EFFECTS OF THE INVASIVE EXOTIC APPLE SNAIL (Pomacea

164 Pages·2008·0.84 MB·English

EFFECTS OF THE INVASIVE EXOTIC APPLE SNAIL (Pomacea insularum) ON THE
SNAIL KITE (Rostrhamus sociabilis plumbeus) IN FLORIDA, USA

By

CHRISTOPHER CATTAU

A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2008
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© 2008 Christopher Cattau
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To Florida
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ACKNOWLEDGMENTS
I would like to thank my committee members (Wiley Kitchens, Phil Darby, and Ken
Meyer) for their mentorship, advice, and encouragement. Although not officially on my
committee, Julien Martin deserves the same gratitude, as his guidance and instruction, like that
of my committee, was indispensable to the development and completion of this work. I would
also like to thank all of the graduate students and field technicians who assisted with the
collection and processing of data, including Andrea Bowling, Brian Reichert, Sara Stocco,
Christina Rich, Danny Huser, Will deGravelles, Jean Olbert, Derek Piotrowicz, Nate Richardson,
Wesley Craine, Michaela Speirs, Melinda Conners, Bridget Deemer, Courtney Hooker, Andrea
Ayala, Melissa Desa, Carolyn Enloe, and all of my fellow coworkers at the Florida Fish and
Wildlife Cooperative Research Unit. I would like to express particular gratitude to Brian
Reichert for helping me with survival analyses. This project would not have been possible
without the unwavering dedication that each of the aforementioned individuals expressed for
conservation of the snail kite and the challenging (and often arduous) work each performed to
advance our knowledge of this endangered species. This cooperative effort has allowed us to
elucidate threats to the snail kite population and to increase our understanding of their ecology,
which will lead to more reliable conservation strategies. I am enormously grateful to everyone
involved with this work.

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TABLE OF CONTENTS

page
ACKNOWLEDGMENTS...............................................................................................................4
LIST OF TABLES...........................................................................................................................8
LIST OF FIGURES.........................................................................................................................9
LIST OF ABBREVIATIONS........................................................................................................13
ABSTRACT...................................................................................................................................14
CHAPTER
1 INTRODUCTION..................................................................................................................16
Study Population.....................................................................................................................17
Invasion of the Exotic Snail....................................................................................................19
Population Demography.........................................................................................................21
Study Objectives and Outline.................................................................................................23
2 EFFECTS OF THE EXOTIC APPLE SNAIL ON SNAIL KITE FORAGING
BEHAVIOR............................................................................................................................27
Background.............................................................................................................................28
Foraging Behavior...........................................................................................................28
A Note on Pomacea Measurements................................................................................30
The Native Apple Snail...................................................................................................30
The Exotic Apple Snail...................................................................................................31
Previous Foraging Studies...............................................................................................32
Prey availability........................................................................................................32
Prey negotiability and drop rate...............................................................................34
Searching and handling time....................................................................................35
Age and sex effects on foraging behavior................................................................36
Energy budgets and profitability..............................................................................37
Economic models of foraging behavior..........................................................................38
Predictions.......................................................................................................................39
Methods..................................................................................................................................40
Time Activity Budgets....................................................................................................40
Sampling locations...................................................................................................41
Selection of focal individuals...................................................................................41
Timing and duration of observations.......................................................................42
Classification of individual kites..............................................................................43
Collection of behavioral data...................................................................................45
Assumptions of behavioral observations..................................................................46

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Apple Snails.....................................................................................................................47
Collection and measurement of empty snail shells..................................................47
Collection and processing of live snails...................................................................48
Statistical Analysis and Confidence Intervals.................................................................49
Analysis of Foraging Behavior........................................................................................49
Searching and handling time....................................................................................51
Drop rate...................................................................................................................52
Capture rate (i.e., consumption rate)........................................................................52
Analysis of Energetics.....................................................................................................53
Regression models and estimation of average snail weight and caloric content......53
Profitability...............................................................................................................54
Daily activity times and energy budgets..................................................................54
Results.....................................................................................................................................56
Diet..................................................................................................................................56
Nutritional content of apple snails...........................................................................57
Live exotic snail measurements...............................................................................57
Empty snail shell dimensions...................................................................................58
Estimates of total snail weight.................................................................................58
Foraging Behavior...........................................................................................................59
Comparing adults, subadults, and juveniles.............................................................59
Effects of the exotic snail on average searching times.............................................60
Effects of the exotic snail on average handling times..............................................60
Effects of the exotic snail on drop rates...................................................................61
Effects of the exotic snail on capture rates...............................................................62
Effects of the Exotic Snail on Energetics........................................................................63
Estimates of caloric content.....................................................................................63
Profitability...............................................................................................................64
Validation of time activity budget extrapolations....................................................64
Daily activity patterns..............................................................................................65
Daily energy balances..............................................................................................65
Discussion...............................................................................................................................66
3 DEMOGRAPHIC EFFECTS OF THE EXOTIC APPLE SNAIL ON THE KITE.............104
Introduction...........................................................................................................................104
Reproduction.................................................................................................................105
Survival..........................................................................................................................105
Predictions.....................................................................................................................106
Methods................................................................................................................................107
Nesting Effort and Reproductive Success.....................................................................108
Survival..........................................................................................................................111
Results...................................................................................................................................113
Reproduction.................................................................................................................113
Nesting effort..........................................................................................................113
Nest success and productivity................................................................................114

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Survival..........................................................................................................................114
Apparent annual survival.......................................................................................114
Apparent monthly survival.....................................................................................115
Discussion.............................................................................................................................116
4 IS LAKE TOHOPEKALIGA FUNCTIONING AS AN ECOLOGICAL TRAP FOR
THE SNAIL KITE IN FLORIDA?......................................................................................137
Introduction...........................................................................................................................137
Ecological Trap Theory.................................................................................................137
A Hypothetical Example...............................................................................................137
Recent Nesting History..................................................................................................138
Lake Tohopekaliga........................................................................................................139
Methods................................................................................................................................139
Hypothesis 1..................................................................................................................139
Hypothesis 2..................................................................................................................140
Hypothesis 3..................................................................................................................140
Results...................................................................................................................................141
Hypothesis 1..................................................................................................................141
Hypothesis 2..................................................................................................................142
Hypothesis 3..................................................................................................................142
Discussion.............................................................................................................................143
APPENDIX DERIVATION OF DAILY ENERGY EXPENDITURE.......................................152
LIST OF REFERENCES.............................................................................................................153
BIOGRAPHICAL SKETCH.......................................................................................................164

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LIST OF TABLES
Table page

2-1 Number of TABs conducted by month and location in 2003, 2004, 2005, 2006 (post-
invasion) and in 1993, 1994, 1996 (pre-invasion).............................................................71
2-2 Nutritional contents of P. insularum..................................................................................71
2-3 Nutritional composition of P. insularum versus P. paludosa............................................72
2-4 Average daily activity pattern of the snail kite in Florida.................................................72
3-1 The number of nests initiated range-wide and the contribution from Toho, 1995-2007.121
3-2 Model selection table for apparent annual survival of kites hatched on Toho................121
3-3 Model selection table for apparent monthly survival of kites hatched on Toho..............121

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LIST OF FIGURES
Figure page

1-1 Major habitat fragments within the range of the snail kite in Florida...............................24
1-2 Confirmed locations, as of 2007, of the exotic snail (P. insularum) within the range
of the snail kite in Florida. Larger circles encompass multiple small populations in
close proximity...................................................................................................................25
1-3 Movements of approximately 50 radio-tagged adult snail kites among wetland
fragments over a one-year period. April 1992-April 1993................................................26
2-1 Relative sizes of exotic apple snails...................................................................................73
2-2 Measurement of snail shells...............................................................................................74
2-3 Location of apple snail traps on Toho................................................................................74
2-4 Linear regression models of exotic snail weight and morphology....................................75
2-5 Number of native and exotic apple snails captured per year with funnel traps on
Toho, 2005-2007................................................................................................................76
2-6 Proportion of native to exotic apple snails captured in five locations on Toho, 2005-
2007....................................................................................................................................77
2-7 Average length of apple snail shells collected from feeding perches and nests in nine
wetlands throughout the range of the snail kite, 2004-2007..............................................78
2-8 Average shell dimensions of native and exotic apple snails consumed by kites, 2004-
2007....................................................................................................................................79
2-9 Estimated whole weight of native and exotic snails negotiated by foraging kites
during the post-invasion era...............................................................................................80
2-10 Average handling times for adult, juvenile, and subadult kites on Toho and Kiss-
WCA3A during the post-invasion era................................................................................81
2-11 Average drop rates for adult, juvenile, and subadult kites on Toho and Kiss-WCA3A
during the post-invasion era...............................................................................................82
2-12 Average capture rates for adult, juvenile, and subadult kites on Toho and Kiss-
WCA3A during the post-invasion era................................................................................83
2-13 Average searching times for adult, subadult, and juvenile kites on Toho and Kiss-
WCA3A during the post-invasion era................................................................................84
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2-14 Average searching times for adult male and female kites on Toho and Kiss-WCA3A
during the post-invasion era...............................................................................................85
2-15 Average searching times for adult kites on Kiss and WCA3A during the post-
invasion era and on Toho during the pre- and post-invasion eras.....................................86
2-16 Average searching times for juvenile kites on Toho and Kiss-WCA3A during the
post-invasion era................................................................................................................87
2-17 Average handling times for adult male and female kites on Toho and Kiss-WCA3A
during the post-invasion era...............................................................................................88
2-18 Average handling times for adult kites on Kiss-WCA3A during the post-invasion era
and on Toho during the pre- and post-invasion eras..........................................................89
2-19 Average handling times for juvenile kites on Toho and Kiss-WCA3A during the
post-invasion era................................................................................................................90
2-20 Raw group drop rates for adult and juvenile kites on Toho and Kiss-WCA3A during
the post-invasion era..........................................................................................................91
2-21 Average drop rates for adult male and female kites on Toho and Kiss-WCA3A
during the post-invasion era...............................................................................................92
2-22 Average drop rates for adult and juvenile kites on Toho and Kiss-WCA3A during the
post-invasion era................................................................................................................93
2-23 Average capture rates for adult male and female kites on Toho and Kiss-WCA3A
during the post-invasion era...............................................................................................94
2-24 Average capture rates for adult kites on Kiss and WCA3A during the post-invasion
era and on Toho during the pre- and post-invasion eras....................................................95
2-25 Average capture rates for juvenile kites on Toho and Kiss-WCA3A during the post-
invasion era........................................................................................................................96
2-26 Estimated energetic content of native and exotic snails consumed by kites during the
post-invasion era................................................................................................................97
2-27 Average proportion of time spent flying during day-long and hourly observations by
kites on Toho, Kiss, and WCA3A in the post-invasion era...............................................98
2-28 Average capture rates achieved by foraging kites during morning, afternoon, and
evening observations on Toho and Kiss-WCA3A in the post-invasion era......................99
2-29 Average proportion of time spent flying by all kites on Kiss, Toho, and WCA3A
during the post-invasion era.............................................................................................100
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