Giant tortoises returned to Madagascar after 600 years
A six-year-old project to return giant tortoises to the wild in Madagascar could result in thousands of the 350kg megaherbivores re-populating the island for the first time in 600 years.
The first group of Aldabra giant tortoises (Aldabrachelys gigantea) were brought in from the Seychelles in 2018, and have been reproducing on their own since.
The Aldabra giant is the second-largest species of land tortoise in the world. It has a fascinating history.
It evolved from ancestors of Aldabrachelys abrupta, one of two giant tortoises that inhabited Madagascar for 15 million years.
Four million years ago, the Aldabrachelys abrupta lineage migrated, likely via a combination of drifting with floating vegetation and assisted by their natural buoyancy and good swimming abilities, to the Seychelles.
From there it moved on to Aldabra (an island 1 000km southwest of the Seychelles), evolving into the Aldabra giant of today.
Six hundred years ago, all giant tortoises were wiped out on Madagascar by hunters.
In 2018, the Aldabra giant was reintroduced to the Anjajavy Reserve in the northwest of Madagascar. The first group of 12, five males and seven females, were fitted with transponders before being released.
Two babies were born the year after and in the five years since, another 152 have hatched.
All the hatchlings were taken to live in a tortoise nursery in Anjajavy soon after they were born, and will be returned to the wild once their carapace (the convex part of the shell which is made up of the tortoise’s ribs, fused with bone) is large enough to protect them from predators.
Hatchlings are very small so feral cats, dogs and rats are potential predators, as are raptors and the fossa, Madagascar’s largest endemic carnivore.
Research has shown that much of Madagascar is burned annually to create grazing land for cattle. In other areas, woodland and forest is cut down, and the ground then burned for cropland.
Research predicts that reintroducing the Aldabra giant tortoise will limit such fires because they feed on any grass or dry leaves on the forest floor, leaving less dry fuel to catch alight.
On Rodrigues and Île aux Aigrettes islands in Mauritius, research shows that ebony forests returned after giant tortoises were reintroduced.
Miguel Pedrono is a conservation biologist, Andrinajoro R Rakotoarivelo is a research associate, department of zoology and entomology, University of the Free State, Colleen Seymour is a honorary research associate, and Grant Joseph is a research scientist, FitzPatrick Institute of African Ornithology, University of Cape Town.