TORTOISES: TestudinidaeGALÁPAGOS TORTOISE (Geochelone nigra): SPECIES ACCOUNTS
DESERT TORTOISE (Gopherus agassizii): SPECIES ACCOUNTS
Tortoises are small- to large-sized, land-living turtles. Most of them have a tall upper shell, or carapace (KARE-a-pays). Their back legs are thick and somewhat resemble the legs of an elephant. The front legs, on the other hand, are rather flat and covered with large scales. Their toes have no webbing between them, and many species have five claws on each front foot. The largest members of this family can weigh as much as 562 pounds (255 kilograms) and have upper shells that grow to 4 feet 7 inches (1.4 meters) long. Some of them have a hinge in the carapace or in the lower shell, which is called the plastron (PLAS-trun).
Tortoises exist on all large islands and continents, except Australia and Antarctica.
Tortoises live in many habitats, including deserts, grasslands, shrubby areas, and forests. Most live in warmer climates in North and South America, Europe, Asia, and Africa, and many make their homes on large islands in the ocean.
The tortoises are mainly plant-eaters, eating everything from grasses, flowers, and leaves to fruits and seeds. If they come across them, a few tortoises will also eat insects, worms, or other living or dead animals.
BEHAVIOR AND REPRODUCTION
Tortoises are known for their slow, lumbering movements on land. The males often fight among themselves, either by ramming their shells against one another or by biting at each other's legs. A male will also do the same things to a female in an attempt to convince her to mate with him. In addition, he will bob his head at her and chase her. Females lay from one to 51 eggs at a time. Each of the round or oblong eggs is about 1 to 2 inches (3 to 6 centimeters) in diameter and is typically quite brittle, or easily broken. Some females may not nest every year, but when they do, they may have more than one clutch, or nest of eggs, per season. Although scientists have not tested all of the species, the eggs in most become males or females based on the temperature of the nest. A particularly warm nest produces mostly females, and an especially cool one produces males. The eggs typically hatch in 100 to 160 days, but one species' eggs hatch only after 18 months. Some species may live 200 years or more.
Many tortoises become inactive in the summer when the weather is very dry. Many simply hide during the day in a shady spot, but some will dig a hole, or burrow, and spend the hottest part of the day there. On cooler days, some of these tortoises will seek out a warm spot and sunbathe, or bask, to increase their body temperature. Those species that live in colder climates may become inactive in the winter months.
TORTOISES AND PEOPLE
People hunt these tortoises for food and traditional medicines and collect them for the pet trade.
TORTOISES AND BIRDS
Galápagos tortoises have an unusual relationship with small birds, known as Darwin's finches. Ticks and other small biting insects often hitch a ride on a tortoise's skin, but the tortoise frequently cannot reach them to remove them. The birds feed on these same organisms. Darwin's finches and Galápagos tortoises seem to have struck a deal. When the finches fly in, the tortoises stand up as tall as they can and stretch out their necks, so the birds can pick off the insects and mites from every nook and cranny on their skin. Both the birds and the tortoises benefit: The bird gets an easy meal, and the tortoise gets some needed relief.
According to the World Conservation Union (IUCN), one species is Critically Endangered or facing an extremely high risk of extinction in the wild, seven are Endangered or facing a very high risk of extinction in the wild, and sixteen are Vulnerable or facing a high risk of extinction in the wild. The U.S. Fish and Wildlife Service lists two U.S. species as Threatened or likely to become endangered in the near future and five foreign species as Endangered, or in danger of extinction throughout all or a significant portion of their range. Although most countries make collecting illegal, it still continues. People find these land-living turtles easy to find and collect.
Physical characteristics: This large, bulky tortoise usually has a tall and rounded, dark-colored upper shell that may be black, gray, or brown. Sometimes the upper shell, or carapace, is saddle-shaped. The carapace can measure up to 51 inches (130 centimeters) in length.
Geographic range: They only live on the Galápagos Islands.
Diet: The Galápagos tortoise eats almost nothing but plants, including grasses, cacti, fruits, and leaves.
Behavior and reproduction: Active during the day, they spend their nights sleeping among plants or rocks. Males of this species, like the males of some other species, fight one another by ramming their shells together. Males do the same thing to females during mating season, which runs from December to August. During mating, he will make roaring noises. The female lays up to four sets, or clutches, of eggs from late June to December. She digs a hole, drops in two to nineteen eggs, and then buries them. She provides no other care for the eggs or young. The round eggs measure 2.2 to 2.6 inches (56 to 65 millimeters) in diameter. The eggs hatch eighty-five to two hundred days later.
Galápagos tortoises and people: Rarely collected for its food, this tortoise has become a prized tourist attraction on the Galápagos Islands.
Conservation status: According to the World Conservation Union (IUCN), the Galápagos tortoise is Vulnerable, which means it faces a high risk of extinction in the wild. Certain populations of this tortoise have disappeared completely. The U.S. Fish and Wildlife Service lists the tortoise as Endangered, or in danger of extinction throughout all or a significant portion of its range. Many of them die from attacks by cats, rats, dogs, and pigs. ∎
Physical characteristics: This medium-sized tortoise has a tall, dome-shaped upper shell, or carapace, and flat front legs. The carapace can reach up to 19 inches (49 centimeters) in length.
Geographic range: Desert tortoises live in the United States and Mexico.
Habitat: Found in the southwestern United States and northwestern Mexico, this species makes its home in cactus deserts and spots with thorny shrubs.
Diet: The desert tortoise eats mostly plants, including grasses, cacti, and flowers.
Behavior and reproduction: The desert tortoise is unusual in that it makes burrows into which it crawls to escape attackers and hot, dry weather. In some cases, the burrow is barely big enough for the tortoise to fit inside, but in others, it can be up to 33 feet (10 meters) long. In especially cold weather, the tortoises will crawl to the deepest part of the burrow and enter a deep sleep, called hibernation (high-bur-NAY-shun). When they are active, desert tortoises notice and interact with one another. When two meet each other, they bob their heads back and forth. During mating season, which runs from spring to fall, a male will try to convince a female to pair with him by biting at her legs, bobbing his head at her, and occasionally by ramming into her shell with his. A male frequently will ram shells with other males, too. He often hisses or grunts while mating with a female. The female lays eggs one to three times a year, usually laying five or six eggs at a time, although she may lay as few as two or as many as fifteen. Sometimes, she skips an entire year. The eggs range from 1.6 to 1.8 inches (4.0 to 4.5 centimeters) long and 1.3 to 1.5 inches (34 to 38 centimeters) wide. They hatch in about three to four months.
Desert tortoises and people: People hunt these tortoises for their meat, which is often shipped to Asian food markets located in the western United States.
Conservation status: According to the World Conservation Union (IUCN), the desert tortoise is Vulnerable, which means that it faces a high risk of extinction in the wild. The U.S. Fish and Wildlife Service lists the tortoise as Threatened, or likely to become endangered in the foreseeable future. The danger to the tortoises comes from both loss of their habitat and a dangerous bacterial infection. ∎
FOR MORE INFORMATION
Ballasina, D., ed. Red Data Book on Mediterranean Chelonians. Bologna, Italy: Edagricole, 1995.
Burnie, David, and Don E. Wilson, eds. Animal: The Definitive Visual Guide to the World's Wildlife. United Kingdom: DK Publishing Inc., 2001.
Pritchard, Peter C. H., and Pedro Trebbau. The Turtles of Venezuela. Athens, OH: Society for the Study of Amphibians and Reptiles; Oxford, OH, 1984.