Aldabra Tortoise

Location

In the Zoo

Scientific Information

Scientific Name: Geochelone gigantea
Class: Reptilia
Order: Testudines
Family: Testudinidae
Genus: Geochelone

Size

Male

Female

Height:
Length: 5 feet 3 feet
Weight: 560 lbs 350 pounds
Maturity:

Lifestyle and Lifespan

Diet: Herbivorous
Activity Timeframe: Diurnal
Interactivity: Social
Sexual Dimorphism:
Gestation: 73-160 days
Lifespan in the Wild: 152 years
Lifespan in Captivity: 170 years

Geographic Range

Found in Africa, exclusively in the Aldabra Island on the Indian Ocean, near the Seychelles.

Conservation

Status in the Wild: Vulnerable
Threats: Introduced Species

Characteristics

The Aldabra giant tortoise is the second largest species of tortoise, second only to the Galapagos tortoise. They have high, homed shells that are dark brown or gray. Hind legs are cylindrical and columnar like the legs of an elephant. The anterior surface of the forelegs are covered by thick, often bony scales. Toes are short; two-jointed. Snake-like neck and legs are retractile. The very small pointed head is covered with scales. High domed gray shell can measure up to 56' in length. Males can weigh up to 560 pounds while females average 350 pounds. Males have longer, thicker tails.

Species Specifics

There are four subspecies of Aldabra tortoises. There is the Aldabra tortoise, Seychelles giant tortoise, Arnold's tortoise, and hololissa.The carapace has a small neck plate absent in other species. They can stretch their necks up to three feet high.

Physical Characteristics

Able to go without food for several weeks. Knife-like jaws can easily crush a person's hand. Captive tortoises sometimes experience conical 'pyramiding' of the carapace scutes related to a dietary deficiency and possibly growth that is too rapid. Their clawed feet are efficient at digging.

Ecology

Habitat

Grasslands, scrub areas, and mangrove swamps.

Distribution

Diet

Herbivorous. They eat grasses, sedges, herbs, and woody plants. In captivity they feed on cabbage and other produce.

Ecological Web

Aldabra tortoises are herbivorous. They graze on low-growing grasses and herbs, using their beaks to clip at the vegetation. This constant grazing has put evolutionary pressure on the vegetation, causing creation of 'tortoise turf' which is a mix of low-growing plants and herbs that grow their seeds low to the ground as to avoid being eaten by the tortoises. They also browse on woody plants which they can reach for with their long necks, up to three feet high. They occasionally feed on small invertebrates and carrion. As the largest animal on the Aldabra atoll, it fills a similar role to elephants. They will alter their habitat in search for food, knocking over small trees and shrubs, and creating pathways used by other animals. They are also seed distributors as the seeds they eat passes through their digestive system and are scattered.

Activity and Behavior

Activity Pattern

They are active during the day, but they avoid the midday heat by finding shady shelter under trees and bushes or cooling off in pools or mud holes. They can sleep around 18 hours a day.

Behavior

Wallows in mud to protect against mosquitoes and keep cool in the hot sun.

Social Behavior

One of the more social tortoise species. Males fight for breeding rights and territory. An easily domesticated species, they quickly learn to recognize their keepers.

Reproductive Behavior

Normal breeding season is from February to May. A few months after breeding, females dig a nest and bury 4-14 eggs. A female living where there is a large population of tortoises will lay fewer eggs than those living around less tortoises. After around 3-6 months, the eggs hatch and the hatchlings are only three inches long.

Offspring

9 to 25 eggs the size of tennis balls. Typically, only three to five viable young are hatched from a clutch. In high-density populations females may only lay 4-5 eggs.

Conservation

Status

Listed as Vulnerable by the IUCN. They are currently protected on Aldabra and some neighboring islands, where small populations have been introduced.

Historical

Of the four types of giant tortoises once present on islands in the Indian Ocean, only the Aldabra Tortoise survived beyond the beginning of the 19th century. The rest were wiped out due to humans over-hunting. In the late 1880's Charles Darwin and other eminent naturalists signed a formal petition with the hope of saving the Aldabra Tortoise, whose population was heading quickly to extinction. Fortunately, this protection and restriction in trade of the reptile has helped the species recover.

Current Threats

Introduced Species

Our Role

How You Can Help

Fascinating Facts

It is difficult to know the precise age and overall lifespan of aldabra tortoises because they usually outlive the humans observing them.

Male tortoises' plastron (the shell on their underside) is usually concave, or curved inward. This allows them more stability when mounting a female during copulation. Males have longer tails than females.

References

Alderton, David. 1988. Turtles and Tortoises of the World. Facts on File, Inc, NY.

Ernst, Carl and Barbour, Roger. 1989. Turtles of the World, Smithsonian Press. Hayes, Alycin.

"The Aldabra Tortoise: Land Giant", Reptile and Amphibian Magazine, March/April 1994.

"The identification of Seychelles giant tortoises", Island Biodiversity. http://islandbiodiversity.com/tortid.htm

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