Galapagos Tortoise

Fall 2009 076
photo by Camilla_081


Class: Reptilia
Order: Testudines
Family: Testudinidae
Genus species: Chelonoidis nigra

Range: the Galápagos Islands, 600 miles west of Ecuador

Habitat: open, grassy areas to rocky, volcanic outcrops

Conservation Status: Endangered. At best, there are about 10,000 to 15,000 tortoises living today on the islands.

Physical Characteristics: males can reach up to 6 feet (1.83 meters) from head to tail and between 4 and 5 feet (1.22 to 1.53 meters) across the curvature of their shell; females are generally smaller. Males weigh up to about 573 pounds (260 kilograms); females—up to about 300 pounds (136 kilograms). Shell size and shape vary between 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. The tortoises have a large bony carapace (shell) of a dull brown color. The plates of the shell are fused with the ribs in a rigid protective structure that is integral to the skeleton. Lichens can grow on the shells of these slow-moving animals.[65] Tortoises keep a characteristic scute (shell segment) pattern on their shell throughout life, though the annual growth bands are not useful for determining age because the outer layers are worn off with time. A tortoise can withdraw its head, neck and forelimbs into its shell for protection. The legs are large and stumpy, with dry scaly skin and hard scales. The front legs have five claws, the back legs four.

Longevity: More than 150 years on record. The oldest life span on record belongs to an adult female Galápagos tortoise in an Australian zoo that was documented to be at least 171 years old.

Active Time: Diurnal 

Wild: They are herbivores that eat prickly pear cactus (a favorite) and fruits, as well as flowers, water ferns, leaves, and grasses.

Zoo: Carrots, apples, lettuce, and a pre-made tortoise chow

Behavior: Giant tortoises tend to lead a peaceful, lazy life that centers on grazing, relaxing in the sun, or wallowing in water puddles. Because they are cold-blooded like other reptiles, they like to soak up the sun to warm up. At night, they sleep partially submerged in mud, water, or brush to keep warm during cool nights

Reproduction: Galapagos Tortoises reach maturity in 20-25 years in zoos, and 40 years in the wild. Females lay between 2 to 16 eggs, depending on the subspecies. Gestation lasts between 4 to 8 months. In the wild, their breeding season is generally between January and August. After mating, the females begin a journey of several miles (kilometers) to reach nesting areas. They look for dry, sandy ground and dig a hole about 12 inches (30 centimeters) deep. Here they lay hard-shelled eggs the size of tennis balls, then cover them up with sand. Temperature plays a role in whether a tortoise hatchling is male or female: if the nest temperature is low, more males will hatch; if it is high, more females will hatch. When the young tortoises emerge from their shells, they must dig their way to the surface, which can take up to one month! Then it’s up to them to survive on their own.

Interesting Facts:

  • Las Islas de los Galápagos, or the Islands of the Tortoises, are named for the famed giant tortoises found nowhere else in the world. Galápago is one of the Spanish words for tortoise.
  • When a fight breaks out among males, the tortoises face each other, open their mouths, and stretch their heads as high as they can. Whoever is highest wins, even if he is much smaller overall than the other male.
  • Although they are massive animals weighing several hundred pounds (kilograms), their shells are not solid. Instead, they are made up of honeycomb structures that enclose small air chambers. This makes it possible for the tortoises to carry the weight of the shell. The shell is also attached to their ribs, so a tortoise cannot "walk out" of its shell.
  • The tortoise’s lungs are located on the top of its body, under the top dome of the shell, which is why the tortoise can be in trouble if it is turned over—the weight of its body can crush the lungs

Relationship with People:
Today, the greatest threats to the tortoises come from introduced nonnative species to the islands, such as rats, dogs, and cats, which eat tortoise eggs and young tortoises. They also must compete for food with goats and cattle, which causes food shortages. Due to these factors, there are only 10,000 to 15,000 tortoises living today on the islands.