Desert tortoises reach sexual maturity when they attain a size of roughly 20 centimetres, which may take up to 15 years (3). Mating begins in early spring; male courtship involves head bobbing and nipping the female's carapace and legs (2). Males also compete amongst each other at this time, using their gular horn they attempt to overturn their component or to chase them away (2). Females construct nests in the desert sand, burying their clutch of around 5 eggs (3). The temperature of the developing eggs determines the sex of the hatchlings; females develop at higher temperatures (3). Hatchlings emerge 90 – 135 days after laying, but the mortality rate of both eggs and hatchlings is very high (2).  These tortoises graze on desert grasses, obtaining almost all of the water they require from their food (2). Rocks and soil are also ingested, possibly as a means of obtaining minerals (2). As cold-blooded animals, tortoises adopt behavioural means of regulating their temperature; they hibernate in burrows during the winter months and are also dormant through the hottest part of summer in a behaviour known as aestivation (2). In some areas, extensive burrow systems are constructed and these may be shared by a number of tortoises (2).