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Comparing growth and body condition of indoor-reared, outdoor-reared, and direct-released juvenile Mojave desert tortoises

December 1, 2018

Desert tortoise 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 years 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). Direct-release hatchlings were released shortly after hatching in September 2015 and monitored 1–2x 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 5x per week (Sep–Mar). Outdoor-reared tortoises had access to native forage and were given supplemental water and food once per week while active before winter dormancy. Indoor-reared tortoises grew >16x faster than direct-release tortoises and >8x faster than outdoor-reared tortoises. However, indoor-reared tortoises weighed less and had softer shells than comparatively sized older (3–4 year-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.

Citation Information

Publication Year 2018
Title Comparing growth and body condition of indoor-reared, outdoor-reared, and direct-released juvenile Mojave desert tortoises
DOI
Authors J. A. Daly, K. A. Buhlman, B. D. Todd, Clinton T. Moore, J. M. Peaden, T. D. Tuberville
Publication Type Article
Publication Subtype Journal Article
Series Title Herpetological Conservation and Biology
Series Number
Index ID 70227784
Record Source USGS Publications Warehouse
USGS Organization Coop Res Unit Atlanta

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