Rodents are mammals such as rats, mice, squirrels, chipmunks, gerbils, hamsters, lemmings, beavers, guinea pigs, and porcupines. In fact, more than half the mammals living on Earth are rodents.

Where rodents live

Rodents are found on all the major land masses except Antarctica, New Zealand, and a few arctic and oceanic islands. Rodents live wherever there is adequate food supply, but they are most likely to inhabit open country or woodland areas. Many rodents have also adjusted to difficult environments such as deserts. The most commonly found rodents are rats and mice. Mice and rats generally stay on the ground. Most of them can also climb shrubs, bushes, and trees.

Physical characteristics

Rodents are generally among the smallest animals. Some mice and dormice are among the smallest of living mammals. The adults can be as small as 3 inches (75 millimeters) long, including the tail. They might weigh as little as ⁷/₁₀ ounce (20 grams). An exception is the South American capybara, which is about the size of a half-grown pig. It is 4 feet (1.3 meters) in length and about 110 pounds (50 kilograms) in weight.

All rodents possess a single pair of upper and lower incisors (teeth). These incisors grow throughout the animal's life. If they are not used enough they will grow past each other. When this happens, either the rodent would not be able to eat or the incisors will grow back into its skull and cause the animal's death. For this reason, rodents spend a large amount of their time gnawing, or nibbling at, hard objects.

The hind limbs in some rodents, such as kangaroo rats, are enlarged for hopping. In rodents that burrow, such as pocket gophers, the forelimbs are short and massive with strong claws. Aquatic beavers have webbed hind feet and a dense coat.

Behavior

Rodents gnaw at frequent intervals. They nibble at nuts, bark, tree trunks, and occasionally bones. Sometimes they might also chew on human possessions like boards in houses, barns, or even metal telephone cables.

Many rodents build underground homes. These homes have a central nest chamber where they sleep, raise their young, and rest in the winters. Rodents remain in their burrows during bad weather. Some, including the hamster and the woodchuck, hibernate, or spend the winter in a deep sleep-like state. The central nest chamber often has an adjacent chamber for food storage. In many cases, two or more exits provide an opportunity for escape from predators.

Many other rodents have similar nests in grass or trees. For example, squirrels nest in holes in trees or build leafy nests among the branches. Beaver lodges (shelters) in ponds or streams are made of branches covered with mud. The entrance to the beaver lodge is underwater.

Food habits

By and large rodents feed on plants. Seeds are the favorite item. Rodents such as capybaras, holarctic marmots, and woodchucks are grazers. Most of them will also occasionally eat animal food. Muskrats eat freshwater mussels and crayfish, as well as a wide variety of dead or dying water animals. Rodents sometimes eat birds' eggs, nestlings, or even insects.

Life cycle

Rodents have reproductive habits that are extremely varied in nature. Large rodents such as capybaras and beavers breed only once a year. The smaller species breed more often, and some voles, a type of a small rodent, may have up to 13 litters in one year.

Rodents generally have a very short life span. This is because they are one of the major food sources of meat-eating birds and mammals. Small, mouselike rodents may live for only a few weeks or months.

Pests

Rodents can cause great damage to crops and grains. It is estimated that rats damage about twice as much grain as they eat. When rat droppings get mixed with stored grain, the grain is no longer fit for consumption. Black rats and house mice cause the maximum damage. Burrowing rodents may also damage root crops.

Many species of rodents carry diseases such as the bubonic plague and tularemia that may infect humans. Some rodents, including beavers, muskrats, chinchillas, and squirrels, are valued by humans for their fur. Albino mice, rats, hamsters, and guinea pigs are often used for scientific research.