Beavers and Muskrats – Background

Beavers and muskrats, both rodents with round, furry bodies, twinkling eyes, and dexterous front feet, have a certain charm that endears them to us, even though they can be a nuisance. Both animals live in wetland habitats, and, though they are only distantly related, they have many similarities in their behavior and physical adaptations. Muskrats are beneficial to other wetland animals because they keep waterways open and clear of vegetation. But beavers far outshine muskrats in their skill as engineers and in the profound effect they have on their environment.

Beavers and muskrats are superbly adapted to life in wetlands. Though beavers are somewhat ungainly when on land, their torpedo-shaped bodies make them swift and agile under water. The wide, flattened, leathery tail serves as a rudder when swimming and as a prop or third leg when they stand on their hind feet to gnaw on a tree. Beavers’ large, webbed hind feet help to provide the power they need to transport branches and logs through the water and give them stability while walking on land.

Muskrats, more closely related to rats and mice, are much smaller than beavers, weighing only three pounds compared to sixty pounds for an average beaver. Like beavers, muskrats are agile swimmers; their partly webbed hind feet power them through the water. Their tails are also naked, scaly, and used as rudders in swimming. While beaver tails are flattened like a paddle, muskrat tails are flattened on the sides. An alarmed beaver slaps its great flat tail on the water to warn other beaver family members or perhaps to scare away a predator. Muskrats also smack their tails on the water when alarmed, but the sound is not nearly as impressive as the gunshot sound of a beaver tail slap.

Both beavers and muskrats can stay under water for as long as fifteen minutes. Both animals conserve oxygen by slowing the heart rate, relaxing muscles, and constricting blood vessels to their legs and tails. The beaver’s extra large lungs and liver keep its blood well oxygenated. Muskrats have special nostrils that allow them to trap air and recycle it, removing additional oxygen before it is exhaled.

Beavers and muskrats have keen senses of hearing and smell, though neither seems to have very acute vision. The beaver, with ears, nose, and eyes located high on its head, can use all of its senses when it is swimming at the surface. When it dives, the ears, nose, and throat have valves that close automatically to keep water out. Beavers have a third eyelid, a translucent membrane that acts like a pair of goggles, allowing them to see while underwater and protecting their eyes from splinters when gnawing on wood. Although they have small ears, they have large auditory canals, and they are sensitive to vibrations even under water. The sound of running water, especially coming from the dam, triggers a flurry of beaver activity.

A muskrat’s diet consists of grasses, lily pads, cattails, and aquatic plants – all foods that beavers eat as well. In addition, muskrats occasionally eat frogs, crayfish, clams, snails, and fish. Beavers, on the other hand, are strictly vegetarian. Their diet, especially in winter, consists mostly of the inner bark of trees and branches. Beavers use their strong front teeth to cut away chips of wood from standing trees until the tree falls over. Contrary to popular belief, beavers cannot plan where a tree will land, and they are sometimes killed by the fall. Once the tree is on the ground, the beavers can reach the topmost branches. These they cut off, eating the bark much as we would eat corn on the cob. Beavers can’t actually digest wood. They have a special appendix in the digestive tract that contains bacteria that help to break down these woody materials. The stripped branches may then be dragged to water to be used in building dams and lodges or to line canals.

Both beavers and muskrats have lips that close tightly behind their incisors so they can gnaw on food while underwater. Like other rodents, their incisors grow continuously, and a beaver’s may grow as much as four feet in one year. The orange enamel on the outer surface of the front teeth is harder than that on the inside of the teeth. As they chew, the inside wears faster than the outside, maintaining a sharp chisel-like edge that helps them to cut through tough vegetation.

Beavers and muskrats do much of their work with mouth and teeth, but they also use their small, dexterous front feet for many activities. The front feet are not webbed and they are kept balled up like fists to serve as bumpers when swimming. They are used for carrying sticks, leaves, mud, and their own young. To plaster their dam or lodge, beavers scoop up mud between the front legs and chin. They use their hands to spread and pack it in place. Some beavers use their hands to roll up large lily pads, eating them like double-rolled burritos.

Both beavers and muskrats are valued for their fur. They have dense, woolly undercoats covered by long silky guard hairs. They keep their fur waterproofed by grooming it with oil that is produced in glands near their tails. These oils are also used for marking territories. Muskrats make twists of grass along the edges of their territories that they scent-mark with their pungent musk oil. Other muskrats are aware of these signposts and the boundaries that they indicate. Similarly, beavers mark their territories with mounds of mud and grass scented with an oil called castoreum.

Grooming is extremely important for beavers and muskrats, both to keep the fur well oiled and to remove parasites. Beavers have a special split claw on their hind feet that they use for combing parasites and debris out of the fur and even wood chips caught in the teeth. The outer-most claw can be operated like a pair of tweezers for removing parasites. Muskrats don’t have split claws, but they still spend a lot of time running their toes and claws through their hair to clean away parasites and keep the fur waterproofed.

One large difference between beavers and muskrats is in how they reproduce. Beavers produce only one litter a year, while muskrats usually produce up to four litters. Beavers live in family groups made up of a mated pair, their current offspring, yearlings, and sometimes young adults from an earlier litter – often as many as 12 beavers together in a lodge. They show very little aggression within a family group and a high degree of parental care. Older siblings help to rear the young ones. Young beavers, whose early attempts at building and storing branches can be comical, seem to learn by watching their adult family members. Muskrats also live in groups with interconnecting tunnels in their burrows, but they can be highly territorial and aggressive to each other.

Beavers were sought after for their fur and also for their castoreum oil, which is used as a base for perfume. Much of the North American continent was first explored by Europeans as fur-traders searched for beavers to trap. As a result of over-hunting, they were nearly eliminated over much of the country. Conservation efforts in the twentieth century successfully restored beavers to their entire range, and they are plentiful once again. Muskrats, because they reproduce much more quickly and because their habitat and food needs are much smaller, have never experienced a similar decline.

Muskrats excavate extensive burrows deep in the banks of the rivers, ponds, and ditches where they live. Their burrows have one or two underwater entrances and one or more dry chambers above water level. In some locations, they instead build conical lodges made from large piles of aquatic plants and mud that look like small beaver lodges. Like beavers, muskrats are active all year long. In the fall, muskrats build push-ups – piles of plants stacked up above holes in the ice which they can get to for feeding during the winter. The burrows, lodges, and feeding areas are connected by underwater channels that allow them to remain active all winter.

Although muskrat constructions are fairly elaborate, they are nothing compared to a beaver’s engineering marvels. Beavers begin changing a stream by building a dam across it made of mud, rocks, branches, and sticks. This creates a pond and raises the level of the water until it is suitable for a beaver lodge. Now the beaver pair builds a pile of rocks and mud in the middle or near the side of the pond until it is above water. Then they add masses of sticks and more mud as mortar until they have constructed a lodge that will house a family of ten to twelve beavers. With underwater entrance and exit holes, their homes and families are well protected from predators. By burying a supply of sticks near the underwater entrance to their lodge, beavers can stay in their lodge during the coldest winter months, sealed under the ice, and yet still have plenty of food at hand.

Beavers and muskrats have a large impact on the countryside. Muskrat burrows can undermine streambanks, and in some places muskrats do serious damage to farmers’ crops. Beavers block culverts, flood roads, and cut down whole forests. Yet the wetlands they create catch sediments, filter pollutants, and provide homes for many different plants and animals. Muskrats were affectionately called Little Brother of the Beaver by some Native Americans because they look like little beavers, swim like little beavers, gnaw like little beavers, and build houses like little beavers. But beavers, because of their amazing abilities, stand out as giants among rodents.

Suggested Reading

Godin, Alfred. Wild Mammals of New England. Baltimore: Johns Hopkins University Press, 1977.

Graves, Eleanor, ed. Beavers and Other Pond Dwellers. USA: TimeLife Films, 1977.

Richards, Dorothy. Beaversprite. San Francisco: Chronicle Books, 1977.

Rue III, Leonard Lee. The World of the Beaver. Philadelphia: J.B. Lippincott, 1964.

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