Rodents are the world's most successful mammals and are found in just about every habitat on earth. There are 3 main groups: squirrel-like rodents, mouse-like rodents, and cavy-like rodents.
The group we call squirrellike rodents live in all parts of the world except for Australia, Polynesia, southern South America, and the Sahara and Arabian deserts.
The mountain beaver lives in the pine forests of North America, where it builds an elaborate burrow. The North American beaver and the European beaver are larger herbivores (plant-eaters). They spend half their life in the water and have streamlined bodies, a flattened tail, and webbed feet.
Beavers live in family groups consisting of an adult pair and the offspring of several years (they have 1 litter each year). They cut down trees with their teeth and use them for food and for building dams across streams. The dams cause ponds to form. When this happens, the beavers build a lodge shaped like a cone in the pond, with the entrance to the living chamber through an underwater channel.
Squirrels live on all continents except Australia. Tree squirrels are active little animals. They have excellent eyesight and move easily through the trees with the help of sharp claws and a bushy tail that acts as a counterbalance. On the ground they move with a series of arched leaps. They eat fruit, nuts, seeds, shoots, leaves, and sometimes insects.
Flying squirrels glide rather than fly, using membrane down each side of the body as a parachute and the tail as a rudder. When they land, flying squirrels brake by stretching the body and tail upward.
Ground squirrels are widespread and include prairie dogs in America, marmots across the Northern Hemisphere, and chipmunks. Many of them live in burrows, where they raise young, store food, and hide from enemies.
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Pocket gophers and pocket mice. Both these families have external, fur-lined "pockets" or pouches in their cheeks for holding and carrying food. Pocket gophers, found in North and Central America, eat underground roots and tubers. The pocket mice of North, Central, and South America eat grain.
These African rain forest dwellers are, apart from one species, excellent gliders. Because of their gliding membranes, they cannot run from predators and so are very aggressive if cornered.
Mouse-like rodents are found all over the world. They have successfully adapted to nearly all types of habitat and account for more than a quarter of all mammal species.
Rats and Mice
Rats and mice are well known for having many babies. Many species have gestation periods of 20 to 30 days. Litters of 3 to 7 young are born and the parents breed again immediately. Typically, the young are born without fur and with their eyes closed. But within a few months the young themselves are ready to breed. Africa is home to 51 species of rats and mice that are found nowhere else in the world.
Voles and Lemmings
Most of the 121 species of this subfamily are quite small, weighing less than 3 ounces. These rodents are mainly surface-dwellers and burrowers of northern regions. Voles and lemmings are active throughout the winter, surviving beneath the snow in elaborate tunnel systems.
Eastern Europe, Africa, and Asia are hosts to 22 species of subterranean (underground) rat. These rats live in burrows and eat roots and bulbs. The species that have adapted best to living underground are the 8 species of blind mile-rats. They have no external ears, no tail, and eyes that are permanently beneath the skin.
Within this group are hamsters, gerbils, and jerboas. They are confined to Asia and Africa, and the hamster also has a limited range in Europe. Jerboas are different from hamsters and gerbils because they have extended back legs that allow them to move quickly over very long distances. Most gerbils and jerboas live in deserts or very arid areas. During the day they sleep in a deep burrow, with the entrance blocked to keep it moist. They do not need to drink, but get sufficient water from their diet of seeds.
Dormice live in parts of Africa, Europe, Asia, Arabia, and Japan. Most species eat fruit, nuts, seeds, and buds. Dormice can be very vocal: they twitter, shriek, click, growl, and whistle.
This group of rodents gets its name from the South American guinea pig, or cavy. Mammals in this group share similar jaw muscles, and most have a sturdy body, large head, slender limbs, and a short tail.
American porcupines have shorter protective spines than their counterparts in the Old World. They eat plants and are unaggressive and slow-moving. They spend a lot of time in the trees, especially the tree porcupines and prehensile-tailed porcupines. Muscles in the porcupine's skin erect the quills when a porcupine is in danger. Small barbs on the quills ensure they stick in an attacker's flesh.
There are 55 species of spiny rat. Most of these have hard, lance-shaped hair scattered through their fur. Although they are not closely related to porcupines, the spiny rats suggest how quills may have evolved from ordinary hairs.