Effects of artificial rain on survivorship, body condition, and growth of head-started desert tortoises (Gopherus agassizii) released to the open desert
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Published source details
Nagy K.A., Hillard S., Dickson S. & Morafka D.J. (2015) Effects of artificial rain on survivorship, body condition, and growth of head-started desert tortoises (Gopherus agassizii) released to the open desert. Herpetological Conservation and Biology, 10, 535-549.
Published source details Nagy K.A., Hillard S., Dickson S. & Morafka D.J. (2015) Effects of artificial rain on survivorship, body condition, and growth of head-started desert tortoises (Gopherus agassizii) released to the open desert. Herpetological Conservation and Biology, 10, 535-549.
Actions
This study is summarised as evidence for the following.
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Use irrigation systems Action Link |
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Head-start wild-caught reptiles for release: Tortoises, terrapins, side-necked & softshell turtles Action Link |
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Use irrigation systems
A replicated, controlled study in 2003–2008 in a desert scrub site in California, USA (Nagy et al. 2015) found that irrigating the enclosures of Agassiz’s desert tortoises Gopherus agassizii during a head-starting programme resulted in similar hatching success and juvenile survival but higher growth rate compared to tortoises with no supplementary water. Tortoises in irrigated and non-irrigated enclosures had similar hatching success (irrigated: 67% across 5 nests; non-irrigated: 77% across 7 nests) and juvenile survival (90% of 15 tortoises). Growth rate was higher in the first year in irrigated enclosures (15% increase/year) than in non-irrigated enclosures (4% increase/year). For tortoises hatched in 2003, those from irrigated enclosures were larger than those from non-irrigated enclosures after four years (irrigated: 81 cm; non-irrigated: 55 cm; 3 from each treatment; data from other years not provided). Enclosures were constructed in a natural habitat setting, of which six were irrigated (25–38 mm of water delivered through a sprinkler system three times in late winter-spring) and nine received only natural rain. Wild, adult females (number not given) were brought into the pens to lay eggs before being re-released. Hatching success was determined by counting hatchlings and un-hatched eggs, and hatchlings were marked, measured and re-measured after a year.
(Summarised by: Maggie Watson)
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Head-start wild-caught reptiles for release: Tortoises, terrapins, side-necked & softshell turtles
A replicated study in 2003–2008 in a desert scrub site in California, USA (Nagy et al. 2015) found that very few released head-started Agassiz’s desert tortoises Gopherus agassizii survived for a year after release. Three of 47 tortoises (6%) survived for a year after release, with the rest dying from predation or other causes. Enclosures were constructed in a natural habitat setting using fencing and mesh netting, with six being irrigated and nine receiving only natural rain. Irrigated pens received 25–38 mm of water through a sprinkler system once in late winter and twice in spring. From 2003, wild, adult females (number not given) were brought into the pens to lay eggs before being re-released. Yearling tortoises (47 individuals) were released in 2004–2007, with 31 coming from irrigated enclosures and 16 from natural enclosures. Thirty-one were release close to the enclosures and 16 were released 1 km away. All were fitted with radio transmitters and located every two weeks during active time periods and monthly during winter.
(Summarised by: Maggie Watson, Katie Sainsbury)
