SREL Reprint #3611

Comparing husbandry techniques for optimal head-starting of the Mojave Desert Tortoise (Gopherus agassizii)

Pearson A. McGovern1,2, Kurt A. Buhlmann1, Brian D. Todd3, Clinton T. Moore4, J. Mark Peaden3,
Jeffrey Hepinstall-Cymerman2, Jacob A. Daly5, and Tracey D. Tuberville1

1Savannah River Ecology Lab, University of Georgia, Post Office Drawer E,
Aiken, South Carolina 29802, USA
2Warnell School of Forestry and Natural Resources, University of Georgia, 180 East Green Street,
Athens, Georgia 30602, USA
3Department of Wildlife, Fish and Conservation Biology, University of California, Davis, One Shields Avenue,
Davis, California 95616, USA
4U.S. Geological Survey, Georgia Cooperative Fish and Wildlife Research Unit, Warnell School of Forestry
and Natural Resources, University of Georgia, 180 East Green Street, Athens, Georgia 30602, USA
5U.S. Army Garrison Fort Hunter Liggett, Directorate of Public Works, Environmental Division,
Fort Hunter Liggett, California 93928, USA

Abstract: Desert tortoise populations continue to decline throughout their range. Head-starting (the captive rearing of offspring to a size where they are presumably more likely to survive post-release) is being explored as a recovery tool for the species. Previous head-starting programs for the Mojave Desert Tortoise (Gopherus agassizii) have reared neonates exclusively outdoors. Here, we explore using a combination of indoor and outdoor rearing to maximize post-release success and rearing efficiency. We assigned 68 neonates (2016 cohort) to one of two treatments: Outdoor head-starting (HS; n = 38), where neonates were reared exclusively in outdoor predator-proof enclosures, and Combination (Combo) HS (n = 30), where neonates were reared indoors for 1 y followed by outdoor rearing for 1 y. After 2 y of captive rearing, we released 24 Outdoor HS and 24 Combo HS juveniles in the Mojave National Preserve, California, USA, on 25 September 2018. We compared pre-release size, body condition, and shell hardness as well as first year post-release movement and survival between the treatment groups. Body condition was not significantly different between groups. Outdoor HS tortoises, however, were significantly smaller and had significantly softer shells than Combo HS tortoises. Released head-starts experienced 78.2% survival through their first year after release. Combo HS tortoises dispersed significantly shorter distances than Outdoor HS animals. Our findings that Combo HS animals were larger and had harder shells at release, and exhibited high survival but low dispersal following release, support the use of combination head-starting as a recovery tool for the Mojave Desert Tortoise.

Keywords: animal movement; Chelonian; conservation; head-starting; reintroduction; reptile; survival; threatened

SREL Reprint #3611

McGovern, P. A., K. A. Buhlmann, B. D. Todd, C. T. Moore, J. M. Peaden, J. Hepinstall-Cymerman, J. A. Daly, and T. D. Tuberville. 2020. Comparing husbandry techniques for optimal head-starting of the Mojave Desert Tortoise (Gopherus agassizii). Herpetological Conservation and Biology 15(3): 626-641.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).