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Giant tortoise

Scientific name: Aldabrachelys gigantea Giant tortoise - Photo taken by Bob Pitchford

Country: Seychelles

Continent: Africa

Diet: Grasses, vegetation and herbs.

Food & feeding: Herbivorous

Habitats: Tropical grassland, coast

Conservation status: Vulnerable

Relatives: Egyptian tortoise, Galapagos giant tortoise

Description: The male giant tortoise at Bristol Zoo Gardens is currently at the centre of a very exciting debate. Previously it was thought to belong to a species called the Aldabran giant tortoise, but in the last few years, it has been suggested that it may be a survivor from a species that was thought extinct - the Seychelles giant tortoise (Dipsochelys hololissa). Their lifespan is at least 100 years, possibly up to 150. The Zoo's male is thought to be over 80 years old - a survivor from an almost extinct species. Giant tortoises grow steadily for the first 40 years of their lives and, given enough food, can weigh up to 254 kg. The head and legs are much too big to be completely withdrawn into the shells. The shell does not need to serve as protection from predators because there are no predators on the islands where they evolved.

Lifestyle: Little is known about Seychelles giant tortoises in the wild, because none are believed to be alive in the wild. The Aldabran giant tortoises still survive in large numbers on their island home, largely free of predators and competitors. They graze grassy areas on the island in large numbers. There are over 100,000 on the island of Aldabra. So many graze the grass on the island that the grasses themselves have adopted a special low-growing form to avoid being killed completely by the tortoises. The tortoises start to feed early in the morning, before it is too hot, when the dew is thick on the grass. By mid-morning they are still feeding, but now with their heads faced away from the sun to keep their heads cool. By midday, they have stopped feeding and have taken refuge in the shade of the few trees on the island. By late evening they emerge once again to feed. They eventually stop feeding after the sun sets, falling asleep wherever they happened to be feeding, ready for the next day.

Family & friends: Aldabran giant tortoises can be found crammed together, often stacked on top of each other, beneath the shade of the sparse trees and bushes on their island.

Keeping in touch: Tortoises are usually silent, although mating males make a hollow groaning sound that can be heard hundreds of metres away.

Growing up: These tortoises mature at about 20-25 years. When she is ready to lay, the female will dig a large hole in the shallow soil using her back legs and then deposits about 5-19 eggs, before covering them over and departing. After about two months, the 6 cm young hatch. With soft shells, they are very vulnerable to predators, such as robber crabs, frigate birds, or introduced creatures such as rats and cats. Once they are above a few inches in length, they are safe from predators. The main hazard to a giant tortoise is getting caught out in the midday sun too far from shade as they can rapidly overheat and die.

Conservation news: Giant tortoises were found on all islands in the western Indian Ocean until Mauritius was colonised in the 1600s and an increasing number of settlers and explorers visited the Seychelles islands removing and killing tortoises. It was thought that all Seychelles tortoises became extinct around 120 years ago, with the exception of the Aldabran species, until reports of oddly-shaped captive tortoises prompted a re-examination of their identity. In 1998, staff at Bristol Zoo Gardens were excited to find out that their giant tortoise may be one of these individuals in question. After examination, the experts suspected that this tortoise was a Dipsochelys hololissa, of which there may be fewer than 40 individuals left in the world. Experts are still debating. The Nature Protection Trust of the Seychelles has set up a breeding programme to ensure the survival of this rediscovered species.

In 2003, Bristol Zoo Gardens' giant tortoise enclosure was improved to house females with the male.

They have a special flap inside their head that allow them to suck water up their noses continuously without raising their heads. Aldabra is such a dry island that drinking quickly and efficiently like this is an important survival technique.