Why are there fewer muskrats in Minnesota?

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The muskrat houses, once spotted in multitudes, were missing.

That’s what a reader — who recalled seeing the critters’ homes dotting wetlands along the Minnesota River Valley in the past — noticed recently.

He wrote to Curious Minnesota, the Strib’s reader-powered reporting project, to ask: “What happened to all the muskrats?”

The state’s Department of Natural Resources has actually been asking the same question. The furry aquatic rodents’ population has been in decline in Minnesota and North America since the 1980s.

Muskrats are still one of Minnesota’s “most widespread and abundant” furbearers, or mammals with fur that’s commercially valuable, said Jason Abraham, a furbearer specialist with the DNR.

They aren’t considered endangered or threatened.

“However, while they are still present and even flourishing in some well-managed wetlands, we’re finding evidence that muskrat populations are not what they used to be,” he said.

Researchers have several theories about the causes of muskrats’ smaller numbers — including habitat degradation, invasive cattails and water quality problems.

The Minnesota River basin in particular has gone through a number of changes — such as urbanization and shifts in land use and water quality — that could contribute to the decline, Abraham said.

In Minnesota, the DNR uses an annual survey of trappers to monitor muskrats’ “relative abundance,” Abraham said. They take into account that trapping muskrats is not as popular in the state as it once was.

In fact, the number of muskrats trapped in Minnesota each year has plummeted: from more than 240,000 in 2006 to about 19,000 in 2023, according to Abraham.

“That decline reflects both reduced trapper participation and fur market trends, not just population levels,” said Abraham.

“However, even when accounting for those factors, there is scientific and observational support for a broader, gradual decline in muskrat numbers,” he said.

This decline has been documented in habitats across North America.

In 2021, researchers found a more than 90% drop in the numbers of muskrat houses compared to counts in the 1970s and ’80s in two large Great Lakes coastal wetlands (in Canada’s Point Pelee National Park marsh on Lake Erie and Matchedash Bay‐Gray Marsh wetland on Lake Ontario).

Droughts and floods are now happening more frequently, creating volatile water levels. This degrades muskrat habitat and is likely the biggest factor in local populations’ decline, Abraham said.

Stable water levels are vital for muskrats because they eat what’s called “emergent vegetation,” or plants that grow up out of the surface in shallow water.

Biologists and habitat managers in Minnesota have seen muskrats thriving in wetlands in Wildlife Management Areas with water control structures, while finding few or no muskrats in adjacent wetland areas that aren’t managed.

This is “clear evidence that habitat condition plays a critical role,” Abraham said.

There are several other factors that could be affecting muskrat numbers.

Researchers are looking into how muskrats are affected by invasive typha x glauca cattails (these are a cross between native and non-native varieties that crowd out other plants and reduce open water).

Other possible factors include habitat reduction from drainage and agricultural tiling. Reduced water quality from urban runoff and development could also play a role.

“Trapping, predators, or pesticide use are not believed to be major drivers of muskrat decline in Minnesota,” Abraham said.

In Minnesota, the muskrat’s distant furbearer relative the beaver has fared comparatively better in recent decades, Abraham said — beavers’ populations are generally either increasing or stable in the state.

Both animals are aquatic rodents that build and live in lodges. But they are very different in many ways. Muskrats are much smaller (they only weigh 2 to 4 pounds, while beavers can weigh as much as 70 pounds).

That means muskrats are prey to a wider array of animals, from raptors to large fish. Steve Windels, a wildlife biologist at Voyageurs National Park, called a muskrat “a two-pound furry little hamburger” in a 2023 Minnesota Star Tribune article.

Unlike beavers, muskrats don’t build dams, and they use different materials (think cattails and mud instead of logs) to create their lodges. They also create homes by tunneling into the banks of waterways.

The two animals have different diets as well. While beavers can eat trees’ inner bark and leaves as well as plants, muskrats depend on plants that grow in shallow water and poke above the surface.

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