- General Information
- Variations in Morphology
The Aldabra Tortoise (Aldabrachelys gigantea) is a species of giant tortosie found on the Aldabra Islands in the Seychelles of the south pacific. Although Aldabra tortoises may resemble the more commonly known Galapagos tortoise, they are unrelated, and do not share a recent common ancestor. Aldabra is located 200 miles away from the coast of Africa and 200 miles off the coast of Madagascar. The Aldabra Islands have had little human influence throughout its history, and is currently home to an estimated 100, 000 individuals. Aldabra tortoises can also be found on the island of Zanzibar; most likely brought by sailors from the Seychelles or they may have been washed away from the Aldabra Islands.
The Aldabra tortoise has a brown to tan carapace with a high dome shape and armored scales on its legs to support its great weight as an adult. Although the scales may offer some protection, there are no natural enemies of Aldabra tortoises in their natural range. Like the Galapagos Giant tortoise, the Aldabra Giant tortoise has a very long neck for its body size, which it uses to reach tree branches up to a meter off the ground. Trees on the Aldabra atoll are few, and long necks allow these tortoises to reach an otherwise unavailable food source.
Male tortoises have a carapace (upper section of the tortoises body as viewed from above) of around 48 inches in length, whereas the carapace of the female tortoise measures around 35 inches on average. The average weight of a male tortoise is 560 lbs, whereas the average weight of a female tortoise is around 335 lbs. Some Aldabra tortoises have been known to reach lengths of more than 50 inches, supporting a theory that they continuously grow throughout their lives.
The diet of the Aldabra tortoise in the wild consists mainly of grasses, and trees in which the tortoise can reach with their long necks. It is well documented that it will also feed on carrion, even on the carcasses of other tortoises. In an island poor in vegetation, the Aldabra Giant tortoise has no choice but to exploit the high protein and fat content of other tortoises. They do not, however attack their own kind in order to obtain a meal. The extensive cropping of grasses and other plants by the tortoise over thousands of years has resulted in the evolution of grasses and plants that bear their flowers near ground level, in order to avoid having their flowers and seeds being eaten by the tortoises. This allows the grasses and plants to reproduce in the presence of these giant tortoises. In captivity, these tortoises enjoy fruits and vegetables, such as lettuce, kale, collard greens, apples, and bananas. Their diet can be supplemented with cactus pads, commercial tortoise diet such as Mazuri tortoise food, flowers, different types of dried grasses, squashes, melons, and other vegetables; however their main diet should consist of grasses. These tortoises are unable to meet their water requirements through their diet, and must drink freshwater on a near daily basis.
Varieties in Morphology:
In the wild, there are known variations of the Aldabra Giant tortoise. Those that primarily consume grasses and other foods found close to ground level have wide dome shaped bodies, with the top front part of their shell extending downward to the neck. Aldabra tortoises that consume leaves and branches of small trees, on the other hand, have flatter shells and bodies, with the top front part of their shell being raised, to allow their much longer neck to reach trees and shrubs.
In the wild, Aldabra tortoises can be found in herds, or individually. Herds gather in open grasslands, or in areas of carrion where they can feed. During the middle of the day, when the temperature rises above that preferred by the tortoises, Aldabra tortoises will dig holes in the ground to cool off and may also rest in swamps and tide pools. Aldabra tortoises often risk their lives cooling off in muddy swamps, for they often get stuck in the mud, and lose an appreciable amount of energy trying to free themselves. In addition, while exploiting small trees and shrubs, the tortoises have been known to stand on their hind legs and tip over. If unable to turn over, the tortoises will die in the heat of the day.
The Aldabra tortoise usually breeds from February through may, where females usually lay between 10-30 rubbery eggs in a sandy shallow hole. The eggs typically take around 8 months to hatch, and only 50% are usually fertile. In the wild, the young hatch between October through December. In captivity, Aldabra tortoises may breed year round, if housed in large indoor enclosures. One can manipulate the seasons in order to induce breeding of tortoises. Eggs can be incubated artificially at around 82 degrees Fahrenheit and must be kept dry, since oxygen will not penetrate the eggs if kept very moist. There must be some moisture in the incubator, however. In zoos, eggs typically hatch between 105-110 days, when artificially incubated.
Aldabra tortoises have been known to live for more than 200 years. In the case of Adwaita, a tortoise thought to be brought by English seamen as a gift to Robert Clive, a British officer of the British East India Company in the 1700’s, lived for 255 years. Adwaita was brought to the Calcutta Zoo in India in 1875 and lived at this zoo until her death in 2006. Her age was estimated through a technique called carbon dating, and it was determined that she lived for 255 years, making her birth year 1750. In captivity, these giants can live for more than 200 years, due to a continuous supply of food, and protection against starvation due to falling over. Giant tortoises more typically will reach a lifespan of around 100 years, provided they receive good care, and a proper diet.
Aldabra giant tortoises should ideally be kept outdoors year round, as long as the weather permits. Tortoises less than two years old can be kept indoors in large pens or storage containers, however, once they reach about 2 years of age, the tortoises will need ample sunlight and room to roam. While housing your tortoises indoors, we recommend that you use crushed coconut for the substrate of your tortoise’s enclosure. Be sure to watch for signs of your tortoise consuming substrate, as this will cause impaction, and require veterinary attention as well as very frequent warm soaks. Many tortoises keepers have had problems with tortoises consuming bark or mulch used as a substrate. If you notice your tortoise consuming substrate, remove the substrate and switch to an alternative.
Aldabra tortoises should be provided with an area heated to 90 degrees Fahrenheit (32.2 degrees Celsius) and a region with a temperature of around 80 degrees Fahrenheit (26.6 degrees Celsius). Make sure to provide your tortoise with UVB light, as it is required in order for your tortoises to produce vitamin D3, which is crucial for the proper development of your tortoise’s shell. UVB bulbs provide tortoises with both UVA and UVB light.
As a bare minimum, one should be able to provide adult tortoises with at least 400 square feet of living space, however, the more room you can provide, the healthier your tortoises will be. In fact, to realize the importance of space, it is known that the population density of Aldabra giant tortoises (tortoises per unit area) determines the number of eggs a tortoise will lay, and more importantly, the number of fertile eggs a tortoise will lay. It is important to provide your tortoises with a heated shelter during the night. Lamps will provide your tortoises with the necessary heat in order to be comfortable during temperature shifts.
Giant tortoises once existed in the islands of Rodrigues, however, by the 18th century, European sailors had wiped out the endemic species. After the extinction of the native tortoises from the neighboring islands in the Seychelles, thousands of Aldabra giant tortoises were imported to Rodrigues and Mauritius as a food source. Extinct tortoises in neighboring islands include the Reunion Giant tortoise, the Saddle-backed Mauritius giant tortoise, the Domed Rodrigues and Mauritius giant tortoise, the Saddle-backed Rodrigues giant tortoise, the and the Arnold’s giant tortoise. The Seychelles Giant tortoise is currently listed as extinct in the wild, however, accounts of living specimens in zoos and parks has not been confirmed.
Charles Darwin warned the governor of Mauritius of the decline of Aldabra tortoises in the 1800s in a letter written in 1874. With help from Charles Darwin, the Aldabra Atoll began to be protected. Prior to Darwin’s influence in the Seychelles, there were plans to develop the Aldabra Atoll into a coconut plantation, which would have inevitably led to the demise of the native tortoises.
The Aldabra Atoll was once part of the British Indian Ocean Territory until its independence in 1976. The Aldabra Atoll, as a part of the British government’s Ocean Island Policy, was planned to become a Royal Air Force base that was to be funded jointly by the British and U.S. government. The British Broadcasting Corporation (BBC) also considered using the islands as a base in which to broadcast BBC Overseas Service to the African continent. These plans however were never put into fruition, as ecologists and scientists protested against these plans, and instead promoted the creation of a wildlife sanctuary in the Aldabra Atoll. On November 19, 1982, the Aldabra Atoll was selected as a World Heritage Site, which is a site of great natural or cultural importance.
These Giant Tortoises were brought to Mauritius in order to ensure the survival of the species. These tortoises were also brought to Mauritius in an effort to educate the people of the now extinct giant tortoises that once roamed the island. Over 200 Aldabra tortoises can now be found in the Vanilla Crocodile Park in Mauritius.
Ancestors of the Aldabra Giant Tortoise are thought to have come from the African continent. Some tortoises are naturally buoyant, and may remain afloat on a body of water and travel great distances. Thus, tortoises that were washed away in storms from the African continent may have arrived on the Aldabra Islands, and in the absence of any predators, have become giants. Whereas smaller tortoises are usually able to retract their entire bodies into their shell, adult Aldabra tortoises are unable to do this. They are able to retract their heads, however, they are unable to retract their legs. If there had been any predators on the Aldabra Islands, tortoises that grew such great proportions, would have been unable to defend themselves. Thus, those that grew to giant sizes, would have been eaten. In the absence of predators, however, smaller tortoises from the African continent were able to grow to large sizes. Thus, the lack of predators is thought to have given rise to giant tortoises, including Galapagos Giant tortoises.