Muskrats are among the most wetland-dependent of all freshwater mammals, spending nearly their entire lives within the confines of a marsh. They eat, sleep, breed, rear their young, and spend the winter months in wetlands. They normally leave a marsh only for two reasons. One is during a period of spring or fall dispersal, when young muskrats may strike out from crowded habitat, looking for a vacant patch of water. The second is when a completely dry or solidly frozen marsh can force abandonment of a site. Both of these events lead to huge muskrat mortality; they are far safer in the protection of their watery home.
Muskrats are native to North America, ranging from extreme northern Mexico through most of the United States and Canada except for the arctic regions. Normally preferring to keep out of sight, muskrats are unusually visible during November in Minnesota. They perch on ice shelves adjacent to open water, feeding, grooming, and resting. Soon, they will be forced under the ice for the duration of the winter.
During the ice-bound months, muskrats find shelter in their mounded lodges of vegetation, with dry nests in the center and tunnels leading to water. Burrows dug into steep banks below the water line are another common home.
Muskrats primarily feed on vegetation, with cattail roots being a dominant food in our area. They can find food during the winter at the bottom of the marsh. They sometimes store food in the marsh before freeze-up and will even feed on the vegetation comprising the walls of their winter lodges.
Being mammals, muskrats need air to breath even under the ice during winter. They get oxygen from the above-water space in their lodge and from the air pockets often found between the bottom of the ice and the top of the liquid water.
Muskrats are rodents, just like mice, voles, lemmings, and rats. Like other rodents, muskrats are prolific breeders. They have multiple litters per growing season with five to eight young per litter. It does not take long for a muskrat population to explode to very high levels. Then, the muskrat population ultimately crashes either due to a drought drying up the wetland or due to a lack of food remaining in the marsh.
This boom and bust cycle can play an important role in wetland ecology. A shallow marsh in the prairie pothole region typically dries up every five to fifteen years, during a natural dry cycle. During the dry spell, the wetland fills with cattails, bulrush, and other vegetation, with the vegetation often completely covering the surface of the dry marsh bed. When water returns, young muskrats dispersing from their home marsh discover the newly filled wetland, an unoccupied site rich with food.
Within one or two growing seasons, the muskrat population explodes, with lodges dotted across the marsh. The hungry muskrats eat the vegetation around each lodge, creating the small openings preferred by waterfowl and some other marsh birds. Ultimately, the muskrats can completely consume the vegetation, creating an open water shallow marsh. The muskrat population will crash once again and, following the next dry year, the cycle repeats itself.
Featured WPA: Lee Waterfowl Production Area, Stevens County
Lee Waterfowl Production Area is a 186-acre parcel located eight miles south of Alberta, in southwestern Stevens County. Lee WPA includes two large wetlands and several smaller marshes. The large marsh on the west side is a good example of the sort of wetland preferred by muskrats, with deep enough water most years to retain some liquid water under the ice and plenty of vegetation as a food source. It cycles through natural wet and dry precipitation cycles and the muskrat population varies accordingly. The south half of the unit was purchased about 10 years ago and contains a good stand of native grass on the uplands. The north half of Lee WPA was purchased many years earlier and contains mostly non-native grasses.
For a map of Lee WPA or any other WPA in the Morris district, go to http://midwest.fws.gov/ Morris.