FORAGING ECOLOGY OF BREEDING SNAIL KITES (Rostrhamus sociabilis plumbeus) ON LAKE TOHOPEKALIGA, FLORIDA, USA By KYLE E. PIAS 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 2012 1 © 2012 Kyle E. Pias 2 To the kites 3 ACKNOWLEDGMENTS I would first like to thank the field technicians who participated in this project; they are far too often underappreciated, yet their role could not be more vital. Cari Sebright, Shannon Behmke, Megan Ford, Nick Belfry, Carley Jennings, Jeremy Wood, and Emily Butler all spent untold and underpaid hours on airboats watching snail kites, and the project could not have been completed without them. I cannot adequately express my gratitude to my advisor, Wiley Kitchens. He has been a constant supporting force throughout this project. His wisdom and guidance have been invaluable as has his confidence in my abilities to move forward on my own. I have grown immensely as an ecologist because of my time with him and I cannot thank him enough. My committee members Joan Morrison and Rob Fletcher were incredible throughout the process. Joan Morrison’s support and guidance started me down the path of conservation biology when I was a freshman at Trinity College and she once again lent me her knowledge and experience with this project. Rob Fletcher was an amazing source of information and guidance and I would have floundered through much of the analyses without his help. I need to thank the agencies and agency personnel who provided assistance and funding for this work; the United States Fish and Wildlife Service and the Florida Fish and Wildlife Conservation Commission. Paul Souza, Sandra Sneckenberger, and Zach Welch facilitated the partnerships with their respective agencies which both contributed generously to the project. I thank all of my friends and colleagues at the Florida Coop. Brian Reichert, Chris Cattau, Christa Zweig, Zach Welch, Melissa Desa, Lara Drizd, Ellen Robertson, 4 Rebecca Wilcox, and Natalie Williams all helped towards the completion of this project. A special thank you is owed to Brian Reichert who initially hired me to the snail kite project in 2008 as a field technician and opened the world of airboats and snail kites to me. Jean Olbert has been an integral part of my life, both professionally and personally, since I started on the project. She has helped me with every aspect of my work and improved me dramatically as a scientist and as a person. Her intelligence, patience, kindness, pragmatism, and skill in the field are unparalleled and I would not have been able to finish this without her. Finally I would like to thank my parents, David and Wendy, for their constant support in all that I do. They instilled in me my passion to learn and my deep love for the natural world and I would not be where I am today without them. 5 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 8 LIST OF FIGURES .......................................................................................................... 9 ABSTRACT ................................................................................................................... 11 CHAPTER 1 BACKGROUND ...................................................................................................... 13 The Snail Kite ......................................................................................................... 13 Population Status .................................................................................................... 14 The Island Apple Snail ............................................................................................ 15 Lake Tohopekaliga ................................................................................................. 16 Study Objectives ..................................................................................................... 17 2 INFERENCES ABOUT SNAIL AVAILABILITY FROM THE FORAGING BEHAVIOR OF BREEDING SNAIL KITES ON LAKE TOHOPEKALIGA................ 22 Introduction ............................................................................................................. 22 Methods .................................................................................................................. 25 Data Collection ................................................................................................. 25 Home Range Construction ............................................................................... 27 Foraging Behavior Indices Calculations ........................................................... 28 Foraging Substrate Delineation ........................................................................ 29 Analysis of Foraging Substrate Communities ................................................... 30 Comparing Foraging Behaviors between Foraging Substrate Communities .... 30 Foraging Rates and Nest Fates ........................................................................ 31 Relationships between Home Range Area and Foraging Behaviors ................ 31 Results .................................................................................................................... 31 Multivariate Analysis of Foraging Substrate Communities................................ 32 Foraging Behaviors in Different Foraging Substrate Communities ................... 33 Foraging Rates between Years and Nest Fates ............................................... 33 Relationships between Home Range Area and Foraging Behaviors ................ 33 Discussion .............................................................................................................. 34 Management Recommendations ...................................................................... 38 3 ROLE OF HABITAT STRUCTURE IN FORAGING SUBSTRATE USE BY BREEDING SNAIL KITES ON LAKE TOHOPEKALIGA ......................................... 49 Introduction ............................................................................................................. 49 Methods .................................................................................................................. 51 6 Data Collection ................................................................................................. 51 Success Rates in Different Foraging Substrates .............................................. 53 Patterns in Foraging Substrate Use ................................................................. 53 Results .................................................................................................................... 55 Foraging Substrate Use ................................................................................... 55 Success Rates in Different Foraging Substrates .............................................. 56 Trends in Foraging Substrate Use .................................................................... 56 2010 ........................................................................................................... 56 2011 ........................................................................................................... 57 Discussion .............................................................................................................. 57 4 CONCLUSIONS ..................................................................................................... 80 LIST OF REFERENCES ............................................................................................... 84 BIOGRAPHICAL SKETCH ............................................................................................ 91 7 LIST OF TABLES Table page 1-1 Characteristics of the Florida apple snail and island apple snail relevant to each species’ role as a food resource for snail kites. ......................................... 19 2-1 Description of vegetation classes used in delineating foraging substrate within snail kite home ranges.............................................................................. 40 2-2 Indicator values for each foraging substrate class within the foraging communities in snail kite home ranges on Lake Tohopekaliga. .......................... 41 2-3 Significance of the pairwise differences in the least square means estimates of foraging rates for foraging communities of snail kite home ranges on Lake Tohopekaliga. ..................................................................................................... 42 2-4 Significance of the pairwise differences in the least square means estimates of perch hunting frequencies for foraging communities of snail kite home ranges on Lake Tohopekaliga. ........................................................................... 42 3-1 Frequency of use of each foraging substrate on Lake Tohopekaliga in 2010 and 2011. ........................................................................................................... 65 3-2 Frequency of foraging substrate use in shallow water depths (0-0.5 m). ............ 65 3-3 Frequency of foraging substrate use in mid water depths (0.5-1 m). .................. 66 3-4 Frequency of substrate use in deep water depths (>1 m)................................... 66 3-5 Frequency of substrate use in off lake areas. ....................................................