Weather and sex ratios of head-started Agassiz's desert tortoise Gopherus agassizii juveniles hatched in natural habitat enclosures

Published source details Nagy K.A., Kuchling G., Hillard L.S. & Henen B.T. (2016) Weather and sex ratios of head-started Agassiz's desert tortoise Gopherus agassizii juveniles hatched in natural habitat enclosures. Endangered Species Research, 30, 145-155.
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This study is summarised as evidence for the following.

	Action	Category
	Provide artificial shade for nests or nesting sites Action Link

Provide artificial shade for nests or nesting sites

A controlled, before-and-after study in 2006–2009 in desert scrubland in California, USA (Nagy et al. 2016) found that shaded Agassiz’s desert tortoise Gopherus agassizii nests in a hatchery produced similar hatchling sex ratios as unshaded nests. Sex ratios were similar in shaded (0.2 females:1 male) and unshaded nests (0.3 females:1 male). This was despite soil temperatures in shaded areas being on average 13°C cooler mid-morning compared to unshaded areas. The authors report that the hatchling sex ratio from the previous three years of unshaded nests was the opposite way around (2–36 females:1 male) and that the change in sex ratio between the first three years and fourth year of the study could be explained by differences in air temperatures (see original paper for details). In spring 2006–2009, gravid, wild female Agassiz’s desert tortoises were placed in individual pens in one of four predator-proof fenced enclosures with artificial nest burrows in a hatchery. After eggs were laid, tortoises were returned to their capture location. In 2009, fourteen pens were partially covered with 4 m² pieces of black shading cloth suspended 0.5 m above likely nest burrows. A further 10 nest burrows were left unshaded. In 2006–2008, twenty-nine to 37 hatchlings were sexed/year. In 2009, forty-six hatchlings from shaded burrows and 36 hatchlings from unshaded burrows were sexed.

(Summarised by: Katie Sainsbury)