stationary-count and drive-and-count methods for

quantifying roost size was obtained by Spearman rank correlation.


Spatial Patterns of Roosting

Weekly surveys of Millers lake were made by boat during the interval

extending from 2 h pre-sunset to 0.5 h post-sunset to determine the

approximate locations of roosting birds. Early in 1986, it was determined

that birds roosted primarily in the northeastern portion of the lake during

March and April. Hence, after mid-March in subsequent years, only the

northeastern portion of the lake was surveyed by boat for locations of

roosting birds.


RESULTS

Spring Weather Patterns

Air temperatures and precipitation were different in each of the 3 spring

seasons in southwestern Louisiana. Freezes occurred approximately 4 days/mo

in February and 2 days/mo in March of each year. Dates of last freezes in

spring at Eunice, Louisiana, were: March 21-22, 1986; April 2-5, 1987; and








Statistical analyses. Estimates of roost size compiled during 3 spring

planting seasons, 1986-1988, were combined for analysis. The subsequent decay

curve was fitted to polynomial and exponential equations (Rafferty and Norling

1985). A best fit was found by r2, the coefficient of determination. A logo,

transformation was then applied to estimates of roost size to linearize

values. Relationships among roost sizes, and date, air temperatures (mean

minimum and mean maximum for 3 days preceding the count), and precipitation

(sum of rainfall for 3 days preceding the count) were estimated with Pearson

correlation coefficients and multiple linear regressions at alpha=0.05. An

estimate of reliability of stationary-count and drive-and-count methods for

quantifying roost size was obtained by Spearman rank correlation.


Spatial Patterns of Roosting

Weekly surveys of Millers lake were made by boat during the interval

extending from 2 h pre-sunset to 0.5 h post-sunset to determine the

approximate locations of roosting birds. Early in 1986, it was determined

that birds roosted primarily in the northeastern portion of the lake during

March and April. Hence, after mid-March in subsequent years, only the

northeastern portion of the lake was surveyed by boat for locations of

roosting birds.


RESULTS

Spring Weather Patterns

Air temperatures and precipitation were different in each of the 3 spring

seasons in southwestern Louisiana. Freezes occurred approximately 4 days/mo

in February and 2 days/mo in March of each year. Dates of last freezes in

spring at Eunice, Louisiana, were: March 21-22, 1986; April 2-5, 1987; and








March 19-20, 1988. Conditions were dry in 1986, but relatively wet in 1988.

Measures of total rainfall (cm) per month in 1986, 1987, and 1988,

respectively, were: February--5.56, 16.33, 34.93; March--9.47, 17.75, 22.81;

and April--5.41, 11.48, 18.49.


Roost Size and Composition

In spring 1986, the number of blackbirds in the Millers Lake roost

decreased exponentially from approximately 15 million in February (E. A.

Wilson, Louisiana State Univ., Crowely, pers. commun.) to 15,000 in late April

(Table 4-1). A similar pattern of decline was observed in 1987 and 1988. The

decay curve of stationary-count roost estimates recorded for the period,

February-April, 1986-88 (Fig. 4-1), is described by the negative exponential

equation:

Roost size = 3,312,600,000 10(o05143*dae); (r2 = 0.83, P<0.05).


Mean 3-day minimum and maximum temperatures were correlated (r=0.82;

P<0.01); thus only one temperature variable (mean maximum) was used in

multiple regressions. Multiple regression of combined 3-year estimates of

roost size on date, mean 3-day maximum temperature, and summed 3-day rainfall

yielded only date as a significant explanatory variable (Table 4-2). Roost

size logol) and date were correlated among years (r= -0.92, P<0.01).

Temporary increases in roost size were noted after freezes or rains.

Although the drive-and-count method yielded slightly higher estimates than

did the stationary-count method in 5 of 6 paired counts, estimated roost size

derived by the two methods did not differ significantly (P>0.05) (Table 4-1).

Flightlines. Traditional evening flightlines were not observed at Miller

Lake. Instead, birds flew to the Millers Lake roost in wide swaths or waves,










Table 4-1. Estimates of roost size at Millers Lake, Evangeline Parish,
Louisiana, mid-February-late-April, 1986-88. Two methods of estimation were
used: stationary-count (no asterisk); or drive-and-count (*). Paired counts
in 1988, used to test reliability of the 2 methods, are linked by dotted
lines.


Estimated roost size
Date of
count 1986 1987 1988


14,900,000 a*

1,000,000 a*


700,000
500,000
374,000


608,000


Feb
Feb
Feb
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Mar
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Apr
Aor


110,000


22,000


2,000,000
2,000,000

2,500,000



950,000


85,000


45,000


38,000


20,000
58,000
30,000
11.000


18,000,000

6,000,000



450,000a*
:- 150,000


:- 513,000*


125,000a*
185,000*
117,500

73,500
78,000*

89,000*

68,000

20,000
24,000*

12,500
6,300*


"Drive-and-count
Rice Exp. Stn.,


estimates made by E. A. Wilson
Crowley, pers. commun.).


(Louisiana State Univ.,


bStationary-count estimate made by J. Glahn (USDA/APHIS/S&T,
Kentucky Field Stn., Bowling Green, pers. commun.).

cStationary-count estimate made by R. A. Dolbeer (USDA/APHIS/S&T,
Ohio Field Stn., Sandusky, pers. commun.).


434,500




















a + 1986

1987

C' a 1988



4) 10-
N

0
O a
0
m 5-



+ 4W

30 60 90 120

February March April



Figure 4-1. Negative exponential decline in size of blackbird roost during
the period February 15-April 24, 1986-1988, Millers Lake, Evangeline Parish,
Louisiana.










Table 4-2. Multiple linear regression analyses relating log-transformed roost
size to Julian calendar date and 2 weather variables (mean 3-day maximum air
temperature [max] and summed 3-day rainfall [rain]) at Millers Lake,
Evangeline Parish, Louisiana, for the period February 15-April 30, 1986-88.


MLR model Variables Coefficient B-weight

(1) Size = date + max + rain Date -0.0491 -0.9845
Max 0.0202 0.0866
Rain -0.0018 -0.0034

MLR equation: Size = 9.00 0.05 date + 0.02 max

r 0.93, r2 = 0.86



(2) Size = date Date -0.0462 -.09253

MLR equation: Size = 9.21 0.05 date

r = 0.92, r2 = 0.85








covering much of the airspace south of the lake. Altitude of flight waves

ranged from <10 m to approximately 30-40 m. Major flightwaves originated from

the south and southwest of Millers Lake during February and March each year.

However, by late March, the flightwaves from the southwest diminished in size,

being replaced by those from the south and southeast.

Species composition. Species composition at Millers Lake varied weekly

form late winter to spring. The majority of common grackles, cowbirds,

starlings, and adult male redwings had abandoned the roost by late February.

Female redwings comprised 50%-99% of the birds in both roost counts and bird

collections during March and April (Table 4-3).


Spatial Pattern of Roosting

Observations of roosting blackbirds during mid-January to early March

indicated that birds settled on woody vegetation in the lake basin. From mid-

March through April, roosting birds were found only in the secluded northeast

portion of the lake, which is dominated by buttonbush. The spatial area used

by roosting birds diminished during late March and April, reflecting not only

a decline in roost size, but also a more selective use of available woody

vegetation.


Other Roosts

One other major roost, LaFleur Nursery, Grand Prairie, located within 50

km of Millers Lake, comprises 50 ha of mature palms, oaks, and ornamentals

that provide a dense woody substrate for roosting. Other, more distant

roosts, included: Barry's Nursery, Grand Coteau; the coastal marshes south of

Port Arthur; the marshes south of Gueydan; and Bundick Lake, Beauregard

Parish. Roosts occurring more proximate to Millers Lake, previously

documented in the National Roost Surveys, e.g., Cheneyville, Meeker, and








covering much of the airspace south of the lake. Altitude of flight waves

ranged from <10 m to approximately 30-40 m. Major flightwaves originated from

the south and southwest of Millers Lake during February and March each year.

However, by late March, the flightwaves from the southwest diminished in size,

being replaced by those from the south and southeast.

Species composition. Species composition at Millers Lake varied weekly

form late winter to spring. The majority of common grackles, cowbirds,

starlings, and adult male redwings had abandoned the roost by late February.

Female redwings comprised 50%-99% of the birds in both roost counts and bird

collections during March and April (Table 4-3).


Spatial Pattern of Roosting

Observations of roosting blackbirds during mid-January to early March

indicated that birds settled on woody vegetation in the lake basin. From mid-

March through April, roosting birds were found only in the secluded northeast

portion of the lake, which is dominated by buttonbush. The spatial area used

by roosting birds diminished during late March and April, reflecting not only

a decline in roost size, but also a more selective use of available woody

vegetation.


Other Roosts

One other major roost, LaFleur Nursery, Grand Prairie, located within 50

km of Millers Lake, comprises 50 ha of mature palms, oaks, and ornamentals

that provide a dense woody substrate for roosting. Other, more distant

roosts, included: Barry's Nursery, Grand Coteau; the coastal marshes south of

Port Arthur; the marshes south of Gueydan; and Bundick Lake, Beauregard

Parish. Roosts occurring more proximate to Millers Lake, previously

documented in the National Roost Surveys, e.g., Cheneyville, Meeker, and










Table 4-3. Weekly estimates of percentage composition of starlings and
blackbirds in the Millers Lake roost, Evangeline Parish, Louisiana, 1986-88.
Five dominant species are listed: European starling (EUST); red-winged
blackbird (RWBL); brown-headed cowbird (BHCO); common grackle (COGR); and
great-tailed grackle (GTGR). Only red-winged blackbirds were identified to
sex. Methods for obtaining estimates were either counts (CNT) or collections
(CLCT).


RWBL Method
Sample
Date EUST Female Male BHCO COGR GTGR size CNT CLCT


1986
Mar 15 5 55 15 5 20 0 60 x
Mar 22 4 75 10 5 5 1 84 x
Mar 29 0 85 1 5 0 5 78 x
Apr 04 0 90 7 1 1 1 52 x
Apr 11 0 90 7 2 0 1 57 x

1987
Mar 08 5 70 10 5 10 0 1,000 x
Mar 15 0 95 2 2 1 0 1,000 x
Mar 22 0 50 40 5 4 1 800 x
Mar 29 0 95 4 1 0 0 300 x
Apr 04 0 95 3 1 0 1 500 x
Apr 11 0 95 5 0 0 0 500 x
Apr 18 0 99 1 0 0 0 300 x

1988
Feb 15 5 30 30 20 15 0 2,000 x
Mar 15 1 50 30 10 9 0 1,000 x
Mar 22 0 70 20 5 4 1 500 x
Mar 29 0 80 15 4 0 1 500 x
Apr 04 0 90 5 4 0 1 500 x
Apr 11 0 95 3 1 0 1 200 x








LeCompte (Meanley et al. 1976), were not active in 1986, 1987, and 1988. No

roosts were reported from Chicot State Park, 10 km northeast of Millers Lake.

The history of the LaFleur Nursery roost is reported as described by Danny

LaFleur (LaFleur Nursery, Grand Prairie, Louisiana, pers. commun., March 17,

1988):

"The roost has been in existence about 15 years. At first the roost was

made up of mostly robins. About 3 years ago, the roost was estimated to

be about 1 million birds in winter. In the last 3 years, blackbirds

increased in abundance, causing damage to oaks (leaf loss) and palms (leaf

shed). The damage is a nuisance, but does not cause major financial

loss."

In 1988, the LaFleur Nursery roost contained about 1 million birds on

February 19. Although no specific effort was attempted to estimate species

composition at the LaFleur Nursery, the most abundant species were common

grackles and red-winged blackbirds, in that order, with lesser numbers of

robins (Turdus miqratorius), great-tailed grackles, and starlings. On March

17, approximately 250,000 birds were present, with a similar qualitative

species composition. No birds were observed roosting at the nursery on April

12, 1988.


DISCUSSION

The task of estimating roost size at Millers Lake is fraught with

difficulties because of the large size of the lake and the great abundance of

birds at the roost. Techniques used in this study were somewhat inadequate to

estimate the size and species composition of the roost accurately because of

insufficient numbers of observers available to cover the entire area of

Millers Lake. Although differences were not significant, the drive-and-count








method consistently yielded higher estimates than did the stationary-count

method. However, the 2 techniques for estimating roost size yielded values

that were correlated, suggesting internal consistency or repeatability of the

estimates. Both methods possibly underestimated roost size.

Roost size at Millers Lake between mid-February and late April was

correlated with date of the year, and reflected migration patterns related to

onset of breeding activity by species and age classes. Seasonally, both sexes

of starlings, cowbirds, and grackles, along with adult male redwings,

abandoned the roost before adult female and immature male redwings. The

decline began at least 6 weeks prior to breeding season for starlings (April

1-July 20: Kessel 1957, Collins and de Vos 1966), and 8 weeks prior to the

breeding season for red-winged blackbirds and common grackles (April 20-July

20: Erskine 1971, Dolbeer 1976), and brown-headed cowbirds (April 20-June 20:

Scott and Middleton 1968).

In late March, flightwaves were reduced to flightlines and shifted in

location from the southwest to the south and southeast. This late-March shift

in flight pattern might be a reflection of variable planting practices in the

different regions south of the lake, variable distances to feeding sites, or

variable roosting locations in the lake.

The size of the population of roosting blackbirds at Millers Lake during

planting season is dynamic. The roost declined in size with seasonal advance.

Implications to management are clear. If planting could be delayed until

after the roost size declined below a predetermined level, e.g., 50,000 birds,

the likelihood of bird damage would be reduced (Wilson et al. 1989).

Another question important to bird population management remains to be

answered: do blackbirds exhibit fidelity to the roost or is there a shift by

individuals among roosts during the planting season? Circumstantial evidence








suggests that turnover in the Millers Lake roost is high during the early

planting season because (1) there is a large proportion of nonresident birds

at the roost, (2) spring migration occurs throughout April, and (3) Millers

Lake is an isolated, but centrally located, roost that is used by migrants.

Numerous large roosts exist at a distance from Millers Lake (e.g., in the

Louisiana and Texas coastal marshes, approximately 100-500 km to the south and

southwest); however, only one large roost was located within 50 km, or daily

flight range, of Millers Lake. If blackbirds and starlings migrating from

more southerly wintering areas travel along the Louisiana-Texas coast and then

across to the Mississippi River, Millers Lake might serve as a short-term

roost during the spring migration. Accordingly, turnover in the roost might

be expected to be high throughout the early planting period, at least until

migration is completed.

In summary, there are two elements of roost dynamics that influence

potential efforts to implement control measures for reducing the abundance of

blackbirds causing damage to sprouting rice. The first element is the timing

and rate of roost dissolution, as it reflects the total number of blackbirds

to which control measures must be directed at any given point in time. The

second element is the rate of roost turnover. To illustrate, even though a

given roost might exhibit a 5% net loss in numbers daily, the concurrent

change in the composition of individuals in the roost could range from very

low to very high. Thus, if, for example, lethal control measures were

directed at birds causing significant crop damage in a specific locality, the

relief might be short duration because "new" birds in the roost might be

attracted to the same locality for foraging. Thus, given the exponential

decline in roost size with advancing season, delayed planting appears to be








the most cost-effective and reliable recommendation for reducing seed losses

of rice to blackbirds.















CHAPTER 5: FORAGING FLOCK DYNAMICS


INTRODUCTION

Blackbirds wintering at Millers Lake make daily trips from the roost to

forage for grain and insects in surrounding fields, farmyards, and woodlots.

Flocks, which range in size from 2-10,000 birds, often fly to foraging

locations as far as 50 km south and southwest of the roost (Ortego 1976). To

predict location, timing, and intensity of bird damage, baseline data were

needed concerning flock dynamics and movement patterns of blackbirds in the

rice-growing region near Millers Lake. Objectives were to describe: (1) the

size and composition of flocks observed foraging in rice fields; (2) the

spatial and temporal distributions of flocks in the agricultural landscape;

and (3) the daily flocking and movement patterns by individuals.


METHODS

Flocks Size, Composition, and Distribution

Morning flights of birds from the roost were followed to estimate flight

direction and destinations of foraging flocks during January 7-10 and March 6-

10, 1986, and March 6-9, 1987. In addition, 2 survey routes, 30 km in length,

were established to assess the spatial distribution of flocks as well as the

temporal changes in flock size and composition. One route (north), located

from 0-15 km directly south of Millers Lake, was surveyed during March and

April 1986-88, and also during 14-19 February 1988. The second route, located















CHAPTER 5: FORAGING FLOCK DYNAMICS


INTRODUCTION

Blackbirds wintering at Millers Lake make daily trips from the roost to

forage for grain and insects in surrounding fields, farmyards, and woodlots.

Flocks, which range in size from 2-10,000 birds, often fly to foraging

locations as far as 50 km south and southwest of the roost (Ortego 1976). To

predict location, timing, and intensity of bird damage, baseline data were

needed concerning flock dynamics and movement patterns of blackbirds in the

rice-growing region near Millers Lake. Objectives were to describe: (1) the

size and composition of flocks observed foraging in rice fields; (2) the

spatial and temporal distributions of flocks in the agricultural landscape;

and (3) the daily flocking and movement patterns by individuals.


METHODS

Flocks Size, Composition, and Distribution

Morning flights of birds from the roost were followed to estimate flight

direction and destinations of foraging flocks during January 7-10 and March 6-

10, 1986, and March 6-9, 1987. In addition, 2 survey routes, 30 km in length,

were established to assess the spatial distribution of flocks as well as the

temporal changes in flock size and composition. One route (north), located

from 0-15 km directly south of Millers Lake, was surveyed during March and

April 1986-88, and also during 14-19 February 1988. The second route, located















CHAPTER 5: FORAGING FLOCK DYNAMICS


INTRODUCTION

Blackbirds wintering at Millers Lake make daily trips from the roost to

forage for grain and insects in surrounding fields, farmyards, and woodlots.

Flocks, which range in size from 2-10,000 birds, often fly to foraging

locations as far as 50 km south and southwest of the roost (Ortego 1976). To

predict location, timing, and intensity of bird damage, baseline data were

needed concerning flock dynamics and movement patterns of blackbirds in the

rice-growing region near Millers Lake. Objectives were to describe: (1) the

size and composition of flocks observed foraging in rice fields; (2) the

spatial and temporal distributions of flocks in the agricultural landscape;

and (3) the daily flocking and movement patterns by individuals.


METHODS

Flocks Size, Composition, and Distribution

Morning flights of birds from the roost were followed to estimate flight

direction and destinations of foraging flocks during January 7-10 and March 6-

10, 1986, and March 6-9, 1987. In addition, 2 survey routes, 30 km in length,

were established to assess the spatial distribution of flocks as well as the

temporal changes in flock size and composition. One route (north), located

from 0-15 km directly south of Millers Lake, was surveyed during March and

April 1986-88, and also during 14-19 February 1988. The second route, located















CHAPTER 5: FORAGING FLOCK DYNAMICS


INTRODUCTION

Blackbirds wintering at Millers Lake make daily trips from the roost to

forage for grain and insects in surrounding fields, farmyards, and woodlots.

Flocks, which range in size from 2-10,000 birds, often fly to foraging

locations as far as 50 km south and southwest of the roost (Ortego 1976). To

predict location, timing, and intensity of bird damage, baseline data were

needed concerning flock dynamics and movement patterns of blackbirds in the

rice-growing region near Millers Lake. Objectives were to describe: (1) the

size and composition of flocks observed foraging in rice fields; (2) the

spatial and temporal distributions of flocks in the agricultural landscape;

and (3) the daily flocking and movement patterns by individuals.


METHODS

Flocks Size, Composition, and Distribution

Morning flights of birds from the roost were followed to estimate flight

direction and destinations of foraging flocks during January 7-10 and March 6-

10, 1986, and March 6-9, 1987. In addition, 2 survey routes, 30 km in length,

were established to assess the spatial distribution of flocks as well as the

temporal changes in flock size and composition. One route (north), located

from 0-15 km directly south of Millers Lake, was surveyed during March and

April 1986-88, and also during 14-19 February 1988. The second route, located








30-55 km southwest of the lake, was surveyed during March and April 1987. The

surveys were begun 30 min after sunrise and completed within 3 h. In 1987,

the 2 routes were censused on the same days.

Blackbirds and starlings observed within 0.4 km of the road were counted

for 3-min periods at each of 20 stops, located at 1.6-km intervals along each

30-km route. Estimates of flock size, composition, activity, and habitat (for

foraging flocks only) were recorded on a standard checksheet.


Land-use Patterns

In 1987, land-use patterns along both survey routes were quantified twice

each month by mapping all land-use activities within 0.4 km of either side of

routes. Five categories of land-use were designated: out-of-rice production;

disked seedbed; water-planted rice; drill-planted rice; and seedling stand.


Individual Movements

Telemetry. During the period March 17-19, 1986, 6 red-winged blackbirds

(1 after second-year male, 2 second-year males, and 3 after hatching-year

females) were each outfitted with a SM 1 transmitter, 0.312 Hg power cell, and

whip antenna (AVM Instrument Co., Livermore, Calif.). Potential battery life

was 9-14 days. All birds were captured at the same locations east of Millers

Lake. Attempts were made to monitor the roost location and morning feeding

locations of instrumented birds; however, birds often could not be located

because signal range of the transmitter was limited to <0.05 km.

Color marking. In March 1986, 62 individuals from 5 flocks were captured

by mist-netting or rocket-netting. Individual birds were measured, marked

with colored, plastic-leg streamers (Guarino 1968), and released en masse by








30-55 km southwest of the lake, was surveyed during March and April 1987. The

surveys were begun 30 min after sunrise and completed within 3 h. In 1987,

the 2 routes were censused on the same days.

Blackbirds and starlings observed within 0.4 km of the road were counted

for 3-min periods at each of 20 stops, located at 1.6-km intervals along each

30-km route. Estimates of flock size, composition, activity, and habitat (for

foraging flocks only) were recorded on a standard checksheet.


Land-use Patterns

In 1987, land-use patterns along both survey routes were quantified twice

each month by mapping all land-use activities within 0.4 km of either side of

routes. Five categories of land-use were designated: out-of-rice production;

disked seedbed; water-planted rice; drill-planted rice; and seedling stand.


Individual Movements

Telemetry. During the period March 17-19, 1986, 6 red-winged blackbirds

(1 after second-year male, 2 second-year males, and 3 after hatching-year

females) were each outfitted with a SM 1 transmitter, 0.312 Hg power cell, and

whip antenna (AVM Instrument Co., Livermore, Calif.). Potential battery life

was 9-14 days. All birds were captured at the same locations east of Millers

Lake. Attempts were made to monitor the roost location and morning feeding

locations of instrumented birds; however, birds often could not be located

because signal range of the transmitter was limited to <0.05 km.

Color marking. In March 1986, 62 individuals from 5 flocks were captured

by mist-netting or rocket-netting. Individual birds were measured, marked

with colored, plastic-leg streamers (Guarino 1968), and released en masse by








flock. Different colors were used to designate individuals from different

flocks (orange, 13 individuals; green, 9; red, 14; pink, 17; white, 9).

Reports of color-marked birds were solicited from farmers and biologists in

the region.


Statistical Analyses

Spearman rank-correlation was used to estimate the relationship between

logl-transformed roost size and the number of flocking birds observed on road

surveys. Wilcoxon's matched pairs t-test was used to test for differences in

total number of flocking birds, mean flock size, and number of flocks between

north and south survey routes in 1987. Multiple linear regressions were used

to estimate relationships between flock occurrence and roost size, distance to

roost, time, weather, and land-use categories.


RESULTS

Flock Size, Composition, and Distribution

In January and March, morning flights of flocks were followed as far as 60

km southwest of Miller Lake before they were lost to view. Local residents

believe that, in mid-winter, birds may forage as far away as Lake Charles (90

km from the roost) (V. Fruge and J. Ardoin, Ville Platte, Louisiana, pers.

commun.).

Individual 30-km road surveys, conducted during the 3 years, 1986-1988,

yielded counts of blackbirds and starlings that ranged from 182 to 15,229

(Table 5-1). The total number of birds observed per survey declined with

advance of the season. The number of birds per route was significantly

correlated with roost size in 1987 (north: r2=0.71, P=0.03; south r2=0.81,








flock. Different colors were used to designate individuals from different

flocks (orange, 13 individuals; green, 9; red, 14; pink, 17; white, 9).

Reports of color-marked birds were solicited from farmers and biologists in

the region.


Statistical Analyses

Spearman rank-correlation was used to estimate the relationship between

logl-transformed roost size and the number of flocking birds observed on road

surveys. Wilcoxon's matched pairs t-test was used to test for differences in

total number of flocking birds, mean flock size, and number of flocks between

north and south survey routes in 1987. Multiple linear regressions were used

to estimate relationships between flock occurrence and roost size, distance to

roost, time, weather, and land-use categories.


RESULTS

Flock Size, Composition, and Distribution

In January and March, morning flights of flocks were followed as far as 60

km southwest of Miller Lake before they were lost to view. Local residents

believe that, in mid-winter, birds may forage as far away as Lake Charles (90

km from the roost) (V. Fruge and J. Ardoin, Ville Platte, Louisiana, pers.

commun.).

Individual 30-km road surveys, conducted during the 3 years, 1986-1988,

yielded counts of blackbirds and starlings that ranged from 182 to 15,229

(Table 5-1). The total number of birds observed per survey declined with

advance of the season. The number of birds per route was significantly

correlated with roost size in 1987 (north: r2=0.71, P=0.03; south r2=0.81,








flock. Different colors were used to designate individuals from different

flocks (orange, 13 individuals; green, 9; red, 14; pink, 17; white, 9).

Reports of color-marked birds were solicited from farmers and biologists in

the region.


Statistical Analyses

Spearman rank-correlation was used to estimate the relationship between

logl-transformed roost size and the number of flocking birds observed on road

surveys. Wilcoxon's matched pairs t-test was used to test for differences in

total number of flocking birds, mean flock size, and number of flocks between

north and south survey routes in 1987. Multiple linear regressions were used

to estimate relationships between flock occurrence and roost size, distance to

roost, time, weather, and land-use categories.


RESULTS

Flock Size, Composition, and Distribution

In January and March, morning flights of flocks were followed as far as 60

km southwest of Miller Lake before they were lost to view. Local residents

believe that, in mid-winter, birds may forage as far away as Lake Charles (90

km from the roost) (V. Fruge and J. Ardoin, Ville Platte, Louisiana, pers.

commun.).

Individual 30-km road surveys, conducted during the 3 years, 1986-1988,

yielded counts of blackbirds and starlings that ranged from 182 to 15,229

(Table 5-1). The total number of birds observed per survey declined with

advance of the season. The number of birds per route was significantly

correlated with roost size in 1987 (north: r2=0.71, P=0.03; south r2=0.81,










Table 5-1. Total number of birds and flocks, and mean (SD)
per 3-min stop and flock, recorded along north and south (s)
Evangeline Parish, Louisiana, 1986-1988.


number of birds
survey-routes,


Air
temp. Total number Mean number (+SD)
Date (0C) Birds Flocks Stop Flock


1986
Mar
Mar
Mar

Mar
Apr
Apr
Apr
Apr

1987
Mar
Mar
Mar
Mar
Apr
Apr
Apr

Mar
Mar
Mar
Mar
Apr
Apr
Apr

1988
Feb
Feb
Mar
Mar
Mar
Mar
Apr
Apr
Apr


95 (156)
562 (1,183)
164 (236)


15.5
-1.0
3.3

5.0
11.7
16.7
10.0
8.8


11.0
13.0
14.3
12.5
10.0
19.0
18.0

10.0
13.3
16.6
13.3
8.3
18.3
18.8


7.2
8.3
2.7
14.4
14.4
21.6
18.3
12.2
11.1


2,029
11,361
3,847

2,584
1,395
1,968
1,071
1,338


15,229
4,687
5,361
5,824
1,053
723
704

3,870
3,516
671
1,177
1,263
361
182


3,056
1,966
1,179
4,011
790
1,229
1,135
1,392
703


64 (102)
295 (155)
102 (134)


82
53
58
26
29


276
77
155
155
28
19
24

62
63
10
37
21
7
3


51
41
36
152
33
50
52
35
29


(170)
(117)
(74)
(38)
(67)


(763)
(106)
(380)
(254)
(26)
(29)
(53)

(122)
(136)
(23)
(84)
(75)
(10)
(2)


(79)
(67)
(67)
(409)
(33)
(62)
(53)
(61)
(64)


118
56
78
41
54


762
245
271
294
47
31
30

188
174
31
56
55
13
4


152
97
57
198
38
58
52
60
31


(314)
(122)
(127)
(55)
(113)

(1,452)
(356)
(671)
(537)
(61)
(60)
(122)

(268)
(359)
(45)
(116)
(130)
(16)
(8)

(227)
(182)
(102)
(500)
(63)
(87)
(80)
(117)
(69)








P=0.01) and 1988 (north r2=0.75, P=0.009), but less so in 1986 (north:

r2=0.71, P=0.055).

Numbers of flocks observed per survey and mean flock size declined with

advance of the season (Table 5-1). Large flocks (>500) were not observed

after the first week of April (Table 5-2). Flock size and the number of birds

per stop were highly variable among surveys.

The number of flocks observed per survey and mean flock size also declined

with increasing distance from Miller Lake. In the 1987 paired surveys, the

total number of birds observed on the north survey route (<15 km of the roost)

was greater than on the south route (>30 km from the roost) (t=2.19, P<0.02).

Similarly, mean flock size was greater on the north surveys than on the south

surveys (t=2.34, P<0.01) (Table 5-1).

Red-winged blackbirds comprised the majority of identifiable birds in each

survey (Table 5-3). Great-tailed and common grackles, brown-headed cowbirds,

and starlings were observed infrequently along the north route. However,

great-tailed grackles were observed frequently along the south route in late

March and early April.

The sex ratio among red-winged blackbirds observed per route was female-

dominated in 6 of 8 surveys in 1986, 11 of 14 surveys in 1987, and 7 of 9

surveys in 1988 (Table 5-4). The preponderance of female red-winged

blackbirds was most prominent in the latter half of March in all years.

Flocks near Millers Lake (north route) were female-dominated in late March and

early April, whereas those more distant (south route) were male-dominated

throughout March and April.

There was high variability in the activities of flocks among surveys

within and among years: 4-81% of flocks were in flight; 0-55% were foraging in










Table 5-2. Temporal distribution of flock sizes observed along north and south
(s) survey-routes, Evangeline Parish, Louisiana, 1986-1988. Percentage of
total is given only for flocks with <25 birds.

Number of birds in flock
Number
Date of Flocks <25 (%) 25-99 100-199 200-499 500-999 1,000+


1986
Mar
Mar
Mar
Mar
Apr
Apr
Apr
Apr

1987
Mar
Mar
Mar
Mar
Apr
Apr
Apr

Mar
Mar
Mar
Mar
Apr
Apr
Apr

1988
Feb
Feb
Mar
Mar
Mar
Mar
Apr
Apr
Apr


(47)
(26)
(59)
(60)
(76)
(52)
(77)
(81)

(38)
(40)
(51)
(47)
(62)
(79)
(80)

(56)
(62)
(95)
(70)
(85)
(95)
(100)

(55)
(67)
(65)
(56)
(48)
(43)
(40)
(66)
(71)










Table 5-3. Percentage species composition of birds observed along north and
south (s) survey-routes, Evangeline Parish, Louisiana, 1986-1988.


Percentages species composition
Red- Brown- Great-
winged headed Common tailed European
Date blackbird cowbird crackle crackle starling Unknown


1986
Mar
Mar
Mar
Mar
Apr
Apr
Apr
Apr

1987
Mar
Mar
Mar
Mar
Apr
Apr
Apr

Mar
Mar
Mar
Mar
Apr
Apr
Apr

1988
Feb
Feb
Mar
Mar
Mar
Mar
Apr
Apr
Apr


09s
16s
23s
29s
06s
13s
21s








Table 5-4. Sex ratios of red-winged blackbirds observed along north and south
(s) survey-routes, Evangeline Parish, Louisiana, 1986-1988.


Percentage Sex
identified ratio Dominant sex in flocks
Date to sex M:F Male Female None


1986
Mar
Mar
Mar
Mar
Apr
Apr
Apr
Apr

1987
Mar
Mar
Mar
Mar
Apr
Apr
Apr

Mar
Mar
Mar
Mar
Apr
Apr
Apr

1988
Feb
Feb
Mar
Mar
Mar
Mar
Apr
Apr
Apr


95
100
85
91
78
98
97
96


1.2:1
1:3.8
1:6.7
1:7.3
1:2.2
1:1.5
1.1:1
1:2.1


1:2.3
1:3.5
1:5.7
1:8.0
1:3.8
1:2.6
1:2.6

1:2.3
1:9.1
1:1.4
1:2.2
1.1:1
3:1
6:1


9.3:1
3.9:1
1:1.7
1:11.1
1:3.4
1:5.3
1:4.7
1:3.7
1:1.9


4
2
0
2
3
2
4
5


3
10
4
2
2
6
5

10
7
11
3
15
11
9


8
18
8
5
4
6
2
5
8








stubble or cultivated rice fields; and 0-63%.were observed loafing in trees or

shrubs near rice fields (Table 5-5).


Land-use Patterns

Rice-field preparation in the region south of Millers Lake began during

the first week of March each year. In 1986 and 1987, several experimental

research fields were planted earlier than normal, with planting being

completed by 16 March (Wilson et al. 1986, 1987, 1989). The earliest rice

plantings by producers occurred on March 9, 1987, and March 17, 1988.

In 1987, approximately 93% of land along the north route and 83% along the

south route had been planted to rice by the third week of April. Land close

to Millers Lake was prepared earlier than that more distant from the lake; on

March 23, 39,000 ha were in rice cultivation along the north route as compared

to 18,500 ha along the south route (Table 5-6).


Individual Movements

Telemetry. Radio-tagged birds were detected no farther than 8 km from

their capture site during 11 days of tracking from March 17-28, 1986 (Table 5-

7). The adult male remained alone near an irrigation canal 1 km east of

Millers Lake for the first 7 days and nights, after which time he returned to

the roost. Then, his signal was lost for 3 days. He was last located

roosting in the eastern portion of the lake on the night of March 28.

One second-year male was located in feeding flocks east of Millers Lake on

the mornings of March 20 and 21. Thereafter, no daytime locations were

obtained. The other second-year male was located daily with flocks foraging

1-8 km south and southwest of the roost. Both second-year males returned to

Millers Lake nightly to roost.








stubble or cultivated rice fields; and 0-63%.were observed loafing in trees or

shrubs near rice fields (Table 5-5).


Land-use Patterns

Rice-field preparation in the region south of Millers Lake began during

the first week of March each year. In 1986 and 1987, several experimental

research fields were planted earlier than normal, with planting being

completed by 16 March (Wilson et al. 1986, 1987, 1989). The earliest rice

plantings by producers occurred on March 9, 1987, and March 17, 1988.

In 1987, approximately 93% of land along the north route and 83% along the

south route had been planted to rice by the third week of April. Land close

to Millers Lake was prepared earlier than that more distant from the lake; on

March 23, 39,000 ha were in rice cultivation along the north route as compared

to 18,500 ha along the south route (Table 5-6).


Individual Movements

Telemetry. Radio-tagged birds were detected no farther than 8 km from

their capture site during 11 days of tracking from March 17-28, 1986 (Table 5-

7). The adult male remained alone near an irrigation canal 1 km east of

Millers Lake for the first 7 days and nights, after which time he returned to

the roost. Then, his signal was lost for 3 days. He was last located

roosting in the eastern portion of the lake on the night of March 28.

One second-year male was located in feeding flocks east of Millers Lake on

the mornings of March 20 and 21. Thereafter, no daytime locations were

obtained. The other second-year male was located daily with flocks foraging

1-8 km south and southwest of the roost. Both second-year males returned to

Millers Lake nightly to roost.










Table 5-5. Percentage of red-winged blackbird flocks engaged in different
activities (when first observed) in relation to habitat types along north and
south (s) survey-routes, Evangeline Parish, Louisiana, 1986-88.


Number Loafing Foraging Flying
Date of flocks (Shrubs) (Stubble Cultivated Other) (All)


1986
Mar
Mar
Mar
Mar
Apr
Apr
Apr
Apr

1987
Mar
Mar
Mar
Mar
Apr
Apr
Apr

Mar
Mar
Mar
Mar
Apr
Apr
Apr

1988
Feb
Feb
Mar
Mar
Mar
Mar
Apr
Apr
Apr










Table 5-6. Area (ha) of cropland by stage of rice production along the north
and south survey-routes, Evangeline Parish, Louisiana, 1987. The total area
surveyed along each route was 12.8 km2; approximately 93%of cropland along
the north route and 85% along the south route was committed to the production
of rice in 1987.


Stage of rice production
Out-of- Flood- Drill- Seedling
Date Route production Tilled planted planted stand


Mar 10 N 91,630 22,610 4,760 0 0

S 103,550 545 4,905 0 0


Mar 23 N 79,730 15,470 23,800 0 0

S 90,470 0 18,530 0 0


Apr 6 N 58,310 32,130 11,900 8,330 8,330

S 63,220 27,250 13,080 327 5,123


Apr 21 N 47,600 29,750 11,900 3,570 26,180

S 52,000 29,430 7,630 320 19,620








Table 5-7. Summary of movements of 6 radio-instrumented red-winged blackbirds
that were monitored between 17 and 28 March 1986 in Evangeline Parish,
Louisiana. All birds were captured 1 km east of Millers Lake. Evening roost
locations were determined between 1800 and 2000 hours, and daytime feeding
locations between 0700 and 0900 hours.


Maximum
distance Number of Found
Dates from capture Days Nights Nights with
Sex Age" monitored site (km) found found in roost flocks

M ASY Mar 17-28 1 7 8 2 no

M SY Mar 19-25 2 2 3 3 yes

M SY Mar 19-28 8 4 7 7 yes

F AHY Mar 17-24 5 4 6 6 yes

F AHY Mar 17-23 6 5 2 1 no

F AHY Mar 17-24 2 3 4 4 yes

aASY = after second-year; SY = second-year; AHY = after hatching-year.

b The first date denotes date of capture/radio-instrumentation.








Radio contact with the 3 adult females was maintained between March 17-24.

One bird fed daily with flocks east of the lake and roosted in the

northeastern portion of the lake each night. The second female was recorded

roosting 50 m east of the lake the first night, then spent subsequent days and

nights in fallow fields <2 km from the lake; this bird appeared to be

solitary. The third female was located 3 mornings in feeding flocks east of

the lake and 4 nights in the Millers Lake roost.

Color marking. Color-marked birds from 4 flocks were sighted 16 times (10

orange, 4 green, 1 red, 1 pink), always as the only tagged bird in a flock,

during the 3 weeks, March 24-April 13, 1986. One flock color (white) was

never resighted.


DISCUSSION

Sex-segregated flocks of red-winged blackbirds remained active in rice

fields of Evangeline Parish throughout the spring (March-April) planting

seasons. Female-dominated flocks of redwings were observed most frequently

along the north route and were the primary cause of bird damage to newly

planted rice in this area. Although the total number of birds and mean flock

size declined with seasonal advance after mid-March, flocks of 25-500 birds

were active, causing damage to unprotected fields, along the north route until

the third week of April.

Large flocks (>1,000 birds) were observed along the north route in the

mid-March, but not in February or April. On January 7-10, 1986, March 5-8,

1986, and February 15-19, 1988, large flocks were observed in Jefferson Davis

and Acadia parishes, 40-80 km south and southwest of Millers Lake, but not in

Evangeline Parish. If the birds observed in Jefferson Davis and Acadia

parishes were birds that roosted at Millers Lake, their choice of feeding








sites might reflect local food-resource availability. During the winter,

local food-resource depression proceeds outward from Millers Lake as the

millions of birds feeding on waste grain and weed seeds create a ring of

depleted feeding sites around the lake; thus, by late winter, birds must fly

greater distances from the lake to locate food. Because fields near Millers

Lake are prepared for rice planting earlier than more distant fields, birds

are attracted to the closer and richer feeding sites diskedd fields) during

March. This shift to foraging sites near the lake results not only in

selective gleaning of weed seeds, insect larvae, and waste grains from fields,

but also possibly in extending residence time of flocking birds that might

otherwise migrate or begin territory establishment.

Daily movements of red-winged blackbirds in this rice-growing region are

poorly understood; however, there is weak evidence suggesting fidelity to

foraging areas. The radio-telemetry findings suggest that redwings, like

starlings, may forage in local areas, or daily activity centers (Bray et al.

1975, Martin 1977, Morrison and Caccamise 1985), for several days before

moving to a different locality. However, radio-instrumented birds may have

moved more often or farther than was detected because radio signals were often

lost and tracking efforts were discontinuous. Alternatively, the short radius

of movement identified in this study might reflect poor adjustment by birds to

transmitters (Gessaman and Nagy 1988, Wanless et al. 1988). Observations of

orange-tagged birds were made repeatedly in fields within a 1-km radius,

suggesting fidelity to feeding sites.

There was no evidence for stability of flock membership during the spring

planting season in the Millers Lake region of southwestern Louisiana. None of

the 62 color-marked birds was resighted in the company of another marked

individual. More importantly, flock size decreased with distance from the








roost, a finding consistent with a radial model of flock dispersal, i.e.,

large flocks break up as they disperse from the roost. The model is distance-

based and suggests a dynamic pattern of membership of birds in the flocks

feeding in the vicinity of the roost.




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