Kelso Dunes and Providence Mountains, San Bernardino Co., CA Copulating Sidewinder Rattlesnakes (Crotalus cerastes), Kelso Dunes, CA MATE-LOCATION BEHAVIOR OF TIMBER (CROTALUS HORRIDUS) AND SIDEWINDER (CROTALUS CERASTES) RATTLESNAKES DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of Ohio State University By Bradford Houston Coupe, B.S., M.S. ***** Ohio State University 2005 Dissertation Committee: Approved by Thomas E. Hetherington, Adviser Tom Waite __________________________________ W. Mitch Masters Adviser Graduate Program in Evolution, Ecology, & Organismal Biology Copyright by Bradford Houston Coupe 2005 ABSTRACT For many animals mate location is a matter of following widely broadcast signals (e.g., visual, auditory) to the signaler. However, due to their morphology or habitat many animals are not able to broadcast signals widely. In these cases little is known about the methods used in mate location. I discuss three hypothesized mate-location methods potentially used in these situations by timber (Crotalus horridus) and sidewinder (Crotalus cerastes) rattlesnakes. (1) It has been suggested that scent-trailing of lipid-based pheromones left by females is an integral part of snake mate location. (2) Because many snakes are long-lived (some >25 years) and have a capacity for spatial memory, it is likely that males can use prior experience to remember female locations. (3) Males might use an efficient search strategy by moving in a pattern that will maximize their chances of encountering a female. A fourth method, males patrolling their home range for females, is suggested by movements made by some male sidewinders. Individuals of both species were tracked using radiotelemetry. I describe the movements made by males that brought them in contact with females. I also discuss various aspects of sidewinder spatial biology and their relevance to mate-location methods. In addition, I developed an individual-based, spatially explicit simulation of mate-location methods using parameters appropriate for sidewinders. ii Each hypothesized mate-location method is compatible with at least some of the data. As sidewinder males were able to follow female trails for >100 m, it is clear that trail following is an important mate-location method that is likely used in conjunction with the other methods. Thus, I think males are searching for female trails rather than for females themselves. In the model, both prior experience (with map-and-compass navigation) and efficient searching (straight-line) performed well, with males having a >40% chance of finding a female during a search. Timber and sidewinder males might use different mate-location methods as many sidewinder movements did not appear as directed as those of timbers. iii DEDICATION Dedicated to my grandparents: Hope Kimbrough McCroskey Helen Whitehill Coupe Joseph Stewart McCroskey Ernest Lincoln Coupe iv ACKNOWLEDGMENTS No work of this magnitude is undertaken alone despite the single authorship indicated on the title page. The list of people who made this possible is interminable, so here I will thank those individuals who played major roles (hang on, there are still a lot of them). If I have forgotten anyone I deeply apologize. First and foremost, I thank my wife Melinda for her love, friendship, and support. She endured long periods of my absence without complaint and was always willing to listen to my ramblings and grumblings concerning the work I was doing, even if I wasn't listening to hers. I'll never be able to fully repay her for the support she's given me during this time, but I'll keep trying the rest of my life. I am, quite plainly, lucky to be married to her. She is my best friend. I love you lady! While I'm thanking those in my household, I must thank my dog Shelly. She also endured long periods of my absence, but unlike Melinda she never understood why I left her for months at a time. Still, she was always the most enthusiastic individual upon my return. Melinda's cat, Henry, I thank for tolerating my existence when I was home and for keeping Shelly company when I wasn't. My parents, Jill and Brad, have always supported everything I've tried to do even when it was unconventional (like studying rattlesnakes). Their support has been unwaivering and that has helped pull me through times of frustration. They have taught me a great deal about life and how to live it, though I don't think I ever let on that it was v true. They have been interested in my research and always made the effort to understand it. The feeling of being able to give some knowledge back to them is unparalleled. My grandparents – to whom I've dedicated this work – have, each in their own very different way, infused my personality and life with traits and lessons of their own. Helen Whitehill “Grama” Coupe, through kind words and stern, taught me about honor and fairness. She was a beloved leader of her clan and all who met her learned those lessons. Ernest Lincoln “Gramp” Coupe taught me what little I know on the piano, but mostly taught me to live my life so that I'm happy. The memories I have of him all include his laughter and smile. Joseph Stewart “Granddaddy” McCroskey was not known to be a patient man, but ironically patience was his lesson. It is a lesson I'm still learning, but all the more powerful that it came from him. Only Hope Kimbrough “Grandmama” McCroskey survives to see me complete this work. Perhaps the lesson I have learned from her is perseverance. Every time I talk to her she tells me she is proud of me and confident that I will excel. Her unfailing encouragement has always been much needed support, especially when I wasn't so sure of myself. I have been lucky to have the collective kindness, love, and support of these four amazing people. The other members of my extended family – aunts, uncles, and cousins too numerous to name – have likewise been unfailing in their support. I am always amazed at how genuinely interested they are in what I'm doing. That has meant a lot to me, though I don't think I've ever really said it. I especially thank Anita for being the thoughtful, wonderful person she is. My in-laws – Janet & Don and Dan & Sue – and their families have been so supportive and welcoming of me that at times I just didn't know how to respond! In many ways what I am and what I do are so different from them that in lesser families it might cause tension, but their support of me, my work, and my marriage with Melinda vi defies description. As individuals and as groups, they are models of how families should work. Academically, I would not have completed this work without the help of some phenomenal teachers. Mr. George Wright, my high school biology teacher, was the first teacher of any kind to really spark my interest in academics. Although biology is, of course, fascinating, it was Mr. Wright himself that motivated me. Had he taught history or art what follows might have differed somewhat in subject matter. John Winkelmann and Kazuo Hiraizumi opened my eyes as an undergraduate to two very different worlds. John to the world of vertebrate and field biology and Kazuo to molecular genetics. Both taught me a great deal and that I chose the path of the former reflects only the greater allure to a wide-eyed city boy of snakes when compared with fruit flies. I hope I can be to my students what my professors were to me. As a graduate student, I benefited greatly from the direct and indirect tutelage of many. My adviser, Tom Hetherington, deserves tremendous thanks for giving me enough rope to hang myself, but not quite letting me do it. His faith in my abilities has allowed me to try things that I otherwise wouldn't have and I learned much even and especially from those things that didn't quite work out. His patience to let me make mistakes and help me sort out the resulting mess is much appreciated. Tom Waite has an uncanny ability to look at problems in novel ways and suggest numerous possible solutions. I benefited as a scientist and as a person from his generously donating hours and hours of his time. Occasionally I was frustrated, but it was always clear that in his role as committee member he was helping me maintain my course and the work that follows is far better for it. In his role as friend and mental sparring partner he taught me much about how and why science is done. vii Mitch Masters is a quiet and unassuming person, but his help to me when I needed it is not overlooked. Mitch was always willing to think critically and to challenge both of us not just with my dissertation, but with any subject that would come up. As such Mitch is a valued member of my committee. As a result of scheduling, Jerry Downhower was not able to serve as member of my dissertation committee, though his support and suggestions in that arena were helpful and appreciated. However, he is in many ways my teaching rather than research role model. Over many quarters I learned from him a craft that will serve me well the rest of my career. There is much that Jerry would recognize in the style and structure of the courses I'm teaching at Castleton State College. Libby Marschall did not serve on my committee and was not directly involved in my research, but her courses on theoretical ecology were the best courses I've ever taken anywhere.