Bats in Pennsylvania: where to look and what signs to watch for

Bats in Pennsylvania are most common in the central and northern parts of the state, where large tracts of forest provide roosting and foraging habitat. Look for them near lakes, rivers, and wetlands, especially around old-growth forests. Bridges, barns, and abandoned mines serve as popular roosts during the day. Start at state parks like Rickets Glen or Pine Creek Gorge.

Foraging happens wherever insects gather, so wetland edges, meadows, and slow stretches of stream tend to draw the most activity. In summer, female bats gather in maternity colonies inside warm, sheltered spaces such as attics, barn lofts, and tree cavities, while males often roost alone. In the colder months many species retreat underground to caves and mines that hold a steady temperature, and these hibernation sites can shelter thousands of bats at once.

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Bats are nocturnal, so your best viewing window is from about 30 minutes before sunset to an hour after dark. Spring through early fall is prime time, with June to August being peak activity for most species. In winter, many bats hibernate in caves or mines, so sightings are rare unless you visit known hibernacula.

Warm, still evenings produce the most insects and the most active bats. Look on nights without heavy wind or rain, when the air is calm enough for moths and beetles to fly. Activity tends to peak in the first hour after sunset, then settle into a steadier rhythm through the night. By late October most Pennsylvania bats have either moved to hibernation sites or migrated, so plan your watching for the long evenings between late April and early September.

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The most obvious sign is seeing bats themselves at dusk, but you can also look for guano (droppings) under roosts, which resembles crumbly black pellets. Listen for high-pitched squeaks and rustling noises from roosts. Stains on building walls or bridges from their oily fur are another clue. Moth and beetle activity near lights often attracts bats too.

Unlike rodent droppings, bat guano crumbles to a fine, glittery dust because it is made almost entirely of insect parts. A buildup under an eave, beam, or bridge joint usually marks a roost above. Around buildings, you might notice small greasy smudges near a gap where bats squeeze in and out night after night. On a quiet evening you may even hear soft chittering from inside a wall or attic just before the colony leaves to feed.

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Bats have a distinctive erratic, fluttering flight pattern, unlike the steady wing beats of birds. They also appear to be somewhat jerky and may dive suddenly after insects. Their wings are membranous and lack feathers, so if you get a close look, you'll see the skin. At dusk, use a pair of binoculars to spot the wing shape: bats have long, slender wings that curve back.

Timing helps too. Most birds settle down as the light fades, while bats are just starting their night. The one bird you might confuse with a bat is the common nighthawk, which also hunts insects at dusk, but it flies in long, sweeping arcs and shows a white bar on each pointed wing. Bats turn far more tightly and change direction in an instant as they chase prey, so their path looks looping and unpredictable against the sky.

Pennsylvania is home to nine bat species, and learning to tell them apart adds a lot to an evening of watching. The big brown bat is the most widespread and the one most people see hunting over meadows and yards. The little brown bat was once just as common but has declined sharply because of white-nose syndrome. The tricolored bat, one of the smallest in the state, has suffered similar losses.

The Indiana bat is federally endangered and roosts in summer under loose tree bark along streams. The northern long-eared bat, named for its long ears, is also federally protected after steep declines. Three tree-roosting species spend summers in the foliage rather than in caves or buildings: the eastern red bat, the hoary bat, which is the largest in the state, and the silver-haired bat. The eastern small-footed bat, one of the rarest, prefers rocky slopes and talus.

Each species has its own habits. Red bats roost alone in trees and migrate south for winter, while big brown bats often shelter in buildings and can stay active later into the fall than most. Check the bat animal hub for more details.