CANE RATS: Thryonomyidae

PHYSICAL CHARACTERISTICS

The two species in the cane rat family, the greater cane rat and the lesser cane rat, are very similar in appearance, except for the fact that one is larger and heavier than the other. The second-largest rodents in their native continent of Africa after the South African porcupine, the cane rats range in length from 1.3 to 2.6 feet (40.9 to 79.3 centimeters) and in weight from 3.1 to 14.3 pounds (1.4 to 6.5 kilograms). Males are much larger and heavier than females. Cane rats are sturdy-looking animals, with solid, stocky bodies, short, brown, bristly, scaly tails, and small ears. Their speckled fur is sharp-ended and coarse, and can be any shade between grayish and yellowish brown. Cane rats have white lips, chins, and throats, with large, chisel-like incisor teeth that grow continuously. The upper teeth are grooved and bright orange. Their muzzles are squared and padded at the nose. These rodents have short, thick legs with heavily padded feet and straight, powerful claws with five digits in front and four in back. Their skin is very thin and tears easily, although it also heals quickly. Likewise, the tail will break off easily if the animal is caught by it. Sexually mature, those ready to mate, cane rats have orange-tinted fur in their genital areas. Cane rats do not seem to see well, but their senses of hearing and small are keen. Despite their heavy appearance, they are extremely fast and agile creatures.

GEOGRAPHIC RA\NGE

Both species are native to Africa, where they occupy habitats south of the Sahara Desert. They may be found everywhere in west, central, and southern Africa all the way down to the eastern Cape in South Africa.

HABITAT

Although they look similar, the greater and lesser cane rats prefer different environments. The greater species is semi-aquatic and searches out marshes and reed beds near rivers and streams, while the lesser species looks for dry ground in moist savannas, or grasslands. Both animals are excellent swimmers and require tall grasses for hiding and foraging purposes.

DIET

Cane rats are herbivores, plant eaters, and eat a wide variety of grasses and other plant matter, as well as fruits, nuts, bark, and cultivated crops. Cane rats ferment their food in a special organ called the cecum (SEE-kum) to help digest it. They produce two kinds of feces: hard and soft pellets. Both are excreted, but the animals eat the soft pellets to extract any nutrients remaining in them.

BEHAVIOR AND REPRODUCTION

Cane rats earned their African nickname of "grass cutter" because of their method of eating: after using their powerful incisors to cut grasses at their base, the animals take the bunch of grass in their forefeet, sit upright on their haunches, and begin to feed the grass into their mouths slowly, cutting it up into small bits. When eating and when relaxed, they make soft grunting noises.

A GENTLE GIANT

When threatened, cane rats thump their powerful rear feet on the ground to alert others while emitting a piercing whistling sound. Although its teeth are formidable, a frightened cane rat will virtually always run with great speed into dense vegetation and toward the nearest open water rather than turning to fight. If captured, the animals thrash frantically and are frequently injured. When enclosed in a box or crate, the rats often use their padded noses as battering rams to try to escape.

Primarily nocturnal, cane rats create and use narrow trails through the grass and reeds to move around their territories. Biologists think they live in groups of no more than twelve individuals. Males, who live with their young and a few mature females, do not tolerate the presence of other mature males, and aggressively defend their family groups. Males fight by pressing their padded noses together until one eases up on the pressure, at which point his opponent may swiftly swing his rump around to knock the weaker rat off balance.

Despite their well-developed claws, cane rats use burrowing only as a last resort for shelter and even then would rather use abandoned porcupine or aardvark burrows or holes in stream banks cause by erosion if dense vegetation for hiding is absent. Cane rats have been observed gnawing on rocks, pieces of tusk, and bones, presumably to sharpen their teeth.

The cane rats mate with multiple partners throughout the year, although primarily during the rainy season when more food is available. In captivity, pairs reproduce at any time of the year. Pregnant females create a special nursery nest, carving out a shallow depression in a sheltered area and using leaves and grass to line it. She gestates, is pregnant, for 137 to 172 days, and may have two litters of one to eight pups each year. The pups are born with open eyes and are completed furred. They nurse for about a month, but stay with the adults until they reach sexual maturity at five months of age, when males begin to show aggression toward each other.

CANE RATS AND PEOPLE

The meat of both cane rat species is highly prized as an excellent and good-tasting protein source in an often harsh environment. Organized hunts for the animals are frequently held. Some farmers have even started to domesticate "microherds" of them, and families sometimes rely on sale of their meat for income. In Ghana, the price of cane rat meat reportedly surpasses that of beef, sheep, and pork. Farmers are often angered by the rats' frequent raids on their crops, and encourage pythons to come into their fields to feed on the animals.

CONSERVATION STATUS

Abundant in all areas with suitable habitat, neither the lesser nor the greater cane rat is threatened.

GREATER CANE RAT (Thryonomys swinderianus): SPECIES ACCOUNT

Physical characteristics: The larger of the two cane rat species, the (male) greater cane rat ranges in length from 26.1 to 30.9 inches (67.0 to 79.2 centimeters) and in weight from 11 to 14.3 pounds (5 to 6.5 kilograms), although there are reports of these animals weighing as much as 19.8 pounds (9 kilograms). Females are generally smaller. Greater cane rats have powerful, stocky bodies, massive heads, and small, broad, fur-covered ears. Perhaps their most striking feature is their gigantic, bright-orange incisor teeth. The animals have thick, coarse, pointed hair over its body that varies in shades of brown on top and much lighter fur underneath, with orange-tinted fur in the genital areas of mature adults. The forefeet are smaller than the back feet, but both have large, well-formed claws. The forefeet have five digits, but the first and fifth are very small. There are reports of captive greater cane rats living for four years or more.

Geographic range: The greater cane rat is present in almost all countries west of the Sahara Desert except in areas of rainforest, dry scrubland, or desert. Their existence has been recorded in Gambia, Cameroon, the Central African Republic, Uganda, Sudan, Kenya, Tanzania, Malawi, Zambia, Mozambique, Angola, Namibia, Botswana, South Africa, and Zimbabwe.

Habitat: Greater cane rats favor low-lying, swampy places along streams and riverbanks where there are dense patches of reeds and tall grasses.

Diet: This species eats primarily the tender new shoots of elephant grass, pennisetum grass, kikuyu (kee-KUH-yuh), and buffalo or guinea grass, along with the plant roots and stems. They feed on bark, fruits, and nuts in more limited quantities. The greater cane rat also eagerly forages for vegetables in cultivated gardens and are voracious consumers of such crops as cane sugar, maize, pumpkins, sweet potatoes, millet, peanuts, sorghum, wheat, and cassava.

Behavior and reproduction: Mostly nocturnal, this polygamous (puh-LIH-guh-mus) cane rat lives alone or in small family groups with a dominant male, several adult females, and their young. They startle easily and run immediately for the closest water, using their excellent swimming, speed, and agility to outmaneuver predators. Females gestate for 152 to 156 days, giving birth to two to four pups on average, although the range is from one to six.

Greater cane rats and people: Like their smaller cousins, the greater cane rat is viewed by humans as both an important food source and a serious threat to cultivated crops.

Conservation status: These animals are abundant in all locations with habitat suitable for them, and not threatened. ∎

FOR MORE INFORMATION

Books:

De Graff, G. The Rodents of Southern Africa. Durban and Pretoria: Butterworths, 1981.

Mills, M., et al. The Complete Book of South African Mammals. Cape Town: Struik Winchester, 1997.

National Research Council. Microlivestock: Little-Known Small Animals with a Promising Economic Future. Washington, DC: National Academic Press, 1991.

Nowak, Ronald M. "Cane Rats." In Walker's Mammals of the World Online 5.1. Baltimore: Johns Hopkins University Press, 1997. http://www.www.press.jhu.edu/books/walkers_mammals_of_the_world/rodentia (accessed on June 15, 2004).

Periodicals:

Van der Merwe, M. "Breeding Season and Breeding Potential of the Greater Cane Rat Thryonomys swinderianus in Captivity in South Africa." South African Journal of Zoology 34, no. 2 (1999): 69–73.

Web sites:

Animals Online. "Great Cane Rat Thryonomys swinderianus: Fact Sheet." http://www.animals-online.be (accessed on June 15, 2004).