A muskrat perches above the water on an early winter day at North Star.

One can only wonder how many visitors to North Star Nature Preserve have proclaimed “beaver!” at the sight of a brown, furry face cruising effortlessly through the water. Chances are they were actually watching a muskrat going about its business.

North Star is home to both the North American beaver (Castor canadensis) and the muskrat (Ondatra zibethicus) – two semi-aquatic mammals that share some common characteristics, but are not closely related. While the beaver has garnered a great deal of attention of late as a wetland architect capable of creating riparian ecosystems, the unsung muskrat makes its own beneficial contributions as a maintainer of wetland habitats.

The sight of greenery trailing alongside a swimming muskrat sums up the vital role this creature plays in wetlands upkeep. By continually harvesting the favored plants that make up most of its diet, muskrats help maintain the open water that is required by other wildlife. In some marshes, they are crucial to thinning dense stands of cattails. Muskrats are largely herbivores, though they will also consume small animals such as frogs, crayfish and fish, as needed. As prey, they provide an important food source for raptors and a variety of other predators.

It’s not unusual to find muskrats and beavers co-existing in slow-moving streams, ponds and lakes. North Star is prime habitat for both species. Muskrats do not build dams – that’s the beaver’s task – but they do live in lodges, burrowing into steep streambanks, or building small mounds of mud and vegetation (called push-ups) in marshes. They may also build feeding platforms in the water constructed with branches and cut pieces of vegetation.

It is easy to see how, at first glance, a muskrat could be mistaken for a beaver. Both species present cute, brown faces with whiskered noses and rounded ears protruding from the water as they swim. A muskrat’s long, thin, scaled tail is often visible as it swims, though, while the wide, paddle-like tail of the beaver is under water unless the beaver raises it for a loud slap on the surface. Most telling, beavers are much larger than muskrats, weighing 40 to 70 pounds as adults, compared to 2 to 4 pounds for the muskrat.

Both animals are native to North America and both are rodents, but beavers belong in the Castoridae family, which contains only two living species – the American and Eurasian beavers. Muskrats, which are are closely related to voles, are part of the large Cricetidae family. They are not rats, which belong to yet another family.

The muskrat’s musk glands, in combination with its rat-like tail, may have inspired its name, but some sources suggest the name is derived from indigenous descriptions.

Muskrats are excellent swimmers, using partially webbed rear feet to move forward and backward in the water. Their tails are uniquely flattened vertically, acting as rudders and potentially helping with propulsion. They can hold their breath underwater for 12 to 17 minutes and, like beavers, close off their ears to keep water out. Two layers of fur keep muskrats warm in cold water.

Like beavers, muskrats spend a lot of time in their lodges in the winter, but they do not hibernate. While both animals are active at night, dusk and dawn, Open Space and Trails frequently sees muskrat activity during the day at North Star. Take close look if you see one of these expert swimmers in the water and celebrate the sighting of a muskrat!

– By Pitkin County Open Space and Trails