Summer Bat Habitat

Order your Northern Woodlands summer issue. Photos by Heather Kaarakka.

Two of the regular columns in the Summer 2023 issue of Northern Woodlands magazine are related to northeastern bats. Forest Insights describes opportunities to promote summer bat habitat in forests, and Discoveries includes a summary of DNA analysis by researchers at the University of New Hampshire, to determine the summer diets of little brown bats in a specific region.

To complement these articles, we asked Heather Kaarakka, a conservation biologist with the Wisconsin Department of Natural Resources, to share some of her photographs related to bat habitat. Our thanks to Kaarakka for generously providing these images and explanatory captions.

Some bat species such as tricolored bats prefer to roost in leaf clusters and under birch bark. A tricolored bat was tracked to the underside branch of this river birch. The radio transmitter antenna can be seen sticking out from the bark confirming presence of the tagged bat. In Wisconsin, tricolored bats have also been tracked to oaks and hickories where they roost in clumps of dead and live leaves, as well as in abandoned squirrel nests.

For cavity roosting bats such as endangered northern long-eared bats and Indiana bats, typically the tree species isn’t as important as the features in and on the tree. This red maple developed a crack from frost damage, creating an ideal roosting cavity for a dozen northern long-eared bats.

For bats that use forests, ideal habitat is most often mature hardwood and mixed forests. In Wisconsin, northern long-eared bats frequently roost in forests with open understory and canopy gaps for increased thermal exposure. This bat species roosts in live trees and snags. Bats that roost in trees frequently switch roosts, suggesting that a large number of suitable roost trees are required by bats in a season.

This female northern long-eared bat roosted in the cavity of a red maple snag at the edge of a canopy gap where it received some desired solar exposure.

To research roosting ecology of northern long-eared bats, biologists such as J. Paul White of the Wisconsin DNR capture flying bats in mist-nets, record morphology including weight and reproductive condition, apply a temporary radio transmitter and release the tagged bat. Biologists can track tagged bats to identify the specific roost tree and surrounding characteristics. These details can help determine required summer habitat for species heavily impacted by white-nose syndrome.

About half of the bat species in North America do not hibernate in winter and instead migrate to warmer climates. These species, such as the hoary bat pictured here, still use forests for roosting and foraging habitat. This big bat is usually solitary and roosts in tree branches during the day.

Some forest bats, such as this cluster of tricolored bats, will roost in man-made structures like bat houses and buildings. This maternity colony chose the eaves of a cabin in a forested area next to a stream. The lighter-colored pups are still nursing and will remain in the roost at night until they can fly while mothers forage on the landscape. Because pups remain alone in the roosts, safe, warm roost sites are critical for reproductive success of bats.

The fact that bats select roosts based on the features of the tree rather than the tree species itself is reinforced by this unusual roost of northern long-eared bats behind peeling bark about two feet off the ground.

Two species, little brown bats and big brown bats, frequently roost in man-made structures but still use forests and riparian areas for foraging. Unlike tricolored bats, little brown bats prefer tight crevices such as between the baffles of this packed bat house. Little brown bats can form colonies of hundreds and sometimes thousands of bats.

This web extra accompanies the articles Managing Forests for Bats by Ethan Tapper and Characterizing Community Forests by Catherine Schmitt in the Summer 2023 issue of Northern Woodlands.