Indiana bat (endangered): Slightly larger than the eastern pipistrelle; usually roosts in clusters but may roost singly; forms large, dense clusters up to 300-400 per square foot, sometimes of hundreds or thousands of bats; fur brown with a reddish/pinkish tone; belly fur lighter than back fur, but not a strong contrast; overall appearance of fur and membranes dull, not glossy; pink nose sort of flattened; vulnerable to disturbance during hibernation (arousal causes the depletion of fat reserves); not in caves in summer.
Gray bat (endangered): About twice the size of the eastern pipistrelle; hibernates in very large numbers in only a few, vertical caves; forms looser clusters than Indiana bats but common habit of bats hanging upon other bats produces multiple layers in some clusters; frequently hangs with wings unfolded; fur uniform medium gray but bleaches to reddish by spring and early summer; summer colonies form in caves in river valleys or near lakes; makes large guano mounds in summer caves; highly vulnerable to disturbance during all seasons (arousal during hibernation causes depletion of fat reserves; disturbance of maternity colonies causes panic and may produce mortality of young).
Little brown bat: Slightly larger than the eastern pipistrelle; may roost singly, in pairs, or in clusters of a dozen or more bats, likes attics in summer; fur medium to dark brown, glossy highlights; belly fur distinctly lighter than back fur; dark forearms with chocolate brown wing membrane; overall appearance of fur and membranes glossy; fur sometimes covered with condensation.
Northern long-eared bat: Slightly larger than the eastern pipistrelle; often roosts solitarily but sometimes in small clusters of 5 or 10; frequently tucked into holes in ceiling or tight crevices in formations; ears proportionally longer than other common bats (15-19 mm or 2/3-3/4 in) but less than the big-eared bat; tragus long, narrow, and pointed.
Warmer, Interior Cave Passages