Muskrats, Reshaping Chicago Wetlands for Marsh Birds
Written by Leo Chan Gaskins.
We’ll start off with the problem to solve – unfortunately, many marsh birds are in decline in the Great Lakes due to habitat loss and degradation. Marsh bird populations thrive under specific wetland conditions, which we call hemi-marsh. This is a fancy word for an even and interspersed 50:50 mix of open water and vegetation. In the last century, we’ve seen a decline in hemi-marsh, mostly due to invasive species. Invasive common reed can fill in a wetland and make it too dense. And on the opposite side of the spectrum, invasive carp can eat a lot of native vegetation, turning a wetland into an open pond. It can be challenging to create hemi-marsh, because you may need to mow down tons of dense, 6-ft tall vegetation in about 2-3 feet of standing water. Generating hemi-marsh ends up being a huge challenge for wetland managers.
But what if there was an animal that could do this naturally and generate huge openings in wetlands to create hemi-marsh and potentially benefit birds? Turns out there is – the muskrat! Could studying how muskrats impact wetlands potentially help bird conservation? This is the question my research with Audubon Great Lakes tackles directly.
How do muskrats reshape wetlands?
First off, what are muskrats? Muskrats are a native Midwest mammal that are known for building absolutely enormous homes, or lodges, averaging 5 feet wide and 5 feet tall. Muskrat lodges have an igloo shape to accommodate an interior dry chamber above the water line that the muskrats access using an underwater tunnel. Because muskrats do not hibernate, they live inside of their lodges all winter allowing them to stay warm and dry in a relatively harsh climate. During the winter, muskrats will swim out of their lodges each day, even under the ice, grabbing cattails, vegetation, roots, or whatever they can find to survive, and bringing it back to their homes to eat. Though muskrats can opportunistically eat a wide range of foods, their diet mostly consists of plants.
Not only does their diet consist mostly of plants, but muskrat lodges are also made mostly of wetland plants combined with mud. In order to get enough material to create a structure so huge, they clear an average of six to twelve feet of vegetation around their lodge and mouthful by mouthful create a pile that becomes their home. This construction project often leaves a huge ring of open water surrounding their house. Once built, an average muskrat lodge can accommodate about five muskrats on average. Although their homes are quite large, muskrats are actually rather small, only 2 to 4 pounds in size, or about the size of a kitten. For such a small animal, it is shocking that the lodges and ring of open water that muskrats generate are so big that they are visible from space! If you zoom into wetlands on satellite images, you can see muskrats’ handiwork.
By creating piles of vegetation and openings in marshes, muskrats can help create conditions that help marsh birds thrive: hemi-marsh! But is this truly what’s happening and how or why might birds benefit specifically from muskrat lodges in a wetland? I wanted to investigate this connection more deeply with a scientific study.
Using trail cameras to look into the world of muskrats
I decided to deploy trail cameras in urban wetlands of southeast Chicago to study how animals use the areas around muskrat lodges. The wetland sites were selected as they are already part of an ongoing marsh bird monitoring program led by Audubon Great Lakes. For positioning the cameras, half of the cameras were pointed at the muskrat lodges and the other half were focused on a part of the wetland near the lodge but containing a stand of vegetation. This served as a control and point of comparison to understand how birds would use a part of the wetland unaltered by muskrats.
I programmed the cameras to take one photo every five minutes and left them out for two weeks during spring bird migration season. Although I am still processing the full data set, since it’s tens of thousands of photos to look through, so far, the results have been incredibly promising! I found 35 different species of animals in the muskrat lodge photos and only 23 species in the controls. The majority of the animals I found (26 out of 35 total species) were birds, but I also found reptiles such as turtles and snakes, frogs, and mammals like coyote or raccoon. Most importantly, I found seven of the key marsh birds that Audubon Great Lakes targets for conservation in just two weeks! Specifically, the American Coot, Black-crowned Night Heron, Blue-winged Teal, Common Gallinule, Pied-billed Grebe, Sora, and Virginia Rail! This was incredibly exciting!
There are many different ways that I saw the birds using the muskrat lodge and surrounding open water, which likely explains the high level of diversity of animals around the lodges. For example, I saw Canada Geese nesting directly on the lodges and using them as safe places to sleep overnight with their goslings, Soras foraging, herons using it as a fishing platform, and Pied-billed Grebes using the open water to dive for food around the lodges. Reptiles such as turtles use the lodges as place to bask in the sun and thermoregulate. The muskrat lodges also sadly attract muskrat predators such as coyote and mink.
These results strongly suggest that muskrats may be an important piece to the puzzle in terms of helping improve marsh bird conservation in the Great Lakes. Because muskrat populations have been in decline for the last 50 years, they likely can’t create enough of these lodges and openings to generate hemi-marsh on a large scale. But if structure is what mediates benefits for birds, a new question came to mind: what if I built the lodge structures and created mimic muskrat lodges? That’s what I am currently testing, to see if building mimic muskrat lodges can create the same benefits that muskrats generate naturally. My next step is to continue this research with Audubon Great Lakes with funding support from the Walder Foundation’s Biota Award. I am hoping to develop mimic muskrat lodges as a novel marsh bird conservation solution that can be used in wetland restoration designs until muskrat populations hopefully rebound.
Over the next two years, I will be focused on analyzing camera trap images collected from muskrat mimic lodges in comparison to natural lodges. I’m excited to share what I have learned so this work can inform wetland restoration projects in the Calumet region and beyond. I also hope as a side benefit, that this work will help birders love and appreciate muskrats, who are wonderful neighbors and friends to marsh birds.
Leo Chan Gaskins is a community ecologist, Walder Foundation Biota Awardee Postdoctoral Fellow at University of Chicago, and research partner with Audubon Great Lakes.
