POCKET MICE, KANGAROO RATS, AND KANGAROO MICE: Heteromyidae

PHYSICAL CHARACTERISTICS

Pocket mice, kangaroo rats, and kangaroo mice, sometimes called heteromyids (members of the family Heteromyidae), are small- to medium-sized rodents with external, fur-lined cheek pouches. The pouches open in front of the mouth and go back along the shoulders. They have fairly large eyes and short, rounded ears. Pocket mice use all four feet while walking, while kangaroo rats and mice use only their rear two feet for walking. Kangaroo rats and mice have long tails with white tips or tufts on the end, along with relatively short front limbs. Pocket mice have shorter, less noticeable tails. Kangaroo rats and mice have good hearing. Kangaroo rats and mice have soft and silky fur, while pocket mice have coats that range from silky to spiny. The coat color varies from light to dark, depending on species and habitat, often matching the soil color on which they live.

Adults are 1.7 to 14.6 inches (4.3 to 37 centimeters) long and weigh between 0.2 and 6.9 ounces (5 and 195 grams). Kangaroo rats weigh between 1.2 and 6.9 ounces (33 and 195 grams); kangaroo mice weigh between 0.4 and 0.6 ounces (10 and 17 grams); and pocket mice weigh between 0.2 and 3.0 ounces (5 and 85 grams).

GEOGRAPHIC RANGE

Heteromyids are found in the western United States, southwestern Canada, Mexico, Central America, and northern South America.

HABITAT

Heteromyids live in deserts, dry grasslands, and, in a few cases, wet and dry tropical forests. Desert pocket mice and kangaroo rats like arid, dry, climates that contain sand, scrubs, sagebrush, grasses, and chaparral. Kangaroo mice prefer sandy habitats. In all cases, heteromyids like areas that contain many seeds.

DIET

Heteromyids eat mostly seeds, but also eat green vegetation and, in some species, insects. Desert species can go without water for long periods of time. They leave their burrows at night to dig through soil with their forelimbs to gather seeds into their cheek pouches. When pouches are full, they return to one of their caches (KASH-uhz), hidden supply areas, which are used throughout the animal's home range. Heteromyids defend their territory aggressively when they have collected many seeds.

BEHAVIOR AND REPRODUCTION

Heteromyids are nocturnal, active at night, rodents. Kangaroo rats and mice move about mostly by hopping on their hind limbs, while pocket mice use all four of their limbs in a walking motion. They have a very basic social structure, mostly living alone except for females and young. They do interact with nearby neighbors, which are often relatives. Most species burrow tunnel systems with multiple chambers and surface openings.

Heteromyids have well-developed communication systems. Medium- and large-sized kangaroo rats communicate by drumming or thumping the ground with their large hind feet; familiar thumping identifies neighbors, while strangers are not recognized. Each species has its own set of drumming patterns, which are heard through the air and ground.

Male home territories overlap with those of other males and females. Females occupy a territory that contains no other females. They regularly bathe in sand, which helps to clean their hair and to deposit their scents onto the ground. Their scent informs other heteromyids and other animals about their sex, identity and mating status. When a predator, an animal that hunts other animals, is seen, heteromyids use their body coloring to hide and avoid them. If needed, they will run away along a crooked path. Desert heteromyids also have strong hearing that lets them hear approaching predators.

Males always travel to female territories during breeding season in order to mate. Mating relationships range from one male and one female, to several males competing for access to one breeding female. Larger and medium sized kangaroo rats drum their feet in order to chase away competing males. Females prefer to mate with males they know, but will mate with strangers if necessary. Males will mate with any females. Breeding occurs only when enough moisture is available for nursing females to provide milk to young. Females produce several litters, group of young animals born at same time from the same mother, each year, but the number depends on environmental conditions. Litter sizes range from one to nine, but average three to four in most species. They live ten years or longer.

POCKET MICE, KANGAROO RATS, KANGAROO MICE, AND PEOPLE

Kangaroo rats are considered keystone species because their burrows provide habitat for a variety of plants and animals. A keystone species is a species that is important in maintaining the biodiversity, the variety of different animals and plants, of an area.

CONSERVATION STATUS

Four species of pocket mice, kangaroo rats, and kangaroo mice are listed by the World Conservation Union (IUCN) as Critically Endangered, facing an extremely high risk of extinction in the wild. One species is listed as Endangered, facing a very high risk of extinction in the wild, and one species is Vulnerable, facing a high risk of extinction. The IUCN also lists nine species as Near Threatened, not currently threatened, but could become so. Many species are threatened with excessive destruction and fragmentation, breaking up, of habitat and the loss of plant life.

SAN JOAQUIN POCKET MOUSE (Perognathus inornatus): SPECIES ACCOUNTS

Physical characteristics: San Joaquin (san-wah-KEEN) pocket mice are small sand-colored mice with soft coats, sparse darker back hairs, and yellowish undersides. They do not have spiny hairs that are often found on other pocket mice species. A line separates the lighter belly hairs from the darker back hairs. San Joaquin pocket mice have short ears that sometimes have a base patch of lighter hair. Their hind feet have hair on the soles and their long tails are covered with hair with a small hair tuft on tip. They have external fur-lined cheek patches that are used for storing and transporting food. Adults are 5.0 to 6.3 inches (13 to 16 centimeters) long and weigh between 0.22 and 0.39 ounces (7 and 12 grams).

Geographic range: They are found in west-central California.

Habitat: San Joaquin pocket mice inhabit arid grasslands, deserts, and scrublands, especially areas with fine soils.

Diet: Their diet consists of seeds of grasses, shrubs, and forbs, broad-leaved herbaceous plants that grow in prairies and meadows. San Joaquin pocket mice forage, search for food, within shrub branches. They also eat soft-bodied insects such as cutworms and grasshoppers, and rarely drink water, getting almost all moisture through their food.

Behavior and reproduction: San Joaquin pocket mice do not travel far to forage, and stay away from open areas. They bathe by rubbing their sides and ventrum, external opening by which wastes pass in primitive mammals, in the sand. Their breeding season is from March to July. Females have at least two litters of four to six babies per litter.

San Joaquin pocket mice and people: San Joaquin pocket mice help to scatter seeds, which helps to maintain a healthy environment where it lives.

Conservation status: San Joaquin pocket mice are listed by the U.S. Fish and Wildlife Service as a species of special concern. Two subspecies, populations of a species in a specific area, are listed as Near Threatened. ∎

GIANT KANGAROO RAT (Dipodomys ingens): SPECIES ACCOUNTS

Physical characteristics: Giant kangaroo rats are the largest members of heteromyids. They have long and powerful hind limbs that are used for hopping, and small and relatively weak front limbs that are used for digging. These animals have very long tails that are used for balance. Their dark tail has white lines along either side. They have large eyes, small rounded ears, and a somewhat rounded body. Their coat is sandy-colored with a white underside and a white stripe across the hindquarters. Adults are 12.3 to 13.7 inches (31 to 35 centimeters) long and weigh between 3.0 and 6.3 ounces (93 and 195 grams).

Geographic range: Giant kangaroo rats are found in San Joaquin Valley, California.

Habitat: They inhabit arid grasslands that contain sandy soils and are sparsely populated by desert shrubs.

Diet: Their diet consists of seeds, which are first stored in burrows. Sometimes seed heads are cured, preserved, in surface caches. They also eat insects and other vegetation.

Behavior and reproduction: Giant kangaroo rats are nocturnal animals, hiding in their burrows during the hottest parts of the day. Burrows are usually shallow tunnels that contain larger chambers, one that acts as a nest and the others used to store food. They are usually found alone, and move by hopping on their back legs. Their back, hind, legs let them jump over 6 feet (2 meters) when escaping predators. Their front limbs are smaller and used only for digging. They defend their territory, but live peacefully with their close neighbors.

Both sexes drum their hind feet in order to tell visitors to stay away, or to tell other giant kangaroo rats that predators, such as snakes and kit foxes, are around. Males drum their feet while competing with other males for the right to mate with a mature female. This mating sound may include up to 300 individual thumps that are repeated many times. The breeding season is from January to May. Females have more than one breeding cycle per year, and have an average of three breeding cycles in a breeding season. The gestation, pregnancy, period is thirty to fifty-five days. Typically, females are able to breed again three days after giving birth. Young are able to breed after only two to three weeks of being born.

Giant kangaroo rats and people: Giant kangaroo rats are considered keystone species.

Conservation status: Giant kangaroo rats are listed by the IUCN as Critically Endangered. They are also considered endangered by the California Fish and Game Commission and the U.S. Fish and Wildlife Service. Their populations have drastically decreased due to habitat loss as deserts are converted to agricultural lands. They no longer occupy over 95 percent of their former habitat, but are protected within the Carrizo Plain Natural Heritage Reserve and a number of federal lands. ∎

FOR MORE INFORMATION

Books:

Feldhemer, George A., Lee C. Drickamer, Stephen H. Vessey, and Joseph F. Merritt. Mammalogy: Adaptation, Diversity, and Ecology. Boston: WCB McGraw-Hill, 1999.

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

Vaughan, Terry A., James M. Ryan, and Nicholas J. Czaplewski. Mammalogy, 4th ed. Philadelphia: Saunders College Publishing, 2000.

Whitfield, Dr. Philip. Macmillan Illustrated Animal Encyclopedia. New York: Macmillan Publishing Company, 1984.

Wilson, Don E., and DeeAnn M. Reeder, eds. Mammal Species of the World, 2nd ed. Washington, DC and London: Smithsonian Institution Press, 1993.