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Sunday, December 15, 2013

Species Fact Profile: Aldabra Tortoise (Geochelone gigantea)

Aldabra Tortoise
Geochelone gigantea (Schweigger, 1812)

Range: Aldabra Atoll (Seychelles)
Habitat: Scrub, Grassland, Mangrove Swamp
Diet: Grasses, Fruits, Invertebrates, Carrion
Social Grouping: Solitary or in Herds
Reproduction:  Mating season is February through May; up to 25 eggs are laid in a shallow nest hole, hatchlings appear 4-8 months later.  Fertility seems to be low, both in the wild and in captivity, with less than half of the eggs hatching
Lifespan: 150 years + (up to 200 years?)
Conservation Status:  IUCN Vulnerable, CITES Appendix II

  • Rivals the Galapagos tortoise as the world's largest tortoise species: body length is 1.2 meters, with a weight of 250 kilograms; record-size individuals are 360 kilograms.  Males are larger than females and have longer, thicker tails
  • The carapace is brown or tan; the shape varies from island to island, depending on whether the tortoises are browsers and grazers.  Despite this variation, no subspecies are recognized
  • Aldabra tortoises can be distinguished from the similar looking Galapagos tortoise by the presence of a "keystone" scute on the carapace, directly above the neck
  • The neck is very long, allowing tortoises to reach tree branches 1 meter off of the ground; many plants on the islands grow their seeds low to the ground to escape the attention of tortoises
  • Despite their bulky size, they can swim and are surprisingly buoyant; their ability to float has allowed them to spread natural to islands throughout the Indian Ocean
  • Most of the islands where they are found have little drinkable water; as such, they are capable of obtaining most of their moisture from plants in their diet; they will also dig shallow watering holes, mud wallows, or burrows
  • Through clearing bushes and felling small trees, these tortoises create patches of grassland called "tortoise turfs", which serve as habitat for many species
  • Adults have no predators, but eggs and hatchlings may be preyed upon by crabs, birds, and feral cats
  • Approximately 75% of the Seychelles tortoise species are now extinct, having been killed off by colonists and sailors.  They have been protected by law since the late 1800s
  • Captive breeding and reintroduction programs have resulted in the establishment of populations on Zanzibar, Mauritius, and Reunion.  On some of these islands, the Aldabra tortoise is used as an ecological substitute for now-extinct giant tortoise species
  • As China uses the giant panda as an "animal ambassador", the Seychelles will sometimes gift Aldabra tortoises to other nations as a good-will kept.  A pair were donated to China in 2010

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