Study

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

  • Published source details Daly J.A., Buhlmann K.A., Todd B.D., Moore C.T., Peaden J.M. & Tuberville T.D. (2018) Comparing growth and body condition of indoor-reared, outdoor-reared,and direct-released juvenile mojave desert tortoises. Herpetological Conservation and Biology, 13, 622-633.

Actions

This study is summarised as evidence for the following.

Action Category

Release reptiles born/hatched in captivity from wild-collected eggs/wild-caught females without rearing

Action Link
Reptile Conservation

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

Action Link
Reptile Conservation

Relocate nests/eggs for artificial incubation: Tortoises, terrapins, side-necked & softshell turtles

Action Link
Reptile Conservation
  1. Release reptiles born/hatched in captivity from wild-collected eggs/wild-caught females without rearing

    A before-and-after study in 2015–2016 in desert scrubland in California, USA (Daly et al. 2018) found that almost all released captive-born desert tortoise Gopherus agassizii hatchlings from wild-collected eggs survived at least six months in the wild, and that hatchlings that were head-started outdoors or indoors had similarly high survival during their head-starting. Survival rates of released hatchlings was similar to that of tortoises during head-starting over six months (released: 15 of 20, 75% survived; during outdoor head-starting: 20 of 20, 100%; during indoor head-starting: 29 of 30, 97%). After six months, released tortoises in the wild were a similar size compared to tortoises during outdoor headstarting (released: 49 mm long; during outdoor head-starting: 51 mm long), but were smaller than tortoises during indoor head-starting (78 mm long). The relative weights and body conditions of tortoises were similar after six months, regardless of rearing approach (see original paper for details). Eggs from 25 wild adult female tortoises were collected, incubated in artificial burrows outside and hatched in August–September 2015. In September 2015, seventy hatchlings (21–46 days old) were either released directly into the wild (20 hatchlings) or moved to either an indoor enclosure (30 hatchlings) or outdoor enclosure (20 hatchlings). Direct-release hatchlings were released in a 0.7 km2 unfenced area and monitored using radio telemetry twice weekly until November 2015, once a week in winter and twice weekly from March 2016. The indoor enclosure was climate controlled and hatchlings were fed five times/week and watered weekly (see paper for details). The outdoor enclosure (30 x 30 m) was semi-natural, predator-proof and hatchlings were provided supplemental food and water weekly until the end of the active season (November 2015). Hatchling morphometrics were assessed prior to their release or before being moved to their head-starting enclosure in September 2015 and again at least once in March–April 2016.

    (Summarised by: Katie Sainsbury)

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

    A replicated, before-and-after study in 2015–2016 in desert scrubland in California, USA (Daly et al. 2018) found that survival during head-starting of desert tortoises Gopherus agassizii was similar compared to survival of tortoises that were released directly into the wild after hatching over six months. Survival rates of head-started and directly released juvenile desert tortoises were similar after six months (head-started indoors: 29 of 30, 97% survived; head-started outdoors: 20 of 20, 100% survived; directly released: 15 of 20, 75% survived). In August–September 2015, eggs from 25 wild female tortoises were collected and incubated outdoors in artificial burrows. In September 2015, seventy hatchlings (21–46 days old) were moved to either an indoor enclosure (30 hatchlings), outdoor enclosure (20 hatchlings; 30 x 30 m, semi-natural enclosure) or were released directly into the wild (20 hatchlings). Food was provided in indoor and outdoor enclosures (see paper for husbandry details). Directly released hatchlings were released in a 0.7 km2 unfenced area and monitored using radio telemetry once or twice/week until March 2016.

    (Summarised by: Katie Sainsbury)

  3. Relocate nests/eggs for artificial incubation: Tortoises, terrapins, side-necked & softshell turtles

    A study in 2015 in desert scrubland in California, USA (Daly et al. 2018) found that just over half of artificially incubated desert tortoise Gopherus agassizii eggs collected from wild adult females hatched in captivity. In total, 74 of 123 desert tortoise eggs hatched after being incubated in captivity (60% emergence success). Eggs were collected from 25 wild adult female desert tortoises in May-June 2015. Eggs were incubated in artificial burrows in an outdoor predator-proof nesting enclosure (in individual 5 x 9 m pens inside a 30 x 30 m enclosure).

    (Summarised by: Katie Sainsbury)

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