Squirrels and Relatives: Sciuridae

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SQUIRRELS AND RELATIVES: Sciuridae

SOUTHERN FLYING SQUIRREL (Glaucomys volans): SPECIES ACCOUNTS
EASTERN CHIPMUNK (Tamias striatus): SPECIES ACCOUNTS
BLACK-TAILED PRAIRIE DOG (Cynomys ludovicianus): SPECIES ACCOUNTS
ALPINE MARMOT (Marmota marmota): SPECIES ACCOUNTS
GRAY SQUIRREL (Sciurus carolinensis): SPECIES ACCOUNTS

PHYSICAL CHARACTERISTICS

Squirrels are some of the most familiar rodents. They are small to medium-sized animals with relatively long tails. Squirrels have five toes on the back feet and four on the front feet, with a well-developed claw on each digit. Eyes are relatively high on the head and spread apart to allow them a wide range of vision. Size, fur, shape, and tail features depend upon the type of squirrel. There are three general body forms in these animals: flying squirrels, ground squirrels, and tree squirrels.

Flying squirrels have large, bushy tails and bodies adapted for moving between trees. They are generally slim with long legs. A furred membrane, double layer of thin skin, extends between the wrist and ankle, which allows them to glide. They have large eyes. Their fur is soft and dense and is generally brown, gray, or blackish in color. The underside is a paler color.

Ground squirrels range widely in size. The marmots are the largest ground squirrels, with weights of up to 16.5 pounds (7.5 kilograms); the smallest are the American chipmunks, which weigh up to 5 ounces (142 grams). These squirrels are typically short legged with muscular bodies. Their tails are furry, but generally not as bushy as those of tree squirrels.

Tree squirrels have long, bushy tails, sharp claws and large ears. Some have well-developed ear tufts. Tree squirrels also range extensively in size, from the pygmy squirrels that is about the size of a mouse, to the fox squirrels that can measure 18 to 27 inches (46 to 69 centimeters). Their hind legs are extremely long and they have long curved claws. Their tails are almost as long as their bodies.

GEOGRAPHIC RANGE

Squirrels are found throughout the world, except in Australia, Madagascar, southern South America, and certain desert regions, such as in Egypt.

HABITAT

There are many types of flying squirrels found in south and southeast Asia, especially in tropical, hot and humid, forests. Some species live in northern temperate, not too hot or too cold, regions, up to the Arctic Circle.

Ground squirrels live in many different habitats, such as grassland, forests, meadows, and the arctic tundra. Chipmunks are the one type of ground squirrel that are often found in dense shrubs or closed forests.

Tree squirrels live in forests, woodlands, gardens, cities, and farmlands.

DIET

Most squirrels eat primarily plant materials. Tree squirrels and flying squirrels often eat nuts and seeds, and will occasionally also feed on fungi, eggs, insects, young birds, and small snakes. Ground squirrels also eat seeds, fruits, and nuts, but often have diets made up of large amounts of grasses and leafy materials.

BEHAVIOR AND REPRODUCTION

Most squirrels are active during the day, yet some species, such as all the flying squirrels, are nocturnal, active at night. Squirrels communicate by making shrill sounds. They also communicate by tail gestures, such as "flicking" the tail to indicate that another squirrel should go away. Most squirrels wrap their tail around themselves when resting. Squirrels build nests high in the trees called dreys, which are made of twigs and leaves. They line the inside of dreys with fur, feathers, or other soft material. The nest typically will have two exits. Squirrels also will build a nest called a den in the hollow of a tree.

NEW TREES FROM FORGETFUL SQUIRRELS

For squirrels, a little forgetfulness can turn into a lot of trees. Every autumn, squirrels "squirrel away" numerous nuts. For example, it is estimated that each gray squirrel buries at least 1,000 nuts every fall, possibly as many as 10,000 nuts in one season. The squirrels can bury the nuts several inches deep. They locate their buried nuts by smell, and are able to find nuts buried under a foot or more of snow. But they can forget. It is estimated that millions of trees in the world are accidentally planted by squirrels that bury nuts and then forget where they hid them.

Flying squirrels do not actually fly, as bats and birds do—they leap and glide. They leap from a high point, flattening their bodies and extending the legs widely, and then land at a lower point. Some species can glide for as much as 1,476 feet (450 meters). The squirrels can even turn at a right angle to avoid a branch.

Ground squirrels make burrows, tunnels or holes, which they use to rest in during the heat of the day and escape predators, animals hunting them for food. Many of the ground squirrels hibernate, become inactive to conserve energy, for varying periods of time. Some squirrels can hibernate for up to nine months.

Tree squirrels are solitary animals, yet some African species travel in pairs or small groups. These squirrels build nests of leaves or needles in hollow trees or limbs. They are active and maneuver (mah-NOO-ver) easily in trees.

For ground squirrels, the breeding season follows shortly after hibernation. Some species will skip a year of breeding; others can reproduce more than once a year. Baby ground squirrels are generally born underground without fur. There are usually four in a liter. Flying squirrels typically give birth to small litters of one to two offspring, which are generally blind and naked at birth. Tree squirrels generally have a polygamous (puh-LIH-guh-mus) mating system, meaning the male and female can have more than one mate. Litter sizes vary, depending upon the habitat and food availability.

SQUIRRELS AND PEOPLE

People have hunted squirrels for their fur and meat, and for sport. While squirrels are generally considered playful and harmless creatures, these animals can destroy crops and some people consider them pests. Their burrows occasionally damage irrigation systems and can harm livestock, but these rodents also destroy undesirable weeds and insects. Some squirrels are also carriers of organisms that transmit human disease, such as the plague and Rocky mountain tick fever. People have caused a decline in many squirrel populations by destroying their habitats and hunting them.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists two squirrel species as Critically Endangered, facing an extremely high risk of extinction in the wild; nine species as Endangered, facing a very high risk of extinction; twenty-six species as Vulnerable, facing a high risk of extinction in the wild; and thirty-four species as Near Threatened, not currently threatened, but could become so.

SOUTHERN FLYING SQUIRREL (Glaucomys volans): SPECIES ACCOUNTS

Physical characteristics: Southern flying squirrels are generally about 8 to 10 inches (20 to 25 centimeters) long, and have a black ring around their large eyes. They have gray fur with white bellies.

Geographic range: These squirrels are found in eastern Canada south through the eastern United States. Isolated populations stretch to Honduras.

Habitat:

Southern flying squirrels live primarily in deciduous forests. They usually make their nests in tree hollows.

Diet: These squirrels eat nuts, seeds and berries. They will also eat bird eggs, bird nestlings, insects and occasionally dead mice.

Behavior and reproduction: Southern flying squirrels are nocturnal. These squirrels will form small groups in the winter and share a common nest to keep warm. They typically glide an estimated 20 to 30 feet (6 to 9 meters) from the top of one tree down to the trunk of another tree, though they may glide farther.

Southern flying squirrels mate in early spring and summer. Females give birth to two litters of two to seven offspring. Mothers will defend their young and move them to another nest if they are threatened.

Southern flying squirrels and people: These squirrels are considered gentle and are popular as pets.

Conservation status: Southern flying squirrels are not listed as threatened by the IUCN. They are generally common with some isolated populations threatened due to habitat loss. ∎

EASTERN CHIPMUNK (Tamias striatus): SPECIES ACCOUNTS

Physical characteristics: The largest of the chipmunks, eastern chipmunks are about 8.9 to 10.6 inches (22.5 to 26.8 centimeters) long. They have grayish to reddish brown fur, white fur on their bellies, and five stripes from the neck to their tail. Two of the stripes are white bordered by black stripes, and one black stripe is in the center. They also have light strips above and below their eyes, and pouched cheeks.

Geographic range: Eastern chipmunks are found in southeastern Canada and most of the northeastern United States, south to Mississippi and Virginia and west to North Dakota and Oklahoma.

Habitat: Eastern chipmunks generally live in open deciduous forests with rocks, logs, and stumps. They can also be found in more open, bushy areas.

Diet: Eastern chipmunks primarily eat nuts, acorns, seeds, mushrooms, fruits, berries, and corn. They also eat insects, bird eggs, snakes, snails and small mammals, such as young mice.

Behavior and reproduction: Eastern chipmunks construct elaborate burrow systems. They are solitary, prefer to burrow alone, except for offspring. In warmer months they spend much of their time gathering and storing large amounts of food—they can gather up to 165 acorns in a single day. These animals remain in their dens for the winter and sleep frequently. They wake up every few weeks to eat the food they have stored.

These chipmunks breed from late June to early July. Litter sizes average three to five offspring. In some areas a female may have a second litter. Offspring will come above ground five to seven weeks after birth.

Eastern chipmunks and people: There is no special connection between these chipmunks and people.

Conservation status: Eastern chipmunks are not considered threatened. ∎

BLACK-TAILED PRAIRIE DOG (Cynomys ludovicianus): SPECIES ACCOUNTS

Physical characteristics: Black-tailed prairie dogs have sharp teeth, a black-tipped tail, and are about 14 to 15.7 inches (35.5 to 39.8 centimeters) long. Their fur is brown, golden brown, or reddish brown, and whitish on the underside.

Geographic range: These prairie dogs are found in areas from Canada to Mexico. In Canada they are found in Saskatchewan; in the United States they live from Montana to eastern Nebraska, south to northern Mexico.

Habitat: Black-tailed prairie dogs live in open, flat and arid, extremely dry, grassy plains.

Diet: These animals eat primarily leaves, stems, grass roots, weeds, and wildflowers. They will sometimes eat grasshoppers, beetles and other insects.

Behavior and reproduction: Black-tailed prairie dogs are extremely social. They dig a complex series of tunnels deep into the ground, which is called a town. Towns can spread over hundreds of acres and contain thousands of prairie dogs. They communicate to one another frequently, using yips, growls, chattering, barks and chirps.

Black-tailed prairie dogs have one litter a year. Breeding occurs from February to March. A month after mating, the female will have three to four offspring. Female prairie dogs are extremely protective of their young. They will often fight with other females to guard their territory and babies.

Black-tailed prairie dogs and people: Some farmers and ranchers consider black-tailed prairie dogs pests. Livestock can hurt a leg if they step into a prairie dog's burrow, and they may compete with livestock for food.

Conservation status: Black-tailed prairie dogs are listed as Near Threatened by the IUCN. ∎

ALPINE MARMOT (Marmota marmota): SPECIES ACCOUNTS

Physical characteristics: Alpine marmots are relatively large with a head and body length of about 20 to 24 inches (50 to 60 centimeters). Their fur is thick and color varies from gray to yellow-brown to reddish. They have large heads; short, powerful legs; short, hairy tails; and a white bridge on their noses.

Geographic range: Alpine marmots are found in the French, Swiss and Italian Alps, South Germany, West Austria, the Carpathian mountains, and the Tatra Mountains. They have been introduced into the Pyrenees, east Austria, and Yugoslavia.

Habitat: These animals live in open mountainous grassland areas, at approximately 4,300 to 9,800 feet (1,300 to 3,000 meters).

Diet: Alpine marmots feed primarily on a wide variety of vegetation, including grasses, flowers, bulbs and seeds. They may also eat insects, birds' eggs and occasionally each others' young.

Behavior and reproduction: Alpine marmots are social animals that form burrows. They live in family groups generally made up of an adult pair and their offspring from previous years. Colonies, groups, can be as small as two or three to as large as fifty, all living in one burrow system. During warmer weather they eat heavily, and then hibernate as a family from September to mid April or May. The last animal into the burrow, usually an adult male, plugs the entrance with hay and earth to keep the burrow warm and safe from predators. These animals have distinctive calls. One long whistle warns of a threat in the air, such as an eagle, while a series of whistles may warn of an approaching fox.

Female marmots are able to breed at the age of two. Breeding occurs once a year, a few days after they emerge from hibernation, but females do not typically reproduce as long as the offspring remain in the family group. Females have an average of three to four offspring.

Alpine marmots and people: Some people have long believed that alpine marmot fat rubbed into the skin could relieve arthritis. In Europe these animals have been a source of fur, meat, and fat for the last thousand years. The reliance of these animals for their food has decreased and some people consider them agricultural, farming, pests. They are also hunted for trophies in some areas, and hunting has caused the population of these animals to decline. Alpine marmots have become a symbol for the Alps.

Conservation status: Alpine marmots are not listed as a threatened species by the IUCN. ∎

GRAY SQUIRREL (Sciurus carolinensis): SPECIES ACCOUNTS

Physical characteristics: Gray squirrels have a head and body length of 9.4 to 11.2 inches (24 to 29 centimeters). Fur color varies widely within the species, generally fur is black to pale gray with a white to pale gray belly. They have broad, bushy tails that are about the length of their head and body combined.

Geographic range: Gray squirrels are found in eastern and central United States, reaching southern Canada in the north. They have also been introduced into Texas, California, Quebec, Vancouver Island, and South Africa.

Habitat: Gray squirrels prefer forests and woodlands but they are often seen in urban parks and yards.

Diet: Gray squirrels eat primarily tree seeds and nuts, including acorns, hickory nuts, beechnuts, and butternuts. They also feed on berries, mushrooms, buds, and flowers.

Behavior and reproduction: Gray squirrels climb and jump well. They are considered solitary. They have well-developed senses of sight, smell, and hearing and are alert, especially on the ground. They are active year round, sheltering in tree hollows during the winter months. In the fall, gray squirrels gather and bury, at random, a winter food supply. When food is needed, these squirrels sniff the ground to recover their supply.

Gray squirrels have two breeding peaks during the year, generally December to February and May to June. After a forty-four–day gestation period, females give birth to a litter of two to seven young. Offspring are blind and helpless at birth, becoming somewhat independent at eight to ten weeks old.

Gray squirrels and people: These squirrels are hunted for sport and food. They are considered attractive and enjoyable for many park visitors. For homeowners, these squirrels may enter their homes for shelter, dig up their gardens, or eat the seeds in their bird-feeders. They are also considered a pest in areas where they damage the trees by stripping them of bark.

Conservation status: Gray squirrels are not considered threatened by the IUCN. ∎

FOR MORE INFORMATION

Books:

Clutton-Brock, Juliet, and Don E. Wilson, eds. Smithsonian Handbooks: Mammals. New York: Dorling Kindersley Publishing, 2002.

Macdonald, David, ed. The Encyclopedia of Mammals. New York: Facts on File Publications, 1984.

Periodicals:

Cohen, Jonathan. "Squirreley Fun." Ranger Rick (December 2001): 10.

Marchand , Peter J. "A Squirrel's Glide to a Long Life ." Natural History (October 2001): 18–19.

McMahan, Kim Hone. "Outwit, Baffle Squirrels ." Knight Ridder/Tribune News Service (June 5, 2003): K6208.

Nowak, Ronald M. "Squirrels, Chipmunks, Marmots, and Prairie Dogs." 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.sciuridae.html (accessed on June 2, 2004).

Phillips, John E. "Calling All Squirrels: Get Vocal to Grab More Bushy-tails." Outdoor Life (August 1, 2003): 89.

Tangley, Laura. "News of the Wild (Ground Squirrels Warning System)." National Wildlife (August–September, 2002).