(Van Denburgh, 1907)
Española (Hood) Island tortoise
Recognition
Geochelone hoodensis is one of the smallest (to 81.3 cm) members of the Galápagos complex. Its black, saddleback carapace has a deep cervical indentation, the anterior rim only weakly upturned, and posterior marginals downturned and slightly serrated. It is narrow anteriorly and wider posteriorly. Height at the cervical indentation is 42% or more of the carapacial length. Vertebrals are broader than long; the 5th is expanded. Vertebrals and pectorals are roughened with growth annuli, and their centers are raised. There are 11 marginals on each side, and the single, undivided supracaudal is downturned. Anterior marginals are not expanded or much upturned; their ventral surfaces are never vertical. Lateral marginals are vertical or downturned, and the 8th is reduced with a narrow anterior border. The black, well-developed plastron is shorter than the carapace and narrow at each end; no posterior notch, or only a shallow one, is present. The plastral formula is: abd > hum > fem > an >< gul > pect; the paired gulars may project to slightly beyond the carapacial rim. The bridge is about 37% of the carapace length, and has single axillary and inguinal scutes. The head is small with a nonprojecting snout and a bicuspid upper jaw. Its divided prefrontal and frontal scales are small. The head is dark gray to black with yellowish or white pigment on the jaws, chin, and throat; elsewhere, the skin is gray or black. The neck is long with a biconvex 4th cervical vertebra. Anterior surface of each forefoot is covered with large, nonoverlapping scales. The short tail lacks a large terminal scale.
Males are larger than females, are more saddlebacked, and have slightly thicker tails.
Distribution
Geochelone hoodensis lives on Española (Hood) Island, Galápagos.
Habitat
Rocky, brushy areas are inhabited. This species is often found around areas with Opuntia cacti (Linda J. Cayot, pers. comm.).
Natural History
Males gain sexual maturity at 14 years and a carapace length of 69 cm, while females are mature at 15 years and 64 cm (Siaca-Colon, 1994). Márquez et al. (1991) reported that a repatriated female first nested when 17 years old, and thought that females first reproduced when 16-19 years of age. Mating occurs from December to August and nesting from late June to December. Possibly two to four clutches of three to seven (average six) spherical, brittle-shelled eggs are laid each year (MacFarland et al., 1974b).
Natural foods include grass, herbs, shrubs, and cacti.
IUCN Red List Status (1996)
The entire Galápagos group (listed as Geochelone nigra) is considered Vulnerable (A2c, B1+2c). G. hoodensis (listed as Geochelone nigra hoodensis) is considered Critically endangered (D1).
In the 1960s, the estimated wild population on Española was very small, consisting only of 20-30 individuals (MacFarland et al., 1974a), and the tortoises were so dispersed they seldom found each other to reproduce. Seafarers in the 1800s exploited this species almost to extinction, and the large population of feral goats on the island destroyed any nests and hatchlings, as well as competed with adult tortoises for food plants. A breeding colony of 15 adults was established at the Charles Darwin Research Station (Caporaso, 1991), and through August 1972, 25 young G. hoodensis had been raised to be used to restock Española Island (MacFarland et al., 1974b). By the end of 1993, 575 have been released, with an additional 288 held at the CDR Station awaiting release (Cayot and Morillo, 1997). Recently discovered nests and live hatchlings indicate that the released tortoises are reproducing (Pritchard, 1996a).