Overview

Brief Summary

Introduction

Geochelone gigantea, the Aldabra giant tortoise, is one of the largest tortoises in the world.The Aldabra giant tortoise lives on the remote Aldabra atoll, one of the Seychelles group of islands in the Indian Ocean.The Aldabra giant tortoise's current IUCN conservation status is 'vulnerable' to extinction. Many giant tortoise species around the world have become extinct due to
  • hunting
  • habitat loss
  • introduced predatory species such as dogs, rats and pigs that eat tortoise eggs and babies.
The Aldabra tortoise almost suffered the same fate, but its plight was recognised just in time, and its bleak Aldabra atoll home is now a World Heritage Site. However, the Aldabra atoll is only a few metres above sea level so the wild tortoises are now being threatened by climate change and rising sea levels.To aid conservation, the giant tortoises are also being bred in captivity in reserves on the islands of Mauritius and Rodrigues, where they are thriving.
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Taxonomy

The taxonomy and systematics of the Indian Ocean giant tortoises is under review by the International Commission on Zoological Nomenclature (ICZN). The many species suggested by Walter Rothschild were 'lumped' together by the Natural History Museum’s Nick Arnold in the 1970s, then 'split' by Roger Bour in 1982.Recent genetic studies indicate that the Aldabra and Seychelles giant tortoises were all the same species. As the Aldabra tortoise has been given many different scientific names over the years, the ICZN now has the tricky task of deciding which name is valid.

Synonyms
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Biology

The breeding season occurs from February to May (5), and females lay small clutches of 9 to 25 eggs, of which less than half are fertile in the wild (2). Hatchlings emerge anything from 3.5 to 7 months later. Aldabra tortoises have a predominately vegetation-based diet although they will supplement this intake with carrion (2) (7).
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Description

The Aldabra giant tortoise is indeed a giant, with individuals reaching over one metre in length (2). The thick, domed carapace is dark grey to black in colour and the robust limbs are covered in bony scales, as is the small, pointed head (5).
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Comprehensive Description

Biology

Giant tortoises are slow-growing and usually outlive their human owners when kept in suitable conditions. It has been claimed they can live over 250 years however it is hard to be certain exactly how long they can live.

Reproduction
Giant tortoises do not reach sexual maturity until their 30s.Mating is a noisy process, with the males bellowing like a bull, and chasing after the females. The male’s tail guides his penis into position, and copulation lasts for 10-15 minutes.

Egg laying
The females seek a soft sandy spot and lay between 9 and 25 eggs.
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Distribution

Geographic Range

Aldabra giant tortoises (Dipsochelys dussumieri) are endemic to the Aldabra Atoll of the Seychelles, an archipelago nation in the western Indian Ocean about 930 miles east of Africa and northeast of Madagascar. Populations have also been introduced to Mauritius, Réunion, and islands in central Seychelles.

Biogeographic Regions: ethiopian (Introduced , Native )

Other Geographic Terms: island endemic

  • Hambler, E. 1994. Giant Tortoise Geochelone Gigantea translocation to Curieuse Island (Seychelles): Success or failure?. Biological Conservation, 69: 293-299.
  • Karanth, K., E. Palkovacs, J. Gerlach, S. Glaberman, J. Hume, A. Caccone, A. Yoder. 2005. Native Seychelles tortoises or Aldabran imports? The importance of radiocarbon dating for ancient DNA studies. Amphibia-Reptilia, 26: 116-121.
  • 2006. Aldabra giant tortoise (Geochelone gigantea). Pp. 335-340 in B Freedman, ed. Encyclopedia of Endangered Species, Vol. 2, 1 Edition. Detroit: Thomson Gale.
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Continent: Asia
Distribution: Aldabra Atoll (Indian Ocean, Grande Terre, Picard, Malabar), introduced on Curieuse and Fregate (granitic Seychelles). Small groups exist on Cerf, Moyenne, Silhouette, Cousin, Cousine, Bird and Denis in the central Seychelles, on several of the Amirantes, and on Changu Island near Zanzibar (Tanzania).  
Type locality: Aldabra [same for Testudo elephantina DUMÉRIL & BIBRON 1835]
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Distribution habitat

Distribution
The Aldabra giant tortoise, as the name suggests, lives on the remote Aldabra atoll, one of the Seychelles group of islands in the Indian Ocean.Other tortoise species lived on other Indian Ocean islands, but most of these were hunted to extinction in the 1700s and 1800s.

Habitat
Aldabra tortoises tend to spend their lives grazing low-growing vegetation, but will cover surprising distances in search of food.They are very much at home on bare rock and thin soil, but like to keep cool in pools or shady places.They can drink from very shallow pools through their nostrils, and the name Dipsochelys refers to this remarkable adaptation.
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Range

Endemic to the islands of Aldabra and the Seychelles in the Indian Ocean, populations have also been introduced to Mauritius, Reunion (6), and granitic islands of Seychelles such as Curieuse and Fregate (7).
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Physical Description

Morphology

Physical Description

Aldabra giant tortoises are the largest living terrestrial species of tortoise (Testudinidae). They are dark gray to black in color and have a high, thick, domed carapace, a very long neck (to aid in branch feeding), and short, thick legs. The limbs and head are covered in bony scales.  Mature males have an average carapace length of 120 cm and can weigh up to 250 kg. They have longer and lower carapaces which widen near the rear and longer, thicker tails. Females are smaller than males, with an average carapace length of 90 cm and weight of 160 kg.

Range mass: 160 to 250 kg.

Range length: 90 to 140 cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: male larger; sexes shaped differently

  • Hutchins, M. 2003. Tortoises. Pp. 70 in B Grzimek, N Schlager, D Olendorf, eds. Grzimek's Animal Life Encyclopedia, Vol. 7, 2 Edition. MI: Gale Cengage.
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Type Information

Neotype for Geochelone gigantea
Catalog Number: USNM 269962
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Sex/Stage: Male;
Preparation: Dry
Year Collected: 1985
Locality: Dune Patates, on east side of, Grande Terre, Aldabra Atoll, Aldabra Islands, Indian Ocean
  • Neotype: Frazier, J. G. 2006. Herp. Review. 37 (3): 278.
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Ecology

Habitat

Habitat and Ecology

Systems
  • Terrestrial
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Aldabra giant tortoises are terrestrial and occur in a wide variety of habitats, including scrub forests, mangrove swamps, and coastal dunes and beaches, each with their respective vegetation. The largest populations of tortoises are found on grasslands called "platins."  Due to prolonged periods of heavy grazing, a habitat known as “tortoise turf”, consisting of a variety of grasses, has developed in certain areas.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: desert or dune ; savanna or grassland ; scrub forest

Aquatic Biomes: coastal

Wetlands: swamp

  • Grubb, P. 1971. The Growth, Ecology and Population Structure of Giant Tortoises on Aldabra. Biological Sciences, 260/836: 327-371.
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Inhabits a wide variety of vegetation on the islands where it is found, from scrub and mangrove swamp to grassy plains known as 'platins' (2).
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Trophic Strategy

Food Habits

Aldabra giant tortoises are primarily herbivores and feed mainly on vegetation such as grasses, leaves, woody plant stems, a variety of herbs and sedges. They are flexible and opportunistic and will sometimes supplement their diets with small invertebrates or carrion, even carrion of its own species.  In captivity, Aldabra giant tortoises have been known to enjoy fruits, such as apples, pears, tomatoes and bananas, carrots, peas, beans, almonds, and compressed vegetable pellets. Little fresh water is available in their natural habitat and they must obtain most of their water from food sources.

Animal Foods: carrion ; insects; terrestrial non-insect arthropods

Plant Foods: leaves; wood, bark, or stems; seeds, grains, and nuts; fruit; flowers

Primary Diet: herbivore (Folivore , Frugivore )

  • Stoddart, D. 1968. The Aldabra affair. Biological Conservation, 1/1: 63-69.
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Associations

Ecosystem Roles

Because of their heavy grazing, Aldabra giant tortoises have created a habitat known as tortoise turf. Tortoise turf is a combination of a variety of grasses and herbs and serves as the natural habitat for several smaller species. Tortoises also clear pathways in the forest for smaller animals.  Seeds pass through their digestive tracts and are dispersed through their feces. Coenobita rugosus (a species of land hermit crab) is dependent on tortoise feces for food.

Ecosystem Impact: disperses seeds; creates habitat

Commensal/Parasitic Species:

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Predation

Humans hunt tortoises and their eggs for meat. Adult Aldabra giant tortoises have no other natural predators.

Known Predators:

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Life History and Behavior

Behavior

Communication and Perception

Aldabra giant tortoises are limited in their social communication. The only non-sexual social behavior observed is ‘nosing’. One tortoise will approach another, lie down, and rub its nose on the latter’s head or neck. This lasts for several minutes. There currently does not exist an explanation for this behavior.

Communication Channels: tactile

Perception Channels: visual ; tactile ; acoustic ; chemical

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Life Cycle

Development

In young tortoises, the carapace is black and shiny. As they grow, tissue is added concentrically and is marked by radial striations, or growth rings. As growth continues, the head protrudes outward, while the limbs grow larger and stockier.

Sexual maturity is determined by size rather than by age; most individuals begin to reproduce when they reach approximately half their full-grown size, usually around 25 years of age. The growth of Aldabra giant tortoises is likely discontinuous and episodic, and research suggests that growth rate slows with increased age.

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Life Expectancy

Lifespan/Longevity

Lifespan in the wild is unknown in Aldabra giant tortoises. The estimated lifespan is over 100 years, possibly up to 150 years. These tortoises tend to outlive researchers and no sufficient records have been kept. However, a positive correlation between age and carapace size has been reported.  One zoo estimates the age of their tortoise to be 176 years old.

Range lifespan

Status: captivity:
176 (high) years.

  • Stoddart, D., D. Cowx, C. Peet, J. Wilson. 2003. Tortoises and tourists in the Western Indian ocean: The curieuse experiment. Biological Conservation, 24/1: 67-80.
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Lifespan, longevity, and ageing

Maximum longevity: 152 years (captivity) Observations: Anecdotal evidence suggests that these animals do not age. Still, increased mortality with age and size in the wild has been reported, though it could be due to increased predation (Caleb Finch 1990). An individual apparently died accidentally after 152 years in captivity. Because this animal was caught as an adult, it was probably around 180 years old (Castanet 1994). One male specimen called "Adwaita" was reported to have been anywhere between 150 and 255 years of age when he died at Alipore Zoo in Calcutta, India. Allegedly, "Adwaita" was a pet of British general Robert Clive before arriving at the zoo in 1875. This anecdotal report has not been confirmed.
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Reproduction

Mating attempts only occur when tortoises are active, during early morning or late evening. Mounting results from casual encounters, but it is possible that males undergo a period of heightened sexual activity during the mating season. The initiation of the mating attempt begins with a male approaching a female and climbing onto her back with his neck fully extended. Once in this position, he pushes off his forefeet and thrusts forward in four-second intervals. The male emits a loud moan or grunt with each thrust and up to 44 thrusts are performed. Sometimes the male appears to bite at the female’s head. Often the female will respond to the male’s mount by walking away or propping herself up on her forelegs, forcing her rear into the ground and dislodging the male. Males appear to be promiscuous in their selection of prospective partners, not all of which are necessarily female. One selective criteria is the relative size of the partner; males with a carapace length of 50 cm or more generally will only select smaller mates between 45 and 65 cm in length. Most mating attempts are not successful.

Mating System: polygynandrous (promiscuous)

The breeding season of Aldabra giant tortoises occurs from February to May. Females lay between 4 and 14 rubbery eggs in a shallow, dry nest, of which less than one half are fertile. The average clutch size increases in captivity, where females lay about 9 to 25 eggs. The incubation period is largely dependent upon temperature: in warm temperatures, incubation lasts 110 days, but in cooler temperatures, hatchlings emerge after about 250 days of incubation, between October and December. Females often produce a second clutch within the same breeding season, especially in healthy, uncrowded populations.

Breeding interval: Aldabra giant tortoises breed once or twice yearly.

Breeding season: Aldabra giant tortoises breed from February to May.

Range number of offspring: 4 to 25.

Range gestation period: 110 to 250 months.

Average gestation period: 243 months.

Average age at sexual or reproductive maturity (female): 25 years.

Average age at sexual or reproductive maturity (male): 25 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous

Like other turtles, Aldabra giant tortoises do not care for their young after females have deposited the eggs in a safe nest. The young hatch and dig out of the nest on their own.

Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female)

  • Grubb, P. 1971. The Growth, Ecology and Population Structure of Giant Tortoises on Aldabra. Biological Sciences, 260/836: 327-371.
  • Stearns, B. 1987. Captive husbandry and propagation of the Aldabra giant tortoise Geochelone gigantea: at the institute for Herpetological Research. International Zoo Yearbook, 27/1: 98.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Dipsochelys dussumieri

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
D2

Version
2.3

Year Assessed
1996
  • Needs updating

Assessor/s
Tortoise & Freshwater Turtle Specialist Group

Reviewer/s

Contributor/s

History
  • 1994
    Rare
    (Groombridge 1994)
  • 1990
    Rare
    (IUCN 1990)
  • 1988
    Rare
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Rare
    (IUCN Conservation Monitoring Centre 1986)
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Aldabra giant tortoises are one of the few surviving species of Indian Ocean giant tortoises. They are considered vulnerable due to years of human poaching and encroachment. Translocation of these tortoises has been unsuccessful, partly due to inadequate attention to human-related habitat interactions. Human poaching has significantly jeopardized chances of establishing populations that will survive far into the future.

Public concern has increased dramatically since the 1960's, and efforts at conservation are currently underway. The Seychelles Islands Foundation (SIF) under the Seychelles National Parks and Conservancy Act has been managing Aldabran affairs. Aldabra was also designated a World Heritage Site by UNESCO in 1982.

US Federal List: no special status

CITES: appendix ii

IUCN Red List of Threatened Species: vulnerable

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Conservation

The Aldabra giant tortoise’s conservation status is currently 'vulnerable'.Many giant tortoise species around the world have become extinct due to:
  • hunting
  • habitat loss
  • introduced predatory species such as dogs, rats and pigs that eat tortoise eggs and babies
The Aldabra tortoise almost suffered the same fate, but its plight was recognised just in time, and its bleak Aldabra atoll home is now a World Heritage Site. However, the wild tortoises' Aldabra atoll is now threatened by climate change and rising sea levels - the Aldabra atoll is only a few metres above sea level.

Giant tortoise reserves
Aldabra giant tortoises are also being bred in capativity in reserves on the islands of Mauritius and Rodrigues where they are thriving.
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Status

Classified as Vulnerable (VU) on the IUCN Red List (1), and listed on Appendix II of CITES (3), on both as Geochelone gigantea although it is also referred to as Dipsochelys dussumieri or D. elephantine (4).
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Threats

Giant tortoises throughout the islands of the Indian Ocean represented an important food source for sailors visiting these shores in the 17th to 19th Centuries and live individuals were often captured and stored for meat in the ship's hold (2) (7). In addition, the destruction of habitat and the introduction of mammalian predators such as rats and cats, and competitors such as goats further decimated the previously isolated populations (2). The Aldabra species is one of only three giant tortoises in the area to survive today, as a result of this past exploitation (8), and the only one to survive in the wild, with the others surviving only in a captive breeding programme (4) (8).
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Management

Conservation Actions

Conservation Actions
It is listed on CITES Appendix II.
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Conservation

Charles Darwin himself was involved with gaining this species protection in the Aldabra Atoll (2). International trade is restricted by the listing of this species on Appendix II of the Convention on International Trade in Endangered Species (CITES) (3), and there is a captive breeding programme of these giant tortoises on the island of Mauritius (2).
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

There are no known adverse affects of Dipsochelys dussumieri on humans.

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Economic Importance for Humans: Positive

Humans have hunted Aldabra giant tortoises and their eggs for food. They have also been bred in captivity as tourist attractions. Aldabra giant tortoises have also been the subjects of numerous research experiments including population studies, classical and operant conditioning, and conservation practices.

Positive Impacts: food ; body parts are source of valuable material; ecotourism ; research and education

  • Klemens, M. 2000. Turtle Conservation. Washington and London: Smithsonian Institution.
  • Weiss, E., S. Wilson. 2003. The Use of Classical and Operant Conditioning in Training Aldabra Tortoises (Geochelone gigantea) for Venipuncture and Other Husbandry Issues. Journal of Applied Animal Welfare Science, 6/1: 33-38.
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Wikipedia

Aldabra giant tortoise

(video) A pair of Aldabra giant tortoises at Tobu Zoo in Saitama, Japan.

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.[6] The carapace 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 105 cm (41 in) in length with an average weight of 120 kg (260 lb).[7] Females are generally smaller than males, with average specimens measuring 90 cm (35 in) in length and weighing 150 kg (330 lb).

Historically there were giant tortoises on many of the western Indian Ocean islands as well as Madagascar and the fossil record indicates that there were once giant tortoises on every continent and many islands with the exception of Australia and Antarctica.[8] It is believed that many of the Indian Ocean species were driven to extinction by over-exploitation by European sailors and it would seem they were all extinct by 1840 with the exception of the Aldabran Giant Tortoise on the island atol of Aldabra.[9] Although it appears there may be some remnant individuals of A. g. hololissa and A. g. arnoldi in captivity,[9] in recent times these have all been reduced as subspecies of A. g. gigantea.[5]

Nomenclature and Systematics[edit]

This species is widely referred to as Aldabrachelys gigantea, however, in recent times attempts were made to utilise the name Dipsochelys as Dipsochelys dussumieri but after a debate that lasted two years with many submissions the ICZN eventually decided to conserve the name Testudo gigantea over this recently used name (ICZN 2013)[10] this also effected the genus name for the species establishing Aldabrachelys gigantea as nomen protectum.

Four subspecies are currently recognized as follows:[5]

  • A. g. gigantea Schweigger 1812:327,[2] Aldabra Giant Tortoise from the Seychelles Island of Aldabra.
  • A. g. arnoldi Bour 1982:118,[11] Arnold’s Giant Tortoise from the Seychelles island of Mahé (extinct).
  • A. g. daudinii Duméril and Bibron 1835:123,[3] Daudin’s Giant Tortoise, from the Seychelles island of Mahé (extinct 1850).[5]
  • A. g. hololissa Günther 1877:39,[4] Seychelles Giant Tortoise, from the Seychelles islands of Cerf, Cousine, Frégate, Mahé, Praslin, Round, Silhouette (extinct).

Extinct Subspecies[edit]

Seychelles giant tortoise

The Seychelles giant tortoise (Aldabrachelys gigantea hololissa) has been thought to be extinct since the mid-19th century due to overexploitation on the granitic Seychelles islands. Similar giant tortoise species on other Indian Ocean islands such as Mauritius, Réunion, and Rodrigues Island are also extinct.

This species inhabited islands of the Seychelles group, where it thrived on vegetation on the edges of marshes and streams. By 1840, it had disappeared from the wild and was assumed to be extinct. As a grazing species, it somewhat resembled the Aldabra giant tortoise (A. g. gigantea) with its domed shape.

In 1999, some Seychelles island tortoises (12 known individuals) were suggested to have survived in captivity. The report of oddly shaped captive tortoises prompted the Nature Protection Trust of Seychelles to examine the identity of the living tortoises. Examination of museum specimens of the "extinct" Seychelles species by Dr. Justin Gerlach and Laura Canning seemed to show some living tortoises possess characteristics of the extinct species. With DNA testing, tortoises of the "extinct" species were identified and were acquired by The Nature Protection Trust of Seychelles for conservation. They were brought to Silhouette Island, where the only breeding population exists.[12]

An approximately 182-year old tortoise on Saint Helena, named Jonathan, is believed to be a survivor of the species (as well as potentially the oldest living land creature in the world).[13]

Possible A. g. arnoldi

Arnold's giant tortoise (Aldabrachelys gigantea arnoldi), also known as the Seychelles saddle-backed tortoise, inhabited the granitic Seychelles islands until around 1840, when it was presumed to be extinct, along with the Seychelles giant tortoise; a species which shared the same islands.

The report of oddly shaped of tortoises in captivity in the mid-1990s prompted the Nature Protection Trust of Seychelles to investigate the identity of these captive tortoises. Examination of museum specimens of the 'extinct' Seychelles and Arnold species seemed to confirm some living tortoises do show characteristics of the supposedly extinct species. However, some recently published scientific papers on the genetics of the Seychelles and Indian Ocean tortoises provide conflicting results. Some studies suggest only one species was ever present in the islands, whilst others suggest three distinct, but closely related species.

These different views derive from studies of different genes. A synthesis of all available genetic data indicates Arnold's tortoise is genetically the most distinctive Aldabrachelys tortoise.[14] This fits with the ecology and morphology of the species, as a highly distinctive tortoise adapted to feeding on low vegetation rather than the grazing habits of the Seychelles giant tortoise and Aldabra giant tortoise. Due to its unusual 'saddlebacked' shape, this is the only Seychelles tortoise species that regularly basks in the sun. The other species will do so occasionally, but Arnold's tortoises rapidly lose heat from the skin of their exposed necks and need to heat up in the sun in the mornings.

A captive-breeding program was established in 1997, and in December 2006, the five adult tortoises were returned to the wild on Silhouette Island, forming the first wild population of this species since the early 19th century.

Range and distribution[edit]

An isolated population resides on Changuu island in Zanzibar

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.[15] 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.

Ecology[edit]

Habitat[edit]

A peculiar kind of habitat has coevolved due to the grazing pressures of the tortoises: "tortoise turf", a comingling of 20+ species of grasses and herbs. Many of these distinct plants are naturally dwarfed and grow their seeds not from the tops of the plants, but closer to the ground to avoid the tortoises' close-cropping jaws.

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.

Feeding ecology[edit]

Primarily herbivores, Aldabra giant tortoises will 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 shell. 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.

Tortoise turf[edit]

Tortoise turf is composed of the following plant species:(Grubb, 1971;[16] Hnatiuk 1979)[17]

A herd of Aldabra tortoises at the Botanical Gardens, Mahé


An Aldabra giant tortoise at Beauval Zoo, France
Aldabra giant tortoise Aldabrachelys gigantea at Bristol Zoo, England


Esmeralda, the world's oldest living giant tortoise, Bird Island, Seychelles
Seychelles Giant Tortoise in Prague Zoo, The Czech Republic. Prague zoo is the 7th best zoo in the world.

Behavior[edit]

Adwaita: 254 years old at the time of the photograph at Kolkata zoo in India

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 underground burrows or rest in swamps to keep cool during the heat of the day.

While they are characteristically slow and cautious, they are capable of appreciable speed. They are also known to attempt perilous acrobatic feats, rising precariously on their hind legs to reach low branches.[citation needed] They risk death by tipping onto their backs and being unable to right themselves. This unusual behavior led famous Mexican biologist José Antonio de Alzate y Ramírez to famously refer to the Aldabra as the "ninjas" of the tortoise world.

Life history[edit]

Large tortoises are among the longest-lived animals on the planet. 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 of the British East India Company 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 life span of 255 years (birth year 1750).[18] Today, Jonathan, a Seychelles giant tortoise, is thought to be the oldest living giant tortoise at 182 years old and Esmeralda second at 170 years old, since the death of Harriet at 176, a Galapagos giant tortoise. Esmeralda is an Aldabra giant tortoise.

Child riding an Aldabra giant tortoise at the Mt. Kenya Wildlife Conservancy

Breeding[edit]

Mating Aldabra giant tortoises

Between February and May, females lay between 9 and 25 rubbery eggs in a shallow, dry nest. Usually less than half of the eggs are fertile. Females can produce multiple clutches of eggs in a year. After incubating for about eight months, the tiny, independent young hatch between October and December.[19]

In captivity, oviposition dates vary. Tulsa Zoo[20] maintains a small herd of Aldabra tortoises and they have reproduced several times since 1999. One female typically lays eggs in November and again in January, providing the weather is warm enough to go outside for laying. The zoo also incubates their eggs artificially, keeping two separate incubators at 27 °C (81 °F) and 30 °C (86 °F). On average, the eggs kept at the latter temperature hatch in 107 days.[21]

Conservation[edit]

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 (enlisting Charles Darwin and other famous scientists to help him) worked with the government of Mauritius to establish a preserve at the end of the 19th century. The related, but distinct, species of giant tortoise from the Seychelles islands (Seychelles giant tortoise A. g. hololissa and Arnold's giant tortoise A. g. arnoldi) are the subject of a captive-breeding and reintroduction program by the Nature Protection Trust of Seychelles.[22][23]

References[edit]

  1. ^ Tortoise & Freshwater Turtle Specialist Group (1996). "Geochelone gigantea". IUCN Red List of Threatened Species. Version 2012.2. International Union for Conservation of Nature. Retrieved 2013-04-23. 
  2. ^ a b Schweigger, Augustus F. 1812. Prodromus monographiae Cheloniorum. Königsberger Archiv für Naturwissenschaft und Mathematik 1:271–368, 406–462.
  3. ^ a b Duméril, André Marie Constant and Bibron, Gab riel. 1835. Erpétologie Générale ou Histoire Naturelle Complète des Reptiles. Tome Second. Paris: Roret, 680 pp.
  4. ^ a b Günther, Albert C.L.G. 1877. The Gigantic Land-Tortoises (Living and Extinct) in the Collection of the British Museum. London: Taylor and Francis, 96 pp.
  5. ^ a b c d Turtle Taxonomy Working Group [van Dijk, P.P., Iverson, J.B., Rhodin, A.G.J., Shaffer, H.B., and Bour, R.]. 2014. Turtles of the world, 7th edition: annotated checklist of taxonomy, synonymy, distribution with maps, and conservation status. In: Rhodin, A.G.J., Pritchard, P.C.H., van Dijk, P.P., Saumure, R.A., Buhlmann, K.A., Iverson, J.B., and Mittermeier, R.A. (Eds.). Conservation Biology of Freshwater Turtles and Tortoises: A Compilation Project of the IUCN/SSC Tortoise and Freshwater Turtle Specialist Group. Chelonian Research Monographs 5(7):000.329–479, doi:10.3854/ crm.5.000.checklist.v7.2014.
  6. ^ Pritchard, Peter C.H. Encyclopedia of Turtles. Neptune, New Jersey: T.F.H. Publications, Inc. Ltd., 1979.
  7. ^ Ernst, C.H., Barbour, R.W., 1989. Turtles of the World. Smithsonian Institution Press, Washington, DC.
  8. ^ Palkovacs, E., Gerlach, J. and Caccone, A. 2002. The evolutionary origin of Indian Ocean tortoises (Dipsochelys). Molecular Phylogenetics and Evolution 24:216–227
  9. ^ a b Palkovacs, E., Marschner, M., Ciofi, C., Gerlach, J. and Caccone, A. 2003. Are the native giant tortoises from the Seychelles really extinct? A genetic perspective based on mtDNA and microsatellite data.Molecular Ecology (2003) 12:1403–1413 doi: 10.1046/j.1365-294X.2003.01834.x
  10. ^ International Commission on Zoological Nomenclature [ICZN]. 2013. Opinion 2316 (Case 3463). Testudo gigantea Schweigger, 1812 (currently Geochelone (Aldabrachelys) gigantea; Reptilia, Testudines): usage of the specific name conserved by maintenance of a designated neotype, and suppression of Testudo dussumieri Gray, 1831 (currently Dipsochelys dussumieri). Bulletin of Zoological Nomenclature 70(1):61–65.
  11. ^ Bour, Roger. 1982. Contribution à la connaisance des tortues terrestres des Seychelles: définition du genre endémiqueet description d’une espéce nouvelle probablement originaire des îles grantiques et bord de l’extinction. Comptes Rendus de l’Académie des Sciences 295:117–122.
  12. ^ "Pearls of the Indian Ocean". Frangipani Reisen. Retrieved 2013-08-21. 
  13. ^ Kettle, Sally (13 March 2014). "Meet Jonathan, St Helena's 182-year-old giant tortoise". BBC News. Archived from the original on 9 April 2014. 
  14. ^ Eric P. Palkovacs, Monique Marschner, Claudio Ciofi, Justin Gerlach & Adalgisa Caccone (2003). "Are the native giant tortoises from the Seychelles really extinct? A genetic perspective based on mtDNA and microsatellite data" (abstract page). Molecular Ecology 12: 1403–1413. doi:10.1046/j.1365-294X.2003.01834.x. PMID 12755870. 
  15. ^ Payne, Roger (2004-04-05). "Losing Aldabra". Voyage of the Odyssey. PBS. Retrieved 2008-10-21. 
  16. ^ Grubb, P. The Growth, Ecology and Population Structure of Giant Tortoises on Aldabra. Phil. Trans. Roy. Soc. Lond. B, Vol. 260, 1971, pp. 327–372.
  17. ^ Hnatiuk, R.J. and L.F.H. Merton, Vegetation of Aldabra, a Reassessment. Atoll Research Bulletin No. 239, The Smithsonian Institution, 1979
  18. ^ BBC News - South Asia (2006-03-23). "'Clive of India's' tortoise dies". BBC News (BBC Online). Retrieved 2014-01-23. 
  19. ^ Stearns, Brett C. Captive Husbandry and Propagation of the Aldabra Giant Tortoise. Int. Zoo Yb., Vol. 27, 1988, pp. 98–103.
  20. ^ Collins, Dave. "Captive Breeding and Management of the Aldabra Tortoise". Presented to 8th International Herpetological Symposium, Jacksonville Zoo, Jacksonville, Fl., 1984.
  21. ^ Bourn, D. Reproductive Study of Giant Tortoises on Aldabra. J. Zool., London, Vol. 182, 1977, pp. 27–38.
  22. ^ Spratt, David M.J. Operation Curiesue: A Conservation Programme for the Aldabra Giant Tortoise in the Republic of Seychelles. Int. Zoo Yb., Vol. 28, 1989, pp. 66–69.
  23. ^ Swingland, Ian R. Aldabran Giant Tortoise. The Conservation Biology of Tortoises, Occasional Papers of the IUCN Species Survival Commission (SSC), No. 5, 1989.
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