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The African Hinge-back Tortoises

David T. Kirkpatrick, Ph.D


Often in nature the same type of adaptation will be found in unrelated families of animals, attesting to the survival benefits of that particular change. In chelonians, many families have developed a hinged plastron, which affords greater protection to the vulnerable limbs and body of the turtle. However, one genus, Kinixys, is unique among turtles and tortoises in that it has turned that protective adaptation upside down. Kinixys comes from the fusion of two Greek words: kineo (to move) and ixus (back or waist); together they mean 'movable back'. The Hinge-back Tortoises, as they are commonly called, develop a hinge that allows them to close the rear of their carapace, protecting their back legs.

Hinge-back tortoises appear to be typical tortoises on first inspection. Hinge-backs are considerably longer than they are wide, more closely resembling a Red-footed Tortoise (Geochelone carbonaria) than a Leopard Tortoise (G. pardalis), for example. In overall size Kinixys species are on the smaller end of the tortoise range. The largest species, K. erosa, the Serrated Hinge-back Tortoise, attains an adult size of 32 centimeters. The smallest species, K. natalensis, the Natal Hinge-back Tortoise, only grows to half that size. Hinge-backs possess the elephantine feet associated with tortoises, although the front feet are not quite as blunt as the rear. Their forelegs usually have a series of enlarged, downward-pointing scales while the rear legs lack these scales. In these chelonians the head is only of medium size, somewhat longer and flatter in profile when compared to a Leopard or a Spurred Tortoise. Their tail ends in a nail-like spike. Of course, the Hinge-back's distinguishing characteristic is the unique hinge that develops in adults at the rear of the carapace, between the seventh and eighth marginal scutes.

Kinixys' carapacial hinges allow the tortoises to clamp down the rear of their carapaces, giving increased protection to their tail and legs. Hinge-backs also have effective defenses for their front legs and head. When threatened, a tortoise can retract its head quite far. Its front legs then seal the anterior opening in the carapace; the knees meet in front of the head with the feet pointing to either side. The enlarged scales on the forelegs face outward in this position, protecting the legs themselves and effectively closing the tortoise off from the world.

Coloration of the carapace and plastron is quite variable in Hinge-backs, both between species and among individuals of a particular species or subspecies. Individuals in the various subspecies of Bell's Hinge-back, Kinixys belliana, exhibit the greatest variation. Some shade of tan, yellow or brown is common, with the lighter central region of each scute surrounded by a darker shade. The coloration of Kinixys erosa is even more dramatic - usually a dark reddish brown color predominates. In contrast, Home's Hinge-back, K. homeana, is a much duller tan, although faint radiating lines of darker color occasionally can be seen in some specimens. The Natal Hinge-back often has an orange cast to it, with alternating rings of lighter and darker material on each scute. Coloration may also vary between sexes in Hinge-backs, with females possessing a more intense coloration or distinct pattern.

The exact number of species of Kinixys depends on the authority that is consulted. Until fairly recently, only three species were recognized; K. belliana, K. erosa, and K. homeana. In 1981 the species K. natalensis was revived by Donald Broadley. Originally it had been designated a subspecies of K. belliana. A number of subspecies have been proposed for Bell's Hinge-back; some of these are now considered invalid and have fallen out of favor. Others, such as K. natalensis, have been elevated to species status. Broadley recently reviewed the genus again and indicated that two more subspecies, K. belliana lobatsiana and K. belliana spekii, should be listed as full species. These alterations give species status to six tortoises: K. belliana (with three subspecies, K. b. belliana, K. b. nogueyi, and K. b. zombensis), K. erosa, K. homeana, K. lobatsiana, K. natalensis, and finally K. spekii(See Table 1).

As might be expected from the shuffling around of species and subspecies designations, some of the Hinge-backs are difficult to tell apart. Perhaps the most distinctive is K. homeana, Home's Hinge-back. The posterior portion of this tortoise's carapace has an almost 90 degree downward bend in it after the fifth vertebral scute. Viewed from the side, it appears as if the shell comes to a knob or point before dropping off precipitously. The scutes are planar, meeting neighboring scutes at a distinct angle. No other Hinge-back has this combination of features. Bell's Hinge-back, for example, has a much smoother domed carapace without the sheer drop-off in the rear. Also, unlike Home's Hinge-back, the rear edge of K. belliana's upper shell is smooth. This feature distinguishes it from the Serrated Hinge-back, K. erosa. As its common name implies, the rear carapacial edge of K. erosa is quite jagged. The Natal Hinge-back, K. natalensis, can be identified by its small size and by the tricuspid shape of its upper beak. Finally, K. spekii most closely resembles K. belliana, but can be distinguished by its flatter carapace and coloration.

Differences between the sexes in various species of Kinixys can be somewhat subtle also. As with most other tortoises, the plastron of a male Hinge-back is more concave and the tail is longer and thicker than in the female. In some species the female's coloration is more vivid than the male's; this characteristic is also age-dependent, making it somewhat unreliable however. Another characteristic that has been mentioned as varying between the sexes is the profile of the shell when viewed from the side. For example, females of K. belliana and K. natalensis are believed to have a more steeply sloped posterior profile when compared to that of a male tortoise.

Male Hinge-backs possess a territorial instinct and will battle with suspected intruders, especially other males during breeding season. This tendency may make it difficult to keep more than one male Hinge-back in an enclosure. Rod Patterson, in his book Reptiles of Southern Africa, relates a story that demonstrates the ferocity with which male Hinge-backs defend their territory. A number of native tortoises were kept together in a garden in South Africa. One hot afternoon a male Hinge-back went to get a drink from a water tray and spied a Leopard Tortoise twice his size who had just finishing drinking. "With an alacrity belying his shape the Hinged Tortoise engaged ramming speed, making contact with the unsuspecting Leopard Tortoise some 2 m later and hitting him so forcibly that he rolled over twice, finally coming to rest upside-down." After inspecting the beleagured tortoise, the Hinge-back decided that the Leopard Tortoise was no longer a threat, and went back for his drink.

Courtship in Kinixys does not seem to be an elaborate affair. The male will nudge and shove the female for a short while, and then mount. The shape of the carapace presents some difficulties to successful mating, especially in K. homeana, where the carapace comes to a sharp point and then drops off at a right angle down to the tortoise's tail. Home's Hinge-backs owned by the author were observed during mating. The male tortoise climbed onto the female and then lowered his back until it was touching the ground, leaving the male pointing upward at about a 70 degree angle to the ground. With front feet dangling or just touching the top of the female's carapace, the male moved his tail under the female's carapace. During mating the male stretched his neck out as far as it would go and opened his mouth in a wide gape, emitting a number of low moaning hisses.

The carapacial hinge in female Kinixys tortoises might help them during egglaying. A normal clutch for Hinge-back females is two to four oval eggs, although larger K. belliana are capable of producing twice as many eggs. Females also can produce multiple clutches in a breeding season. Artificially incubated eggs take between three and four months to hatch when incubated at 30 degrees C; in the wild much longer incubation times have been reported.

Hatchling tortoises are approximately 1.5 to 2 inches long when they first hatch. While hatchling Bell's Hinge-backs have a smooth carapacial rim, baby Home's and Serrated Hinge-backs have a spiny margin. Hatchling and juvenile Hinge-backs actually do not possess a hinged carapace - the hinge develops later in life. Young Kinixys tortoises strongly resemble tortoises in the genus Homopus. Indeed, experts in the field can be fooled; the type specimen for Kinixys belliana nogueyi, a juvenile, was originally placed in Homopus until its true identity was discovered.

The Hinge-backs inhabit a diverse array of habitats in central and southern Africa. Kinixys belliana lives primarily in grassland and savannah regions, although some individuals can be found in coastal forests. These regions often go through times of drought, and Bell's Hinge-back estivates underground to survive these periods. This tortoise has large anal sacs which can be filled with water, taking up a large percentage of the abdominal cavity, to help it during the dry season. This stored water may be used by females when building nests to help loosen and moisten the soil in and around the nest. Another threat to these tortoises is fire; unfortunately carapacial hinges do not provide adequate protection from grass fires. Grasslands also are inhabited by Kinixys natalensis, whereas K. homeana and K. erosa prefer forested regions. The Serrated Hinge-back especially is fond of moist habitat, often living around marshes, wetlands and river banks. It is capable of swimming, unlike many tortoises.

When keeping Kinixys in captivity, the wide variety of biotypes inhabited by Hinge-backs makes it difficult for the tortoise-keeper to provide the appropriate environment without some experimentation. However, some generalizations can be made. Hinge-backs are relatively active tortoises, so a large enclosure should be provided. As with most tortoises, outdoor arrangements are preferable to indoor setups if the climate is appropriate. A secure hiding spot or area that allows burrowing is essential. In the wild these tortoises often utilize burrows or excavate hollows in which to rest. Another vital element is a water hole in which the tortoises can soak. These chelonians prefer a more humid, moist environment than might be expected and will suffer if kept too dry. Keepers should vary the amount of heat and direct light; species from forested regions, such as K. homeana, generally prefer more shade than grassland species. However, individual tortoises may differ, so experiment with conditions to determine the specific tortoise's optimal environment.

Hinge-backs are omnivorous feeders in the wild. In addition to greens, they consume snails, insects such as millipedes and beetles, and will scavenge corpses when encountered. In captivity they will eat a wide variety of vegetable matter, including green beans, broccoli, squash, mushrooms, and bananas. They readily take mealworms and mealworm beetles, cooked chicken, and liver. Earthworms are relished; they are grabbed, whipped from side to side, and swallowed rapidly. As mentioned above, fresh water for drinking and soaking is essential for a Hinge-back's health.

Although Hinge-backs are often available on dealer price lists and in pet shops at a fairly low price, they are not an ideal tortoise for beginners. Virtually all of these tortoises have been removed from their native habitat in Africa and shipped to the United States. They often arrive in a stressed condition, with no information available as to their place of origin. They require a complete veterinary examination as soon after purchase as possible. Determining an appropriate environment for the tortoise can be a daunting task also. Many turtle-keepers report instances of Hinge-backs appearing to thrive for a few months (or more) in captivity, but then suddenly declining. These deaths may be due to a number of factors, such as an undiagnosed parasitic infection or failure to provide some necessary component of the tortoise's diet or environment. For beginning tortoise keepers, a much wiser investment would be a captive-born Redfoot, Leopard, or African Spurred Tortoise (Geochelone carbonaria, G. pardalis, or G. sulcata, respectively).

Experienced tortoise keepers with the desire to work with Kinixys should attempt to establish viable breeding colonies. A large number of Hinge-backs currently enter the United States pet market, even though they are listed as a CITES II animal, because their native countries allow a high level of export. This high level of trade cannot continue indefinitely without depleting the wild populations. The breeding successes of tortoise keepers within the native range of the various Kinixys species indicate that it is possible to keep these chelonians in captivity. As a further example, three European zoos successfully produced captive-born Hinge-backs (listed in the 1994 edition of Frank Slavens' Reptiles and Amphibians in Captivity: Breeding, Longevity and Inventory), demonstrating that breeding is possible outside of their native range. Outdoor maintenance and duplication of their native environment may increase the chances of successful breeding in the United States. Hopefully, captive-born individuals will prove much hardier in captivity than their wild-caught ancestors, as has happened with other reptiles.

Hinge-backs are unique among the tortoises of the world. Their carapacial hinge is a fascinating adaptation, affording the turtle increased protection from predators. Many details of the life history of Kinixys are still unknown. Hopefully the current levels of export will not damage native populations to the extent that these details will never be worked out. People keeping Hinge-backs should make every effort to care for them as the valuable creatures they are, and not as the cheap pets they currently appear to be.

Bibliography and Other Books to Consult:

Boycott, Richard C. and Ortwin Bourquin. 1988. The South African Tortoise Book. Southern Book Publishers, Johannesburg, SA.

Ernst, Carl H. and Roger W. Barbour. 1989. Turtles of the World. Smithsonian Press, Washington, DC.

Highfield, A. C. 1990. Keeping and Breeding Tortoises in Captivity. R & A Publishing, Ltd., Avon, England.

Iverson, John B. 1992. A Revised Checklist with Distribution Maps of the Turtles of the World. Privately published.

Obst, Fritz Jurgen. 1988. Turtles, Tortoises and Terrapins. St. Martin's Press, New York.

Patterson, Rod. 1987. Reptiles of Southern Africa

Pritchard, Peter C. H. 1979. The Encyclopedia of Turtles. T.F.H. Publications, Neptune City, NJ.

Slavens, Frank L. and Kate Slavens. 1994. Reptiles and Amphibians in Captivity: Breeding, Longevity and Inventory. Slaveware Publishing, Seattle, WA.

 

This article copyright © 1998 by David T. Kirkpatrick.

 

Reprinting of this article for non-profit purposes is permitted provided that it is unaltered and appropriate attribution, including copyright information, is included. Please notify the author of any reprinting.

 

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