Radiated tortoises, known locally as “sokake”, live in the dry spiny forests of southern and southwestern Madagascar. They are found mainly within about 100 km of the coast in scrub and tamarind forest, which provides a degree of shade in the arid conditions. The species is also found on the island of Réunion, where humans have introduced them.
These large tortoises grow up to half a metre in length, and their carapace (shell) is beautifully marked with yellow lines radiating from the centre of each section in a star pattern, hence its name.
They are herbivores, feeding mostly on grass, along with some fruit and succulent plants, and occasionally carrion, and spend a large part of their day foraging and feeding.
Like other species of tortoise, radiated tortoises are very long-lived and may regularly reach the age of 100. Although unconfirmed, a radiated tortoise was reported to reach the staggering age of 250.
Radiated tortoises do not reach sexual maturity until they are 15-20 years old. They mate in the wet season, when there is more food available and the ground is not too hard to dig a nest in. Males compete for females, who produce up to three clutches per season with 1–5 eggs per clutch. The soft-shelled eggs hatch after 5-8 months.
In the past radiated tortoises were quite abundant, often being found along roadways. But no longer – the species has disappeared from about 40% of its past range. Deforestation rates in this habitat have increased over the last few years as the land is cleared for agriculture, grazing and charcoal-burning. The remaining tortoise populations have been devastated by hunting for domestic consumption and poaching for the international wildlife trade, both for pets and to harvest their livers.
Humans are the only serious predators of adult radiated tortoises. Tens, perhaps hundreds, of thousands of tortoises are taken each year for their meat, especially at Christmas and Easter. Although there are protected areas, they are not patrolled adequately and resources are insufficient to deter poachers. In addition, introduced species such as rats and pigs have a devastating impact as they eat tortoise eggs and young – as with most reptiles, there is no parental care.
Their very slow rates of growth and reproduction mean that radiated tortoises have no hope of recovering unaided from this crisis. In August 2005, an international meeting of experts produced an alarming prediction – that without immediate action, viable populations would become extinct within 45 years. A systematic monitoring programme is needed, involving training local people. Monitoring trade in tortoises is also vital, along with ensuring that radiated tortoises are adequately covered by Madagascar’s expanding network of protected areas.
Captive breeding may help, and as well as helping to promote the conservation of radiated tortoises in Madagascar, Durrell has kept the species at its Jersey headquarters since 1976, when four males and two females arrived from Madagascar to be the founder members of the breeding programme. The first baby hatched in 1979.