Turtles of the World
Authors: C.H. Ernst, R.G.M. Altenburg & R.W. Barbour
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Scientific name:

Geochelone yniphora

Vernacular name:

Madagascar ploughshare tortoise, Angonoka, Tortue à soc de Madagascar, Madagassische Schnabelbrustschildkröte, Madagascar boegsprietschildpad


Use the links below to jump to previous and next taxa in a text browser:
Geochelone radiata - Radiated tortoise
Geochelone radiata - Tortue rayonnée
Geochelone radiata - Strahlenschildkröte
Geochelone radiata - Madagascar stralenschildpad
Geochelone carbonaria - Red-footed tortoise
Geochelone carbonaria - Tortue charbonnière
Geochelone carbonaria - Köhlerschildkröte
Geochelone carbonaria - Kolenbranderschildpad

(Vaillant, 1885)
Madagascar ploughshare tortoise

Recognition
The oval carapace (to 44.6 cm) is extremely domed with descending sides, a broad cervical indentation, and the posterior marginals slightly flared and serrated. A cervical scute, small dorsally but large ventrally, is present. Vertebrals are broader than long, or as broad as long, and the 5th is expanded. Well-defined growth annuli surround the raised vertebral and pleural areolae. There are usually 11 marginals on each side, and a single, undivided supracaudal. The carapace is yellowish brown and the outer edges of each vertebral and pleural are darker brown. Each marginal has a dark-brown triangle at its anterior seam. The well-developed plastron is usually immaculate yellow, but may contain some brown pigment. Its forelobe is much larger than the hindlobe, and the thickened elongated gular scute is upturned and projects well beyond the carapacial rim. The hindlobe has a broad anal notch. The plastral formula is: abd > gul >< hum > fem > an >< pect; the gular scute is longer in males than in females, which may have the interhumeral seam longer than the gular. The bridge is wide with a small axillary and a larger inguinal scute. The head is moderate with a nonprojecting snout and a slightly hooked upper jaw. Its large prefrontal scale is divided longitudinally and followed by a single large frontal scale; other head scales are small. The head varies from totally black or dark brown to brownish with some large, yellow, lateral spots near the tympanum. Neck, limbs, and tail are yellow to tan. The forelegs are covered anteriorly with large, yellow, overlapping scales. No enlarged tubercles occur on the thigh, and the tail lacks a large terminal scale.
Males have concave plastra, longer, thicker tails, and longer gular scutes than females.

Distribution
The former range probably included more of the western desert of Madagascar, and possibly some nearby islands, but today Geochelone yniphora is restricted to a small area about Baly Bay in northwestern Madagascar, where only a few hundred individuals still exist (Juvik et al., 1981).

Habitat
Geochelone yniphora lives along the tropical coastal plain in bamboo shrub forests. This is an area of distinct seasonal precipitation, and the tortoises seem to prefer the more xeric microhabitats. Vegetation of the habitat typically consists of the plants Chadsia grevei (shrub), Alloteropsis semialata (grass), Clerodendron incisum (herb), and Casaythra sp. (liana) (Joby, 1996).

Natural History
Males are aggressive toward each other, and must be separated in captivity. Aggressive behavior is apparently directed toward the establishment of dominance, and consists of ramming, pushing, and overturning with the enlarged gular scute (Reid et al., 1989). In Madagascar, courtship activity in captives begins in October and lasts into December, with mating occurring in November and December (Reid et al., 1989; Reid, 1995). At the Honolulu Zoo, courtship and breeding behavior have been observed from late May to September (McKeown et al., 1982; Juvik et al., 1997). Courtship behavior is similar to that of G. radiata, and has been described by McKeown et al. (1982). Males trailed and circled females while sniffing at them. This led to subsequent ramming, pushing, and hooking with the elongated gular scute to overturn the female. One male frequently bit at the female's head and forelegs while circling. Mounting and copulation followed, during which the males vocalized.
Nesting occurs about three months after mating. In Madagascar, captives nested from January to May (Reid et al., 1989), but at the Honolulu Zoo nestings occurred in September-November, and March (McKeown et al., 1982; Juvik et al., 1997). Clutches laid before mid-March in Madagascar usually do not produce young. Females nest early in the morning, and are usually done by early afternoon. The nest is always situated beside a log, tree or bush. The nest cavity is dug entirely with the hind feet, and typical nests are flask-shaped, 12-16 cm deep, with a 11-12 cm diameter egg chamber (Reid et al., 1989; Reid, 1996). The female urinates copiously into the nest as she covers it.
Females may lay as many as seven clutches a year at intervals of 24-40 days (Reid, 1995). A typical clutch contains 3-5 eggs, but clutches of 6 and 7 eggs have been recorded (Juvik et al., 1991; Reid, 1995). The eggs are white and spherical (42-47 mm) with brittle shells (McKeown et al., 1982). Hatchlings in Madagascar emerged from the nest 168-266 days after oviposition (Reid et al., 1989). All of the nests hatch at about the same time, and hatching is heavily dependent on the advent of the first rains in November and December. Emergence is always during the daylight hours.
Hatchlings are 42-46 mm in carapace length (Juvik et al., 1991; Reid, 1995). Apparently their shell remains soft and does not harden much during their first year (Reid, 1995).
Juvik et al. (1981) reported that the tortoises remain mostly inactive during the cool dry season from May to October, and do not dig burrows, but instead push under surface litter. During the day, the tortoises are most active in the morning and late afternoon; other times are spent in the dense thickets.
The herbivorous tortoises feed mostly on the leguminous shrub Bauhinia cf. pervillei, but also eat the grass Heteropogon contortus and other sedges and grasses. At the Madagascar breeding programs, captive breeders have accepted approximately 28 wild plant species, and the diet is supplemented with locally grown bananas, papayas, Opuntia cactus, tomatoes, mangoes, and pumpkins (Reid et al., 1989). Hard-boiled chicken and duck eggs, and eggs with early or well-developed embryos are also eaten. Vitamin-mineral powders and crushed egg shells are also added to the diet. In Honolulu, the tortoises are maintained on a diet of chopped butter lettuce, romaine lettuce, kale, grated carrots, tomatoes, papaya, bananas, and apples, and dry dog food and marmoset diet were added (Juvik et al., 1991). Unfortunately, this diet produced abnormal growth, which Juvik et al. (1991) thought related to the extra bananas and apples, as well as the dog chow, provided during the first two years of life.

IUCN Red List Status (1996)
Endangered (A1c,B1+2cd). Wild populations have continued to decline (Curl, 1986a; Burke, 1990), until this tortoise is one of the most endangered in the world. It now occurs only on a few fragmented patches of bamboo scrub habitat in western Madagascar. As of 1985 only 100-400 wild tortoises were thought to remain in the wild (Smith et al., 1996). The critical endangered status is the result of habitat destruction by frequent brush fires and past collection for the pet trade, and predation of eggs and young by the African bush pig (Potamochoerus larvatus) probably eliminates all viable recruitment. Fortunately, a captive breeding program has beenestablished at Ampijoroa, Madagascar (Curl, 1986b), and the progeny from this project may be used to restock wild populations in the[t] future. The project is responsible for the greatest amount of breeding data currently available on the species (Reid et al., 1989; Reid, 1995, 1996).

Geochelone yniphora
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Madagascar boegsprietschildpad
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