Tortoises reach sexual maturity between the ages of 12 and 20 and usually mate from spring to fall, mostly during the summer. Factors such as aggression, glandular secretions and head bobbing determine whether a female will accept a male mate, retain its sperm and lay a clutch of eggs.
How often a male tortoise mates with a female is determined by how aggressive his behaviour is toward other males. Combat between male tortoises happens during spring and summer; males stand up and charge at an opponent, overturning or pushing away the other tortoise with its gular horn.
Male tortoises have glands that release secretions that can potentially attract a mate. Males also bob their head and make grunting or hissing sounds that coincide with courtship. A male will also bite at a female's legs before mating, and if a female accepts the mate, she will allow him to mount her.
A receptive female will be patient while her mate circles her, stamps his feet and prods her with this tail. The male has a longer tail than a female, which helps the male to penetrate the female. A concave plastron on the male helps the male fit onto the female. The male usually emits a series of grunts during mating.
Female tortoises are able to retain sperm in the cloaca for as long as a year and a half. Viable sperm retained by females will fertilise much later after copulation. This is an adaptation that has aided greatly in the survival of tortoises, especially endangered species.
A female digs a nest hole with her hind legs and buries her eggs. The nest is usually dug near her den and she will urinate on the nest in order to scare off potential predators. Depending on temperature, the tortoise eggs are usually incubated for around 100 days. It is rare that many of the offspring survive, usually only one tortoise from every 15 to 20 in the nest will survive long enough to mate.