Family: Testudinidae - Tortoises
Order: Testudines - Turtles
Phylum: Chordata - Vertebrates
Red List status: Critically Endangered
Female: 242-365 mm
Hatchling: 32-40 mm
Southern Madagascar, where it generally occurs within 100 km of the coast. The total core range for this species is around 10,000 km2, although this is declining and the species may already be extinct in some areas in the north of its range
One of Madagascar's iconic species, the radiated tortoise is the only large tortoise in southern Madagascar. The strongly contrasting reddish or tan pattern of lines radiating from the centre or base of black scutes is unmistakeable. Additional identifying features are the strongly domed carapace, the yellowish body colour, and the immobile (not hinged) plastron.
Similar species: The only other large tortoise with a domed shell in Madagascar is the agonoka (Astrochelys yniphora), which occurs in a very restricted area in northern Madagascar. The agonoka is duller in colouration, somewhat larger, and has a large, thick frontal spur protruding from the plastron. The spider tortoise (Pyxis arachnoides) exhibits superficially similar colouration to and is sympatric with Astrochelys radiata, but is smaller, has a more box-shaped carapace without a prominent dome, and exhibits a squarer 'spider-web' pattern rather than radiating lines. This species also has a hinged front to the plastron, allowing it to close its shell completely when threatened.
Dry regions with irregular rainfall, including spiny forest and xeric scrub, from coastal dunes to inland plateaux. Historically radiated tortoises occurred alongside roads, where they could be quite abundant, suggesting resilience to a degree of habitat modification. However, the species is dependent on the vegetation of dry forest, and has lost over 40% of its habitat in recent years.
Diet: The species is predominantly herbivorous; although it will supplement its diet with animal matter, it depends primarily on grasses. Tortoises obtain moisture by drinking from water that pools on rocks.
Breeding biology: Radiated tortoises produce an average of two (1-3) clutches per year, each with an average of 4 eggs (2-5 being normal, but up to 12 have been recorded - Glaw & Vences, 2007). Eggs measure up to 42 x 39 mm in diameter. It is estimated that 82% of mature females will breed in an average year.
Life cycle: Radiated tortoises have a slow generation time of around 33 years. Incubation of new eggs takes 69-231 days, and adults can live for over a century, with 137 being the greatest age reported for this species.
In 2008, having been regarded as Vulnerable for many years, the radiated tortoise was upgraded to Critically Endangered to reflect a historical range contraction of 20% over 25 years, the continuing and accelerating loss of spiny forest habitat, and overharvesting for both international export (the species is prized in the pet trade, but a greater issue is the use of its liver in Chinese medicine) and domestic use. Although numbers are hard to come by, up to 241,000 tortoises a year may be taken as food by migrants from other regions of Madagascar, who don't share traditional local taboos against eating tortoise meat. Several analyses conducted in 2005 indicated that Astrochelys radiata is likely to be extinct in the wild within 45 years.
Glaw, F. and Vences, M. (2007) A Field Guide to the Amphibians and Reptiles of Madagascar. Third Edition. Cologne, Vences & Glaw Verlag: 496pp
Leuteritz, T. & Rioux Paquette, S. (2008) Astrochelys radiata. In: IUCN 2008. 2008 IUCN Red List of Threatened Species