Birch Mice, Jumping Mice, and Jerboas: Dipodidae
BIRCH MICE, JUMPING MICE, AND JERBOAS: DipodidaeHAIRY-FOOTED JERBOA (Dipus sagitta): SPECIES ACCOUNT
The Dipodidae family includes small to medium-sized rodents that walk on two or four legs. In general, their back legs are slightly or much longer than their front legs. They have long tails, and the jerboas' tails often have a distinctive black-and-white "banner" at the end. These mammals' fur is either coarse or soft and colors range from soft brown to brownish yellow to purplish-brown. The Dipodidae rodents range in length from 1.8 to 9 inches (4.5 to 23 centimeters) and weigh from 0.2 to 15 ounces (6 to 415 grams). The birch mice and jumping mice walk on four legs and are small, mouselike creatures with long tails and small, narrow heads. Birch mice have four legs of equal length, while the back legs of jumping mice are somewhat longer than their front legs. Both birch mice and jumping mice have short, blunt claws. Jerboas can be small or medium sized, and jump or walk on their back legs. Unlike the birch mice and jumping mice, which are mainly nocturnal but are sometimes active during the day, jerboas are strictly nighttime creatures. They can run very quickly through sparse brush. Their heads are large, with wide muzzles and flat snouts, and they have large eyes for better nighttime vision. Jerboas have compact, short bodies with short front legs and long, strong back legs. They can have either long or short claws and three, four, or five toes. All members of the Dipodidae family are remarkable for their jumping ability—probably an adaptation for evading predators in open country. Many of the mammals can cover 10 feet (3 meters) in a single jump, using their long tails to balance. In most species, the three central bones of the foot are fused, creating a single bone that provides major strength and support.
The Dipodidae family is widespread throughout the world, and its species are present in North America, northern Africa, the Arabian Peninsula, Europe, and Asia, where they are believed to have originated.
Birch mice, jumping mice, and jerboas occupy a wide range of habitats around the world. Birch mice are most often found in thickets, forests, fields, moors, and steppes. Jumping mice tend to live in woodlands, grasslands, and alpine meadows, where they concentrate in the thick growth near streams, rivers, and marshes. Jerboas are adapted to desert environments and occupy moving sands, rocky plateaus, dry mountainsides, and even clay depressions. Many of the species will live in only very specific places, while others are less selective.
Birch mice and jumping mice eat berries, fungus, nuts, fruits, and insects. Jerboas are omnivores, and eat insects, fruits, seeds, bulbs, plant parts, and even other jerboas.
BEHAVIOR AND REPRODUCTION
Birch mice are able to mate after their first hibernation, and usually have one litter per year containing three to eleven pups. Their gestation period is two to five weeks, and parents care for the young for one month, which is quite long by rodent standards. In jumping mice, which (with a few exceptions) are also ready to mate after hibernation, mating pairs sometimes produce two or three litters. The gestation period is seventeen to twenty-three days and the litter size is usually two to nine pups. Among jerboas, some species breed only once a year during the spring and summer and produce litters of two to nine pups. Others breed in the spring and fall and can produce up to three litters a year, although their litter size is smaller (one to eight pups). In the majority of jerboa species, pups stay in the burrow for five to six weeks before emerging, probably because it takes extra time for them to develop the coordination required for bipedal movement.
Birch mice and jumping mice, while quadrupeds (animals that move about on all fours), also hop and use their tails to hang onto twigs and grasses. Jumping mice can hop up to 6 feet (1.8 meters) long and 3.3 feet (1 meter) high. Both types of mice are strong swimmers as well, and hop straight up when startled. Jerboas move on their hind feet exclusively and are very fast runners. The five-toed jerboa, for instance, can maintain speeds of 25 miles per hour (40 kilometers per hour).
Jumping mice and birch mice seldom dig, finding shelter under logs, in other animals' abandoned burrows, among roots, or under boards. Jerboas, on the other hand, typically dig and live in complex burrows with multiple chambers that they plug during the day to seal out heat and keep in moisture. Sometimes they have different burrows for daytime shelter and for nighttime escape from predators.
Most members of the Dipodidae family hibernate, but for how long and when varies widely based on geography and species. Birch mice hibernate for six or seven months of the year, and can lose up to half of their body weight. Species that breed in the spring and fall hibernate for shorter periods, while those that live in tropical regions experience only a few days of lethargy.
Species of this family are typically solitary and every individual has its own burrow for sleeping and hibernating. In general, these mammals seem tolerant of other individuals' presence, although females are reportedly more aggressive in defending their areas. Neighboring birch mice and jumping mice species even share shelter burrows, but jerboas actively avoid contact with other jerboas in overlapping areas. This is problematic in places where the abundance of jerboas results in population densities of forty to fifty individuals per 2.5 acres (1 hectare). Some jerboas mark their territories by rolling in sand, while others rub their genital areas on the ground.
SANDSHOES FOR THE JERBOA
Jerboas have evolved tufts of coarse, bristly hair under the soles and toes of the hind feet. These act like snowshoes, keeping the animals from sinking into or slipping on loose sand. The tufts also help jerboas to kick sand backward while digging, preventing it from sliding back into their burrows.
None of the species in this family store food. Many of them, however, have specialized ways of finding prey, such as highly developed inner ears that help them hear tiny vibrations in the earth and powerful hind legs that allow them to jump extremely quickly into the air to catch passing insects.
BIRCH MICE, JUMPING MICE, JERBOAS, AND PEOPLE
While the Dipodidae family plays an important role in numerous ecosystems, they have very little interaction with or significance to humans.
Two species, the Armenian birch mouse and the Iranian jerboa, are listed as Critically Endangered, facing an extremely high risk of extinction, dying out, by the IUCN. Three other species are Endangered, facing a very high risk of extinction; three are Vulnerable, facing a high risk of extinction; and nine are considered Near Threatened, not currently threatened, but could become so.
Physical characteristics: Also known as the feather-footed jerboa, rough-legged jerboa, and northern three-toed jerboa, the hairy-footed jerboa was first discovered in 1773. Its body ranges in length from 4.5 to 6 inches (11.5 to 14.5 centimeters), while its tail is typically 7 to 7.1 inches (17.5 to 18 centimeters) long. These mammals weigh between 2.4 and 4 ounces (69 to 104 grams). Underparts are white, and upperparts change from orangey and black in the winter to pale, sandy buff color in summer.
Geographic range: A resident of the Middle East, Asia, and Europe, the hairy-footed jerboa occupies ten isolated, large areas and several smaller fragments of habitat in the northern Iranian sand deserts, Turkmenistan, Uzbekistan, southwestern Kazakhstan, Mongolia, China, and eastern Russia.
Habitat: At the northern extreme of its range, the hairy-footed jerboa lives in sparsely vegetated areas of pine forests, but in general this mammal occupies sandy expanses of steppes, deserts, and semi-deserts. In central Asia, this jerboa also lives in places with hard rocky or gravel-strewn surfaces.
Diet: While the hairy-footed jerboa subsists mainly on desert plant greens and seeds, it occasionally preys on insects as well.
Behavior and reproduction: Hairy-footed jerboas mate with more than one individual during the breeding season in spring. Female bear two or three litters per season, in spring and fall. The spring-born animals can mate at two-and-a-half to three months, and usually participate in the fall mating. Pregnancy lasts thirty-five days, and the number of young varies from one to eight. In springtime, female adults are usually still nursing their fall litter when they mate again.
Hairy-footed jerboas are solitary creatures, although they willingly tolerate overlapping home ranges. The vast majority of their contacts in nature (versus those in captivity) are non-aggressive. When captive, males and females form pairs and sleep together in a single nest.
Hairy-footed jerboas and people: There are no records of significant interactions between this species and humans.
Conservation status: The hairy-footed jerboa is common in all of its habitats, with the exception of one subspecies, which is listed as Vulnerable because of the expansion of steppes through areas of open sand dunes in southeastern Russia. ∎
FOR MORE INFORMATION
Boitani, Luigi. Simon and Schuster's Guide to Mammals. New York: Fireside Books, 1990.
Corbet, G. B., and J. E. Hill. A World List of Mammalian Species. Oxford, U.K.: Oxford University Press, 1991.
Nowak, Ronald M. "Birch Mice and Jumping Mice." Walker's Mammals of the World Online 5.1. Baltimore: Johns Hopkins University Press, 1997. http://www.press.jhu.edu/books/walkers_mammals_of_the_world/rodentia/rodentia.zapodidae.html (accessed on June 13, 2004).
Nowak, Ronald M. "Jerboas." Walker's Mammals of the World Online 5.1. Baltimore: Johns Hopkins University Press, 1997. http://www.press.jhu.edu/books/walkers_mammals_of_the_world/rodentia/rodentia.dipodidae.html (accessed on June 13, 2004).
Simon, Noel. Nature in Danger: Threatened Habitats and Species. Oxford, U.K.: Oxford University Press, 1995.
"Family Dipodidae." Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/information/Dipodidae.html (accessed June 24, 2004).