Astrochelys radiataRadiated Tortoise

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Geographic Range

Astrochelys radiata only occur naturally in the extreme southern and southwestern part of the island of Madagascar. A. radiata have also been introduced to the nearby island of Reunion (LPZ 1999).

Habitat

A. radiata prefer dry regions of brush, thorn (Diderae) forests and woodlands of southern Madagascar (LPZ 1999).

Physical Description

Growing to a carapace length of up to 16 inches and weighing up to 35 pounds, A. radiata is considered to be one of the world's most beautiful tortoises. A. radiata 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 A. radiata is brilliantly marked with yellow lines radiating from the center of each dark plate of the shell, hence the name radiated tortoise. 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. A. radiata 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 A. radiata usually have longer tails and the notch in the plastron beneath the tail is more noticeable (Kirkpatrick 1992).

Reproduction

Males first mate upon attaining lengths of about 12 inches; 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 will then proceed to mount the female from the rear while striking the anal region of his plastron against the females carapace. Hissing and grunting by the male during mating is common. Females lay from 3 to 12 eggs in a pre-excavated hole 6 to 8 inches deep and then depart. Incubation is quite long in this species, lasting usually between 145 and 231 days. Juveniles are between 32 to 40 mm 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 (Kirkpatrick 1992).

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)

Lifespan/Longevity

Behavior

Food Habits

A. radiata is an herbivore. Grazing makes up approximently 80-

90% of their diet. They feed during the day primarily on

grasses, fruit, and succulent plants. A favorite food in the

wild is the Opuntia cactus. In captivity A. radiata is known to eat sweet potatoes, carrots, apples, bananas, alfalfa sprouts,

and melons. According to some sources A. radiata seem to be

partial to red foods. 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 (Behler and Iaderosa 1991).

Conservation Status

Unfortunately, A. radiata is severely endangered due to loss of

habitat, being poached for food, and being over exploited in the

pet trade. A. radiata is listed in Appendix I of the Convention

on International Trade in Endangered Species (CITES) 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 stud book, 400 specimens are listed as participating in captive breeding programs such as the Species Survival Plan in zoos. Captive breeding of A. radiata has shown great promise (Behler and Iaderosa 1991).

Contributors

Jayson Egeler (author), Michigan State University, James Harding (editor), Michigan State University.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

References

"Radiated Tortoise" (On-line). Accessed November 12, 1999 at http://members.aol.com/gonysoma/radiated.html.

"Santa Barbara Zoological Gardens" (On-line). Accessed November 12, 1999 at http://www.santabarbarazoo.org/animals/ssp_torts.html.

Behler, J., J. Iaderosa. 1991. "A review of the Captive Breeding Program for the radiated tortoise at the N.Y. Zoological Society's Wildlife Survival Center" (On-line). Accessed November 12, 1999 at http:// www.tortoise.org/archives/radiata.html.

Kirkpatrick, D. March/April 1992. Reptile and Amphibian Magazine.

Obst, F. 1986. Turtles, Tortoises, and Terrapins. New York: St. Martins Press.

no author specified, "Lincoln Park Zoo Species Data Sheet" (On-line). Accessed November 12, 1999 at http://www.lpzoo.com/animals/herps/facts/radiated_tortoise.html.