The Galápagos Tortoise or Galápagos Giant Tortoise, Chelonoidis niger, is a very large species of tortoise in the genus Chelonoidis and is the largest living species of tortoise, with some weighing up to 417 kg (919 lb). They are also the largest extant terrestrial ectotherms (cold-blooded).
In the wild, a lifespan of over 100 years is not uncommon, and it is one of the longest-lived vertebrates. Some can even been known to live to the ripe old age of 177 years. Spanish explorers, who discovered the islands in the 16th century, named them after the Spanish galápago, meaning tortoise.
Galápagos tortoises are native to seven of the Galápagos Islands. Shell size and shape vary between subspecies and populations. On islands with humid highlands, the tortoises are larger, with domed shells and short necks. On islands with dry lowlands, the tortoises are smaller, with ‘saddleback’ shells and long necks.
Tortoise numbers declined from over 250,000 in the 16th century to a low of around 15,000 in the 1970s. This decline was caused by overexploitation of the subspecies for meat and oil, habitat clearance for agriculture, and introduction of non-native animals to the islands, such as rats, goats, and pigs.
The extinction of a number of giant tortoise species or sub-species is primarily thought to have been caused by predation by humans, as the tortoises themselves have no natural predators.
Being cold-blooded, tortoises will bask for 1–2 hours after dawn to absorb the sun’s heat through their dark shells before actively foraging for 8–9 hours a day. Tortoises are herbivores, and their diet mainly consists of such things as cacti, grasses, leaves, lichens, berries, melons, oranges and milkweed.
Females will journey up to several kilometres in July to November to reach nesting areas of dry, sandy coast and to start the long and arduous task of digging a nest. She will then lay up to 16 spherical, hard-shelled eggs.
The female makes a muddy plug for the nest hole out of soil mixed with urine, seals the nest by pressing down firmly on it and leaves them to be incubated by the sun. Young animals emerge from the nest after four to eight months and must then dig their way to the surface.