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Muskrat
Wildlife Species Guide | Furbearers Guide
| Distribution
| Habitat
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Foods
| Mortality
| Importance
 Description:
The muskrat is a medium-sized mammal that at first glance, looks like a common rat, though
it is not closely related to that rodent. The name "muskrat" stems from a mild, unobjectionable
musty odor that emanates from the animal. Adult muskrats average about 2 ¼ pounds, with some
animals exceeding three pounds, and are usually 16 to 25 ½ inches long. The muskrat's fur
has a dense undercoat that is virtually waterproof and provides excellent buoyancy for
swimming. Its back and head are a rich, dark brown, which gradually shades to lighter
brown on its sides and becomes grayish on its under parts. The long tail is scaly, nearly
hairless, vertically flattened, and serves as a rudder. The muskrat's front legs and feet
are short with heavy claws, with good dexterity for feeding, grooming, digging and lodge
construction, while the powerful, partly-webbed toes on its hind feet provide propulsion
for swimming. Muskrats have developed special respiratory controls, which allow them to
remain submerged for nearly 20 minutes. Even the eyes, ears, nose and mouth are highly
specialized to serve well during underwater excursions.
In common with other rodents, muskrats possess four large front incisors adapted for
gnawing. These specialized teeth are unroofed and grow throughout the life of the animal.
Each incisor has a layer of hard enamel on the front surface, with progressively softer
material toward the back. This assures that through gnawing, the softer tooth surface in
the back wears faster than the front surface. The result is a sharp, chisel-shaped edge
well adapted for gnawing and carrying food and building materials through water, which
also commits them to a basically herbivorous mode of feeding.
Distribution and abundance:
Muskrats are found throughout Nebraska wherever suitable aquatic habitat exists, and are among
the most abundant furbearers in Nebraska. In general terms, muskrats require readily
accessible water, food and secure lodging throughout the year, though these requirements
vary with the season. In the case of water, the muskrat can tolerate minimal water
conditions during summer and fall. However, muskrats are virtually entombed under a layer
of ice in the winter and need at least three feet of water to survive. Habitat and Home:
Muskrats live in marshes, sloughs, streams, rivers, ponds and lakes. A muskrat will dig its
home in a stream or pond bank if convenient, or it may gather vegetation from nearby areas
and build a large house in shallow water. Cat- tails and bulrushes are packed in a conical
pile three to four feet high and five to eight feet in diameter. Passages into the house are
under water and lead to two to four chambers in the dome, which are connected by tunnels.
Each lodge contains at least two exits, one of which must be to deep water to ensure access
in the winter. The inner chamber of the lodge serves a multitude of purposes from bearing
and raising young to a home for eating and sleeping. The foot-thick walls of the house act
as insulation, keeping out the summer heat and the winter cold. Where strong current, wind,
wave action or lack of adequate water depth or construction materials preclude a freestanding
conical lodge, a burrow and bank den are excavated. Muskrats will readily dig burrows into the
banks of creeks and farm ponds, where soils and water depth permit safe year-round access to
dens. As with the lodges, burrows lead to an above- water chamber or chambers providing both
comfort and security.
Habits:
As fall approaches, muskrats turn their attention to building new lodges or excavating new
burrows. This construction activity begins in late August and peaks in October. Increased
feeding activity during that time builds body fat reserves for the long winter when it is
more difficult to find food. Food and space are usually in shortest supply in winter. The
quality and quantity of vegetation, water, habitable dwellings, and the density of muskrats
using this habitat will dictate body condition for the breeding season. Foods:
Muskrats are essentially vegetarians. Because they do not hibernate but remain active throughout
winter, food must be readily accessible even under ice and snow. Muskrats prefer aquatic stands
of cattail, bulrush and pond weeds, both for the green shoots during the growing season and for
under-ice foraging for tubers and roots during late fall and winter. Muskrats readily utilize
Dryland weeds, grasses, white clover and cultivated corn. On occasion, they
will eat fresh- water clams, snails, frogs, crayfish, fish and salamanders. In hard times,
they can subsist on dried stems and leaves and may resort to cannibalism.
Reproduction:
Muskrats produce large numbers of young, but offer little parental care. They can potentially
have up to four litters and 45 young a year, but Nebraska muskrats normally have two to three
litters of five to seven young each. Additionally, first-litter females will sometimes have a
litter late in the same year they were born. In the spring, dispersal and mating are the two
most noticeable activities of muskrats. Dispersal is associated with ice break-up and is
primarily the result of increased aggression between animals. Dispersal movements can be
long, cross-country treks or shorter, less dramatic movements within a marsh. Dispersing
muskrats experience extremely high mortality from predators, exposure, starvation and
accidents, but the movements play a vital role in repopulating vacant habitat.
In Nebraska, the breeding season begins in March and runs through summer. After pair bonds are
established, muskrats establish territories and defend them fiercely against neighbors. Peaks
in litter production occur in April, May and June, and there is another small peak during
August-September. Litters are born blind and helpless, four weeks after mating occurs. The
young go on short excursions within two weeks and are weaned at about three weeks. Adult
females breed soon after the birth of a litter and prepare their dens for the new arrivals
soon after the litter is weaned.
Mortality:
While muskrats are prolific, they are short-lived. Most muskrats live less than one
year, and two- to three-year-olds are extremely rare. Muskrats are prey for a wide range of
predators, including hawks, owls, mink and northern pike. Many muskrats are killed or seriously
wounded in territorial battles throughout spring and summer, and few spring dispersers make it
safely to a new home. Muskrat populations can fluctuate wildly from year to year, based on
vegetation and water conditions, and populations can actually be too successful for their own
good. Sometimes a marsh produces so many muskrats during the summer that there is
insufficient vegetation left in the fall for food and lodge construction. This is
called an "eat out'-the muskrats eat themselves out of house and home. When muskrat
numbers get too high in late summer and fall, the population becomes stressed. Fighting
and cannibalism increase, reproduction decreases and mal- nutrition increases. Two
contagious diseases, Tyzzer's disease and tularemia, can have devastating effects
on local muskrat populations under these conditions. Muskrat numbers can be reduced
to a fraction of the original population in just a few weeks by these diseases.
Unfortunately, these diseases will persist in a marsh and continue to depress
muskrat populations for a number of years. Regulated trapping can reduce the impacts
of disease, starvation and fighting on muskrat populations, by removing surplus animals
when numbers are high and populations are under stress.
Importance:
Muskrats have both positive and negative economic values to the people of Nebraska.
Positive values center on the income generated by the harvest of muskrats by trappers for their
meat and fur, as well as the recreational value derived from their pursuit. From 1942-89, an
estimated 6.1 million muskrats were taken by fur trappers in Nebraska. Harvest totals from
1980-89 indicate an average annual harvest of 95,900 muskrats valued at over $283,000 . Muskrat
is highly desirable for the manufacture of women's coats because the fur is very durable
and the skin is tough and makes excellent leather which takes and holds dye well. People
who eat muskrat say its flesh has a moderate gamy flavor that is in no way unpleasant. Musk
dried from the animal's glands is used to make perfumes and a scent used for trapping other animals.
Management:
Muskrats are also important in the management of wetlands. Muskrat lodge construction provides
openings in vegetation-choked wetlands, which greatly increase the wetland's value to waterfowl
and shorebirds. The negative economic impacts of muskrats center on burrowing activities that can
cause shoreline erosion and structural damage to farm ponds, stock dams and dikes. This damage can
be controlled, however, with proper population regulation. Nature made the muskrat prolific, but
most of each year's production dies before the next year's breeding season begins. It is from
this surplus that trappers take their pelt crop, causing no harm to the breeding stock. Ease of
trapping and pelting make the muskrat a great favorite of young trappers.
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