(Günther, 1875)
Volcan Cerro Azul tortoise
Recognition
Geochelone vicina is one of the five tortoise populations from Isabela (Albemarle) Island. This is another species with a thick, heavy shell intermediate between saddlebacked and domed, and not appreciably narrowed anteriorly. Its black carapace (to 125 cm) has a shallow cervical indentation, little upturning of the anterior rim, and the posterior marginals somewhat serrated and flared. Height at the cervical indentation is less than 45% of the carapacial length. Vertebrals are broader than long; the 5th is expanded. Surfaces of the vertebrals and pleurals are roughened with growth annuli, but may be very smooth in old tortoises. Eleven marginals lie on each side, and the single, undivided supracaudal scute is downturned between the posterior marginals. Anterior marginals have prominent anterior points, are not greatly expanded and never upturned; their ventral surfaces are horizontal. Lateral marginals are vertical or downturned, the 8th is not reduced and has a well-developed dorsal border. The black plastron is well-developed, but shorter than the carapace, and narrowed (tapered) at both ends with a posterior notch. The plastral formula is: abd > hum > fem >< an >< gul > pect; the paired gulars do not reach the carapacial rim. The bridge is broad (47-49% of carapace length), and its axillary is smaller than the inguinal. The head is moderate in size with a nonprojecting snout and a bicuspid upper jaw. Its divided prefrontal and single frontal scale are large. Head, neck, limbs, and tail are blackish gray. The neck is long with a biconvex 4th cervical vertebra. The anterior surface of each forelimb is covered with large, irregularly shaped, nonoverlapping or slightly overlapping scales. The short tail lacks a large terminal scale.
Males are larger and more saddlebacked; females are more domed. The male's tail is longer and thicker at the base than that of the female.
Distribution
Geochelone vicina is found near Cerro Azul on southern Isabela (Albemarle) Island, Galápagos. Its range may overlap that of G. guentheri.
Habitat
Geochelone vicina lives in various habitats such as grass patches, brush, and woodlands.
Natural History
A female hatched in 1969 laid her first clutch in 1986 (Noegel and Moss, 1989). Natural nesting occurs from late June into November; in captivity it has been observed from January to April (Throp, 1976). The internesting period is 30-45 days (Noegel and Moss, 1989). Three to 20 (X = 9) eggs are laid at one time, and more than one clutch is laid during the nesting season (Throp, 1976; Pritchard, 1979; Noegel and Moss, 1989) The spherical eggs (diameter 59-65 mm, Van Denburgh, 1914) have brittle shells. Incubation may take 91-112 days.
Natural foods include grasses and cacti.
Remark
The species vicina and guentheri are very closely related and may be sympatric. Van Denburgh (1914) had difficulty distinguishing between them, and MacFarland et al. (1974a) thought they may eventually be combined. Pritchard (1996a) proposed synonymization of G. microphyes, G. vandenburghi and G. guentheri with G. vicina.
IUCN Red List Status (1996)
The entire Galápagos group (listed as Geochelone nigra) is considered Vulnerable (A2c, B1+2c). G. vicina (listed as Geochelone nigra vicina) is considered Endangered (C2a).
In the 1970s, the remaining population of Geochelone vicina was estimated only to be 400-600 tortoises, and, while mating and nesting occurred, virtually all nests and hatchlings were destroyed by black rats, pigs, dogs, and cats (MacFarland et al., 1974a). In spite of this, Cayot and Márquez (1994) estimated there are 1,000-2,000 tortoises on Cerro Azul (including 100-300 on Cinco Cerros that are flat-backed and probably should be regarded as guentheri). Nowadays, nearly all dogs have been eradicated from southern Isabela, whereas black rats and cats probably are incidental predators. The main predators now are pigs and introduced ants (Linda J. Cayot, pers. comm.). A breeding and rearing center run by the Galápagos National Park Service, in collaboration with the Charles Darwin Research Station, was constructed in Puerto Villamil in Isabela. This center, operational during most of the 1990s, is dedicated to the tortoise populations of Isabela. Currently it has tortoises from most of the subpopulations from Sierra Negra and some of the subpopulations of Cerro Azul (Linda J. Cayot, pers. comm.).