Galápagos giant tortoise (Chelonoidis nigra)

Some facts of Galapagos giant turtle :

Where do they live?: Galápagos Islands in the South Atlantic

Habitat: Upland areas

Size: Shell length from 29 in. (74 cm) to more than 4 ft. (1.2 m); weighs 500 lb. (227 kg)

Coloration: Dull brown; males often have a yellow area on the lower jaw and throat

Diet: Wide range of vegetation— even cactus shoots

Breeding: Females lay 2–10 eggs that hatch after 3–4 months

Life span: Up to 200 years

Status: Vulnerable

The largest tortoises in the world live on the Galápagos Islands in the Pacific Ocean. These reptiles probably drifted across the ocean from Central America, perhaps on floating tree trunks. The biggest Galápagos tortoises weigh as much as three men and may live for 200 years.

The Galápagos Islands were formed when volcanoes erupted through the seafloor about 600 miles off the coast of Ecuador in northern South America. The first giant tortoises washed up on the beaches of the island of Española. Later, more giant tortoises landed on the islands of southern Isabela, Volcan Darwin, and Volcan Alcedo. A third batch of tortoises landed on other islands in the group. It may seem unlikely that tortoises could just drift across the ocean for hundreds of miles and end up on some remote islands. Yet tortoises are often carried far from land during floods and they can survive very well at sea. They stay afloat with little effort, bobbing along on the ocean waves. They can survive for long periods without eating. They use the stores of body fat to supply them with energy. A giant tortoise can live without food for up to 14 months.

One female is all that is needed to start a new population of tortoises if she already carries a male’s sperm inside her body. Female tortoises can lay eggs for up to four years without a male being present. The young giant tortoises on the Galápagos Islands would have hatched in a safe environment, with plenty to eat and few predators, allowing their numbers to build up very quickly.

Three Types of Tortoise

Dome-shaped shells

Saddleback

Scientists put the different groups of Galápagos giant tortoises into three separate groups based on the way in which they have adapted to their environment. The first group is the saddlebacks. They are named for the way the front of their shells rise up above their necks, similar to a horse’s saddle. These tortoises live on dry islands where they need to stretch up to feed on taller plants. The smaller plants on these islands die back during dry periods. Saddlebacks have long legs and long necks, so they can stretch as high as possible. The second group is the tortoises with dome-shaped shells and short necks. This group lives on upland areas of the islands, where there are plenty of lush plants at ground level. The third group includes tortoises with characteristics partway between the saddlebacks and the dome-shelled tortoises.

 

Island Races

Several groups of the Galápagos giant tortoise live isolated from each other on the twenty different islands in the Galápagos group. Each group has adapted to the different conditions on the islands. The shape of their shells, their maximum size, and the lengths of their necks and limbs vary according to where they live. These differences helped the British naturalist Charles Darwin to figure out his ideas on evolution when he visited the islands as the zoologist on board the HMS Beagle in 1835.

Tortoise Troubles

In the nineteenth century, many Galapágos giant tortoises were taken from the islands and used to feed the crews of European whaling ships. So many tortoises were taken that three groups became extinct—on Charles Island, Barrington Island, and Narborough Island. Hunting is now banned, and the tortoises are fully protected by laws passed by the government in Ecuador. However, the Galápagos giant tortoises still face many problems. Goats left on the islands by sailors long ago now compete with the tortoises for food and can destroy their nests as well. Other introduced species include pigs and rats, and these eat the tortoises’ eggs.

Saving the Tortoises

Many conservation programs have been set up to help the Galápagos giant tortoises. The introduction of foreign species is being controlled to prevent competition for food or danger to the eggs and young tortoises. These tortoises are also being bred in captivity. Over the last forty years, the Darwin Foundation on the Galápagos Islands have hatched more than 2,500 young tortoises, adding to a total population of about 10,000 individuals. The tortoises are kept safely in pens and protected from predators, such as birds of prey, until they are three years old. Then they are released into the wild.

Mating games

The courtship rituals of the Galápagos giant tortoises are extremely aggressive. The larger male tortoises bash the shells of the females and pin them down by clambering on top of them. The males often make a roaring sound when they mate with the females. The females lay between two and ten hard, spherical eggs from July to December. The young tortoises hatch during the rainy season when there is fresh grass and plenty of other vegetation to eat. The shell of a newly hatched giant tortoise measures only 2.5 in. (6 cm) in length.