Michigan is home to a diverse population of bat species, with nine distinct types inhabiting the state throughout the year. These nocturnal mammals are the only mammals capable of sustained flight, and all Michigan species are insectivores, consuming vast quantities of agricultural and nuisance pests nightly. Understanding the specific bats present in the state is important for conservation efforts, as many species face significant threats to their survival. These bats occupy varied habitats across the Upper and Lower Peninsulas, ranging from isolated forests to suburban attics, contributing to natural pest control statewide.
Identifying Michigan’s Common Bat Species
The Big Brown Bat (Eptesicus fuscus) is one of the most frequently encountered species, particularly in residential areas across the southern and central parts of the state. This robust species features a reddish-brown to dark brown coat and a wingspan up to 13 inches. They are recognized by their slightly broader nose and tend to roost in large colonies within human-made structures, often selecting the warm, protected spaces of attics and barns for their maternity colonies. Big Brown Bats are late-dusk fliers, emerging about 20 minutes after sunset to forage for beetles and other hard-bodied insects.
The Little Brown Bat (Myotis lucifugus) is similar in appearance but noticeably smaller, possessing a wingspan closer to 10 inches and a dark brown coat. This species is often confused with its larger relative, but it can be distinguished by its smaller size and lack of the Big Brown Bat’s broad nose. Historically, the Little Brown Bat was abundant throughout the state, forming massive colonies of hundreds or even thousands of individuals that frequently roosted in hot attics or cabins during the summer months.
The Eastern Red Bat (Lasiurus borealis) presents a striking contrast to the brown species and is rarely found inside buildings. This solitary bat has a bright, rusty-red to orange coat; males typically display a more vibrant coloration than females. The reddish fur, often complimented by white patches on the shoulders, helps this bat blend with the dead leaves of trees where it prefers to roost. This species is a migratory tree bat, flying south for the winter instead of hibernating in caves or structures.
Rare and Protected Bat Species
Several of Michigan’s bats are facing population collapse due to a fungal disease, White-Nose Syndrome (WNS), prompting federal protection under the Endangered Species Act.
Northern Long-eared Bat
The Northern Long-eared Bat (Myotis septentrionalis) is federally listed as endangered due to the rapid spread of WNS. This species is characterized by its long ears, which are larger than those of other Myotis bats. It typically roosts under tree bark or in tree cavities during the summer.
Tri-colored Bat
The Tri-colored Bat (Perimyotis subflavus), formerly known as the Eastern Pipistrelle, is also federally listed as endangered and severely impacted by WNS. This small bat, with a wingspan of only about 9 inches, is one of the smallest species found in North America. Tri-colored Bats are identifiable by their pale, yellowish-brown fur that has three distinct color bands on each hair.
Indiana Bat
The Indiana Bat (Myotis sodalis) has been federally listed as endangered since 1967 and remains vulnerable to WNS. This species has dull brown to gray fur and primarily uses dead or hollow trees for its summer maternity roosts, often in forested areas of southern Michigan.
WNS, a fungus that arrived in Michigan in 2014, has caused catastrophic declines in these three species by infecting them during their winter hibernation. The infection causes bats to awaken from their deep sleep, known as torpor, more frequently than normal, prematurely burning through their limited fat reserves and leading to starvation before spring arrives.
Habitats and Seasonal Activity
The yearly cycle of Michigan’s bats is driven by the availability of insects. As temperatures drop and the insect supply disappears, bats must choose between migration and hibernation to survive the winter. Tree-roosting species, such as the Eastern Red Bat and the Hoary Bat, are migratory, flying to warmer climates south of the Ohio River Valley.
In contrast, the cave-dwelling species, including the Big Brown Bat and the endangered Myotis species, enter hibernation beginning in the late fall, generally between September and November. These bats seek out stable, cool, and humid environments known as hibernacula, which include natural caves, abandoned mines, or quiet, dark spaces within man-made structures. Attics and wall voids, which provide stable temperatures and protection from freezing, are sometimes used by colonial species like the Big Brown Bat for overwintering. Bats remain in this low-energy state until the return of warm weather and flying insects in the spring, usually around late March or early April.