Feature: The Aldabra Giant Tortoise
The Aldabra giant tortoise (Aldabrachelys gigantea), from the islands of the Aldabra Atoll in the Seychelles, is one of the largest tortoises in the world.
Historically, giant tortoises were found on many of the western Indian Ocean islands, as well as Madagascar, and the fossil record indicates giant tortoises once occurred on every continent and many islands with the exception of Australia and Antarctica.
Many of the Indian Ocean species were thought to be driven to extinction by over-exploitation by European sailors, and they were all seemingly extinct by 1840 with the exception of the Aldabran giant tortoise on the island atoll of Aldabra.
Although some remnant individuals of A. g. hololissa and A. g. arnoldi may remain in captivity, in recent times, these have all been reduced as subspecies of A. gigantea.
The carapace which is the upper section of the exoskeleton or shell in a number of animal groups, such as turtles and tortoises is a brown or tan color with a high, domed shape.
It has stocky, heavily scaled legs to support its heavy body.
The neck of the Aldabra giant tortoise is very long, even for its great size, which helps the animal to exploit tree branches up to a meter from the ground as a food source.
Similar in size to the famous Galápagos giant tortoise, its carapace averages 122 cm in length with an average weight of 250 kg.
Females are generally smaller than males, with average specimens measuring 91 cm in length and weighing 159 kg.
The main population of the Aldabra giant tortoise resides on the islands of the Aldabra Atoll in the Seychelles.
The atoll has been protected from human influence and is home to some 100,000 giant tortoises, the world’s largest population of the animal.
Another isolated population of the species resides on the island of Changuu, near Zanzibar, and other captive populations exist in conservation parks in Mauritius and Rodrigues.
The tortoises exploit many different kinds of habitat, including grasslands, low scrub, mangrove swamps, and coastal dunes.
As the largest animal in its environment, the Aldabra tortoise performs a role similar to that of the elephant.
Their vigorous search for food fells trees and creates pathways used by other animals.
Although primarily herbivores, Aldabra giant tortoises eat grasses, leaves, and woody plant stems, they occasionally indulge in small invertebrates and carrion, even eating the bodies of other dead tortoises.
In captivity, Aldabra giant tortoises are known to consume fruits such as apples and bananas, as well as compressed vegetable pellets.
Little fresh water is available for drinking in the tortoises’ natural habitat, so they obtain most of their moisture from their food.
The Aldabra tortoise has two main varieties of shells.
Specimens living in habitats with food available primarily on the ground have more dome-shaped shells with the front extending downward over the neck.
Those living in an environment with food available higher above the ground have more flattened top shells with the front raised to allow the neck to extend upward freely.
The Aldabra giant tortoise is a herbivorous animal, spending much of its time browsing for food in its surrounding well-vegetated environment.
Aldabra tortoises are found both individually and in herds, which tend to gather mostly on open grasslands.
They are most active in the mornings when they spend time browsing for food.
They dig burrows or rest in swamps to keep cool during the heat of the day.
Large tortoises are among the longest-lived animals.
Some individual Aldabra giant tortoises are thought to be over 200 years of age, but this is difficult to verify because they tend to outlive their human observers.
Adwaita was reputedly one of four brought by British seamen from the Seychelles Islands as gifts to Robert Clive who was the first British Governor of the Bengal Presidency in the 18th century and came to Calcutta Zoo in 1875.
At his death in March 2006 at the Kolkata (formerly Calcutta) Zoo in India, Adwaita is reputed to have reached the longest ever measured lifespan of 255 years (birth year 1750).
As of 2016 Jonathan, a Seychelles giant tortoise is thought to be the oldest living giant tortoise at the age of 188 years and Esmeralda is second at the age of 176 years, since the death of Harriet at 176, a Galapagos giant tortoise. Esmeralda is an Aldabra giant tortoise.
Between February and May, females lay between 9 and 25 rubbery eggs in a shallow, dry nest with usually less than half of the eggs fertile.
Females can produce multiple clutches of eggs in a year and after incubating for about eight months, the tiny, independent young hatch between October and December.
The Aldabra giant tortoise has an unusually long history of organized conservation.
Albert Gunther of the British Museum, who later moved to the Natural History Museum of London worked with the government of Mauritius to establish a preserve at the end of the 19th century.