Wednesday, December 30, 2015

Adirondack Wildlife In Winter: Big Brown Bats

Despite remarkable similarities in appearance, flying styles and behaviors, not all bats are created equal. In the Adirondacks, there are approximately nine species of these dark, winged mammals during the summer months, yet all possess their own unique physical characteristics and habits.

The manner in which bats deal with the total lack of flying insects that occurs with the onset of winter is one feature that illustrates how bats are different. Even though more than half the species that populate our region migrate to and then enter caves or mines that extend deep underground, all have definite preferences for below the surface. While some species proceed far from the entrance in order to reach warmer and damper locations, others favor cooler and drier spots closer to the world above.
The big brown bat is the species best adapted to deal with cold temperatures and the one that often shuns caves and mines in favor of cooler places closer to its summer roosting site in which to pass the winter. Loose cedar shingles that cover a roof near a chimney or an unheated attic that allows for easy access to the outside, yet which contains numerous cracks and crevices through which warmth from the living space below seeps upward are favored by this hardy species as a winter retreat.

Cracks around older windows, holes along the eaves that connect to the ceiling of a bedroom, or a poorly installed piece of siding that sets against a vent are other spots where the big brown bat has been known to successfully pass the winter in this climate. The presence of year-round homes in the Park, especially older ones that are not as air tight or as well insulated as newly constructed houses allows the big brown bat to spend the winter in residential areas, rather than in some subterranean chamber deep underground.

Prior to human settlement within the Adirondacks, the big brown bat was believed to spend the winter in hollow trees in old growth forests. In such deep, wooden cavities, a dozen or two of these sizable winged mammals could warm the air with their own body heat enough to make it tolerable, even during periods when the temperature dropped well below zero.

The near total lack of big brown bats in the Adirondacks during the initial survey of mammals conducted by Merriam in the late 1800s may have been the result of a very limited number of permanent human dwellings in the Park at that time. Also, since many of the stands of tall timber had already been harvested during that era of intense logging, the more natural over-wintering sites may have already been destroyed.

Despite being exposed to much colder temperatures than other species of bats, the big brown bat often fails to congregate into large clusters as do several other species. It is not uncommon for a single big brown bat to find a favorable nook or cranny in an attic or against a chimney and tuck itself there without the company of any winged associates.

The time when bats enter their winter dormancy varies from one species to another and depends upon the availability of their primary sources of food. While all bats in the Adirondacks feed heavily on bugs that they pluck from the air, each species has its own distinct preference. Some bats strongly favor mosquitoes and gnats while others target various types of beetles and moths. As the seasons change and the numbers of specific invertebrates dwindle or disappear, each species of bat will respond accordingly. Since the big brown bat is known to prey on those few hardy varieties of moths that linger well into the autumn, this bat is often able to find enough to eat into the early days of November. This is why big brown bats may be noticed flying near a street light or past a full moon on a warm evening around Veteran’s Day.

It is hard to say for certain why the big brown bat was so rare in the Park 130 years ago. It is not difficult to conclude why this species may become the number one bat in the Adirondacks in the near future. Its exposure to caves and mines that contain the bacteria responsible for white nose syndrome is far less than that of any of our other species of bats. Also its limited social nature allows for a reduced chance of contracting this disease from other individuals.

Photograph of big brown bat courtesy of Julie Zickefoose.

A version of this story first appeared in the Adirondack Almanack in 2011.

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Tom Kalinowski


One Response

  1. William Miner says:

    “Its exposure to caves and mines that contain the bacteria responsible for white nose syndrome is far less than that of any of our other species of bats.” – White Nose Syndrome is caused by a Fungus.

