Geochelone

These tortoises spend a large part of the day grazing in small groups (2); they eat a wide range of vegetation from grasses and flowers to cactus fruits (8). During the rainy season a lot of time is spent wallowing in shallow pools, and at night tortoises can be found in depressions dug into the ground (9). On some islands, Galapagos finches clean parasites from the skin of tortoises, which raise themselves up on their legs to facilitate this process (10). Males become territorial during the mating season (2), rivals will size each other up by standing tall on their legs and stretching their necks out, the taller tortoise will be dominant (10). Females lay their clutch of 2 to 16 eggs into nests dug into sandy ground; the nest is then covered over with soil and leaves and the hatchlings emerge around 4.5 months later (10). These giant tortoises are one of the longest-lived of all vertebrates and the oldest recorded individual reached the formidable age of 152 (3).

These tortoises are fully protected within the Galapagos National Park, which was established by Ecuador in 1959 (discover). International trade is also prohibited by the listing on Appendix I of the Convention on International Trade in Endangered Species (CITES) (6). The Charles Darwin Foundation and the Galapagos National Park Service have been running a highly successful tortoise-restoration programme since the 1970s, by raising hatchlings from eggs until they are robust enough to be released into the wild without falling victim to predation (8). One of their major achievements has been to increase the population of the Critically Endangered Hood Island tortoise (G. hoodensis), which numbered just 13 individuals in the 1970s but now boasts over 1,000 members in the wild (4) (8). It is hoped that these concerted conservation efforts will help to secure the Galapagos' giant namesake for future generations.

This enormous giant tortoise was once so numerous that Spanish explorers of this region named the archipelago after one of its more extraordinary inhabitants; 'Galapagos' means 'tortoise' in Spanish (7). These reptiles are the largest living tortoises and the heavy carapace can reach lengths of up to 150 centimetres (7); they have relatively heavy limbs and a long neck (2). These tortoises illustrate the principal of adaptive radiation that Darwin coined after insights in the Galapagos; populations isolated on islands or on parts of larger islands have adapted to different conditions and now have distinct appearances. Presently 11 species are recognised (5), relating to isolated populations on certain islands within the Galapagos chain (8). The species can be generally separated into those with 'domed' shells, which occur on the larger, wetter islands, and smaller tortoises with 'saddleback' carapaces that are found on smaller islands with dry vegetation (9). It is thought that the distinctive saddleback shell enables its bearer to reach taller vegetation; these tortoises also have longer limbs and necks (9).

During the dry season, tortoises are likely to be found on higher slopes, whilst after the rains they come down to feed on the newly grass-covered flats (8).

Endemic to the islands of the Galapagos in the eastern Pacific Ocean, of the original 14 species, three are now extinct (10) and two are extinct in the wild (G. abingdoni and G. ephippium) (1).

The Charles Island tortoise (Geochelone galapagoensis) is classified as Extinct (EX) on the IUCN Red List and the Abingdon Island tortoise (G. abingdoni) and Duncan Island tortoise (G. ephippium) are classified as Extinct in the Wild (EW). The Hood Island tortoise (G. hoodensis) is classified as Critically Endangered (CR) and the James Island tortoise (G. darwini), Sierra Negra tortoise (G. guntheri), Indefatigable Island tortoise (G. porteri) and Iguana cove tortoise (G. vicina) are classified as Endangered (EN). The Volcan wolf tortoise (G. becki), Chatham Island tortoise (G. chathamensis), Volcan Darwin tortoise (G. microphyes) and Volcan Alcedo tortoise (G. vandenburghi) are all classified as Vulnerable (VU) on the IUCN Red List (1) (5). The Galapagos giant tortoises are also listed on Appendix I of CITES (6).

When mariners first began to arrive in the Galapagos Islands in the 1600s they captured giant tortoises and stored them live on ships as a source of meat (10). The trend continued and throughout the 19th Century whaling ships took a large number of tortoises for food, whilst further numbers were killed for turtle oil (10). Today the greatest threat to the survival of the Galapagos' giants comes from introduced species; feral dogs, cats and rats depredate juvenile tortoises before their carapace has fully developed and goats and cattle compete with tortoises for vegetation (9). The population of giant tortoises originally numbered in the 100,000s (8), but following centuries of persecution it is estimated that a mere fraction of this population remains; three species have become extinct and there is only one sole survivor of the Abingdon Island tortoise (G. abingdoni) known as 'Lonesome George' (9).