Crowding affects health, growth, and behavior in headstart pens for Agassiz's desert tortoise

Published source details Mack J.S., Schneider H.E. & Berry K.H. (2018) Crowding affects health, growth, and behavior in headstart pens for Agassiz's desert tortoise. Chelonian Conservation and Biology, 17, 14-26.
Share Tweet Email

This study is summarised as evidence for the following.

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

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

A replicated study in 2003–2012 in a desert region of California, USA (Mack et al. 2018) found that some head-started Agassiz’s desert tortoises Gopherus agassizii survived the head-starting process, but growth was slower than in two wild populations. Growth of head-started tortoises was slower (4 mm/year) than in two wild populations (9–10 mm/year). After seven years, the captive facility contained 261 tortoises (1,718 tortoises/ha; range: 789–2,758 tortoise/ha), and after the following two years there were 142 tortoises (900 tortoises/ha; range: 0–2,049 tortoise/ha). In 2003–2010 (months not specified), around 24 adult females were brought in to one of nine enclosures to lay eggs before being returned to the wild. No further females were brought into the enclosures in 2011–2012, and no captive-born individuals are reported to have bred. The nine enclosures ranged from 0.01–0.03 ha in size and were covered with mesh to exclude avian predators and reinforced with exclusionary fencing at the base. Counts of tortoises in each enclosure in 2003–2012 (months not specified) were used to calculate density of tortoises/ha. Tortoises raised in the enclosures were intended for release into the wild.

(Summarised by: William Morgan)