Illinois Department of Natural Resources
November 2020
November 2, 2020
Sunrise at Burning Star State Fish and Wildlife Area.

Small Mammal Responses to Habitat Structure in Southern Illinois Grasslands

By Alex Glass, Michael W. Eichholz

Photos courtesy of the authors.

Habitat loss and degradation have been changing natural areas across the world for decades, and the grasslands of Illinois are no exception. Illinois grasslands, along with those of Iowa, Missouri, and Indiana, once formed the tallgrass prairie peninsula, which represented the easternmost reaches of a historically vast and uninterrupted prairie that stretched across the Great Plains. These days, however, the state of grasslands in Illinois is strikingly different. Less than 0.1 percent of the state’s original tallgrass prairie remains, and most of the remaining prairie is made up of small, isolated patches.

The situation is further complicated because simply preserving or restoring more grasslands is not enough. Grasslands are dynamic systems that evolved to depend on regular disturbance in the form of wildfires and wandering herds of bison or other large grazers. Since these disturbances are mostly absent today, modern grasslands can’t simply be preserved and then set aside. They must be actively managed in order to thrive, by using tools such as prescribed fire that mimic historical disturbances.

Restoring and managing grasslands in Illinois can be a tricky process, especially considering how little space is available, since most of the state now consists of agriculture and urban areas. Many questions arise: How big do the grassland patches need to be? What should the vegetation look like? How important is the landscape surrounding the grassland? Which management tools should be prioritized? In order to answer these questions, the Illinois Department of Natural Resources has teamed up with researchers from Southern Illinois University-Carbondale to investigate how the structure of grasslands and the surrounding landscape can influence wildlife communities. For the first piece of this puzzle, we focused on small mammals.

A small, brownish gray deer mouse (Peromyscus spp.) caught in a metal rectangular trap that was baited with oats.
A deer mouse (Peromyscus spp.) caught in a Sherman trap that was baited with oats.

Small mammals, such as mice and voles, are often overlooked in favor of more charismatic wildlife, but they play several important roles in grassland communities. Seed-eating species help plants disperse seeds, while other species feed on insects or vegetation, which helps regulate insect populations and influences plant growth and plant species diversity. Additionally, they represent an important prey source for predators such as snakes, hawks and large mammals. However, too much of a good thing can cause problems, especially for wildlife communities. Overabundant small mammal populations can decrease plant diversity and consume vegetation to the point where it harms grassland health.

We worked on 10 grassland patches at Burning Star State Fish and Wildlife Area outside De Soto. These grasslands varied in their sizes and plant communities, and were surrounded by different habitats such as forest, agriculture, other grasslands or lakes. Since 2018, we have gone out each summer and used live trapping methods to capture, mark, release and recapture small mammals at each of the 10 grasslands patches. The mark-recapture method allows us to estimate small mammal abundance for each patch, and by identifying the species of each critter we catch, we can estimate community composition of these populations.

A biologist wearing a gray glove holds a brownish gray deer mouse by the scruff of its neck, and the mouse has a newly applied metal ear tag. In the background is green vegetation.
A captured deer mouse with a newly applied ear tag. Each ear tag is imprinted with a unique four-digit number used to identify marked individuals.

So far we’ve found that the land cover surrounding the grassland had a greater influence on small mammal abundance than the characteristics of the grassland itself. Grasslands surrounded by wetlands or riverbanks had a higher small mammal abundance. This may be because wetlands and riverbanks support grass species, such as Virginia wild rye which voles love to eat, and more trees, including sycamore and swamp white oaks that deer mice can use for food, nesting and shelter. To our surprise, we also found lower abundance of small mammals in grasslands that were surrounded by more grassland habitat. This result may be unique to our study area, however, because deer mice were the most abundant small mammal at our sites and deer mice typically require forests nearby to survive in grasslands.

Within the grasslands, the amount of dead plant material that covers the ground (often referred to as plant litter) seems to have a big effect on small mammal abundance. Specifically, more plant litter was related to lower abundance. The same pattern was noticed for plant diversity—more diverse grassland patches had fewer small mammals.

These results suggest that prescribed burns, which remove plant litter in grasslands, are an important tool for increasing small mammal abundance. Promoting plant diversity might be useful in strategically lowering small mammal populations to prevent overabundance.

Many questions remain to be answered, but the investigation of wildlife communities in Burning Star’s grasslands is still in its early stages. Meanwhile, the land managers and researchers working at Burning Star are excited to be part of the effort to restore and maintain Illinois’ grasslands.

Michael Eichholz is an avian ecologist in the Cooperative Wildlife Research Laboratory and Associate professor in the School of Biological Sciences at Southern Illinois University Carbondale.

Alex Glass is a graduate research assistant in the Cooperative Wildlife Research Laboratory at Southern Illinois University Carbondale advised by Dr. Eichholz. He obtained an undergraduate degree in Environmental Studies from Eckerd College in 2012.