I never dreamed that islands, about 50 or 60 miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted but we shall soon see that this is the case. “I have not, as yet, noticed by far the most remarkable feature in the natural history of this archipelago it is, that the different islands, to a considerable extent, are inhabited by a different set of beings. These differences, as described in The Voyage of the Beagle, contributed to the development of Darwin’s theory of evolution: One of the best ways to distinguish those still in existence, apart from geographic distribution, is by the differences in the shape of their shells. Of these 14 varieties, three are extinct. Fourteen subspecies, each in some way distinctive to the island of its residence, comprise the sole giant tortoise species. In fact, the word Galapagos is Spanish for “shape of a saddle,” which is what many tortoise shells actually resemble. A species of land hermit crab called Coenobita rugosus is dependent for its food on tortoise feces.The giant tortoise best symbolizes the Galapagos Islands. Seeds in the food they eat are dispersed via their feces. Aldabra giant tortoises also clear pathways through the forest for smaller species. Ecological nicheĭue to their heavy grazing, these tortoises have created a ‘tortoise turf’ habitat, which is a combination of grasses and herbs and also serves as the natural habitat for a number of smaller species. Overall, currently, Aldabra giant tortoises are classified as Vulnerable (VU) on the IUCN Red List. According to the A-Z-animals resource, the total population size of this species is around 152,000 individuals. Population numberĪccording to the British Chelonia Group (BCH) resource, the total population size of the Aldabra giant tortoise is over 100,000 individuals. In addition to this, the destruction of their habitat, mammalian predators like rats and cats being introduced, and competition from animals such as goats decimated further the previously isolated populations. These animals were often captured and kept in the ship’s hold for meat. Giant tortoises of the Indian Ocean islands were an important source of food for sailors who visited these shores during the 17th - 19th centuries. An Aldabra giant tortoise is a very slow-growing reptile and often does not reach maturity until 20-30 years old.Īldabra giant tortoises are one of only three species of giant tortoise in the region to survive today, due to past exploitation, and they are the only species that survive in the wild, the others being in a breeding program in captivity. Like other tortoises, this species does not care for its young once the eggs are laid in a safe nest, with the young hatching and digging out of the nest by themselves. A second clutch is often laid within one breeding season, especially in uncrowded, healthy populations. The period of incubation is largely dependent on temperature: it lasts 110 days in warm temperatures, and about 250 days in cooler temperatures, with hatchlings emerging between October and December. In captivity, the average clutch size is larger, about 9-25 eggs. 4-14 rubbery eggs are laid in a dry, shallow nest, less than half being fertile. The breeding season runs from February to May. One criterion for selection is a partner’s relative size males who have a carapace of 50 cm or more in length generally only select mates that are between 45 and 65 cm long. At the time of the first rain, they migrate towards the coastal scrub areas and open grasslands.Īldabra giant tortoises appear to be polygynandrous (promiscuous), both males and females having multiple partners. During dry seasons, they are evenly dispersed throughout the various habitats. This species has been known to move between habitats on a seasonal basis. A tortoise will fully extend its neck while browsing and sometimes rear up against trees. When an individual is threatened, it will quickly withdraw its head and walk away. These tortoises are found both on their own and gathered in herds in areas where there is plenty of food. Large males will walk with their limbs extended fully vertically and their carapace high up above the ground. When resting, they will lie with the underside of their shell on the ground, their limbs and head retracted slightly. They dig wallows, hide under shade trees or in small caves, as well as submerge themselves in pools to keep cool during the heat of the day. Aldabra giant tortoises are mainly active during the early morning and in the late evening and they spend the remainder of the day in burrows or swamps keeping cool.
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