|At Roger Williams Park Zoo, US|
The radiated tortoise (Astrochelys radiata) is a species in the family Testudinidae. Although this species is native to and most abundant in southern Madagascar, it can be also be found in the rest of this island, and has been introduced to the islands of Réunion and Mauritius. As the radiated tortoises are herbivores, grazing constitutes 80-90% of their diets, while they also eat fruits and succulent plants. A favorite food in the wild is the Opuntia cacti. They are known to graze regularly in the same area, thus keeping the vegetation in that area closely trimmed. They seem to prefer new growth rather than mature growth because of the high-protein, low-fiber content. These tortoises are, however, endangered, mainly because of the destruction of their habitat by humans and because of poaching.
Anatomy and morphology
Growing to a carapace length of up to 16 in (41 cm) and weighing up to 35 lb (16 kg), the radiated tortoise is considered to be one of the world's most beautiful tortoises.
This tortoise has the basic "tortoise" body shape, which consists of the high-domed carapace, a blunt head, and elephantine feet. The legs, feet, and head are yellow except for a variably sized black patch on top of the head.
The carapace of the radiated tortoise is brilliantly marked with yellow lines radiating from the center of each dark plate of the shell, hence its name. This "star" pattern is more finely detailed and intricate than the normal pattern of other star-patterned tortoise species, such as G. elegans of India. The radiated tortoise is also larger than G. elegans, and the scutes of the carapace are smooth, and not raised up into a bumpy, pyramidal shape as is commonly seen in the latter species. There is slight sexual dimorphism. Compared to females, male radiated tortoises usually have longer tails and the notches beneath their tails are more noticeable.
Range and distribution
Radiated tortoises occur naturally only in the extreme southern and southwestern part of the island of Madagascar. They have also been introduced to the nearby island of Reunion. They prefer dry regions of brush, thorn (Diderae) forests, and woodlands of southern Madagascar.
Males first mate upon attaining lengths of about 12 in (31 cm); females may need to be a few inches longer. The male begins this fairly noisy procedure by bobbing his head and smelling the female's hind legs and cloaca. In some cases, the male may lift the female up with the front edge of his shell to keep her from moving away.
The male then proceeds to mount the female from the rear while striking the anal region of his plastron against the female’s carapace. Hissing and grunting by the male during mating is common. This is a very dangerous procedure and cases have been recorded where the female's shell has cracked and pierced the vaginal and anal cavities. Females lay from three to 12 eggs in a previously excavated hole 6-8 in (15-20 cm) deep, and then depart.
Incubation is quite long in this species, lasting usually between five and eight months. Juveniles are between 1.25 and 1.6 inches (3.2 to 4 cm) upon hatching. Unlike the yellow coloration of the adults, the juveniles are a white to an off-white shade. Juveniles attain the high-domed carapace soon after hatching.
These tortoises are critically endangered due to habitat loss, being poached for food, and being over exploited in the pet trade. It is listed in Appendix I of CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora), which prohibits the import or export of the species under most conditions. However, due to the poor economic conditions of Madagascar, many of the laws are largely ignored.
No estimates of wild populations are available, but their numbers are declining, and many authorities see the potential for a rapid decline to extinction in the wild. In the North American studbook, 332 specimens are listed as participating in captive-breeding programs such as the Species Survival Plan. Captive breeding has shown great promise as in the captive breeding program for the radiated tortoise at the New York Zoological Society's Wildlife Survival Center. In 2005, the Wildlife Survival Center was closed, and the radiated tortoise captive-breeding program was continued with the inception of the Behler Chelonian Center.
In March 2013, smugglers were arrested after carrying a single bag containing 21 radiated tortoises and 54 angonoka tortoises (Astrochelys yniphora) through Suvarnabhumi International Airport in Thailand.
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