Muskrat

Scientific Name	Ondatra zibethicus
Survival Strategy	Active All Winter
Conservation status	Least Concern

Phenology

Spring
Muskrats begin mating soon after the ice breaks up in March or April. Females will have two to three litters each year, with four to eight pups in a litter. Pups are weaned at about three weeks and independent after six weeks.

Summer
Muskrats continue breeding throughout the summer, with the last litters born in August.

Fall
When late fall weather forms ice in the marsh, muskrats build domes of reeds and mud called push-ups to serve as temporary winter shelters while foraging for food.

Winter
Although actively feeding all winter, muskrats spend much of the winter in their sleeping lodge, which they often dig into a steep bank with an underwater entrance.

Behavior

Push-Ups
In early winter, muskrats create small shelters called “push-ups” by chewing holes in the newly-formed ice and covering it with a mound of mud and plant debris. These mounds are often three feet in height and up to 90 meters (300 ft) from the main lodge. Unlike beavers, muskrats do not cache food for the winter and must forage underwater regardless of weather conditions. Even when extreme temperatures eliminate open water and access to oxygen, daily foraging must continue under the ice. Muskrats can stay underwater for about ten minutes and then use push-ups to catch their breath out of the weather and out of the view of predators.

Physiology

Cold Feet and Tail
Muskrats conserve energy by using regional heterothermia, which controls the blood flow to the feet and tail. This adaptation allows the furless body parts to be colder while keeping internal organs warm. This ability is similar to turning off the heat in a seldom-used back bedroom to save on fuel bills.

Musk Glands
Muskrats get their name from the perineal musk glands found near the base of their tail. They use these glands to mark territory and attract females.

Warm Coat
The muskrat’s dense waterproof fur traps air and serves as insulation and a lifejacket. The coat consists of two layers of hair. Guard hairs are dark brown to reddish-brown and create the water repellant top layer. The underfur is the inner layer of grayish fur. The underfur strands are shorter and thinner than guard hairs and form a dense, interlocking mat. This waterproof matted layer is vital to the muskrat’s ability to thrive in near-freezing water.

Diet

The muskrat’s diet is mainly aquatic vegetation, including cattails, sedges, water lilies, and pond weeds. They will also feed on crops within their territory. Although not a large part of their diet, they eat small aquatic animals such as snails, crayfish, and frogs.

Lifespan and Mortality

Muskrats live for about three years. 87% of muskrats do not survive their first year.

The primary causes of muskrat mortality are hunting and trapping, diseases and parasites, rabies, ticks, climatic conditions, and predation.

Predators
Predators include American mink, raccoons, river otters, and coyotes.

Never Stop Learning

History: In 1905, a wealthy landowner released five muskrats (two males and three females) near Prague, Czechoslovakia. Today muskrats can be found across Europe and are considered an invasive species.

Fashion: A Klondike hat made from muskrat fur and wool is a standard issue to all Royal Canadian Mounted Police.

First Nations: The Ojibwe word for muskrat is “wazhashk-na”.

References

Newell, T. 2000. “Ondatra zibethicus” (On-line), Animal Diversity Web. https://animaldiversity.org/accounts/Ondatra_zibethicus/

Ojibwe People’s Dictionary: Muskrat https://ojibwe.lib.umn.edu/main-entry/wazhashk-na

Frank E Fish, Thermoregulation in the muskrat (Ondatra zibethicus): The use of regional heterothermia, Comparative Biochemistry and Physiology Part A: Physiology, Volume 64, Issue 3, 1979, Pages 391-397, ISSN 0300-9629, https://doi.org/10.1016/0300-9629(79)90459-6.