SPINY RATS: Echimyidae

PHYSICAL CHARACTERISTICS

The physical characteristics of spiny rats vary greatly from species to species, from rat-sized to the size of a small cat. Their head and body length is from 4.13 to 18.9 inches (10.5 to 48 centimeters) and a tail length of 0.2 to 16.6 inches (0.5 to 42 centimeters). They weigh from 0.46 to 2.9 pounds (210 to 1,300 grams). In appearance, most species of spiny rat are rat-like, with pointed noses, although several species have blunt noses and resemble squirrels. Their front feet have four toes while their hind feet have five.

Spiny rats got their name because most species have spiny or bristly fur, most noticeably on their backs and rumps. The spiny qualities vary between species: the armored rat has well-developed spines, spiny rats, or casiragua, have broad and stiff hair, and the punaré has soft fur with no hint of spines.

Fur color also varies greatly between species, with upper body fur being gray or various shades of brown, and white or cream on their undersides. Several species, including the toro and the white-faced arboreal spiny rat have black-and-white or white faces.

GEOGRAPHIC RANGE

Spiny rats are found throughout southern Central America and northern and central South America, from southern Honduras to northern Argentina and Chile.

HABITAT

Spiny rats live in a wide variety of habitats, from species that live exclusively in treetops, to forest floor dwellers to those that live underground in complex burrow systems. Many species live near the coast, rivers, or streams. The rato de Taquara lives exclusively in bamboo thickets along stream and river banks. They are found in both old growth and new-growth forests, but are most abundant in forests of intermediate age where there are large numbers of fruit trees, such as palm and fig. Spiny rats are often the most abundant animal in their geographic range.

DIET

Spiny rats are mostly herbivores, meaning they eat only plants, although some species eat insects. Their diet includes fruits, nuts, grass, and sugar cane. Several species, including rato de Taquara, eat only bamboo shoots and leaves.

BEHAVIOR AND REPRODUCTION

Spiny rats are nocturnal, meaning they are mostly active at night. Most die if they are exposed to heat or dryness. Depending on the species, they live either individually, in small groups, or like the broad-headed spiny rat, in large colonies. The average lifespan is two to four years in the wild.

They are generally territorial, meaning they are protective of an area they consider home and claim exclusively for themselves. Males and females have separate territories. Males defend their burrows against other males but females are less aggressive and their territories frequently overlap. Territories are usually small, from 1.2 to 14.8 acres (0.5 to 6 hectares) and can vary greatly between the seasons.

Spiny rats play a critical role in the health of the rainforest of Central and South America by dispersing the seeds from a wide variety of trees and other forest plants through their excretions. They are also an important source of food for predators such as ocelots, owls, boa constrictors, anacondas, and jaguars.

A RAT'S TAIL

As a defensive feature against predators, spiny rats have a tail that easily breaks off. If grasped by the tail, it will break off between the fourth and fifth vertebrae. The rat can then escape to its burrow. There is little blood loss and the break does not appear to harm the rats. However, this way of escape can only be used once since the tail does not grow back. A survey of spiny rats in central Panama found that 15 to 20 percent of all adult spiny rats did not have tails.

Little is known about the breeding habits of many species. In general, spiny rats breed throughout the year and females can give birth to four to six litters a year. The litter size ranges from one to seven babies, with the average being two to four. Gestation period, the time the female carries the young in her womb, varies but is generally sixty to seventy days. In the punaré, a species of spiny rat, the females produce two or three litters per year and gestation period is from ninety-five to ninety-eight days.

SPINY RATS AND PEOPLE

Several species are hunted and eaten by humans, some are killed by farmers who consider them agricultural pests, and several species are used as laboratory animals.

CONSERVATION STATUS

The IUCN lists three species of spiny rats as Extinct, or died out; one species as Critically Endangered, facing an extremely high risk of extinction; five species as Vulnerable, facing a high risk of extinction in the wild; and nine species are Near Threatened, not currently threatened, but could become so. The remaining species are not listed as threatened by the World Conservation Union (IUCN).

SPINY RAT (Proechimys semispinosus): SPECIES ACCOUNT

Physical characteristics: The spiny rat is about the size of a common house rat, except with a larger head and smaller ears. Head and body length is 6.4 to 12 inches (16.0 to 30.0 centimeters) and a tail length of 4.4 to 12.8 inches (11.2 to 32.5 centimeters). They weigh from 10.5 to 17.5 ounces (300 to 500 grams). Their fur is orange-brown on the upper body and white underneath.

Geographic range: The spiny rat is found in Colombia, Costa Rica, Ecuador, Honduras, Nicaragua, and Panama.

Habitat: The spiny rat lives in rainforest, usually in dense underbrush and near rivers and streams.

Diet: They are mostly herbivores, feeding primarily on fallen fruit but sometimes on fungi.

Behavior and reproduction: The spiny rat is nocturnal, meaning it is mostly active at night. It sleeps, nests, and stores food in burrows dug by other animals, rock crevices, or hollows in trees or logs. It does not dig its own burrow. The male defends its burrow against other males. The lifespan of the spiny rat is two to four years.

The species breeds throughout the year and the females may have three to six litters per year. The gestation period, the time the female carries a litter in her womb, is sixty-three to sixty-six days, with the number of babies ranging from one to five. They reach sexual maturity at six to seven months.

Spiny rats and people: Spiny rats are trapped and eaten by local people.

Conservation status: The IUCN does not consider the spiny rat to be threatened. ∎

FOR MORE INFORMATION

Books:

Leite, Yuri L. R. Evolution and Systematics of the Atlantic Tree Rats, Genus Phyllonrys (Rodentia, Echimyidae). Berkeley, CA: University of California Press, 2003.

Macdonald, David. The New Encyclopedia of Mammals. Oxford, U.K.: Oxford University Press, 2001.

Nowak, Ronald M. Walker's Mammals of the World, 6th ed. Baltimore: Johns Hopkins University Press, 1999.

Wilson, Don E., and DeeAnn M. Reeder. Mammal Species of the World— A Taxonomic and Geographic Reference, 2nd ed. Washington, DC: Smithsonian Institution Press, 1993.

Periodicals:

Adler, Gregory H. "Impacts of Resources on Populations of a Tropical Forest Rodent." Ecology (January 1998): 242–255.

Lambert, Thomas D., and Gregory H. Adler. "Microhabitat Use by a Tropical Forest Rodent, Proechimys semispinosus, in Central Panama." Journal of Mammalogy (February 2000): 70–76.

Lara, Marcia C., and Patton, James L. "Evolutionary Diversification of Spiny Rats (Genus Trinomys, Rodentia: Echimyidae) in the Atlantic Forest of Brazil." Zoological Journal of the Linnean Society (December 2000): 661–686.

Marcomini, Monique, and Elisabeth Spinelli de Oliveira. "Activity Pattern of Echimyid Rodent Species from the Brazilian Caatinga in Captivity." Biological Rhythm Research (April 2003): 157–166.

Matacq, Marjorie D, et al. "Population Genetic Structure of Two Ecologically Distinct Amazonian Spiny Rats: Separating History and Current Ecology." Evolution (July 2000): 1423–1432.

Morato, Manaf P., et al. "Profile of Wild Neotropical Spiny Rats (Trinomys, Echimyidae) in Two Behavioral Tests." Physiology and Behavior (July 2003): 129–133.

Web sites:

Myers, Phil. "Family Echimyidae." Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/information/Echimyidae.html (accessed on July 12, 2004).