What do they look like?

Muskrats have large, robust bodies, with a total body length of twelve and a half inches. The tail is flat and scaly and is nine and a half inches in length. Muskrats have dense fur that traps air underneath for insulation and buoyancy. Their heads are very large and their ears are almost invisible underneath the fur. Muskrats have short legs and big feet; their rear feet are webbed for swimming. Adult muskrats have glossy upperparts that are dark brown, darker in winter and paler in the summer

Where in the world do they live?

Muskrats are only native to the Nearctic region, but have been introduced to the Palearctic and Neotropical regions. They are found throughout North America as far south as the southern United States, they are excluded from the southernmost portions of the United States by lack of appropriate habitat. The placed muskrats have been introduced to are Japan, parts of South America, Scandinavia, and Russia.

What kind of habitat do they need?

Muskrats are semi-aquatic and prefer locations with four to six feet of water. Muskrats are found in ponds, lakes, and swamps, but their favorite locations are marshes, where the water level stays constant. Marshes provide the best vegetation for eating and constructing nests and burrows. Muskrats find shelter in bank burrows and nests that they build. Bank burrows are tunnels excavated in a bank. Nests are made by piling vegetation on top of a solid base, for example a tree stump, generally in 15 to 40 inches of water.

How do they reproduce?

Southern muskrat populations can breed year round while northern populations only breed in the warmer months (March to August). Females are pregnant for 25 to 30 days and have usually 6 to 7 young per litter. Northern populations have larger litters. Young are born in a grass lined nest. When born, muskrats have short dark fur, closed eyes, and weigh around 22 grams. They are able to swim at 10 days and by 21 days can eat green vegetation. In 3 to 4 weeks young muskrats begin to feed on their own. They will reach their adult size by 200 days old.

Young are cared for and nursed by their mothers in the nest until they are about 2 weeks old, when they begin to swim and eat vegetation. They are fully weaned by 3 to 4 weeks old and leave their mother's home range after their first winter, usually when they are less than a year old.

How long do they live?

Although muskrats have been known to live to 10 years old in captivity, they probably live about 3 years in the wild.

How do they behave?

Muskrats live in large family groups with definite territories. If conditions are crowded, females will kick their offspring out of the group. Muskrats continue to live in large groups even when they fight amongst themselves. Muskrats are active at all times of the day but most active from mid-afternoon until just after dusk, and at night. Muskrats are good swimmers and can stay underwater for about 15 minutes. They paddle with their large, webbed rear feet and use their long, flat, and scaly tail to change their direction. Muskrats move slowly on land. They are affected by quick changes in temperature, and dry, hot weather is especially bad for them. Their homes and burrows protect them from the elements. Muskrats also have a special adaptation called regional heterothermia, which regulates the flow of blood to the feet and tail, allowing these structures to be cooler than the body core. This adaptation allows them to stay warm in cold water.

How do they communicate with each other?

Muskrats communicate by a secretion from their glands called musk. This scent also serves to warn intruders. They are capable of vocalizing by squeaks and squeals. Muskrats have poorly developed senses of sight, hearing, and smell.

What do they eat?

Muskrats are mainly vegetarians but will eat animals as well. Muskrats consume about one-third of their weight every day. Their digestive system is designed for green vegetation. In the summer they eat the roots of aquatic plants. In the winter, they swim under the surface ice to get to the plants. Muskrats also eat agricultural crops.

What eats them and how do they avoid being eaten?

Muskrats are excellent swimmers and can evade many predators by escaping into water or into their burrows and nests. They can remain under water for up to 15 minutes.

What roles do they have in the ecosystem?

Muskrats are very abundant in areas of good habitat, making them important prey animals for predator populations. By grazing on vegetation, muskrats influence the composition of local plant communities.

Do they cause problems?

Muskrats not only eat the grain on a farm but they have also been known to plug the drain tiles on farms. Muskrats have a habit of building their homes around dikes. These homes make the dikes weak and eventually destroy the structure

How do they interact with us?

Muskrat fur is important in the fur industry. Also meat from muskrats is suitable for human consumption, though it is not widely eaten.

Are they endangered?

Muskrats are widespread and abundant. Populations remain stable even when they are being hunted for fur, affected by disease, or a target for large predator populations because muskrats have the ability to reproduce quickly.

Contributors

Toni Lynn Newell (author), University of Michigan: October, 2000.

References

Baker, R.H. 1983. Michigan Mammals. Michigan State University Press. United States of America.

"Animal Life Histories Database" (On-line).