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Changing the Survival Formula for the Mojave Desert Tortoise

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CHANGING THE SURVIVAL FORMULA FOR THE MOJAVE DESERT TORTOISE (GOPHERUS AGASSIZII) THROUGH HEAD-STARTING by PEARSON A. MCGOVERN (Under the Direction of Tracey D. Tuberville and Clinton T. Moore) ABSTRACT Mojave desert tortoise populations are in decline and improving juvenile survival pre- release (head-starting) is being evaluated to augment populations. We released three treatment groups to evaluate the potential of combination head-starting. Treatment groups consisted of tortoises reared outdoors for 6-7 years (n = 30), outdoors for two years (n = 24), or indoors for one year followed by outdoors for one year (‘combination head- started’; n = 24). Combination head-starts were smaller than 6-7-year-old outdoor reared animals at release, and both groups were significantly larger than animals reared solely outdoors for two years. All treatment groups had nearly identical body conditions, while two-year-old outdoor animals had significantly softer shells than either of the other treatments pre-release. Combo head-starts exhibited strong post-release site-fidelity in comparison to the solely outdoor reared treatments. Size was a significant predictor of survival, with combo head-starts and 6-7-year-old outdoor head-starts exhibiting particularly high survival rates 10-months post-release. INDEX WORDS: Reptile, turtle, desert tortoise, Gopherus agassizii, population augmentation, head-starting, applied conservation, survivorship, recruitment CHANGING THE SURVIVAL FORMULA FOR THE MOJAVE DESERT TORTOISE (GOPHERUS AGASSIZII) THROUGH HEAD-STARTING by PEARSON A. MCGOVERN B.S., Texas A&M University, 2017 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2019 © 2019 PEARSON A. MCGOVERN All Rights Reserved CHANGING THE SURVIVAL FORMULA FOR THE MOJAVE DESERT TORTOISE (GOPHERUS AGASSIZII) THROUGH HEAD-STARTING by PEARSON A. MCGOVERN Major Professors: Tracey D. Tuberville Clinton T. Moore Committee: Kurt A. Buhlmann Jeff Hepinstall-Cymerman Electronic Version Approved: Ron Walcott Interim Dean of the Graduate School The University of Georgia December 2019 ACKNOWLEDGEMENTS Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the United States Government. Funding for this research was provided by the National Park Service (PSAC‐CESU Cooperative Agreement numbers P08AC00193 and P17AC01606), California Energy Commission (Agreement numbers 500‐10‐20 and EPC-16-038), and by the U.S. Department of Energy under award DE- FC09-07SR22506 and DE-EM0004391 to the University of Georgia Research Foundation. All procedures were conducted in accordance with permits issued by the U.S. Fish and Wildlife Service (TE-17838A-3), U.S. National Park Service (MOJA- 2018-SCI-0016 [under study MOJA-00258]), and California Department of Fish and Wildlife (SC-0011221). Animal protocols were approved by the University of Georgia under Animal Use Permits A2013 02-017-Y1-A0 and A2017 01-021-Y3-A3. I thank the Warnell School of Forestry and Natural Resources at the University of Georgia for funding through the Warnell Assistantship program. Roy C. Averill-Murray (USFWS - Desert Tortoise Recovery Office) and Rebecca Jones (California Department of Fish and Wildlife) provided assistance with permitting. Drs. Brian Todd and Mark Peaden provided immeasurable support and commitment to the completion of this project. Jacob Daly was instrumental in providing both field and analytical support. I also want to thank Melia Nafus, Max Steele, Carmen Candal, and Collin Richter for their valuable contributions in both husbandry and field work. iv It was my choice of committee that made this project and my entire master’s experience such an unforgettable time in my life. To Dr. Tracey Tuberville, a huge thank you for the time and effort you put into making this thesis a valuable addition to the conservation of the desert tortoise. The thoughtfulness and care that you place into each detail of the scientific process is something I will draw from for the rest of my career. To Dr. Kurt Buhlmann, I will always remember the many talks we shared on the excitement and joy that all things nature bring to us both. There is still so much to be seen and discovered, and I look forward to pursuing these countless opportunities with the unceasing excitement with which you live life. You and Tracey have solidified my love for turtles while expanding my skills and knowledge to really make a change! To Dr. Clint Moore, I have been impressed with you since the first day I walked into your office, and I will be forever thankful that you were willing to serve as my co-advisor. This project benefitted greatly from your perspective and unrivaled skill. To Dr. Jeff Hepinstall-Cymerman, incorporating your expertise was a crucial component of not only this study but my growth as a scientist. Dr. Mark Peaden (‘Marky mark’), you already know how much you’ve done for me and this project, so instead my thanks is for the friend you have been since day one. Having you and Hankster around made the field feel like home. A huge thanks to my lab mates, all of whom embraced me into their lab and always had my back. I also want to thank Adam Clause for showing me how to be a true professional in this field. When contemplating the pursuit of this degree, it was the support of loved ones that made the decision a no-brainer. My parents have supported me from day one and for v that I will be forever grateful. Cam, your love and endless patience deserve so much credit in the completion of this project. vi TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ............................................................................................... iv LIST OF TABLES ............................................................................................................. ix LIST OF FIGURES .............................................................................................................x CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW .........................................1 Literature Cited ..........................................................................................10 2 COMPARING OUTDOOR ONLY REARING VERSUS A COMBINATION OF INDOOR-OUTDOOR REARING FOR HEAD-STARTING THE MOJAVE DESERT TORTOISE (GOPHERUS AGASSIZII) .........................19 Introduction ................................................................................................19 Methods......................................................................................................23 Results ........................................................................................................34 Discussion ..................................................................................................38 Literature Cited ..........................................................................................45 3 SIZE AS A PREDICTOR OF POST-RELEASE SURVIVAL FOR HEAD- STARTED MOJAVE DESERT TORTOISES (GOPHERUS AGASSIZII) ....65 Introduction ................................................................................................65 Methods......................................................................................................69 Results ........................................................................................................78 vii Discussion ..................................................................................................80 Literature Cited ..........................................................................................85 4 SUMMARY AND CONCLUSIONS ..............................................................99 Literature Cited ........................................................................................102 viii LIST OF TABLES Page Table 2.1: Summary statistics of growth metrics for head-started Mojave desert tortoises (Gopherus agassizii) reared under two different husbandry treatments………………………………………………………………………...56 Table 2.2: Post-release movement metrics for head-started Mojave desert tortoises (Gopherus agassizii) from two treatment groups (Combination head-started and Outdoor head-started) released in September 2018 in the Mojave National Preserve, CA, USA ................................................................................................57 Table 3.1: Candidate models used to evaluate which predictors (Age, MCL, Total Displacement, Surface activity, Burrow switching) have the greatest effect on the post-release fate of head-started Mojave desert tortoises released into the Mojave National Preserve, CA, USA. ................................................................................94 Table 3.2: Predicted 10-month survival rates and 95% confidence intervals for juvenile Mojave desert tortoises derived using a generalized linear model with fate as a binary response variable and both MCL at release (mm) and proportion of surface activity as predictor variables ................................................................................95 ix LIST OF FIGURES Page Figure 2.1: Midline carapace length (MCL) of 2016 cohort juvenile Mojave desert tortoises (Gopherus agassizii) in two treatment groups ........................................58 Figure 2.2: Mass of 2016 cohort juvenile Mojave desert tortoises (Gopherus agassizii) in two treatment groups..............................................................................................59 Figure 2.3: Body condition
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