some notes for a project that my oldest is doing -
The little brown bat is especially abundant throughout the state and is the most seen species. A light brown to dark brown in color, little browns are fairly small in size with a wingspan of 8 1/2 to 11 1/2 inches, small ears, and large feet. In summer, colonies of the species live in hot attics and under shingles and siding; in winter, they hibernate in caves, crevices, houses, hollow trees, or mines. Females form nursery colonies away from the males. Little brown bats like to feed on aquatic insects and are frequently seen dipping and diving over water but will also forage over lawns and pastures, among trees, and under street lights.
There are in Michigan nine species of bats, and much of what is known about them comes from studies of the two gregarious (that roost in large groups) species most commonly found here -- the big brown bat and little brown bat. Keen's bat is another gregarious species widely distributed in Michigan, and the tiny eastern pipistrelle is an uncommon year-round resident of the western Upper Peninsula.
The Millie Mine is a critical hibernating and breeding location for up to 50,000 bats—one of the largest known concentrations of bats in the Midwest. Big brown and little brown bats from all over the region come here to hibernate during the cold winter months. They are believed to migrate in from throughout the Great Lakes region–Wisconsin, Minnesota, Ontario, perhaps even Michigan’s Lower Peninsula. Bats start arriving at the mine in late August and early September. They remain in the mine shaft throughout the winter and begin emerging in late April and May. Some use the mine as their permanent home. Most, however, will fly back to their forested home areas to spend the summer where they roost during the day under the bark of dead trees or in other small crevices. The females will typically use large hollow trees, abandoned buildings, or other human structures as maternity roost sites where they raise their young with other females during ; the summer. Males live a separate and more solitary life during this time.
Fiborn Karst Preserve - a set of limestone caves in an old limestone quarry in Mackinac County, MI:
Both the Little Brown Bat and Keen's Bat have been found using the caves for swarming or hibernation. Keen's Bat was most common in the swarming studies. Following the winter of 1978-79 a large number of dead Little Brown Bats were found in Kochab Cave; they had possibly been trapped by an ice block at the entrance for too long after they emerged from hibernation. Studies of the bats and other small mammals are being conducted by scientists from Eastern Michigan University.
While the primary significance of the Fiborn Karst Preserve is geological, the plants and animals of the Preserve are important components, and their protection is part of the management objectives. The MKC would welcome further biological studies in the Preserve.
For lots more information, see the Bat Conservation International site.