Galpagos tortoise

Geochelone nigra

TAXONOMY

Testudo nigra Quoy and Gaimard, 1824, Hawaiian Islands (in error). Twelve subspecies are variably recognized, and the taxonomy of the various island populations is controversial.

OTHER COMMON NAMES Spanish: Tortuga galápago.

PHYSICAL CHARACTERISTICS

This is a large tortoise (up to 51 in [130 cm] carapace length) with a uniform black, dark brown, or gray carapace that varies in shape from domed and rounded to saddle shaped. The twelfth marginal scutes are fused to form a supracaudal scute, the fifth and sixth marginal scutes touch the second pleural scutes, no nuchal scute is present, no carapacial or plastral hinge is present, the divided gular scute does not strongly project anteriorly, the humeropectoral seam does not cross the entoplastron, the external narial opening is basically rounded, the premaxilla lacks a medial ridge, but the maxilla bears one, the unflattened tail lacks an enlarged terminal scale, and five claws are present on the forefeet.

DISTRIBUTION

Occurs only on the Galápagos Islands off Ecuador. HABITAT

Volcanic islands, from semiarid lowlands to moist uplands. BEHAVIOR

These tortoises are active by day, but sleep under vegetation or overhanging rocks at night. The females in some populations migrate from feeding areas to nesting areas with appropriate soil and sunlight. Combat and courtship behaviors are similar to those in the yellow-footed tortoise, although the males are even more vocal, generating deep basal roars. When approached by Darwin's finches, these tortoises stand erect and allow the finches to glean skin, ticks, and other ectoparasites from their bodies.

FEEDING ECOLOGY AND DIET

This species is almost totally herbivorous, feeding on grasses, forbs, cacti and other succulents, sedges, fruits, and even the leaves of bushes.

REPRODUCTIVE BIOLOGY

Courtship and mating are known from December to August, but vary by island. Nesting has been observed from late June to December, although the season varies in length by island. Possibly as many as four clutches are laid each year. The female excavates a flask-shaped nest, 7-12 in (18-30 cm) deep, with her hind feet. The eggs are almost spherical, brittle-shelled, and measure 2.2-2.6 in (56-65 mm) in greatest diameter. Clutch size ranges from two to 19 eggs depending on the female's size and island, with clutches of six to 10 being most typical. Incubation may take 85 to more than 200 days.

CONSERVATION STATUS

This species is listed as Vulnerable on the IUCN Red List, but one subspecies is listed as Extinct, two as Extinct in the Wild, four as Vulnerable, four as Endangered, and one as Critically Endangered. Predation by cats, rats, dogs, and pigs and competition from goats, donkeys, and pigs all remain as problems.

SIGNIFICANCE TO HUMANS

This species is probably only rarely eaten by locals today, and perhaps their primary current significance is as an attraction for ecotourists. ♦

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