Comparing growth and body condition of indoor-reared, outdoor-reared, and direct-released juvenile Mojave desert tortoises
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 |
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Title | Comparing growth and body condition of indoor-reared, outdoor-reared, and direct-released juvenile Mojave desert tortoises |
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 |
Index ID | 70227784 |
Record Source | USGS Publications Warehouse |
USGS Organization | Coop Res Unit Atlanta |