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Muskrats (Ondatra zibethica) are large wetland rodents. Weighing as much as 4 pounds, they are larger than most other rodents, except beavers (which can weigh as much as a 5-year-old child, about 40 pounds!). Beavers are known for their large, flat tails, while muskrats have a tail that seems ratlike. In fact, the muskrat tail is slightly flattened, but vertically rather than the horizontally like a beaver. Muskrats use this tail, which makes up half their total length, like a rudder to steer. Muskrats can swim backward. Their partially webbed feet help propel them in any direction. Although they breath air, they can stay submerged for 20 minutes.
Muskrats are common. They inhabit most ponds, swamps and marshes, where they play an important ecological role in our waterways. They serve as meals to many, many predators, from mammals (raccoons, coyotes and foxes) to birds (owls and hawks). Even snapping turtles, large fish and bullfrogs eat muskrats. In addition to all the nonhuman predators, people, too, hunt muskrats. But despite this predation, muskrats have persevered, compensating for heavy predation by being prolific breeders. In Massachusetts, female muskrats have two to three litters per year, each with about six kits. In our region, they mate in March and have their first litter a month later.
In addition to their important role as a food source, muskrats help control aquatic plants, thinning cattails and bulrushes to create a patchy ecosystem that sustains greater diversity. When muskrat populations diminish, dense vegetation impedes water flow, changes oxygen levels and reduces fish and invertebrate populations. Muskrats are crucial to maintaining well-functioning wetlands.
In the past, people thought of muskrats as being ubiquitous – much like cockroaches or pigeons, no matter what you did you could not get rid of them, for it only takes a few muskrats to repopulate an area. In the 19th and 20th centuries, muskrats were hunted extensively, but their populations remained stable. For reasons unknown, in many places their population has plummeted dramatically – as much as 90 percent. The muskrat population in Rhode Island is estimated to be only 15 percent of what it was merely 20 years ago. In Connecticut, the story is similar. One study has shown that muskrat populations in the Northeast have declined by 75 percent.
There are hypotheses for why. One is that invasive plants such as water chestnuts and phragmites choke out the cattails that muskrats like to eat. Muskrats rely on the roots of cattails for food, and the leaves and stems to build lodges. Another hypothesis is that waterways have become more fragmented. It used to be that if there was a drought and one pond dried up, muskrats would just move to another. But as habitats become more fragmented, populations become more isolated and less able to move about. If the population in a pond dies out, it is no longer replenished. (Hakai magazine published a beautiful article last year on the loss of muskrats.)
In ponds and rivers, muskrats dig burrows in a bank. The entrance to the burrow is underwater, but the tunnel rises so each room is above the water level. Muskrat burrows may have several rooms connected by tunnels. In marshes, muskrats pile cattails, mud and other plants 3 or 4 feet high to make a conical lodge that can be 8 to 10 feet at the base. Under the pile, they dig out a hollow to form a nest. Large lodges have many entrances. In the winter, several muskrats may occupy one lodge. Together like this, they can raise the temperature inside the lodge 20 degrees higher than the outside temperature. In the summer, when the lodges can get hot, muskrats may shift to burrows in embankments.
Wetlands provide food and hiding places for muskrats. They dig shallow channels to connect deeper pockets of water. These channels provide escape routes from predators and easier travel from water pocket to water pocket. Muskrats often turn a marsh into a series of interconnected channels and in the process improve the waterway for many other species.
Muskrats prevent vegetation from choking wetlands. They dig out and eat the roots of aquatic vegetation. They also eat the stems, leaves and flowers of cattails, lily pads and grasses. They scrape algae from rocks and eat it in floating masses. Occasionally they eat clams, fish or crustaceans. All of these actions help maintain a mix of open water and vegetation that encourages birds and other animals to make the wetlands their home.
During the breeding season, male muskrat scent glands produce an odor – musk – to attract females and communicate territorial boundaries. Baby muskrats, called kits, weigh only about an ounce. Many critters, including bullfrogs, think these babies make a tasty meal. After about two weeks, baby muskrats open their eyes. They begin to swim and nibble on vegetation. At the age of only a month, they are weaned. By six weeks, they leave the nest and are on their own. By six months, they are nearly fully grown, and may travel to other waterways to establish a territory if the wetlands are not too fragmented.
Muskrats do not hibernate. During freezing winter temperatures, muskrats travel underwater to eat from the roots and stems of floating aquatic plants. They make air holes in the ice so they can move from one feeding site to another while still underwater. In snowy winters, if muskrats leave the water, they are vulnerable to predators because their dark body stands out prominently against the snow.
Although only about the size of a football, tiny muskrats play a gigantic role in preserving our wetlands. These hydrologic engineers rework our wetlands to make them more hospitable to the diversity and inclusion of many other species.
Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
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.
The far left and far right of the background on the feature image to this post (not seen above) was generated digitally and is not real. The rabbit was photographed and is real.
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