Tortoise, Galápagos giant

Geochelone nigra (elephantopus)

phylum: Chordata

class: Reptilia

order: Testudines

family: Testudinidae

status: Vulnerable, IUCN Endangered, ESA

range: Ecuador (Galápagos Islands)

Description and biology

The Galápagos giant tortoise is a gigantic tortoise that can weigh up to 580 pounds (263 kilograms). In certain subspecies, its top shell, or carapace (pronounced KAR-a-pace), is high and shaped like a dome. In others, the carapace is high only in front. This low-lying shell—called saddleback—flares out at the bottom. The length of a Galápagos giant tortoise varies depending on the shape of its carapace and its gender. An average saddleback female measures 24 inches (61 centimeters) long, while an average domed-shelled male measures about 50 inches (127 centimeters) long.

Galápagos giant tortoises reach sexual maturity between 20 and 30 years of age. Breeding usually takes places between January and June, the rainy season. After mating, a female Galápagos giant tortoise migrates to an arid (dry), lowland

area to lay her eggs. Beginning in June, she lays between 2 and 20 tennis-ball-shaped eggs in a nest she has dug out in the ground. She then covers the nest and returns to the highlands. The eggs incubate (develop) for four to eight months before hatching. The nest's temperature determines the offspring's sex: warmer temperatures produce more females; cooler temperatures produce more males. Between November and April, the eggs hatch and the young tortoises begin to dig their way out of the nest. At birth, they weigh about 9 ounces (255 grams), or 0.1 percent of their adult weight.

The Galápagos giant tortoise, which may live to be 100 years old, is an herbivore (plant-eater). It feeds on more than 50 different types of plants. The tortoise has a keen sense of smell, and it will smell all of its food before eating. It can survive for a long period without food or water because it can metabolize, or break down, fat stored in its tissues.

Habitat and current distribution

The Galápagos giant tortoise is found only on the Galápagos Islands, a province of Ecuador lying about 600 miles (965 kilometers) off the country's west coast. It inhabits the islands of Hood, Isabela, Pinzon, San Cristobal, Santa Cruz, and Santiago. Biologists (people who study living organisms) estimate that about 15,000 Galápagos giant tortoises currently exist.

This tortoise is found in various areas on these islands, from sea level to the highest points. During the dry season, the tortoise migrates to higher altitudes to find food and water. Most larger Galápagos giant tortoises are found in the higher altitudes.

History and conservation measures

Humans have been a major threat to the Galápagos giant tortoise. When Spanish navigator Tomás de Bertanga and his fellow explorers discovered the Galápagos Islands in 1535, they found so many giant tortoises there that they named the islands Galápagos, Spanish for "tortoise." Biologists estimate that 250,000 tortoises inhabited the islands when Bertanga and his men arrived.

In the nineteenth century, whalers and explorers who visited the islands slaughtered thousands of Galápagos giant tortoises for their meat, oil, and fat. To have fresh meat during their voyages, these men sometimes took live tortoises on-board their ships and stored them in the holds for up to a year before killing them.

The Galápagos giant tortoise is currently threatened by animals introduced by humans into the tortoise's habitat. Dogs and pigs prey on tortoise eggs and young tortoises. Goats compete with the tortoises for food. Donkeys trample or roll in tortoise nesting areas, often damaging eggs.

In 1959, the Ecuadoran government declared all uninhabited areas of the Galápagos Islands to be a national park. This act prevents any island species from being hunted, captured, or disturbed. The Charles Darwin Research Station on Santa Cruz Island has launched a program to control the predator population. Although this program has been successful, the outlook for the survival of the Galápagos giant tortoise remains guarded.