Thursday, June 20, 2024

Although this muskrat in Cambridge looks like a small beaver, the two are not closely related. (Photo: Richard George)

Muskrats (Ondatra zibethicus) are native rodents that live in most of the shallow lakes, ponds, slow rivers and swamps in Massachusetts. Since they are mostly nocturnal, though, you may not see them unless you look for them around dawn or dusk, when they are still active.

Though they have ratlike tails, muskrats are not rats. They are 2-foot semiaquatic rodents (half their length is their tails) with long claws for digging. They have two layers of brownish fur: an outer long, shiny one; and a dense underfur that traps air, insulates and makes the muskrat more buoyant. They are lighter in color in the summer and darker in the winter, which helps regulate their temperature – dark fur absorbs more heat in winter and light fur reflects more sunlight in summer. Their webbed hind feet propel them through the water, and their long, hairless tails, covered with scales, act like a rudder for steering.

A muskrat gnaws vegetation in March 2021. (Photo: Richard George)

Because they spend so much time swimming, muskrats have developed some unusual underwater adaptations, including ears and nostrils that close and teeth that protrude in front of their lips so they can hold vegetation in their mouths and chew without ingesting water. They also maintain different temperature zones in different parts of their bodies, reducing heat loss from their tails and feet. Because they are less sensitive than most mammals to the buildup of carbon dioxide in their blood, they can stay submerged for 12 to 20 minutes.

Muskrats drag their tails when they walk on land or in the snow, so their tracks are distinctive. (Photo: Tom Koerner/USFWS)

Muskrats tunnel into banks to make the burrows they live in. The burrow opening is underwater, but lead to chambers that are above the water line. Muskrats sleep and give birth in these chambers. If muskrats live in a swampy area without banks, they build domed-shaped mounds, called push-ups, out of mud and plants such as cattails. The muskrats hollow out living chambers in the center of the mound. If their pond freezes over in winter, they feed under the ice and sometimes eat their push-ups. According to a U. S. Department of Agriculture Farmers’ Bulletin from 1910:

As cold weather approaches, muskrats are very active, adding to their old winter houses, building new ones, and deepening channels that lead to houses and burrows. The animals do not hibernate, and, aside from the vegetation of which their houses are made, they seem to make little provision for winter.

A muskrat swims in Quebec. (Photo: Simon Pierre Barrette via Wikimedia Commons)

Muskrat pairs mark the border of their territory with musk and large piles of their droppings. Muskrats begin breeding in March or April, and the female gives birth a month later to about six small, hairless babies. After another month, the babies are weaned. A female muskrat can have up to three litters per year from spring until fall. The young stay in the mother’s territory through the winter and set off on their own the following spring. Since muskrats, like other rodents, are so prolific, you might think that our ponds and rivers would have become overrun with muskrats; but muskrats have many enemies, including snapping turtles, coyotes, foxes, weasels, otters and great horned owls. Their biggest enemies, however, are minks and raccoons.

A young mink. Muskrats are the primary prey of adult minks. (Photo: Tom Koerner/USFWS)

Muskrats are omnivores, but 95 percent of their diet is aquatic plants such as cattails and water lilies. If plant sources of food are unavailable, they will eat insects, fish, snails, frogs and freshwater mussels.

Since muskrat pairs mark the border of their territory with musk, you might think this is the origin of the name muskrat – but the name comes from an Algonquian or Abenaki word moskwas, changed in early colonial writing to musquash. Because of their resemblance to rats, the name became altered to muskrat. Although muskrats are native to North America, they are invasive in Europe, where people introduced them at the beginning of the 1900s as a fur resource.

This muskrat in East Arlington uses its 8- to 10-inch hairless tail like a rudder to steer. (Photo: Richard George)

Muskrats were such an important food source for early trappers in North America that the Catholic church in parts of Michigan in the 1700s issued a dispensation that allowed Catholics to eat muskrats on Fridays, Ash Wednesday and during Lent (when eating animal flesh was ordinarily prohibited). The reasoning behind this ruling was that muskrats live in the water, but the fact that trappers and their families were starving probably also had something to do with the ruling. Some people say muskrat has a pleasant taste, but others disagree, including Bishop Kenneth Povish of Lansing, Michigan, who wrote in 1987 that “anyone who could eat muskrat was doing penance worthy of the greatest of the saints.” According to that U. S. Department of Agriculture Farmers’ Bulletin, one person feels that the muskrat’s “musky flavor would keep any but the starving from eating it.” Another declares that “the muskrat is game worthy of an epicure, with a flavor somewhat like the wild duck.” Others felt that its flavor was like “that of the famous terrapin of the Chesapeake.”

A muskrat’s dense fur keeps its body warm and dry even on a cold winter day. (Photo: Richard George)

Muskrat fur is extremely warm and practically waterproof, making it, at one time, a valuable commodity. According to the U. S. Department of Agriculture Farmers’ Bulletin:

The London sales of muskrat pelts for the year 1905 exceed 5,000,000 [surpassed only by rabbit pelts] … Notwithstanding that during the past century and a half nearly a quarter billion of muskrats have been trapped, the supply has not greatly diminished.

Muskrats are not suspicious, and are easily trapped. They take any suitable bait readily, especially in winter and early spring when green food is scarce, but especially carrots, sweet apples, parsnips, turnips or pieces of squash.

A muskrat has long claws for digging and holding food. (Photo: Linda Tanner)

It is ironic that when muskrats were heavily persecuted, their numbers were stable. Today, muskrats are more protected and there are only a few hundred licensed trappers in Massachusetts. Despite this, muskrat populations have declined sharply across North America over the past 50 years – in some places, down as much as 90 percent. Wildlife scientists do not know why, but it may be a result of habitat loss, predation, environmental contamination or disease. To protect muskrats, scientists are conducting research to understand how diseases, ecosystem dynamics and climate change are affecting these mammals.

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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.