Geochelone sulcata

(Miller, 1779)
African spurred tortoise

This is the largest African tortoise (to 83.0 cm), and is surpassed in size only by the island species from Aldabra and Galápagos. The oval carapace is flattened dorsally with abruptly descending sides, a deep cervical notch, both the anterior and posterior marginals serrated, and the posterior marginals upturned. No cervical scute is present. Vertebrals are broader than long; the 5th is smallest and somewhat expanded. Well-defined growth annuli surround the flat vertebral and pleural areolae. There are usually 11 marginals on each side, and a single undivided supracaudal scute which extends downward between the somewhat expanded posterior marginals. The carapace is uniformly brown. The plastron is well-developed with a deep anal notch. Its forelobe tapers to the front, and the two bifurcated gulars project forward beyond the carapacial rim. Both plastral lobes are about the same length, but the forelobe is slightly broader. The plastral formula is: abd > hum > fem > gul > pect >< an. The wide bridge has two axillaries (the inner very small) and two inguinals (the inner small). Plastron and bridge are uniformly cream or yellow. The head is moderate with a nonprotruding snout and a weakly hooked upper jaw. The large prefrontal scale is divided longitudinally and is followed by a large single frontal scale; other head scales are small. The head is brown with darker jaws; limbs and tail are also brown. The anterior surface of the forelimbs is covered with large, irregularly shaped, knobby, overlapping scales in three to six longitudinal rows. The hind surface of the thigh bears two or three large conical tubercles. The tail lacks a large terminal scale.
The larger males have more elongated carapaces, concave plastra with enlarged spur-like gular scutes, and longer, thicker tails than females.

Geochelone sulcata ranges from Ethiopia and Sudan westward through the dry regions of Chad, Niger, and Mali to southern Mauritania and Senegal. Its range generally lies along the southern perimeter of the Sahara Desert.

Geographic Variation
There is only very little geographic variation between populations from Mali and Sudan (Lambert, 1993).

Geochelone sulcata lives in areas varying from desert fringes to dry savannahs. Most habitats have standing water for only limited periods at best, and this turtle relies heavily on metabolic water and the moisture in its food. Lambert (1993, 1996a) reported that the habitat during the rainy season in Mali consisted of lightly wooded savannah thickly carpeted with annual grasses and scattered herbaceous cover. This same area became very dry during the dry season, and was quickly trampled by livestock.

Natural History
Cloudsley-Thompson (1970) reported that mating may occur from June to March, but most frequently from September through November. During courtship, the male circles the female and occasionally rams her with his shell (Grubb, 1971a). Mounting follows during which the male vocalizes; Grubb (1971a) described the mating call as a short grunt or ducklike quack.
Nesting takes place in autumn or winter and the incubation period is long, 212 days (Cloudsley-Thompson, 1970). Up to 17 eggs are laid at a time; the white eggs are almost spherical (41-44 mm) and have brittle shells. Hatchlings are yellow to tan with rounded, serrated carapaces (45-53 mm).
Tortoises are most active in the rainy season (July-October), and often adults aestivate in their cool, moist burrows during the dry season while hatchlings probably enter small mammal burrows (Lambert, 1993). Most activity is at dusk or dawn, and basking may occur in the early morning to raise temperatures after the night chill.
Geochelone sulcata is a vegetarian, relying on succulent plants and annual grasses for food. In Mali, the preferred food is the annual grass Eleusine indica (Lambert, 1993). Captives consume grass, lettuce, berseem (Medicago sativa), morning-glory leaves (Ipomoea), Idigofera linnei, and Euphorbia hirta.

IUCN Red List Status (1996)
Vulnerable (A1cd).