Table Of ContentTHE REPRODUCTIVE AND FORAGING ECOLOGY OF
WADING BIRDS (CICONIIFORMES) AT LAKE OKEECHOBEE, FLORIDA
By
JEFFREY PHILLIP SMITH
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1994
ACKNOWLEDGMENTS
I am first and foremost indebted to my graduate committee chair Michael
Collopy for selecting me to administer this project and for providing guidance and
logistic support throughout the study. Financial support for my research was provided
through the 5.5-year Lake Okeechobee Ecosystem Study contract and a graduate
research assistantship funded by the South Florida Water Management District, West
Palm Beach, Florida. Seasonal field assistants John Humphrey, Todd Morris, Michael
Plotkin and Chris Goguen, laboratory assistants Robin Sansom, Anthony Novack, Lydia
Flewelling, Kim Bjorgo, Darryl Sweetay and Gustavo Hernandez, project members Tim
Harris and Kent Williges, and university associate Howard Jelks all provided essential
field and laboratory support during the project. James Wyatt Enterprises of
Homestead, Florida, and American Aviation, Inc. of Pompano Beach, Florida, provided
aircraft services. am particularly indebted to John Richardson for providing guidance
I
throughout the study in the area of GIS and computer support. Early discussions with
university associate Howard Jelks and with Wayne Hoffman, Tom Bancroft and Rick
Sawicki ofthe National Audubon Society, Tavernier, Florida, helped in the development
ofthe study. Graduate committee member Peter Frederick provided critical guidance
throughout the study with regards to wading bird ecology, and filled an important role
as committee chairman during the final year ofthe study. Graduate committee member
Kenneth Portier provided essential statistical guidance. Discussions with university
associate Rob Bennetts provided additional statistical guidance. Graduate committee
member Carole Mclvor provided guidance and support throughout the study and filled
an important role as committee cochair from 1992-1993. am also indebted to
I
committee member Wiley Kitchens for his participation and to the other staff ofthe
Florida Cooperative Fish and Wildlife Research Unit for logistic support during the
study. Final committee member Mark Brown also contributed to the development ofthe
study and provided specific guidance in the area of population modeling. would also
I
like to extend thanks to the following people for their constructive reviews of early drafts
of various chapters: Nick Aumen, Susan Gray, Pete David, Chuck Hanlon and Karl
Havens ofthe South Florida Water Management District, and Malcolm Coulter and Tom
Sabine.
Lastly, wish to extend special thanks to my wife Ruthe Smith and my parents
I
Phillip and Julie Smith for their constant love and support.
in
TABLE OF CONTENTS
page
ACKNOWLEDGMENTS
ii
LIST OF TABLES vii
LIST OF FIGURES ix
ABSTRACT
xiii
CHAPTERS
PROJECT INTRODUCTION
1 1
Impetus For the Lake Okeechobee Ecosystem Study 1
Wading Birds in Southern Florida and at Lake Okeechobee . . 3
Wading Bird Project Objectives 9
Dissertation Format and Content 13
2 FORAGING HABITAT SELECTION IN RELATION TO
HYDROLOGY AND VEGETATIVE COVER 14
Introduction 14
Methods 18
Study Area and Subjects 18
Survey Design 20
Hydrology, Vegetation, and Analyses of Habitat
Selection 23
Results and Initial Discussion 27
Abundance of Foraging Birds and Hydrologic Trends .... 27
Patterns of Distribution and Hydrologic Trends 34
Vegetation Maps and Changes During the Study 40
Habitat Selection Analyses 50
General Discussion and Conclusions 64
Analytical Caveats 64
Foraging Habitat Selection 67
Management Implications 74
IV
FORAGING-FLIGHT DYNAMICS AND PATTERNS OF
HABITAT USE WITH RELATION TO NEST PRODUCTIVITY,
AND FORAGING SOCIABILITY AMONG FOUR NESTING
SPECIES 82
Introduction 82
Study Area and Methods 88
Study Area 88
Field Methods 89
Analytical Methods 90
Results 95
Foraging Flight Dynamics and Patterns of Habitat Use ... 95
Foraging Sociability 122
Discussion 126
Foraging-Flight Dynamics, Patterns of Habitat Use
and Nest Productivity 126
Foraging Sociability 133
COLONY DYNAMICS, NEST SUCCESS AND
PRODUCTIVITY, AND CAUSES OF NEST FAILURE 139
Introduction 139
Methods 141
Study Species 141
Colony Locations and Composition 141
Nest Monitoring 142
Nest Success and Productivity 144
Identifying Causes of Nest Failure 147
Results and Discussion 148
Colony Establishment and Success 148
Individual-Nest Success and Productivity 158
Causes of Nest Failure 180
Conclusions and Management Implications 191
ENVIRONMENTAL DETERMINANTS OF NEST FAILURE:
LOGISTIC REGRESSION ANALYSES 197
Introduction 197
Study Area and Methods 201
Study Area 201
Nest Monitoring 202
Datasets and Regression Analyses 205
Results 215
Summary of Nesting Activity and Climatic and
Hydrologic Trends 215
Regression Results 219
Discussion 248
Model-Building Strategy 248
Date of Nest Initiation Effects 250
Nest Height and Cover Effects 251
v
Temperature Effects 253
Hydrologic Effects 254
Conclusion 260
6 AN ENERGY-CIRCUIT POPULATION MODEL FOR
GREAT EGRETS 264
264
Introduction
Study Area 269
Model Formulation and Quantification 269
Prey Population Dynamics 274
Prey Consumption by Wading Birds 279
Great Egret Immigration and Emigration 282
Recruitment of Breeding Birds and Reproductive
Dynamics 289
Simulation Results and Discussion 294
Prey Population Dynamics 294
Foraging-Bird Population Dynamics 299
Recruitment of Breeding Birds 303
Reproductive Success and Productivity 307
Conclusion 311
7 PROJECT SUMMARY 314
Species Studied 314
Results and Observations 315
Management Recommendations 329
APPENDICES
A FORAGING WADING BIRD POPULATION ESTIMATES BY
SPECIES AND SURVEY 331
B RATE COEFFICIENT CALCULATIONS FOR GREAT
EGRET POPULATION MODEL 343
REFERENCES 346
BIOGRAPHICAL SKETCH 357
VI
LIST OF TABLES
Table page
2-1 Vegetation types represented on annual, 9.15-m x 9.15-m
resolution, classified satellite-image maps produced by
Richardson and Harris (1994). Cover statistics forthese classes
formed the basis for the 1-km x 1-km resolution classification
scheme developed to match the wading bird survey grid. 41
2-2 Identification codes and composition ofvegetation community
classes assigned to 1-km x 1-km survey grid cells for habitat
selection analyses. 42
3-1 Foraging flight sample sizes (total number of birds followed to
landing) by species, year, and nesting colony. 96
3-2 Chi-square tests for each species comparing annual proportions
of foraging flights that ended on and offthe lake. 98
3-3 Numbers of on and off-lake flights in relation to mean lake stage
(m NGVD), with data pooled across years. 99
3-4 Analyses of variance of flight distances (km) versus year for each
species, with medians and ranges of flight distances shown for
comparison. 100
3-5 Chi-square analysis for Great Egrets examining patterns of
habitat use in relation to mean lake stage (m NGVD), with data
pooled across years. 102
3-6 Annual mean foraging flight distances compared to lakewide
estimates of nestling-period success and nestling production by
species. 105
3-7 Snowy Egret habitat selection in relation to mean lake stage (m
NGVD), with data pooled across years. 111
3-8 Tricolored Heron habitat selection in relation to mean lake stage
(m NGVD), with data pooled across years. 116
3-9 White Ibis habitat selection in relation to mean lake stage (m
NGVD), with data pooled across years. 120
3-10 Chi-square tests examining species' tendencies to travel in
groups to foraging locations. 123
3-1 1 Chi-square tests examining species' tendencies tojoin other birds
at foraging sites, and an ANOVA examining species' differences
with regards to the size ofthe feeding flocks each tended to join. 125
vii
3-12 Nesting adult mean and maximum foraging-flight distances
derived from various studies. 127
4-1 Interannual nesting colony turnover rates: 1989-1992. 153
4-2 Comparison of annual peak nest and species counts at primary
interior-marsh and island colony sites. 154
4-3 Proportion of successful, failed, aborted (no eggs laid), and
uncertain-fate nesting colony initiations by species and year. 157
4-4 Peak-total and marked nest counts, and nest success and
productivity statistics by year for Great Blue Herons. 159
4-5 Peak-total and marked nest counts, and nest success and
productivity statistics by year for Great Egrets. 162
4-6 Hatched-nest survival in relation to nestling age: examination of
bias associated with using threshold ages to estimate nest
success. 165
4-7 Peak-total and marked nest counts, and nest success and
productivity statistics by year for Snowy Egrets. 168
4-8 Peak-total and marked nest counts, and nest success and
productivity statistics by year for Tricolored Herons. 169
4-9 Peak-total and marked nest counts, and nest success and
productivity statistics by year for Little Blue Herons. 174
4-10 Peak-total and marked nest counts, and nest success and
productivity statistics by year for White Ibises. 177
4-1 1 The fate of marked nests and causes of nest failure by species:
1989-1991. 181
5-1 Nest sample sizes considered in logistic regression analyses by
species, year, and colony. 204
5-2 Summary of independent variables and models analyzed. 209
5-3 Summary of variable and reference-model selection and
verification processes. 213
5-4 Logistic regression models identifying environmental
determinants of nest failure for each species. 220
5-5 Means and ranges of independent variables included in the full-
cycle or nestling models for each species. 224
5-6 Example of procedure for interpreting relationships when several
interactions involved; example is for interpreting effects of
minimum temperature on Great Egret nest success based on full-
cycle model. 230
6-1 Comparisons of observed nest production statistics (Chapter 4)
and simulated responses with and without forced adjustments to
annual mean clutch sizes, 1991 and 1992 egg survival rates, and
the 1990 food supply. 310
viii
LIST OF FIGURES
Figure page
2-1 A geographic overview ofthe Lake Okeechobee area. 16
2-2 Aerial survey program used to document the distribution and
abundance of foraging wading birds. 21
2-3 Comparison of daily lake stage records from open-water and
interior-marsh gauging stations, shown in relation to estimates of
average daily rainfall for the Lake Okeechobee basin: January
1988 - September 1992. 25
2-4 Combined-species wading bird population estimates, excluding
birds at nests, in relation to daily lake stage: August 1988 -
August 1992. 28
2-5 Population estimates for White Ibises, Great Egrets, and Small
White Ardeids (i.e., Snowy Egrets and some immature Little Blue
Herons), excluding birds at nests: August 1988 - August 1992. 28
2-6 Population estimates for Glossy Ibises, Great Blue Herons, and
Small Dark Ardeids (i.e., Tricolored and adult Little Blue Herons),
excluding birds at nests: August 1988 - August 1992. 29
2-7 Population estimates for Wood Storks, Roseate Spoonbills, and
Great White Herons: August 1988 - August 1992. 29
2-8 Non-linear regression of combined-species wading bird
population estimates versus a) daily lake stage and b) 90-day
antecedent surface-water drying rate. 32
2-9 Select 1989 combined-species wading bird density maps forthe
transect and Eagle Bay island areas, shown in relation to plots of
mean water depth derived from the OKEEHYDRO hydrologic
model (Richardson and Hamouda 1994). 35
2-10 Select 1990 combined-species wading bird density maps for the
transect and Eagle Bay Island areas, shown in relation to plots of
mean water depth derived from the OKEEHYDRO hydrologic
model (Richardson and Hamouda 1994). 36
2-1 1 Select 1991 combined-species wading bird density maps for the
transect and Eagle Bay Island areas, shown in relation to plots of
mean water depth derived from the OKEEHYDRO hydrologic
model (Richardson and Hamouda 1994). 37
IX
2-12 Select 1992 combined-species wading bird density maps forthe
transect and Eagle Bay Island areas, shown in relation to plots of
mean water depth derived from the OKEEHYDRO hydrologic
model (Richardson and Hamouda 1994). 38
2-13 One km2-scale vegetative cover maps for 1989 and 1990 derived
maps
from 9.15-m x 9.15-m resolution, classified-satellite-image
produced by Richardson and Harris (1994). 44
2-14 One km2-scale vegetative cover maps for 1991 and 1992 derived
maps
from 9.15-m x 9.15-m resolution, classified-satellite-image
produced by Richardson and Harris (1994). 46
2-15 Wading bird foraging habitat selection in relation to vegetation
assemblages in 1989: Chi-square tests of independence with bird
densities summed across surveys. 53
2-16 Wading bird foraging habitat selection in relation to vegetation
assemblages in 1990: Chi-square tests of independence with bird
densities summed across surveys. 54
2-17 Wading bird foraging habitat selection in relation to vegetation
assemblages in 1991: Chi-square tests of independence with bird
densities summed across surveys. 55
2-18 Wading bird foraging habitat selection in relation to vegetation
assemblages in 1992: Chi-square tests of independence with bird
densities summed across surveys. 56
3-1 A geographic overview ofthe Lake Okeechobee area showing
the locations of nesting colonies used by the four study species,
and showing the locations of lake stage and rainfall gauging
84
stations.
3-2 Daily lake stage and total daily rainfall from January 1989 through
86
August 1992.
3-3 Annual distributions of nesting Great Egret foraging flights: 1989-
97
1992.
3-4 Plots by species of colony-specific estimates of nestling-period
success and nestling production in hatched nests versus mean
106
foraging-flight distances.
3-5 Plots by species of the percentages of marked nests that failed-
summed over 15-day periods-versus mean foraging-flight
198
distances.
3-6 Annual distributions of nesting Snowy Egret foraging flights:
109
1989-1992.
3-7 Annual distributions of nesting Tricolored Heron foraging flights:
114
1989-1991.
3-8 Annual distributions of nesting White Ibis foraging flights: 1989-
118
1992.
