Mighty Muskrats: Natural bird conservationists?

Did you know muskrats may be natural conservationists by creating bird habitat through building their homes? Since 2021, I’ve been working closely with conservation partners at Audubon Great Lakes to better understand how muskrats influence Illinois and Indiana wetlands and how birds are better off because of it. This was all part of a research project I initiated as a PhD student and am continuing as a postdoctoral researcher with the University of Chicago.

Muskrats have long been labeled as an ecosystem engineer, but I was curious to dig in more to learn exactly what benefits they might provide to other animals, from invertebrates to birds. My partners at Audubon Great Lakes already had a rich dataset on marsh birds they had been using to inform wetland management across the Calumet region, but had little data on muskrats. Naturally, it made perfect sense to collaborate and get a closer look at these mysterious mammals.

Muskrats (Ondatra zibethicus) are semi-aquatic mammals native to Illinois, as well as most of the U.S. and Canada, and only reach up to 5 pounds in size. Though they may be small, they have a mighty impact on wetlands! They are voracious herbivores that eat large amounts of vegetation, and build enormous homes relative to their size. Muskrats build their houses in two ways, by burrowing into a bank or creating a huge free-standing igloo-shaped lodge, averaging 5 feet wide and 5 feet tall.

Muskrat Lodges

On a high level, the way that muskrats use free-standing lodges is the same as the way that you’d use your home – as a safe place to sleep, eat, raise a family and a find warmth during a cold Midwest winter. Unlike human homes, muskrats don’t simply enter through a door.

Muskrat lodges are constructed in areas with standing water, so imagine accessing your front door by diving underwater, holding your breath and swimming up through a tunnel. From there, you would climb up into a dry chamber above the water line that acts as a combination bedroom/living room/dining room.

To gather enough material to create their homes, muskrats will mow down a large circular stand of wetland plants, such as cattails, mouthful by mouthful. They then stack the vegetation in a big pile. By doing this, they create an opening with a lodge in the center that acts as a platform or island amongst a sea of cattails. Thus, muskrats act as ecosystem engineers, animals that significantly alter habitats they live in and, as a result, change the way other animals interact with that system. As part of the research project I created, I hypothesized that by creating lodges, muskrats may be enabling a larger diversity of animals to live within wetlands.

In particular, I predicted that marsh birds would benefit from muskrat lodges because muskrats help to naturally generate a condition called “hemi-marsh.” Hemi-marsh areas have a 50:50 ratio of open water to vegetation, and it is considered an ideal state that wetland managers work to achieve. At high density, muskrat lodges can create hemi-marsh conditions on their own. Marsh birds also consider this an ideal state because it provides them with a mix of vegetated areas to hide, open water areas to search for food and platforms for resting or nesting on.

Studying the Impacts of Muskrat Ecosystem Engineering

To understand how muskrats transform wetlands and impact use by other animals, I placed cameras at three sites in the Calumet region, an area at the southern tip of Lake Michigan encompassing northeast Illinois and northwest Indiana. I conducted this research during spring bird migration in late April, and programmed each camera to take one photo every five minutes. I had seven pairs of cameras, and in each pair, I had one camera pointed at a muskrat lodge, and one pointed at vegetation nearby as a comparison to understand how animals use wetlands when muskrat lodges aren’t present.

In just two weeks, I saw 18 different species in the lodge photos, and only six species in the control—a three-fold increase. This suggests that muskrats are significantly changing the diversity of species that use wetlands. Also, 85 percent of the animals we saw were birds. These included four focal species that Audubon Great Lakes works to conserve – sora (a type of rail), swamp sparrow, blue-winged teal and black-crowned night herons. In particular, seeing that black-crowned night herons use muskrat lodges was especially exciting, as these herons are considered endangered in Illinois.

Birds weren’t the only type of animals attracted to muskrat lodges based on the camera photos. Reptiles, particularly turtles, also liked using the lodges as basking platforms. The muskrats’ conspicuous homes also drew animals that wanted to eat them. My cameras captured a coyote plunging its head into the top of the lodge to reach the chamber where muskrats were living.

Implications for Conservation

Although my research is still ongoing, the findings so far have many implications for applied conservation work, such as the wetland restoration work Audubon Great Lakes has been leading with partners in the Calumet region. By managing wetlands that are ideal for muskrats, we can indirectly help many other species, including species of conservation concern such as the black-crowned night heron.

For the next step in my work as a postdoctoral researcher through the Smith Fellows Program, I am working to create strategies to harness the impacts of muskrat lodges to improve conservation and restoration efforts throughout the Great Lakes. Through this work, my goal is also to help people learn more about muskrats, and why they are an integral part of the Great Lakes wetland ecosystems.