Study

Effects of artificial rain on survivorship, body condition, and growth of head-started desert tortoises (Gopherus agassizii) released to the open desert

  • 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.

Action Category

Use irrigation systems

Action Link
Reptile Conservation

Head-start wild-caught reptiles for release: Tortoises, terrapins, side-necked & softshell turtles

Action Link
Reptile Conservation
  1. 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)

  2. 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)

Output references
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 19

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.


Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Butterfly Conservation People trust for endangered species Vincet Wildlife Trust