Bats Go Where the Trees Are in Cities

The next time you are walking in a city at sunset, look up. You may spot a bat flittering in the sky above you.

Insectivorous bats in Illinois provide ecosystem services to humans by eating agricultural pests like corn rootworm beetles and disease vectors like mosquitos. Some bats forage over large areas, traveling long distances to reach a variety of habitats in a single night. An urban bat population could benefit city-slickers and country folk alike by consuming pests in local parks and far-flung agricultural fields.

White-nose syndrome, a disease affecting bats, has caused steep population declines in several North American bats since 2006.The widespread and once-common urban dweller, the little brown bat, declined by more than 90 percent in some areas of the eastern U.S. Fewer bats translates to a drop in their free pest-control ecosystem services.

Impacts of Urbanization

Urbanization is also often considered a threat to bat conservation. Cities are expanding, infringing upon natural habitats where bats live. Bats are, however, still able to survive, and in some cases, thrive in urban areas. Cities can provide some benefits to bats compared to the surrounding rural landscape. In dry regions, the artificial water sources found in cities, such as pools and ponds, are often more accessible than natural water sources. In monocrop agricultural landscapes, like the Corn Belt, pesticide-controlled fields may offer a bland dinner plate for bats compared to the rich array of bugs available in the parks, gardens and backyards of cities. Corn Belt cities typically have higher tree cover relative to the surrounding agricultural landscape, providing more roosting habitat for tree-dwelling species.

On the other hand, urban bats face hazards, such as car collisions, novel predators including outdoor cats and extermination by humans (note: extermination of bats is illegal in the state of Illinois per Wildlife Code 520 ILCS 5/1.1). Disturbances such as noise and artificial light at night can also dissuade bats from foraging in an area, and thus exclude them from some urban spaces.

Studying Urban Bats

Studying urban bat ecology helps us to know what we can do to make cities more bat friendly. Previous studies have found that not all bat species respond to urbanization the same way, as some exploit urban environments and others are likely excluded altogether. Urban exploiters often roost in human-made structures like buildings, bridges, culverts, and bat boxes, and are well suited for foraging in large, open spaces. In the Midwest, the big brown bat is an urban exploiter.

In 2023, we organized the Bats in Small Cities project to learn how urban bat ecology relates to the context of the city—how do bats respond to their environment in a city with lots of tree cover versus one with little tree cover?

A volunteer network was used to record bat calls in 36 cities across the Midwest. Generally, we found that local tree cover is important for most urban bats. For big brown bats, however, local tree cover was most important in cities without a lot of forested land. So, if you visited a patch of forest in a city in the Illinois Corn Belt, such as Champaign, you would expect to find bats more easily than in a similar forest patch in a city like Carbondale, which is surrounded by woodlands.

Knowing this, we can develop strategies for improving bat habitat in cities. In cities with little forest, planting more trees will likely provide more habitat for bats. But, for cities with considerable forest, it doesn’t appear that planting more trees will provide additional benefits. In that case, management of habitats in highly forested cities could shift to other strategies, such as augmenting natural roosting habitat for bats by protecting dead trees and promoting the growth of larger trees.

The Champaign-Urbana Bat Community

The bat community of the Champaign-Urbana area was studied to determine how tree management practices might influence urban bat activity. Stationary acoustic monitoring devices were deployed in 183 locations in forests, parks and along streets. The tree canopy structure was then quantified using LiDAR technology to relate bat activity to a three-dimensional digital map of the urban forest. We learned that big brown bats hang out in parks and forests, but that in parks they are most active in areas with higher tree cover. Eastern red bats were mostly found in forests and were most active in areas with thinner tree canopies.

Much like the other study, our results here emphasize the importance of context when thinking about how to manage urban habitat for bats. Certain practices may benefit one species over another, and urban land managers should consider providing varied habitats to support a suite of bat species.

A Federally Endangered Bat in Northern Urbana

We were surprised to discover that the northern long-eared bat, a federally endangered species, was present in the forests of northern Urbana. Like the little brown bat, the northern long-eared bat has declined by up to 99 percent in some parts of the U.S. due to impacts from white-nose syndrome.

We were not expecting to find this species while monitoring an urban area with very little forest cover, however, their diagnostic acoustic calls were recorded at several different sites throughout the summer of 2023. Mist netting confirmed the presence of northern long-eared bats with three individuals caught between 2023 and 2024. Two of these bats were tagged with radio transmitters. A roost tree was successfully located in a public park. Northern long-eared bat activity was only recorded in larger patches of riparian forests, suggesting stream corridors could provide crucial habitat connectivity.

The presence of such an imperiled bat in a very urban environment underscores the important role that city greenspaces have in supporting wildlife.

Next time you walk around your city, be mindful of the bats sharing the streets and parks with you.

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Sean Obrochta recently graduated with his master’s degree at the University of Illinois, where he worked in Dr. Joy O’Keefe’s lab. He researched the ecology of urban bats in the Midwest for his thesis, which formed the basis for the studies described in the article. After graduation, he has worked as a community science coordinator for Lincoln Park Zoo’s Bat Tracker program in Chicago, where he continues studying urban bats.

Joy O’Keefe is an associate professor of human-wildlife interactions and wildlife extension specialist at the University of Illinois Urbana Champaign. Her lab tackles many applied questions related to bat conservation, working closely with state and federal agencies. While she has studied bats in forests for many years, the studies described herein were her first urban bat studies.