Chelonoidis nigranigra

Geographic Range

The bulk of the animals live in the center of the Galapagos archipelego; of the living subspecies, six can be found on Albermale, and six on each of the islands of James, Indefatigable, Duncan, Hood, Chatham, and Abingdon.

Habitat

The animal's habitat is two-fold. It spends the cooler hours of its day in the warm, but completely dry, lava soils in the lowlands of the islands, where the terrain is usually arid and grassy. However, during the warm hours of the day, the tortoise travels along its beaten path to the volcanic highlands to swim and feed on the lush plantlife that grows there.

Physical Description

The Giant Tortoise can be up to 1.1m long and can reach an age of over 100 years. The animal's carapace resembles a black, horny shield, although the lichens that sometimes live on the shell can give it a mottled appearance. In some subspecies, the front part of the carapace is bent upward and shaped like a saddle, enabling the animal to raise its head on long necks to graze on higher parts of plants. The tortoise's elephantine feet have short toes and lack all traces of webbing. Males are typically larger than females.

  • Range mass
    150 to 200 kg
    330.40 to 440.53 lb

Reproduction

The Giant Tortoise practices internal fertilization. Between the months of January and August, the male begins sniffing the air for a female's scent. After he has found a female, he chases her down and begins courtship with intimidation. He rams her with the front of his shell and nips at her exposed legs until she draws them in, immobilizing her. He then mates with her. Nesting occurs at different times, but usually between June and December. The female travels to dry sunny lowlands where the eggs receive adequate warmth for incubation. She lays an average of 10 eggs in a nest, which she buries under the surface with her strong back legs. Incubation time for different clutches ranges from three to eight months, the longer periods most likely having a relation to cooler weather. When the eggs hatch, the baby tortoises are forced to fend for themselves. Most die in the first ten years of life.

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)

Lifespan/Longevity

  • Average lifespan
    Status: captivity
    177 years
    AnAge

Behavior

The Giant Tortoise is very regular in its sleeping, feeding, and nesting habits. In zoos, they are observed to go to their sleeping shelter in a particular sequence, and each tortoise has a specific area inside. A tortoise may shift occasionally within its area, but never changes to a different place. After their approximate sixteen-hour slumber, they leave the shelter in a fixed but different order than the one they entered the shed in.

As far as traveling to the volcanic highlands to feed, this habit is so regular that the paths carved out by thousands of tortoises have become built into the landscape. This behavior is believed to be instinctive based on the fact that in environments where there is no chance of finding volcanic lakes, the tortoises have been observed to go through the same ritual. This behavior is also a social system of sorts, because the animals travel to the lakes in numbers to swim lazily and always return in groups, as well.

In addition to these two very regular habits is nesting. The female tortoise has been known to return to the very same place year after year to lay its eggs.

Food Habits

The Giant Tortoise's diet includes grasses, forbs, and leaves on bushes. They have been known to eat several peculiar foods, such as stinging nettles and crab-apple like fruits of the manzanillo tree, which burn human skin. Individuals that live primarily in warm, but completely dry, lava soils in the lowlands of the Galapagos, often wander over long paths to the volcanic highlands, where they have access to drinking water and an abundance of plants. They may wallow there for hours, drinking and swimming lazily. At night, however, they return down the same path to the lowlands.

Economic Importance for Humans: Positive

They were slaughtered by merchants for their meat and sold.

Conservation Status

The Galapogos Tortoise is near extinction, with only a few surviving subspecies. Pirates, sealers, whalers, and merchant sailors slaughtered them until few remained. A few small wild populations still exist on the islands and are protected under law. Several more are found in zoos. On the islands, survival is very difficult because of the foreign species that have been introduced by the sailing ships. Cats and rats ravage the tortoises' nests and feed on the young. Wild goats and pigs also pose a problem by stripping many areas of covering vegetation, so that nests are more easily accessible.

Other Comments

An interesting note about the tortoise concerns the Galapagos finch. Though the mud-caked tortoises usually deter ticks and mosquitoes, researchers have observed finches landing on the backs of a tortoise, and removing ticks from the tortoise's body.

Contributors

Carmen Fernando (author), University of Michigan-Ann Arbor.

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

scrub forest

scrub forests develop in areas that experience dry seasons.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5? N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

References

Cox, J.A. 1975. The Endangered Ones. Rutledge Books and Crown Publishers, Inc.

Grzimek, B. 1968. Grzimek's Animal Life. Kindler Verlag A.G. Zurich.

Salvadori, F.B. and Pier L. Florio. 1977. Rare and Beautiful Animals. Newsweek, Inc.

Ernst, C.H. and Roger W. Barbour. 1989. Turtles of the World. The Smithsonian Institution Press.

Halliday, T. and Dr. Kraig Adler. 1986. The Encyclopedia of Reptiles and Amphibians. Facts on File, Inc.

Nayman, J. 1972. Atlas of Wildlife. Aldus Books Limited, London.

MacFarland, C. 1972. National Geographic.