The muskrat ( Ondatra zibethicus ) is a widely distributed semi-aquatic rodent that occurs throughout most of the United States and Canada, including all of Kansas. Muskrats live in marshes, swamps, bogs, streams, rivers, ponds, lakes, and other areas where sufficient water exists to offer them protection from predators. In Kansas, muskrats are most abundant in the southcentral and northeastern parts of the state, where the combination of wetland and riparian habitats are most abundant.
Muskrats weigh 2-3 pounds and have long, laterally-flattened tails and large, webbed hind feet. Their thick, waterproof fur is usually light to dark brown, and is soft and velvety. Muskrats prefer still or slow moving water with an abundance of aquatic vegetation, which constitutes their primary food source. Cattail, bulrush, and arrowhead make up a large portion of their diet in Kansas, but they are not exclusively herbivorous, and will occasionally eat fish, crayfish, snails, and mussels.
Like beavers, muskrats primarily use bank dens where sufficiently steep banks are available. But muskrats are better-known for constructing conspicuous houses from aquatic vegetation. Houses are occupied in the absence of banks suitable for denning, or by subordinate muskrats unable to secure a bank den. Muskrat houses are usually up to four feet in height and about six feet in diameter, with one or more underwater entrances that lead to nesting chambers. They are usually occupied by one territorial family during the breeding season but may be occupied by several families in the winter.
Muskrats are the Kansas furbearer most prone to boom-and-bust population cycles. Very prolific, muskrats average two or three litters of young per year. Normally, there are about six kits per litter, with reproductive rates being highest when sparse populations have access to abundant food supplies. Most muskrats don’t survive past their first year, and mortality factors become more pronounced as populations increase.
Muskrats are preyed upon by raccoons, raptors, snakes, red foxes, coyotes, and especially minks, and experience high rates of cannibalism or mortality inflicted over territorial disputes when densities are high. Despite typically high mortality rates, populations can continue to increase until limited by a more catastrophic event such as drought, tularemia, Tyzzer’s disease, or an “eat-out.” All of these can quickly decimate a muskrat population.
At moderate densities, muskrats provide a valuable service for many species of fish and waterfowl by keeping cattails and emergent vegetation from choking out surface water in shallow, marsh-type wetlands. But eat-outs occur when muskrat densities increase beyond their habitat’s carrying capacity, and wetland areas are completely denuded of vegetation by feeding muskrats. Most common in the southern U.S., eat-outs can significantly degrade wetlands for years and negatively impact many species that rely on the wetland ecosystem, including muskrats.
The muskrat was historically one of the most important North American furbearers in terms of total pelt value and number harvested, but has diminished in importance to the Kansas fur trade in recent years. During the 1980s, the Kansas annual harvest averaged more than 30,000 muskrats; in the past five seasons, the annual average has been about 7,000. Muskrats are considered one of the best-eating furbearers and are prized for their meat by some furharvesters.