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| Figure
1. The muskrat has a stocky appearance,
with small eyes and very short, rounded ears. Its front
feet, which are much smaller than its hind feet, are adapted
primarily for digging and feeding. (Photo by John
White.) |
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Muskrats
(Ondatra zibethicus, Fig. 1) get their common name from their
resemblance to stocky rats and from the musky odor produced by their
scent glands.
Muskrats weigh
2 to 4 pounds and reach lengths of 18 to 25 inches, including their
8- to 11-inch, sparsely haired tails. Their coat color is generally
dark brown, but individuals can range from black to almost white.
Muskrats have partially webbed hind feet that function as paddles
and much smaller front feet used primarily for digging.
Muskrats are
found throughout still or slow-moving waterways, including marshes,
beaver ponds, reservoirs, irrigation canals and ditches, and marshy
borders of lakes and rivers. They don’t live in mountainous
areas where cold weather makes their food unobtainable.
Muskrats make
a valuable contribution to aquatic communities. By harvesting plants
for food and den sites, they create open water for ducks, geese,
shorebirds, and other wildlife. In addition, a variety of animals—including
snakes, turtles, frogs, ducks, and geese—use muskrat lodges
and platforms to rest and nest in. However, muskrats are considered
pests when their burrowing activity damages dams and dikes, and
when their feeding activity damages new plantings and crops.
Facts
about Washington’s Muskrats
Food and
Feeding Habits
- Muskrats
eat a wide variety of plants, including cattails, sedges, bulrush,
arrowhead, water lilies, pondweed, and ferns. They also eat
alfalfa, clover, corn, and other crops if muskrats find them
in their territories.
- Although
muskrats will eat shellfish, snails, fish, frogs, and salamanders,
such animal foods are a small part of their diet, and are generally
consumed when plant foods are scarce.
- Muskrats
normally feed within 150 feet of their main dwellings; however,
they will travel much farther in search of food.
- When muskrats
become too numerous, an “eat-out” can occur where
nearly all the available food is eaten. The eat-out area becomes
virtually uninhabitable for muskrats, and only a few animals
may be found where dozens or more once were.
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| Figure
2. In marshes and other areas lacking steep banks, muskrats
build dome-shaped lodges from leaves, stems, roots, and mud. |
Den Sites
- Depending
on site conditions, muskrat dens are located in banks or lodges.
- In dams,
dikes, and banks, muskrats tunnel upward from below the water
surface into the soil to make dens that remain dry (Fig. 2 and
4).
- Bank dens
range from a short tunnel leading to an enlarged nest chamber,
to a long, complex system of chambers, air ducts, and entrances.
- In marshes
and other areas lacking steep banks, muskrats build dome-shaped
lodges from leaves, stems, roots, and mud.
- Lodges
are constructed in open water that is 2 to 4 feet deep, and
are built high enough to keep the den above high-water levels.
Reproduction
and Family Structure
- Muskrats
are prolific breeders and under favorable conditions may raise
20 young per season (Fig. 3).
- The first
litter is born in early spring; one or two litters may follow.
- An average
of six kits are born after a 30-day gestation period. Kits are
dependent on their mother for approximately 30 days, after which
time they can swim, dive, and eat green vegetation.
- At about
six weeks of age, kits leave the den or live in a separate chamber.
- Adult
females are thought to overwinter with surviving offspring from
the last litter and one or more adult males. In spring, the
young seek out their own territories, generally within 300 feet
of the maternal female’s home range.
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| Figure
3. Muskrats are prolific breeders and under favorable conditions
may raise 20 young per season. |
Mortality
and Longevity
- Muskrats
have many predators, including mink (a major predator), otters,
bobcats, house cats, domestic dogs, coyotes, foxes, large hawks
and owls, and largemouth bass.
- Muskrats
are fierce fighters and fights among males are common when densities
are high and food supplies are low.
- Spring
flooding can drown early litters and inundate burrows and lodges,
exposing muskrats to predators.
- Historically,
muskrats have been one of the most commonly trapped animals
in Washington. From 1991 to 2000, an annual average of 6,189
muskrats were trapped. This number has been greatly reduced
with the passing of Initiative
713 in the year 2000.
- Most muskrats
don’t live more than one year.
Viewing
Muskrats
Muskrats are
active throughout the year. Although they may be seen at any time,
they are most active at twilight and throughout the night. During
the day they may be seen feeding, or basking in the sun when temperatures
are low.
Rarely will
muskrats be seen very far from water, and they are usually seen
swimming. Muskrats tend to swim with their narrow, pointed tails
snaking in the water behind them, or arched out of the water.
When startled,
muskrats enter the water with a loud splash, and, being strong
swimmers, they may swim long distances underwater before surfacing.
(They can remain motionless under sparse vegetation, with only
their noses and eyes above water, for 20 minutes.)
When cornered
or captured, muskrats are aggressive biters and scratchers and
can seriously injure pets and humans.
Living
Areas
In
marshes, ponds, and other water areas east of the Cascade mountains,
prominent muskrat lodges are sure indicators of a present muskrat
population.
Look for entrances
into their bank dens along dams, dikes, and stream banks, particularly
west of the mountains. Entry holes are particularly evident where
muskrats are living in tidewater areas near the mouths of rivers.
When the tide recedes, the entrances are exposed until the tide
comes back in.
Similarly,
in dry years the water in ponds and reservoirs can drop and expose
den entrances. Muskrats will then usually dig new dens farther
out in the pond.
Entry holes
are 5 to 8 inches in diameter and are located 3 to 36 inches below
the surface of the water.
Feeding
Areas
Evidence
of muskrat feeding includes plants gnawed to a stubble, floating
cattail roots or other vegetation that has been clipped, and piles
of clipped vegetation under overhanging vegetation or in a well-concealed
spot at the water’s edge.
Muskrats sometimes
use feeding huts or eating platforms that they create from mud
and compacted vegetation. Feeding huts look like small lodges
about 1 foot above the water level and are hollow inside; feeding
platforms look like small piles of cut vegetation.
Both feeding
huts and platforms are built near dens or lodges, and there may
be travel channels through the mud leading to them.
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Figure
4. Muskrat tracks are small, hand like prints, with long,
fingerlike toes. The rear print is 2 to 3 inches long and may
look like a smaller version of a raccoon track. The front print
may appear four-toed, as the inner toe is extremely small and
barely shows in the track. (Washington Department
of Fish and Wildlife.) |
Tracks
Muskrat
tracks can be found in mud or sand along shorelines (Fig. 4).
The mark of a dragging tail is sometimes apparent.
Droppings
Muskrat droppings
can be found floating in the water, along shorelines, on objects
protruding out of the water, and at feeding sites. The animals
may repeatedly use these spots, and more than one muskrat may
use the same spot. Droppings are dark green, brown, or almost
black. They are slightly curved, cylindrical, and about ½
inch long and 3/8 inch in diameter.
Slides
Slides are
the narrow trails muskrats make where they enter and leave the
water. Slides are about the width of a hand, look like muddy trails,
and may be slicked down from the animals’ sliding down them
on their bellies.
Preventing
Conflicts
Although muskrats
are important contributors to natural aquatic systems, their burrowing
may threaten the safety of dams, dikes, and other human-created
embankments. Muskrats may also undermine retaining walls that
shore up homes, bridges, and other structures. Muskrats occasionally
eat new wetland plantings and agricultural crops growing in their
territories.
Muskrat numbers
may increase to the point where an area is denuded of aquatic
plants. After foraging on entire plants, including the roots,
they leave the area pitted with digging sites and deep swimming
canals. This feeding behavior can destroy existing root mats that
bind and secure a wetland together, and the area can be quickly
eroded by wind and wave action.
The following
suggestions will help to reduce conflicts. You can do the work
yourself or hire a company to do all or part of the work (see
Hiring a Wildlife Damage
Control Company). In cases where these methods are not practical,
contact your local County Extension Agent or Department of Agriculture
for further information.
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Figure
5. In dams, dikes, and banks, muskrats tunnel upward from
below the water surface into the soil to make dens that remain
dry. When fluctuating water levels flood their initial den,
they burrow farther into the bank or dig new, higher den chambers
close to the surface.
(Drawing by Jenifer Rees. Adapted from Hygnstrom et al., Prevention
and Control of Wildlife Damage.) |
Water-level
management: Muskrats
(and occasionally voles and Old World rats) dig into dams, dikes,
and other embankments to make dens (Fig. 5). Typically these dens
have 2 feet or more of earth above them. However, when fluctuating
water levels flood their initial den, muskrats burrow farther
into the bank or dig new, higher den chambers close to the surface.
In such cases this can weaken the bank, or livestock and other
large animals can pierce holes in the bank, starting the erosion
process.
To prevent
muskrats from tunneling higher in an embankment, keep fluctuations
in water levels to a minimum. This can require frequently monitoring
the spillway to ensure an unobstructed flow, or widening the spillway
to carry off surplus water so that it never rises more than 6
inches on the dam.
Water-level
manipulation can also be used to force muskrats to other suitable
habitat. Raising the water level in the winter to a near-flood
level, and keeping it there, will force the animals out of their
dens. Similarly, dropping water levels during the summer will
expose muskrat dens to predators, forcing them to seek a more
secure area.
Slope management:
Muskrats prefer to burrow on steep slopes covered with vegetation.
Hence, they can be discouraged by keeping side slopes to a 3:1
or less ratio, and by controlling vegetation growth. Managing
vegetation by hand can be difficult in large areas, but routine
mowing or cutting with a weed whacker can be effective. Only herbicides
registered for use next to water should be used, and then only
per the manufacture’s recommendations.
If possible,
keep livestock off embankments to avoid the chance that an animal
will put a hoof through a den chamber. If a roof is pierced, immediately
fill in the cavity with soil, rocks, or a mudpack (see below).
Embankment
barriers: A barrier installed 1 foot above to 3 feet below
normal water level can prevent muskrats from burrowing into an
earth embankment.
A barrier
can be made from 1-inch mesh hardware cloth (aluminum and stainless
steel are also available), or heavy-duty plastic or fiberglass
netting. The barrier should be placed flat against the bank and
anchored every few feet along all edges. To extend the life of
galvanized hardware cloth, spray it with automobile undercoat
paint or other rustproof paint before installation. Since the
wire will eventually corrode, do not use this material where people
are likely to swim.
Riprapping
areas with stone creates an effective barrier and protects slopes
from wave action. Stone should be at least 6 inches thick. Do
not use rocks larger than 6 inches in diameter because when piled
they tend to form cavities, providing hiding places for muskrats
and Old World rats.
In situations
where muskrats are burrowing into existing rock walls, place gravel
or concrete in between the rocks to block up the holes. A permit
may be needed when working near state waters (see Legal
Status).
Where a burrowing
problem is extreme, use a gas-powered trenching machine (available
at rental stores) to dig a narrow trench along the length of the
embankment. Hand digging will be required to dig to the recommended
depth—3 feet below the high-water level. Next, fill the
trench with a mudpack. A mudpack is made by adding water to a
90 percent earth and 10 percent cement mixture until it becomes
a thick slurry. The resulting solid core will prevent muskrats
from digging through the embankment.
Floating
dock barriers: Muskrats will burrow into floating docks, generally
those floating on Styrofoam, scattering the broken white foam
along the shoreline. This becomes an environmental danger, due
to birds and other small animal eating this foam. To solve this
problem, the dock needs to be pulled up on shore and 1-inch mesh
hardware cloth (aluminum and stainless steel are also available)
needs to be used to cover the Styrofoam.
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| Figure
6. Muskrats are diggers and a fence will need to extend
at least 12 inches below ground. Alternately, a tight fit to
the ground and an L chicken wire or hardware cloth extension
that runs 24 inches out on the soil surface toward the animal
will also prevent entering from underneath an existing fence.
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Figure
7. A mini floppy fence constructed of 1-inch mesh wire or
heavy plastic needs to be at least 2 feet high and staked so
that it’s wobbly to prevent an athletic muskrat from trying
to make the climb. Constructing the fence so that it leans slightly
toward the muskrat will increase its effectiveness.
(Drawings by Jenifer Rees.) |
Fences
and other barriers: Muskrats are not climbers. A properly
designed and maintained 2-foot tall wire fence will prevent muskrats
from entering an area. The fence must be taller if snow or other
materials are likely to build up near it.
Because muskrats
are diggers, the fence will need to extend at least 12 inches
below ground. Alternately, a tight fit to the ground and an L
extension that runs 24 inches out on the soil surface toward the
animal will also prevent entering from underneath and existing
fence (Fig. 6).
Welded-wire
cylinders around individual plants are often used where only a
few plants need to be protected. Note: Lightweight plastic
seedling protectors do not work because muskrats can chew through
them.
A floppy
fence can be constructed as a barrier between an active muskrat
colony and a large area needing protection (Fig. 7). To prevent
muskrats from walking around the fence, connect each end to an
existing, impenetrable solid fence or structure.
Harassment
and repellents: Muskrats are wary animals and will try to
escape when threatened. When new burrows are discovered early
on, the entry holes can be stuffed with rocks, balled-up window
screen, and/or rags sprinkled with predator urine (mink, coyote,
or bobcat—available from trapper supply outlets and over
the Internet) or ammonia. Some people have had success applying
used cat litter in this way. Exposing their tunnels from above
may also work. The success of this type of control depends on
persistence from the harasser and thus is often short-lived.
Large dogs
that are awake during the night can be effective at keeping muskrats
out of areas.
Commercially
available taste repellents may be effective at preventing damage
to crops and other plants.
Crop location:
Unfenced crops and gardens located close to water will be more
attractive to muskrats than those further from water. If you have
a choice of where to locate your garden, consider muskrat damage.
Natural vegetation buffers next to water bodies can provide feeding
areas and reduce the attractiveness of vegetation further from
the water.
Lethal
Control
Since muskrats
are usually found in waterways, there is often an unlimited supply
of replacement animals upstream and downstream from where the
damage is occurring. Rapid immigration coupled with a high reproductive
rate makes ongoing lethal control a “high-effort”
method of damage control that is often ineffective. (Lethal control
can be effective in areas where the local population of muskrats
is still small.) The exclusion methods described and referenced
above are often the best long-term solution.
Trapping
Lethal trapping
has traditionally been the primary form of control. See Trapping
Wildlife and Legal Status for information
on trapping muskrats. Note: State wildlife offices do not
provide trapping services, but they can provide names of individuals
or companies that do.
Shooting
Shooting
has been effective in eliminating small isolated groups of muskrats.
Shooting muskrats requires good marksmanship. For safety considerations,
shooting is generally limited to rural situations and is considered
too hazardous in more populated areas, even if legal.
Fumigants
No fumigants
are currently registered for muskrat control.
Public
Health Concerns
Rabbits, hares,
voles, muskrats, and beavers are some of the species that can
be infected with the bacterial disease tularemia. Tularemia is
fatal to animals and is transmitted to them by ticks, biting flies,
and via contaminated water. Animals with this disease may be sluggish,
unable to run when disturbed, or appear tame.
Tularemia
may be transmitted to humans if they drink contaminated water,
eat undercooked, infected meat, or allow an open cut to contact
an infected animal. The most common source of tularemia for humans
is to be cut or nicked by a knife when skinning or gutting an
infected animal. Humans can also get this disease via a tick bite,
a biting fly, ingestion of contaminated water, or by inhaling
dust from soil contaminated with the bacteria.
A human who
contracts tularemia commonly has a high temperature, headache,
body ache, nausea, and sweats. A mild case may be confused with
the flu and ignored. Humans can be easily treated with antibiotics.
Muskrats
are among the few animals that regularly defecate in water, and
their droppings (like those of humans and other mammals) can cause
a flu like infection, which old-time trappers referred to as “beaver
fever.”
Anyone handling
a dead or live muskrat or nutria should wear rubber gloves, and
wash his or her hands well when finished.
Legal
Status
Muskrats are
classified as furbearers (WAC
232-12-007). A trapping license is required and they can only
be trapped during seasons set by the state.
A property
owner or the owner’s immediate family, employee, or tenant
may kill or trap muskrats on that property if they are damaging
crops or domestic animals (RCW
77.36.030). In such cases, no special trapping permit is necessary
for the use of live traps. However, a special trapping permit
is required for the use of all traps other than live traps (RCW
77.15.192, 77.15.194;
WAC
232-12-142). There are no exceptions for emergencies and no
provisions for verbal approval. All special trapping permit applications
must be in writing on a form available from the Department of
Fish and Wildlife (WDFW).
It is unlawful
to release a muskrat anywhere within the state, other than on
the property where it was legally trapped, without a permit to
do so (RCW
77.15.250; WAC
232-12-271).
A permit
issued by WDFW is required for work that will use, obstruct, change,
or divert the bed or flow of state waters (RCW
77.55). A permit application can be obtained from your WDFW
Regional Office or from the Hydraulic
Project Approval (HPA) web page.
Because legal
status, trapping restrictions, and other information about muskrats
change, contact your WDFW
Regional Office for updates.
Additional
Information
Books
Christensen,
James R., and Earl J. Larrison. Mammals of the Pacific Northwest:
A Pictorial Introduction. Moscow, ID: University of Idaho
Press, 1982.
Hygnstrom,
Scott E., et al. Prevention and Control of Wildlife Damage.
Lincoln, NE: University of Nebraska-Lincoln, Institute of Agriculture
and Natural Resources, 1994. (Available from: University of
Nebraska Cooperative Extension, 202 Natural Resources Hall,
Lincoln, NE 68583-0819; phone: 402-472-2188; also see Internet
Sites below.)
Ingles,
L. G. Mammals of the Pacific States. Stanford, CA: Stanford
University Press, 1965.
Larrison,
Earl J. Mammals of the Northwest: Washington, Oregon, Idaho,
and British Columbia. Seattle: Seattle Audubon Society,
1976.
Link, Russell.
Landscaping for Wildlife in the Pacific Northwest. Seattle:
University of Washington Press and the Washington Department
of Fish and Wildlife, 1999.
Maser,
Chris. Mammals of the Pacific Northwest: From the Coast to
the High Cascades. Corvalis: Oregon State University Press,
1998.
Verts,
B. J., and Leslie N. Carraway. Land Mammals of Oregon.
Los Angeles: University of California Press, 1998.
Internet
Resources (General)
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