The federally endangered Virginia Big-Eared Bat (Corynorhinus townsendii virginianus). Photo by Jesse De La Cruz

Bats are typically associated with caves, attics, and Halloween, not trees. However, all 15 of the bat species within the Chesapeake Bay Watershed use forest habitat for breeding, foraging, and/or shelter. They are a critical part of forest ecosystems, each daily consuming nearly their own body weight in insects and filling a similar ecological niche at night that many songbirds do during the day. Bats also perform valuable functions for humans, controlling insect pests that destroy agricultural crops and harvestable timber. Unfortunately, the majority of American bat species are in steep population declines due to habitat loss and White Nose Syndrome, an exotic disease that has ravaged eastern bats over the last decade. As imperiled as they are, bat habitat needs are easy to accommodate and any landowner can improve their property for these unique and vital mammals.

Roosting habitat is where bats raise young, rest, and take cover during the day. It is a critical but resource that can be limiting for bat populations. About half of eastern bat species roost beneath loose bark or within tree cavities, and others, called “tree bats”, roost exclusively in the foliage of living trees. Bats select roosting trees that receive a lot of solar heat and that are also somewhat open, allowing easy flight to and from the tree. Thus, forest edges and ridgetops are valuable areas to retain potential roosting trees. Ideal roosting sites are tall, large-diameter trees that are either alive with shaggy bark (ie shagbark hickory or white oak) or recently dead trees (also called “snags”) that are still holding bark. Most bat species require multiple roost trees in an area because they will frequently move between them. Switching roost sites helps reduce predation and pathogens and also ensures that the bat will have somewhere to go if their current roost tree falls down. Finding an appropriate roosting site is especially important for bats, as they are very slow breeders. Many species only raise one pup each year, so ensuring breeding success each year is crucial for the population.  

A tagged federally endangered Indiana Bat (Myotis sodalis) roosting under the bark of a dead sugar maple. Photo by Jesse De La Cruz

Bats also require foraging habitat, where there is an ample aerial insect population and enough open space to chase them. Forest edges, forest roads, trails, and canopy gaps created naturally or by timber harvests are important foraging sites. They are open enough for bats to maneuver in and also contain plentiful herbaceous vegetation that support insect diversity and abundance. Bats drink water while flying, and thus need water sources that are open and somewhat free of floating vegetation. Water sources also usually increase aerial insect populations, and many bats will predominantly forage in the vicinity of ponds and streams. Streamside forests are very important; they can contain everything a bat needs from spring through autumn. They provide drinking water travel corridors where bats can safely fly, bountiful insect populations, and often hold dead trees which are ideal for roosting.

Mid-Atlantic bat species enter true hibernation, meaning that they do not just sleep through the winter but fall into a state of dramatically lowered body temperature, breathing and heart rate, and metabolic expenditure. To survive, they need to find hibernation sites (known as  “hibernacula”) that are safe from disturbance and do not fluctuate in temperature. Caves hold a steady temperature year-round and are typically free from stimuli that would rouse hibernating bats, which is why they are the preferred hibernation site for most bat species in the mid-Atlantic. Caves are relatively uncommon, so bats may travel hundreds of miles to reach one that is suitable for hibernation. Human perturbation or alteration of caves is a leading reason for bat population declines, and forests are important for maintaining hibernacula integrity. Tree cover around cave entrances is critical; without the shade that a canopy provides, the hibernaculum’s temperature, humidity, hydrology, and airflow may be altered and the site may become unusable. Because suitable hibernacula are somewhat rare, it is exceedingly important for them to remain unaltered and a forest buffer around them to remain intact.

As much as bats need healthy forests, forests (and humans) need healthy bat populations. Rather than cast bats as spooky creatures of the night this October, Forests for the Bay will shine a spotlight on the bats of our Chesapeake forests and their conservation concerns. Check in all month to learn more about these fascinating mammals. Next week, learn about what you can do on your own property to help support important bat populations. The most frightening thing about bats is that they may soon disappear!