If woodlands become too cluttered with nonnative shrubs such as European buckthorn or honeysuckle, bats may start avoiding these areas. To offset these negative effects, the Forest Preserve District not only removes brushy nonnative trees and shrubs but also reintroduces native plants, which can support a greater variety of insects — and insect meals for bats. These combined efforts provide bats with the healthy ecosystems they need to find food and raise their young.
Habitat restoration projects are important, but they’re not the only management tools the Forest Preserve District uses to help local bat populations. Ecologists also monitor forest preserves at night for bats, an activity that can help them determine which species live where, if any endangered or threatened species, such as the northern long-eared myotis, are present, or if particular habitats are in need of restoration.
One survey technique is mist netting. Researchers hang fine nylon nets in the woods, which harmlessly trap any bats that fly by. They can then identify and measure each animal before releasing it.
A more common technique is acoustic monitoring. Ultrasonic microphones detect and record bats’ echolocation calls, which are produced at a higher frequency than the human ear can hear, and transform them into audible sounds. Acoustic monitoring can be passive, where researchers leave a recording device in an area for a night or two, or active, where they walk a designated route with a microphone to record any calls. In either case, this method provides a better idea of which species are in a particular area because it records more than the individuals that end up in a mist net.
At the Forest Preserve District, ecologists use active acoustic monitoring. As they walk and the microphones record calls, computer software — sometimes even special smartphone or tablet apps — mark the GPS coordinates. This can reveal which habitats certain species prefer.
The software can also help identify species. As with bird songs, bat calls are species-specific, and the call structure (the frequency and shape of the call) can reveal which bat made it. But bats vary their calls depending on the environment, and these variations can make one bat sound like another, making identification difficult at times. With only eight species of bats in DuPage, though, a close look at the frequency and shape of calls can narrow down the possibilities.
As temperatures start to drop in fall, DuPage bats ready for hibernation, moving to sheltered areas where they can rest undisturbed until spring. A few species even migrate to overwintering caves in Wisconsin or southern Illinois. (It’s these cave environments that contribute to the spread of white-nosed syndrome, a fungus that can have a detrimental effect on bat populations.)
Regardless of one’s personal feelings, the fact is bats play an important role in controlling populations of nighttime insects in DuPage forest preserves. By continuing to restore related habitats and monitor bat populations, the Forest Preserve District can ensure these amazing mammals continue to have protected summer places to call home.