Aldabra giant tortoise
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Aldabra giant tortoise ( Aldabrachelys gigantea ) |
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| Aldabrachelys gigantea | ||||||||||||
| ( Schweigger , 1812) |
The Aldabra giant tortoise ( Aldabrachelys gigantea , syn .: Including Geochelone gigantea , Dipsochelys elephantina and Dipsochelys dussumieri ) is the only recent representative in the genus of Seychelles giant tortoises ( Aldabrachelys ) from the family of the real tortoise (.
description
The most striking feature of the Aldabra giant tortoise is its relatively small head, the diameter of which only slightly protrudes from the neck. Other distinguishing features compared to the Galápagos Giant Tortoise are large scalps, the presence of a neck shield, vertically slit nostrils and the ability to drink through the nose.
Like the smaller tortoise species, giant tortoises have a pronounced sexual dimorphism . Males have longer tails, are larger, and have a concave (inwardly curved) belly armor and a flatter back armor than females. Usually they also have longer toenails on their hind legs. These secondary characteristics only appear in the run-up to sexual maturity from a shell length of about 60 cm. Sexual maturity is reached between 15 and 30 years of age.
The largest carapace lengths are given for males with 100–122 cm and for females with 87 cm, including maximum weights of 250 kg for males and 167 kg for females. The average weights of the populations, depending on the age structure and food availability, are, however, significantly lower at 20–50 kg.
Some captive individuals with an unusually shaped, saddle-shaped shell were known for some time as "Arnold's giant tortoise". Based on genetic investigations, Gerlach (1996) initially believed that they were remnants of an extinct species and assigned them their own species status. However, this was refuted in 2003 by renewed investigations by Austin and Palkovacs. This species is not included in the current listing for CITES .
Distribution and way of life
98% of the natural populations live on the main island of the Aldabra Atoll, Grande Terre , in the Indian Ocean , preferring its coastal areas and open grass and scrubland with low vegetation. The temperatures fluctuate between mean minimum values of 22 ° C and mean maximum values of 31 ° C. In these semi-arid areas, through the thousands of years of browsing by turtles, vegetation from genetically dwarfed grasses and sedges has developed, the so-called tortoise turf , which is the main source of food for the animals. It consists of grasses, herbs and flowers. In addition, fruits, occasionally carrion and droppings are eaten.
Aldabra giant tortoises can easily live to be over 100 years old. The male Adwaita , born in the first half of the 18th century , presumably lived a life span of 256 years in captivity.
Reproduction
The main mating season is in the rainy season from October to April, while the egg-laying time is in the cooler months of June to September. One to two, occasionally up to three clutches with 5 to 25 eggs per clutch are laid. The eggs are the size of a tennis ball and weigh between 40 g and 75 g. The nest holes are preferably made in areas with five hours of sun exposure. Temperatures between 27 ° C and 31 ° C are around 25 cm deep. The young animals hatch with a size of 6 to 7 cm shell length in a sex ratio of approx. 1: 1. They can remain in the nest cavity for up to a month until they usually dig themselves to the surface after a rain.
Hazardous situation
The total free-living population is around 100,000 animals (Bourn 1999), in addition around 5,000 specimens are kept in zoos and in private hands (Swingland 1985). Thus it is the only giant tortoise whose survival is considered to be reasonably assured according to the current status. However, due to the small distribution area, natural disasters, epidemics, introduced species and human impact could have drastic effects. The Aldabra giant tortoise is listed in Appendix B of the European Species Protection Ordinance . It is therefore subject to official reporting, but may be bought or sold without a marketing permit.
Postage stamps
In 1985 the Seychelles Post issued a separate issue for the Outer Islands with a 10 rupee pad with a picture of two giant tortoises.
In 1998 the Post of the Kingdom of Cambodia issued a postage stamp depicting a giant Aldabra tortoise with a face value of 1,500 riels .
In 2008 the Indian Post honored Adwaita, who died in Calcutta Zoo after more than 256 years of life, with two hexagonal stamps with a face value of 5 rupees and 15 rupees.
See also
proof
Individual evidence
- ^ Jeremy J. Austin, E. Nicholas Arnold, Roger Bour (2003): Was there a second adaptive radiation of giant tortoises in the Indian Ocean? Using mitochondrial DNA to investigate speciation and biogeography of Aldabrachelys (Reptilia, Testudinidae). - Molecular Ecology, 12 (6)
- ↑ Eric P. Palkovacs, Monique Marschner, Claudio Ciofi, Justin Gerlach and Adalgisa Caccone (2003): Are the native giant tortoises from the Seychelles really extinct? A genetic perspective based on mtDNA and microsatellite data. - Molecular Ecology, 12 (6)
- ↑ CITES Chelonians Checklist , 2007 (PDF)
literature
- D. Bourn: Reproductive Study of Giant Tortoises on Aldabra. In: J. Zool. Vol. 182, London 1977.
- PA Chambers: Sheltered Life: The Unexpected History of the Giant Tortoise . John Murray, London 2004, ISBN 0-7195-6528-6 .
- D. Collins: Captive Breeding and Management of the Aldabra Tortoise. Presented to 8th International Herpetological Symposium, Jacksonville Zoo, Jacksonville, Fl., 1984.
- K. Ebersbach: On the biology and keeping of the Aldabra giant tortoise (Geochelone gigantea) and the Galapagos giant tortoise (Geochelone elephantopus) in human care with special consideration of reproduction. Dissertation . University of Veterinary Medicine Hannover, 2001 ( full text PDF; 3.2 MB)
- J. Gerlach, KL Canning: Evolution and History of the Giant Tortoises of the Aldabra Island Group. 2000. (full text)
- J. Gerlach: The Giant Tortoises of the Indian Ocean. (= Frankfurt contributions to natural history. 21). Frankfurt 2004, ISBN 3-930612-63-1 .
- CWD Gibson, J. Hamilton: Population Processes in a Large Herbivorous Reptile: The Giant Tortoises of Aldabra Atoll. Occologia, Berlin.
- P. Grubb: The Growth, Ecology, and Population Structure of the Giant Tortoises on Aldabra ,. In: Phil. Trans. Roy. Soc. Lond. B, Vol. 260, 1984.
- M. Pfeiffer: Long-term studies on reproductive processes in Aldabra and Galapagos giant tortoises (Geochelone gigantea and Geochelone elephantopus) based on steroid analyzes in the faeces and behavioral observations. Dissertation. University of Zurich, 2000, DNB 960035389 .
- BC Stearns: Captive Husbandry and Propagation of the Aldabra Giant Tortoise. In: Int. Zoo yb. Vol. 27, 1988.
- DR Stoddart: Retrospect and Prospect of Aldabra Research. In: Nature. March 15, 1969, pp. 1004-1006.
- DR Stoddart: The Aldabra Affair. Biological Conservation, 1974.
- IR Swingland: Securing the Tortoises Future. Country Life, Aug. 30, 1984.
- IR Swingland: Aldabran Giant Tortoise. The Conservation Biology of Tortoises, Occasional Papers of the IUCN Species Survival Commission (SSC), No. 5, 1989.
Web links
- Adwaita on Indian postage stamps ( Memento from December 18, 2011 in the Internet Archive ) (PDF; 257 kB)
- Geochelone gigantea inthe IUCN 2013 Red List of Threatened Species . Listed by: Tortoise & Freshwater Turtle Specialist Group, 1996. Retrieved October 7, 2013.
- Aldabrachelys gigantea in The Reptile Database