Scientific Name: Ondatra zibethicus


The muskrat is an overgrown, semi-aquatic vole. Muskrats have dense under-fur and a nearly waterproof "overcoat." Their feet are webbed and fringed with stiff hairs. The ankles are rotated out so the hind feet work as paddles (but rather inefficient walking feet). The tail is flattened side-to-side and serves as a rudder. The animals are dark brown in color, about 26 inches in length (of which the tail comprises nine inches) and weigh about two pounds.


Muskrats live statewide in marshes, ponds and slow streams, often in areas dammed by beavers.


Their lodges, made mostly of cattails and other aquatic plants, may be three feet high and six feet across. Feeding stations are similar but smaller. Inside the lodge is a nest chamber accessible only from below the water. Once inside the lodge, muskrats are safe from predators other than mink and occasionally snapping turtles. Moving awkwardly on land, however, they are killed by coyotes, foxes and large owls. Floods also kill muskrats, and fluctuating water levels increase the risk of death. Muskrats are managed as furbearers in Colorado.


Like other voles, these are runway builders and herbivores, eating mostly grasses, cattails, bulrushes and other marsh plants. They occasionally damage cornfields on flood plains, and their burrowing sometimes weakens ditch banks and levees.


Females breed in spring and summer and produce two or three litters of one to ten (the average is about six) young after a gestation period of about 30 days. The newborn young are blind, naked and vole-like, with round tails. Soon they acquire the muskrat’s proper flattened tail, and at two weeks can swim and dive.


By David M. Armstrong Department of Ecology & Evolutionary Biology Environmental Studies Program, University Museum of Natural History University of Colorado-Boulder

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