Where are the Best Habitats for Bats in Illinois?

While we may not realize it, we are reliant on bats. Some bats are important pollinators and seed dispersers while others feed on nuisance insects. All bat species are vital for the ecological functioning of food webs. Unfortunately, all across North America, bat species are in peril, with more than half of the continent’s species at risk of severe population decline within the next 15 years. Illinois is home to 13 resident bat species, including four threatened species and two endangered species. Many of these species are coping with the loss of vital habitat and are vulnerable to collisions with wind turbines and/or the disease known as white-nose syndrome.

Reasons for Bat Declines

Currently, Illinois is the fifth largest producer of wind energy in the U.S., with wind energy production expanding rapidly across the country. Although a great alternative to fossil fuels, wind turbines can cause fatal collisions for birds and bats and are predicted to be responsible for the deaths of hundreds of thousands of bats across North America each year.

Meanwhile, white-nose syndrome is one the worst diseases affecting wildlife today and has been responsible for the death of millions of bats across the continent within the last two decades. The disease was first documented in upstate New York in 2006 and has since spread west across the United States. It was documented in Illinois in 2013 and currently is known from 40 states and nine Canadian provinces. White-nose syndrome is caused by a white, fuzzy fungus that aggregates on the bare skin of bats, usually the snouts. Some hibernation sites have seen mortalities of up to 90 to 100 percent from the disease.

Furthermore, Illinois has seen significant landscape modification by humans in the last two centuries, reducing vital feeding and roosting sites for bats. To protect our bat populations, it is therefore imperative we understand which habitats are vital for our resident bat populations, so that conservation efforts can be more effectively focused on their protection.

So how do we know which areas are important to protect?

In recently published research in the Journal of Wildlife Management, Sarah Gaulke and fellow researchers at the Illinois Natural History Survey and the University of Tennessee wished to create habitat suitability models for bat species within the state of Illinois. Habitat suitability models identify areas which are commonly used by specific wildlife species, which can indicate to biologists preferable habitat. Identifying these areas allows for targeted management practices that can lead to the persistence of wildlife.

The researchers focused on four bat species in Illinois (eastern red bat, hoary bat, Indiana bat and tri-colored bat), which exhibit a range of different traits and ecologies. A previous study had already developed a habitat suitability model for the Indiana bat, so the authors of this study wanted to create new models for the remaining three species.

In addition to looking at each of the species separately, they also developed a multi-species habitat suitability model for all four species to identify areas that are widely suitable to all focal bat species. These four bat species are vulnerable, either to white-nose syndrome and/or wind turbines, and span the range of physiological and behavioral traits exhibited by bat species across the state. By creating habitat suitability models for these species, the authors thought it could be widely applicable to the more common bat species that inhabit Illinois.

The researchers used summer occurrence data from 1999 through 2021, derived from a combination of live-capture data (from a technique known as mist netting), acoustic monitoring (using audio recording units to hear bat echolocation calls), and wind farm mortality data. Data sources included the Illinois Department of Natural Resources, The North American Bat Monitoring Program and United States Fish and Wildlife Service. The authors constructed a number of biologically relevant habitat variables and used mathematical models to determine what factors best predict the summer occurrences of these bat species. With that information, the authors mapped out areas in Illinois that can provide suitable habitat.

So, What Did They Find?

The hoary bat had the most unique variables associated with its occurrences, with 58 percent of the state deemed as suitable habitat for the species. These areas were farther from roads, with less agriculture, and with more urban land than the average for the state, reflecting the species’ preference for open foraging areas.

Eastern red bats and tri-colored bats, meanwhile, were more associated with forest structure and density, with the former preferring more open, navigable forests for foraging and roosting. Suitable eastern red bat habitat was an even spread of forest and agricultural land, amounting to 52 percent of the state, confirming the species’ ability to thrive in a variety of environments. Whereas suitable tri-colored bat habitat comprised a mere 28 percent of the state, concentrated in the heavily forested southern portion of the state and along river corridors. This species requires much higher canopy cover than the Illinois average, showing a reliance on structured forests with available water and openings for foraging and roosting. These results accompany the previously established model for Indiana bats, whose suitable habitat comprised 30 percent of the state, closely following the forested areas along the Illinois and Mississippi rivers in the south.

The model identified suitable habitat for all four species to comprise 18 percent of the state. These areas were mostly located in the southern third of Illinois, along major rivers and forested areas. It also suggested that 34 percent of the state was unable to provide suitable summer habitat for foraging, roosting or commuting for any of the bat species studied.

This study provided pertinent information on the habitat features that are vital for bat species in Illinois. As Gaulke stated, “this research is important to state land managers and biologists to make informed decisions about prioritizing different land and habitat types for restoration and conservation,” with these models serving as a useful tool “to reduce the amount of monitoring needed for biologists to make informed decisions or allow for targeted monitoring.” In addition, the study highlighted areas that are widely favorable to numerous bat species, which may be particularly useful when determining locations to avoid placing wind farms, as collisions with turbine blades are likely to impact bat populations in these areas.

Even though the multi-species model showed southern, forested reaches of the state as suitable for multiple bat species, it is important we do not neglect the habitats that are important to bat species elsewhere in the state. As Gaulke said, “there are still many areas across the state where a little restoration can promote habitat for all species.” Furthermore, since this study focused on summer habitat only, “it’s important to think of areas that [bats] may be using in the future or at different times of the year,” as there are important winter hibernation spots and bat migration corridors elsewhere in Illinois. In addition, even areas deemed unsuitable bat habitat may warrant restoration efforts, especially when surrounded by suitable habitat, as it can help create more contiguous, interconnected habitat areas, which in turn can support greater bat populations. And that would benefit Illinois!

As Gaulke concluded, “it benefits both us and them to have bats in our local communities. Let’s support their habitat statewide and do what we can to preserve our state’s bats.”

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Nathan Proudman is a Postdoctoral Research Associate at the Illinois Natural History Survey. His research has primarily focused on the ecology of mammals. Currently, he is working on a statewide monitoring program for mammals in Illinois.