Guidelines for Professional Bat Excluders
Bat Conservation International promotes exclusion methods that ensure the safety of both bats and people. We understand that differing architectural structures and/or climatic conditions may require modification of the guidelines given here. Please feel free to share your ideas about these issues when submitting your letter of commitment to humane and effective exclusion methods.
BCI's recommended exclusion professionals should be licensed by the states in which they work, be insured and use only approved exclusion methods. They should also provide the property owner with a guarantee and list of references. All written materials should be accurate and scare tactics should be avoided.
One-way devices made from lightweight polypropylene netting (<1/6" mesh), plastic sheeting or tube-type excluders are the preferred methods for evicting bats from buildings. Exclusion devices should be placed at all active entry points and should remain in place for at least five to seven days. These devices should be removed after all bats have been excluded, and exclusion points should then be sealed with silicone caulking, caulk backing rod, hardware cloth or heavy-duty polypropylene mesh. In some cases, sealing may require repair or replacement of old, deteriorated wood. BCI strongly recommends that exclusion professionals bat-proof the entire building and avoid spot treatments. Moving bats from one corner of a building to another does not solve the problem and may require further exclusions in the future.
Please note that simply waiting until the bats have flown out at night and then permanently sealing entrances without the use of exclusion devices is not approved by BCI. This method often traps some bats inside the building. BCI also discourages the use of “permanent netting” in most situations. Aerosol dog and cat repellents may discourage bats’ use of a particular roosting spot for periods of time up to several months. They have been used effectively to prevent bats from night-roosting above porches. The spray should be applied during the day when bats are not present. Aerosol repellents are not an adequate substitute for exclusion in the case of day roosts and should never be applied when bats are in a roost. For night roosts, we also recommend the use of Mylar balloons or strips of tin foil hung from roosting areas and allowed to move in the breeze.
Maternity season for bats in the US and Canada can range from mid-April through August 31. Eviction of bats, or any activity that directly affects their roosting area, should occur only before or after the maternity season, when young will not be trapped inside.
Some bats hibernate in buildings during winter months. Winter exclusions should be performed only if it can be determined that no bats are hibernating in the building. If bats are present during the winter, exclusions should be postponed until spring temperatures are warm enough for deciduous plants to leaf out and insects to again be abundant.
Ultrasonic devices, chemical repellents and smoke are not approved by BCI as effective methods for evicting bats from buildings. In addition, canned spray foam is not an approved sealant for cracks or holes in most situations. It can result in the death of bats that come into contact with it. This product should never be used when bats are still present.
Traps and relocation are not BCI-approved exclusion techniques. Removing large numbers of bats from a building may seem impressive to a customer, but it is unlikely to be effective. Traps can be fatal to bats if left unattended or if overcrowding occurs. Bats have excellent homing instincts, so relocation attempts are unlikely to succeed. The bats will simply attempt to return to the original capture area upon release. Capturing bats at an exclusion site is not encouraged, although it is acceptable to capture a single bat for species ID or to removal an individual bat from a living space.