A pair of little brown bats (Myotis lucifugus) hang together in the Deschutes National Forest located in Oregon.
U.S. Fish and Wildlife Service

Editor’s Note: This article was reprinted with permission from Techletter, a biweekly training letter for professional pest control technicians from Pinto & Associates. To subscribe, visit www.techletter.com.

By mid-August, in most regions, bat nurseries in homes or other buildings are shutting down for the season. Young bats begin leaving the roost in July and by mid-August should be fully fledged. This is the time of year when pest management professionals can legally pursue bat-proofing of structures. Since bats are federally protected animals, states restrict bat exclusion and management to fall and winter months when bats (and particularly young bats) are no longer in the roost.

Bat exclusion usually first involves the use of a one-way bat door into the attic or other space to make sure that all bats are gone before any sealing is done. If bat-proofing is done prior to mid-August (for most regions), there is the risk of sealing in young bats that may not be fully fledged or able to leave on their own.

In most states, regulators allow bat-proofing and bat removal beginning sometime from early August to late August and continuing until females start caring for young again in early spring, March to May. However, the only times that you can expect all bats to be out of the colony at the same time are early spring (before maternity season) or late summer after the young bats have fledged.

During spring and early summer, a colony might contain a large number of baby bats that are too young to fly or fend for themselves. In late fall, some bats (especially the big brown bat) may return to the structure to hibernate through the winter. Some states may also prohibit, or at least recommend against, winter bat-proofing (November through March) for that reason.

CHECK WITH YOUR STATE. Bat-proofing regulations are different in each state and may change. You must check with your state’s regulators, usually Natural Resources or Fish & Game, to make sure you are working within the allowed dates.

For example, at last check, in New Hampshire, the Department of Fish & Game allows bat exclusion work from mid-August to mid-May when the maternity season begins. In Maryland, the Department of Natural Resources allows bat work from Sept. 1 until March 1. In Florida, bat-proofing ends April 15. New Jersey allows bat exclusion from Aug. 1 to Oct. 15, and again from April 1 to April 30. Arizona Game & Fish allows bat exclusion from Oct. 1 to May 1.

States allow exceptions for certain health and safety situations, such as when a rabid bat may be present.