SREL Reprint #3484

Comparing growth and body condition of indoor-reared, outdoor-reared, and direct-released juvenile Mojave Desert Tortoises

Jacob A. Daly1,4, Kurt A. Buhlmann1, Brian D. Todd2, Clinton T. Moore3, J. Mark Peaden2,
and Tracey D. Tuberville1

1University of Georgia’s Savannah River Ecology Lab, Post Office Drawer E,
Aiken, South Carolina 29802, USA
2Department of Wildlife, Fish and Conservation Biology, University of California,
Davis, California 95616, USA
3U.S. Geological Survey, Georgia Cooperative Fish and Wildlife Research Unit, University of Georgia,
Athens, Georgia 30602, USA
4Center for Environmental Management of Military Lands, Colorado State University,
1490 Campus Delivery, Fort Collins, Colorado 80523, USA

Abstract: Desert Tortoise (Gopherus agassizii) populations have declined, and head-starting hatchlings in captivity until they are larger and older, and presumably more likely to survive, is one strategy being evaluated for species recovery. Previous studies have reared hatchlings in outdoor, predator-proof pens for 5–9 y before release, in efforts to produce hatchlings in excess of 100–110 mm midline carapace length that are believed to be predation-resistant. We began a comparative study to evaluate indoor-rearing to shorten this rearing period by facilitating faster initial growth. We assigned 70 neonates from the 2015 hatching season to three treatment groups: (1) indoor-reared (n = 30), (2) outdoor-reared (n = 20), and (3) direct-release (n = 20). We released direct-release hatchlings shortly after hatching in September 2015 and monitored them 1–2 times per week with radio telemetry. We head-started the indoor- and outdoor-reared treatment groups for 7 mo before releasing them in April 2016. Indoor-reared tortoises were fed five times per week (September to March). Outdoor-reared tortoises had access to native forage and we gave them supplemental water and food once per week while active before winter dormancy. Indoor-reared tortoises grew > 16 times faster than direct-release tortoises and > 8 times faster than outdoor-reared tortoises; however, indoor-reared tortoises weighed less and had softer shells than comparatively sized older (3–4 y-old) tortoises raised outdoors. Increasing the duration of the indoor-rearing period or incorporating a combination of both indoor and later outdoor husbandry may increase shell hardness among head-starts, while retaining the growth-promoting effect of indoor rearing and shortening overall captivity duration.

Keywords: body condition; Chelonian; conservation; husbandry; morphology; reptile; threatened; wildlife management

SREL Reprint #3484

Daly, J. A., K. A. Buhlmann, B. D. Todd, C. T. Moore, J. M. Peaden, and T. D. Tuberville. 2018. Comparing growth and body condition of indoor-reared, outdoor-reared, and direct-released juvenile Mojave Desert Tortoises. Herpetological Conservation and Biology 13(3): 622-633.

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