Water We Talking About? Life in a Lake as a Mammal

Happy Friday! It’s time again for Water We Talking About – when kids send us freshwater-related questions (or queries about the moon!) and we track down real-life scientists to answer them. This week our subject involves the furrier critters that call our lakes home, so we reached out to the Wisconsin Department of Natural Resources’ assistant furbearer ecologist for an answer. Water We Talking About? Muskrats, of course!

The Question:

Five-year-old Ethan was out for a stroll along Lake Mendota, his mom reports, when he saw a muskrat in the water. That got him wondering: “Where do mammals live in or near the lake? And what they do when the lakes are frozen?

The Answer:

Thanks for asking, Ethan! While no one here at the Center for Limnology studies the four-legged animals that live alongside our lakes, we were able to track down Curtis Twellman, the assistant furbearer ecologist at the Wisconsin DNR. (We even managed to catch him in the middle of an online conference all about Wisconsin’s furbearing animals!)

If you’re wondering why we don’t just say “mammals” it because furbearers are the animals that, traditionally were prized for their pelts – like muskrats and beavers.

Anyway, here’s what Curtis had to say:


In Wisconsin we have several mammals that are semi-aquatic, spending a considerable amount of time in the water. Around the Madison chain of lakes, muskrats are commonly seen. Mink, river otter and beaver are all present, too but a little more elusive. All four species can be seen statewide and are abundant across much of the state.

A muskrat carrying food to its den.

There are obvious challenges to a semi-aquatic lifestyle in Wisconsin where, even as far south as Madison, there is typically several weeks of solid ice coverage each winter.

Some critters like beaver (the largest rodent native to North America) create homes to live in. A beaver lodge will have entrances far enough under the water’s surface to remain open under the ice. Inside the lodge or bank den there will be a nest chamber above the waterline that is safe, warm and dry. Beaver collect food and create a food cache near their home that they can access under the ice. This will look like a big wad of sticks with pointy ends and will be less precisely engineered than the dams they are famous for.

Muskrats are similar and often dig dens into the side of the river bank or lake shore and also utilize “huts” made of grasses and brush to feed or rest in. You may see these huts start to pop up in marshes in the fall. Muskrats can travel from their bank dens to multiple huts all under the ice.

On deep water lakes like Mendota you don’t usually see huts but bank dens are common. Both muskrats and beaver will typically have an exit higher up to reach dry ground if needed.

Mink and otter are both in the weasel family and are carnivores. They will often use beaver and muskrat dens to rest in. They have to cover more territory as carnivores than muskrats and beaver do to find enough food. This means they put less effort into their home and more into hunting. Luckily both river otter and mink are athletic enough to hunt on land or in water to take advantage of multiple food sources through the long, tough winter.

While I would never call the Wisconsin winter mild or easy, our native wildlife species are well adapted to it!

Keep an eye out there, Ethan, and maybe you will get to see some of our other semi-aquatic mammals that live in the Madison chain!

Thanks, Curtis, for fielding Ethan’s question. And thank the rest of you for tuning in! Next week, Johnny ponders seashells by the seashore and we’ve got another mystery from the Sarver, Pennsylvania tadpole tank! In the meantime, here is a cool video of a Lake Mendota muskrat under the ice, courtesy of Wisconsin SeaGrant’s Bonnie Willison!

If you’re a kid with a question of your own, ask us at media@limnology.wisc.edu – @WiscLimnology on Twitter – or our Center for Limnology Facebook Page!