Because of factors such as habitat loss and collecting for the food, pet, and biological-supply industries, many turtle and tortoise species are becoming increasingly uncommon in the wild.
Since these animals have a low rate of replenishment through natural breeding, fewer species in fewer numbers are available each year. Fortunately, both for the chelonians and for the hobbyists who are interested in them, some commercial breeding programs have yielded considerable success, and hobbyists are now breeding additional uncommon species.
Since captive-breeding programs will assure that a greater selection of species remain available, the question of how one goes about breeding turtles is an important one.
The basic ground rules for success are much the same as they are for other species. Breeders must start with healthy, sexually mature individuals of both sexes; they must afford the animals the proper habitat; and they have to provide females with a suitable egg-deposition site. For some of the more adaptable turtles (like red-eared sliders and yellow-bellied sliders) this may be all that is necessary. Of course, once the eggs have been laid, they must be incubated.
Preparing Turtles for Breeding
However, many turtles require some additional preparation before they will breed. The additional cues include, but are not limited to, one or more of the following:
Natural climatic and seasonal phenomena stimulate breeding activities. The lengthening days and warming temperatures of spring, often coupled with fluctuating barometric pressures, stimulate temperate species to breed. In equatorial regions, where seasonal day/night-length changes are minimal, tropical chelonians may be stimulated by the advent of the rainy season and/or rising water levels. Lunar cycles may also figure – probably prominently. Although it may not be necessary to replicate all of these diverse stimuli, simulating some may be desirable.
A Turtle's Courtship
Prior to breeding, most turtles indulge in some sort of stimulatory courtship. During the lengthening days of spring, males of some semi-aquatic species swim around the female, titillating her cheeks and face with their lengthened foreclaws. Males of other species nip at the shell of the female, while the males of some tortoises ram the females' shell with the forward portion of their own.
Subtle? No. But then the workings of Mother Nature often aren't.
Breeding may occur only once or several times, and one female may be bred by multiple males. Each male may also breed multiple females. Because sperm retention is possible, a female may produce numerous clutches of fertile eggs over a two- to four-year period from a single successful breeding.
No Turtle Lays Eggs in Water
No turtle or tortoise, no matter how aquatic its lifestyle, lays eggs in the water. In the wild, most use their hind legs to dig a well-formed nest in moist sand or soil. The nest is often as deep as it is possible for the female turtle to reach. Prior to digging, the female may moisten the soil by releasing water from her bladder. If she encounters obstructions, she may discontinue her digging and choose an alternate nesting area later on the same day or a day or two later. Some females may dig several nests before actually laying.
Once the nest is suitably dug, the female lays her complement of eggs – which may vary from one to more than two dozen. (Some marine turtles lay 100 or more eggs at each nesting). The nest is then refilled with the loosened soil, tamped down to the best of the female's ability, and incubation is left to nature.
Preferred incubation temperatures vary by species, but are usually between 78 and 86 degrees Fahrenheit. Temperature-dependent (rather than genetic) sex determination is known to occur in many turtle species. With these, eggs incubated at warm temperatures produce one sex, eggs incubated at the cool end of the temperature-suitability spectrum produce the other sex, and those that incubate at temperatures in between produce both sexes.
Incubation may involve as little time as 45 days or may take a year or longer. The developing eggs of some species undergo a needed diapause – a cessation of development triggered by climatic cues – for a period of several days to several weeks. Some species lay hard-shelled eggs, some lay pliable-shelled eggs. During incubation the integrity of the shell is normally compromised by bacterial breakdown, which allows the hatchlings to more readily escape the egg. The hatchlings cut their way free with a soon-to-be-lost "egg-tooth." In the wild, hatchling turtles and tortoises are very vulnerable to predation, and comparatively few survive their first year of life.