Chicago seems like an unlikely place to find a thriving bat population, but the data says otherwise. In 2024 alone, volunteers with Lincoln Park Zoo’s Bat Tracker program recognized 7,300 bat calls over the course of 105 bat walks across the city and its suburbs. Understanding the types of bats in Chicago starts with a simple fact: eight species regularly move through the metro area, from forest preserves along the Cook County lakefront to alleys just blocks from the Loop.
Each of these bats has its own roosting style, migration timing, and winter survival strategy, and a few are now fighting to survive a fungal disease that has reshaped bat populations across the entire Midwest. This guide walks through the eight species most likely to turn up in Chicago backyards, parks, and forest preserves, along with what makes each one distinct.
| Species | Typical Size | Winter Behavior | Common Chicago Habitat |
|---|---|---|---|
| Big Brown Bat | Wingspan to 16 inches | Hibernates or migrates south | Attics, bridges, tree cavities |
| Eastern Red Bat | Medium, foliage-roosting | Migrates south; some enter torpor | Tree canopy, parks |
| Hoary Bat | Up to 1.25 ounces | Migrates south | Wooded residential areas |
| Silver-Haired Bat | Medium | Migrates south, uses torpor | Tree cavities, loose bark |
| Little Brown Bat | Small | Hibernates in caves/mines | Buildings, forested areas |
| Evening Bat | Small | Variable; more southern range | Tree cavities, loose bark |
| Eastern Pipistrelle | 0.14 to 0.25 ounces | Hibernates in caves/mines | Open woods, golf courses, near water |
| Northern Long-Eared Bat | Small, long ears | Hibernates; solitary | Mature forest interiors |
1. Big brown bat
The big brown bat (Eptesicus fuscus) is the species most Chicagoans will actually encounter. Big brown bats are city-dwellers and Illinois’ most common bat species, known for how easily they adapt to urban environments. With a wingspan reaching 16 inches, these bats will roost in any crevice available and can be found in caves, bridges, mines, and even attics.
Females of this species are highly social. Females can live in groups of 60 or more individuals, raising their pups together in maternity colonies and returning to the same group year after year. Among all the bats tracked by Chicago researchers, big brown bats are the most recorded species by UWI researchers and the Bat Tracker program, and they tend to be low fliers, hunting insects from near the ground up to the treetops.
Because they roost so readily in human structures, big brown bats are also the species homeowners are most likely to discover in an attic or chimney. If you want to see how this species compares to bats found outside Illinois, the different types of bats found across North America share many of the same roosting instincts.
Pro Tip: A big brown bat roosting under loose bark or in a crevice during summer is doing exactly what it should. Leave it alone rather than trying to relocate it yourself, since disturbing a roost can separate mothers from pups.
2. Eastern red bat
The eastern red bat (Lasiurus borealis) is a solitary, foliage-roosting species that spends its days hanging among tree leaves rather than in buildings or caves. Like other bats in the region, eastern red bats may go into torpor, a state of slowed metabolism and suspended animation that can last just a few hours a day, on their way to warmer climates.
Sources differ slightly on how this species handles winter. Some researchers classify it as a strict migrant that heads south before the cold sets in, while others note it among the small number of Illinois bats capable of hibernating locally under leaf litter or bark.
Important Note: Wildlife agencies list the eastern red bat both as a migratory species and, in some assessments, as a species capable of local hibernation. Both behaviors have been documented, and individual bats may choose either strategy depending on local conditions.
Its coppery-red fur and frosted wingtips make it one of the easier species to spot at dusk in Chicago parks. For a look at how this same species behaves in a neighboring state, the guide to types of bats in Indiana covers similar foliage-roosting habits just across the state line.
3. Hoary bat
The hoary bat (Lasiurus cinereus) is the largest bat found in Chicago and one of the most striking. Considered the most widespread bat species in the U.S., hoary bats like forests but can also be found in tree-covered residential areas and parks. Hoary bats are Chicago’s largest bat, weighing up to 1.25 ounces, and are named for their brown-and-gray mottled fur.
Their camouflage is remarkably effective. They spend their days hanging upside down in the foliage, completely camouflaged amongst the leaves, which makes them one of the hardest species to spot during daylight hours despite their size.
Like the eastern red bat, hoary bats are migratory and use torpor to conserve energy on long flights south. This wide-ranging behavior means the species turns up across very different climates; bat watchers who have explored bat species in Canada or the bats found throughout California will recognize the same mottled fur pattern.
4. Silver-haired bat
The silver-haired bat (Lasionycteris noctivagans) is one of the species most consistently detected in dense urban settings. UWI researchers have detected silver-haired bats throughout the Chicago area, including downtown, but in winter most of these bats migrate to southern Illinois or go further south.
This species relies heavily on torpor during migration. One study estimated that torpor can help save 91% of a silver-haired bat’s energy, and in spring and fall these bats can be spotted in Chicago in a state of torpor on tree trunks, brick buildings, and screen doors as they rest.
Habitat preference sets this species apart from some of its neighbors. Like the red bat, the silver-haired bat generally prefers forested habitat and often roosts in tree cavities or loose bark, though unlike red bats, female silver-haired bats live in social groups called maternity colonies during summer.
Anyone curious how migratory corridors shift species mix further south should check the rundown of bat species in Kentucky, a common wintering stop for Illinois’ silver-haired bats.
5. Little brown bat
The little brown bat (Myotis lucifugus) has a long history in the Chicago region, though its numbers have fallen sharply in recent decades. Little brown bats were once common in the Chicago-Calumet River watershed, identifiable by their large, furry toes and dark brown fur on the back.
This species is a colonial hibernator. Both sexes roost together in caves and mines during the winter, and they mate in fall before giving birth to a single pup in spring after a delayed gestation period. A hungry little brown bat can eat close to 1,000 insects in a single night of foraging.
Unfortunately, this once-abundant species has been hit hard by disease. Their population has been decimated by white-nose syndrome, and local researchers now record only a few little brown bat calls each year. Despite that decline, researchers have still detected little browns at Chicago’s Lincoln Park Zoo. If backyard wildlife is a running interest, the guide to types of spiders in Chicago covers another group of insect-eating neighbors that share the same urban habitats.
6. Evening bat
The evening bat (Nycticeius humeralis) is more common south of Illinois but has established a presence in the Chicago area. This forest-dwelling species roosts in tree cavities and loose bark, and while it is more common in the South, it has also found a home around the Chicago area.
Identification can be tricky because of how closely it resembles another local species. Evening bats look similar to little brown bats, though the species’ echolocation calls are quite different, which means acoustic monitoring equipment, not visual inspection, is usually what separates the two in the field.
Evening bats are also one of the species Chicagoans are statistically most likely to run into. According to the Illinois Department of Public Health, as cited by the Forest Preserve District of Will County, big brown bats, evening bats, little brown bats, and silver-haired bats are the four species most encountered by people in the region. For comparison, the species mix shifts further south, as shown in the profile of bat species in Mississippi, where evening bats are considerably more abundant.
7. Eastern pipistrelle (tri-colored bat)
The eastern pipistrelle, now more often called the tri-colored bat, is the smallest bat found in the Chicago area. Weighing between .14 and .25 ounces, about the weight of a penny, it is typically found in open wooded areas or near water, which might explain its presence at local golf courses.
Its small frame comes with a distinct acoustic signature. Because of its size, it can swiftly maneuver through the forest to reach its favorite foraging site, and compared to other local bats, it produces the highest-pitch echolocation call. The species has also gone through a name change; it was formerly known as Eastern pipistrelle before being reclassified as Perimyotis subflavus, the tri-colored bat, and both sexes roost singly or in small groups in caves and mines during the winter.
This species has not escaped the white-nose syndrome crisis affecting bats across the eastern United States. The tri-colored species has been proposed for the endangered list, while little brown bats are under review for federal protection. A 2021 federal study found the disease had already killed roughly 90% of tri-colored, little brown, and northern long-eared bat populations in under a decade.
8. Northern long-eared bat
The northern long-eared bat (Myotis septentrionalis) is the rarest of the eight species covered here and the one facing the steepest decline. It is a small bat associated with mature, interior forest environments, distinguishable from its close relatives by its long ears. Unusually for a bat, it forages along wooded hillsides and ridgelines rather than above valley-bottom streams and riparian edges.
Its roosting habits also set it apart from more social species like the big brown bat. This species is much more solitary in its roosting and hibernating habits, preferring tight crevices and holes instead of open areas within caves.
The northern long-eared bat’s federal status has changed dramatically in recent years. The U.S. Fish and Wildlife Service published a final rule on November 29, 2022, reclassifying the species as endangered under the Endangered Species Act, a status that took effect January 30, 2023. Numbers of northern long-eared bats, gathered from hibernacula counts, have declined by 97 to 100% across the species’ range, driven almost entirely by white-nose syndrome.
- White-nose syndrome was first detected in New York in 2006 before spreading through the Midwest.
- The disease has no known cure as of this writing.
- Illinois is home to 13 bat species in total, though only eight turn up regularly around Chicago.
Anyone tracking how this crisis has played out state by state can compare notes with the bat species found in New York, where white-nose syndrome first appeared, or the more recently affected populations covered in North Dakota’s bat species and Montana’s bat species guides.
Key Insight: Six of Illinois’ 13 bat species hibernate locally, while the rest migrate south for winter. That split explains why Chicago’s bat activity drops sharply once temperatures fall, even though several species never actually leave the region.
Chicago’s bat population is a lot larger and more varied than most residents assume, and every one of these eight species plays a role in keeping the region’s insect populations in check. A single bat can eat thousands of mosquitoes and moths in one night, which makes them a quiet but effective form of pest control for parks, gardens, and forest preserves across the city. If a bat shows up in an unwanted spot, like inside a home, contacting a wildlife professional rather than handling it directly protects both the animal and the resident, since several of these species are already under significant conservation pressure.
For readers who want to see how bat diversity compares elsewhere in the country, guides covering bat species in Texas and bat species in Nebraska offer a useful contrast to the mostly forest- and building-roosting species found around Lake Michigan.