Jan/Feb 2009For Wildlife Watchers: Muskrat by Rob Simbeck, photography by Len Rue Jr.
One subtext of this column is that people impact animals - mostly negatively. The handful of bird species that thrive because of human habitation, with robins, mockingbirds, starlings and house sparrows heading the list, pales in comparison with those whose numbers have been drastically reduced by development.
Still, it's only fair to point out that any number of creatures negatively impact us. Termites consume our homes. Coyotes kill our livestock. Deer and rabbits eat our gardens. Mosquitoes and ticks carry diseases.
One of the lesser-known examples of destruction involves the muskrat. Last summer's devasting floods in the Midwest breached levees in a number of Mississippi and Missouri river towns, and this two- to four-pound rodent played a role in at least one such incident. It happened just north of St. Louis in Winfield, Missouri, where muskrat holes weakened a portion of a levee along the Mississippi and led to one of many disastrous breaches.
Muskrats are burrowers. They construct, out of vegetation and mud, what look like smaller beaver lodges, perhaps 4 or 5 feet across and a couple of feet tall in marshes or ponds, with two or more underwater entrances leading to above-ground, grass-lined dens. It's where the habitat isn't suitable for such a lodge that they tunnel into streambanks, pond dams or, in this case, levees. Such channels weaken man-made structures, so much so that in Europe, where this North American native has been introduced, muskrats have long since worn out their welcome in places like the Netherlands, where dikes and levees hold back the sea.
Muskrat - Ondatra zibethicus
(combining the Iroquois name "Ondatra" with the Latin for "musky")
Description: Beaverlike, thick, brown fur; naked, scaly tail. Head and body 10 to 14 inches long, tail 8 to 11 inches, 2 to 4 pounds.
Range and Habitat: Swamps and marshes in all but the driest portions of the U.S. and the coldest portions of Canada.
Reproduction: 3 to 6 young, up to 5 litters annually. Gestation 28 days; weaned at 4 weeks.
Viewing Tips: Dusk and dawn are best, in swampy areas. Tend to be more common in the piedmont and northern coastal plain. Muskrats drag their tails when they walk, making their tracks easy to identify.
Jay Butfiloski, wildlife biologist and Furbearer Project supervisor for the S.C. Department of Natural Resources, says the DNR gets scattered reports of burrowing activity in yards and dams, as well as of damage to docks and boat wiring caused by the toothy rodent's gnawing.
Muskrats, in fact, look a little like mini-beavers, with thick, glossy brown fur that turns silvery along the belly. They have tiny ears and eyes, lips that close behind the teeth for underwater chewing, webbed hind feet that act as paddles and clawed front feet strong enough for digging yet agile enough for grasping objects. The tail is scaled and rat-like and is an aid to propulsion in swimming. The creature gets its common name from musk glands under the tail used in marking territory, although despite the name and the tail, these animals are not true rats.
Muskrats are mainly nocturnal, with dusk and dawn being good times to spot them. They live primarily on a diet of cattails, bulrushes, sedges, water lilies and other aquatic vegetation, eating at favorite sites along trails leading from the den or taking food inside. In winter, when such vegetation is scarce, they will sometimes eat parts of the lodge itself and supplement their diet with mussels, crayfish, frogs and dead fish.
They begin breeding in their second year, with the female signaling her readiness with squeaks that the male answers with grunts and barks. They are polygamous and territorial and, given their pugnacious nature, they get into a lot of scrapes, many of which leave scars - they have powerful jaws and sharp incisors - and some of which are fatal. Mating occurs in the water several times a year.
"Muskrats can be very prolific," says Butfiloski, "with up to four to five litters of three to six young, and a gestation period of about twenty-eight days. They can breed at any time of the year, but most activity is in the spring and fall."
The eyes of the kits open in two weeks, and they are swimming and diving not long afterward. The mother may breed again while she is still nursing, and after the young are weaned at a month or so, they are driven off. They are especially vulnerable at this point to the many species that prey on muskrats, including minks and raccoons, foxes and coyotes, hawks, owls and water snakes.
Like their relatives the lemmings, muskrats sometimes experience population crashes, "depending on their habitat and population growth," according to Butfiloski. "More common is a cyclical population size rising and falling every six to ten years."
Muskrats remain active in the winter, although they will spend more time in their dens, which may be shared by up to a dozen individuals. They sometimes construct lodges in deeper water in winter, and they are adept at swimming under ice, relying on occasional holes or even trapped air bubbles. They can remain under water for several minutes - up to 15 if necessary - since they can tolerate a build-up of carbon dioxide in their bloodstreams.
Their durable, waterproof fur has made them a favorite of trappers through the centuries. There is still a trapping season in South Carolina, from January 1 to March 1, for the 500 to 600 people with commercial licenses. Depredation permits allow property owners to trap or shoot muskrats, although no permit is required to trap or shoot (if shooting is otherwise permitted) within 100 yards of a home on the homeowner's property. Muskrat flesh, by the way, has been compared to that of duck or turtle, and it is often called "marsh hare."
Pressures on population, whether from drought, flooding or food shortages, can lead to increased fighting and force some muskrats to travel and seek suitable habitat elsewhere. They are susceptible to a range of maladies, including giardia and rabies, and to parasites like worms, fleas and ticks, but loss of habitat is the biggest challenge. And in one of those ironies of human/animal relations, diminishing wetlands caused by human development have forced muskrats to farm ponds and irrigation channels, where their burrowing becomes problematic. It is one more example of the tightly wound interconnection between humanity and the rest of nature.