The Importance of Conflict Resolution Between Bats and Humans

In the US, bats have little legal protection in inhabited buildings, compared to places like the United Kingdom where it is illegal to disturb bats roosting in homes or buildings without consultation with a government wildlife professional. Bats can live in the voids of buildings for years in peaceful coexistence with humans. However, if they simply must be relocated, we can minimize harm to bats by following the steps below.

1. Exclusions should never be performed during baby season, generally from mid-May to mid-September in the Austin area, nor during winter. Non-flying pups would be trapped. Bats can remain in torpor for an entire month of cold weather without flying.

2. Don’t simply wait until after the bats fly and seal the entry/exit points. Not all bats fly each night. This method will inevitably trap bats inside, killing hundreds or thousands of bats that did not fly that night and causing more potential for conflict with humans as bats seek other exits through the living or working space.

3. Secure the interior envelope first. Seal wall and ceiling pipe penetrations, attic stairs, ductwork leading to the attic or exterior, unfinished walls in utility rooms, etc.

4. Close large sections of each entry point, while placing enough exclusion tubes so that bats don’t panic at flight time. Small-meshed netting (OV-7822 purchased at www.industrialnetting.com) could be used on long crevice-like entry points if bats customarily emerge from all along the crevice.

5. Any excessive restriction of their normal exit (perhaps by using too few exclusion tubes) will cause some back pressure, causing bats to fly back into the structure to find an easier way out. This can be a problem if the interior envelope is not sealed.

6. Creativity is needed in some odd-shaped areas, but stiff 1/4″ netting (again OV-7822 purchased at www.industrialnetting.com) can be shaped to fit and combined with exclusion tubes using staples and water-based adhesive caulk. Large boxes of netting can be fashioned around single exit points that accommodate multiple exclusion tubes, causing less back-pressure.

7. Empty caulk tubes can be cleaned out and fashioned into more exclusion tubes.

8. Get an early start when installing exclusion tubes. Any caulk used around the openings must have plenty of time to dry before the bats fly.

9. In unfinished areas, polyethylene sheeting could be installed like a dust barrier, confining bats to a smaller area near the exit so that they re-direct themselves out through the exclusion tubes.

10. Exclusion tubes should be left in place for at least two weeks of good weather, to ensure all bats have been hungry enough to fly out to feed.

11. After that time has elapsed, the entry/exits can be sealed using the same materials with which the buildings are constructed.

Certain locations on buildings, such as overhangs, will naturally attract bats. They commonly seek areas such as these to shelter from inclement weather and to hide from avian predators. If such portions of buildings also have warm air leaking out, then these areas will become bat magnets during cold weather. These areas must be constructed and maintained to prevent bat entry. Architects must draw details to show how they intend to screen expansion joints and air intakes from bat intrusion. Caulks and sealants degrade and fail over time are not a great solution to denying access in and around such areas. LEED credits should routinely be awarded for building designs that avoid inviting bats to take up residence where they are not wanted.
If these details are not worked out in advance, then developers are simply passing down the cost of a bat exclusion to the future owners and tenants. These particular Life Cycle Costs of the building should be anticipated and paid for up front by the developers. Then contractors need to be paid for and contractually obligated to soundly construct those details.

Building managers should routinely inspect the exterior envelope of their buildings and maintain areas of potential problems. If there are signs of bat entry, such as visual confirmation of bat flights or stains from the body oils of many bats, then an exclusion must take place before re-sealing the areas.

In the top floor of commercial spaces, the ceiling is usually comprised of acoustic tiles, inserted into an aluminum gridwork suspended by wires from the roof. These drop ceilings must be kept intact to seal the working space. Replace these lightweight tiles when corners break off and make sure maintenance workers put them back if they are moved to gain access for electrical work. Wires suspending the grid will act as a “harp trap” for bats forced to fly in such areas, causing them to drop as they hit the wire and become impaled on the twisted end of the wire (such pig tails should be angled tightly downward to avoid this). Prevent bats from flying in such spaces by installing polyethylene sheeting prior to exclusion. We have seen exclusion back-pressure cause large numbers of bats to be trapped in open wall cavities, impaled on ceiling grid wires, and stuck on old glue traps left for rodents.