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Bats are truly unique among mammals because they are the only ones in the world that can fly. They navigate in part by emitting high-frequency sounds and then using their funnel-shaped ears to listen for the echoes those sounds make as they bounce off nearby objects. By using this “echolocation,” they can pinpoint tiny insects in complete darkness. This ability has led to the myth that bats are blind, but they actually have excellent eyesight.

All seven species that live in Winnebago County — the little brown (Myotis lucifugus), big brown (Eptesicus fuscus), eastern red (Lasiurus borealis), hoary (Lasiurus cinereus), silver-haired (Lasionycteris noctivagans), Eastern Pipestral (Perimyotis subflavus), evening bat (Nycticeius humeralis) and the federally endangered Indiana bat (Myotis sodalis) — are insectivores. Bats have the reputation of eating thousands of mosquitoes in one night, but mosquitoes make up only a small part of their diet. Bats are more likely to feast on moths, June bugs and other larger insects, which are much easier to catch.

Bats like to roost in secluded, warm locations, such as under loose tree bark or in quiet attics or neglected buildings. Females often roost together in maternity colonies, where young bats are born and raised. Their young are born between May and June; they usually have one at a time but will occasionally have two. As winter approaches and the insect supply diminishes, bats migrate to caves, where they enter a state of “torpor,” or decreased activity. Their heart rates can drop from over a thousand beats per minute to one beat every four or five seconds, which allows them to survive for months on very little fat.

White-Nose Syndrome of Bats in Illinois

White-Nose Syndrome (WNS), a devastating disease of cave- and mine-hibernating bats, is caused by the fungus Geomyces destructans.  The disease was discovered in 2006 in New York state, and has since been spreading to encompass many of the important bat hibernacula of the northeastern United States.  The disease has continued to spread, with recently confirmed WNS sites in Indiana, Kentucky, Tennessee, Alabama, and Missouri. White Nose Syndrome, a fungal infection devastating to bat populations, has not yet been detected in Illinois bat populations.  As a preventative measure, Illinois caves on public lands have been closed to the public since 2010.

Year-round residents

These species are known to hibernate in Winnebago County.

Little Brown Bat

(Myotis lucifugus)

The little brown bat finds a home among the forested areas of Winnebago County and preys on insects throughout the area. This little bat has suffered a 90% decline in population in some regions of the United States making it a species of high conservation concern. Bat Conservation International estimates that the little brown bat provides a $4 billion benefit to the national economy, serving as a natural alternative to chemical pesticides. Colonial. Both sexes roost together in caves and mines during the winter. Females form nursery colonies in hollow trees, under loose bark on trees, or in buildings during the spring and summer. During the summer males live alone or in small colonies, roosting in trees, in rock crevices, or under siding or shingles of buildings. During the fall, both sexes roost in trees.

Eastern Pipistrelle

(Pipistrellus subflavus)

Both sexes roost singly or in small groups in caves and mines during the winter. In summer, females form moderately sized nursery colonies (up to 50 individuals) in caves, cliffs, or under the eaves of buildings. Males are solitary during the summer.

Big Brown Bat

(Eptesicus fuscus)

During the winter both sexes roost in caves, tunnels, rock crevices, hollow trees, or buildings. Females form nursery colonies in hollow trees or attics during the spring and summer. Males are typically solitary during the early part of summer and roost in crevices in buildings or caves. Both sexes may be found together in roosts in late summer and fall.

Potential year-round residents

During the winter, some individuals of these species hibernate in Winnebago County while the rest migrate to adjacent states or farther south.

Eastern Red Bat

(Lasiurus borealis)

Solitary. Roost in trees in both winter and summer. In winter, they use crevices or hollow trees. In summer, they can be found hanging from the outer limbs of trees. In spring and fall, they sometimes use shrubs or tall weeds as a roosting spot.

Endangered Indiana myotis (Myotis sodalis) in day roost beneath hickory tree bark. Roosting

Indiana Bat

(Myotis sodalis)

The Indiana Bat is a medium-sized, dull gray bat. The length of its head and body ranges from 1.5 to 2 inches, and the animal weighs about 1/4 of an ounce. Most bats are very difficult to distinguish from their cousins unless examined closely. The size of the feet and the length of the toe hairs are characteristics used to differentiate the Indiana bat from other bats. Indiana bats live an average of five to 10 years, but some have reached 14 years of age.

A silver-haired bat (Lasionycteris noctivagans) during fall migration in Wisconsin. Roosting

Silver-Haired Bat

(Lasionycteris noctivagans)

Small colonies. Roost under bark and in tree cavities in wooded areas. May occasionally occupy buildings or caves during the winter, though most migrate south.

Summer residents

These species are typically not found in Illinois during the winter.

Hoary Bat

(Lasiurus cinereus)

Solitary. Roost in trees, usually in the foliage, but occasionally in cavities.

An Evening bat (Nycticeius humeralis) in Mexico. Portraits

Evening Bat

(Nycticeius humeralis)

Colonial. Roost in trees or occasionally in buildings.