With tortoises, the genders are quite distinct and sexual dimorphism is visible, especially in the form of the shell: the male supracaudal shell turns inwards to conceal a tail longer than that of the female. It should also be noted that the plastron is hollow among the majority of males.
Among Mediterranean tortoises, females are significantly larger than males while the opposite applies to so-called ‘exotic’ tortoises: the male is larger than the female, apart from a few exceptions, such as the Leopard tortoise.
For most species, reproduction is seasonal.
Mating primarily takes place in the spring after hibernation.
This period varies significantly from one species to another: it starts at the beginning of April, slows down towards the end of June and resumes later in the month of August, lasting until the end of September.
Mating is preceded by a nuptial parade during which the male may be aggressive and cause serious injuries to the female.
During the mating ritual, the male pursues the female, and then spurs her with its shell. Once the female is immobilized, fertilization takes place.
Mating is carried out in the water, often in water that is deep, during the night and early in the morning. Once again, reproduction is preceded by a mating nuptial: males swim around the female and then place their snouts so that they tickle the female while quickly vibrating their very long claws. They then climb up onto the shell of the female.
In both aquatic and land-based tortoise species, the male grips the front or back edges of its partner’s shell during copulation. During this phase, it often emits sounds (certain species are more well known for vocalisation).
Note: Female tortoises are able to store sperm in their reproductive tracts for several years (4-5 years) after mating, thus allowing for several clutches of fertilized eggs.
Two to three weeks after mating, the female finds a place to lay the eggs, which is conducive to the ideal incubation of the eggs.
All tortoises, whether they land-based or aquatic, bury their eggs in a hole dug in the sand, covering them with earth with their hind legs. The depth varies in accordance to the length of the hind legs of the female.
Some females excrete fluid from their bladder, which loosens the substrate and thus enhances the digging.
Once the female has laid the eggs, the hole is covered over. To finish this, she uses her hind legs, which, through large circular movements, place dry leaves, weeds and twigs over the nest. The resulting creation blends into the surrounding earth and makes the nest almost invisible to the naked eye.
For Mediterranean tortoises, this takes between two and three hours. For tropical tortoises, the process can last much longer.
There is no parental care among tortoises: once the eggs have been laid, the female leaves the nest alone. There is only one species that protects its nest against predators, which is Burmese Brown Tortoise (Manouria emys).
The number of eggs laid depends on the particular animal. The number and size of the eggs also depend on the species, the size, the age of the female, and the number of times eggs are laid.