Muskrat (Ondatra zibethicus)

County List:

Rule:

Forested or Nonforested Landscapes

      (Marsh 1 or Marsh 2)
   adjacent to:
      Any Open Water

Habitat List:

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Literature:

It is semiaquatic and always lives near slow-moving streams, lakes, ponds, and especially marshes. It prefers standing water that is about 4-6 feet deep throughout the year.

Muskrats feed primarily on the roots and basal portions of aquatic vegetation, such as cattail, arrowhead, water lily, and various rushes. In addition, it eats small amounts of meat in the form of crayfish, mussels, small fish, turtles, and frogs.

Habitat: Marshes, shallow portions of lakes, ponds, swamps, sluggish streams, drainage ditches. Most abundant in areas with cattails.

Special Habitat Requirements: Wetlands with dense emergent vegetation and stable water levels.

Habitat Preferences: The muskrat is a semi-aquatic rodent which spends most of its time in wetland environments. Year-around water is important, preferably 4 to 6 feet deep so that it will not freeze to the bottom. If water is more than 12 feet deep, aquatic vegetation (as potential food) is often absent. Muskrat living areas, according to Johnson, can be classified as: (1) ponds, lakes, streams, canals, reservoirs with or without marshy borders and related emergent vegetation, (2) swamps, and (3) marshes. The first category provides the least favorable muskrat habitat for it often contains high, sheer banks, muddy, unvegetated shorelines; deep water, fast currents; turbid water and irregular bottom topography resulting from disturbance by water livestock; borders of cultivated fields, sod, pasture, or woods with little transitional vegetation; and fluctuating water levels, especially in streams and dammed farm ponds. In these situations, muskrats primarily use bank burrows as dens and may forage considerable distances for scattered food supplies.

Swamps, as defined here, consist of pools of still water and sluggish streams bordered by dense thickets of water-tolerant growth, such as buttonbush, alder, willow, red-osier dogwood, arrow-wood, and sweet gale. Although swamp water levels may drop considerably during summer, there are usually patches of open water sometimes covered by dense mats of duckweeds, Wolffia, and various algae bordered by patches of cattails, rushes, grasses, sedges, duck potato, and other low-growing and non-woody plants. Muskrats construct trails under the dense canopy of emergent swamp vegetation, mush of which serves as food. The overhead cover also provides protection from flying predators. The muskrat dens in hollow stumps, fallen tree trunks, under exposed root systems of stand timber, in banks of hummocks or other high ground, or in constructed houses.

The third habitat category, marshes, is the most favorable environment in Michigan for muskrat. These consist of wetlands with fairly constant water levels, little or no water currents, and vast stands of cattails and other emergent vegetation among scattered areas of open water. Recent glaciation in Michigan caused a vast array of lakes and ponds. As these shallow due to filling by natural plant succession, ideal marsh situations develop. Some of these also occur along rivers where sluggish water overflows. Extensive muskrat marsh habitats such as along the Maple River in Gratiot County, the Kalamazoo River in Allegan County, in the Erie Marsh in Monroe County, and the Munuscong Marsh in Chippewa County, are also noted concentration areas for waterfowl. Muskrats use marsh vegetations, such as sedges, rushes, grasses and cattails, as food and to construct their picturesque houses.

Key Components of Habitat: Permanent water of sufficient depth or velocity to prevent freezing of entire water column; presence of herbaceous aquatic vegetation and herbaceous vegetation in riparian habitats.

Management Actions to Enhance or Maintain Habitat Quality: Manage vegetative succession (e.g. burning, water level manipulation, chemical treatments) to provide preferred food species; control water levels to provide suitable habitat year around.

Habitat: Muskrats have extremely flexible habitat requirements. In general, they must have a source of permanent water and a protected site for the shelter and rearing of young. The latter can take the form of floating lodges of vegetation or dens built into the banks of a body of water. Muskrats will occupy saline and freshwater marshes, ponds, sloughs, lakes, ditches, streams, and rivers. Water requirements vary from very shallow depths in southern areas to a depth that prevents freezing in northern areas. Muskrats are usually absent from large open bodies of water where wave action can be severe. Muskrat densities on marsh areas are related to the type of emergent vegetation present. On inland marshes of the United States and Canada, highest muskrat densities are associated with cattail. Lower densities are found on bulrush marshes.

Muskrat densities are also related to the degree of interspersion between emergent vegetation and water, which in turn is related to marsh succession. Marshes undergo successional changes that are due to the interaction between water levels, vegetation propagation, and herbivore grazing. Weller argued that freshwater marshes follow a 3- to 7- year cycle, alternating between a situation of dense emergent vegetation and one with relatively open water with submergent vegetation. Emergent plants like cattail cannot propagate well in deep water. If a marsh's water levels remain high for long periods, the rate of propagation of emergent plants cannot match the loss caused by muskrat activity and other sources of mortality. This results in a gradual opening up of the marsh. Natural changes in the water level brought about by drought conditions slow this process. Conversely, in areas where water levels fluctuate considerably, propagation rates are high and the marsh becomes densely vegetated. Muskrat densities are relatively low in both these extremes and much higher when there is an equal ratio of open water to emergent vegetation.

Muskrat densities are also influenced by changes in water depth. Errington argued that drought conditions made muskrats more susceptible to predation. In northern areas, water depths must be great enough to prevent marshes from freezing to the bottom.

To summarize, muskrats occupy a diverse array of habitats but generally reach their highest densities where favorable emergent vegetation and water are equally interspersed. Muskrat densities are influenced by and in turn influence marsh succession, which leads to changes in water vegetation interspersion. Marsh managers have manipulated vegetation and water levels to alter the rate of succession so as to keep marshes in a condition favorable for muskrat production.

Food Habits: Muskrats are primarily herbivorous. They consume shoots, roots, bulbs, and leaves of aquatic plants. Cattail and bulrush are always utilized when present and can constitute as much as 80% of the muskrat's diet. Muskrats consume a wide variety of other aquatic plants. Cultivated crops such as carrots, corn, alfalfa, and soybeans are also eaten. In some cases, muskrats will also consume clams, mussels, fish, and other available animal material.