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Controlling Bats |
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Bats are important members of the wildlife community but they will enter buildings while seeking roosting sites. Bats typically enter structures by following air currents and odor cues. Before designing a bat control program, the professional pest specialist must first be familiar with basic bat identification and biology (see ESPC 043229A).
The PCO is frequently contracted to remove these nuisance mammals from the living space of a stnucture or from more secluded areas such as attics and basements. Occasionally, the service requested involves the removal of an individual bat, but in most situations, a colony of bats must be removed from a structure. In either case, non-lethal control measures should be implemented.
The use of pesticides to kill bats increases the risks (particularly of rabies) associated with bats falling to the ground and being handled by children or eaten by pets. Moreover, if pesticides are utilized for bat control, the applicator may be in violation of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). (NPCA is not aware of any pesticides that are currently or, after the reregistration process, will be labeled for bat control without obtaining a special use permit from USDA-APHIS -Animal Damage Control or a public health agency for extreme circumstances.) One pesticide, napthalene (moth balls), may be placed in confined areas to repel bats, but this practice is of limited value.
In the past, mechanical techniques using glue boards, snap traps on the ends of poles, filed-off nails driven into the ends of broom handles and tennis rackets have been used to kill bats. These techniques are not recommended. Their use may only incapacitate the bats, increasing the risk of human contact with injured bats.
The four steps in a successful bat management program are:
A careful inspection will reveal the location of the individual bat or the roosting colony as well as the access holes to the roosting site. Bats normally enter structures in a variety of places, most being high off the ground. Unlike rodents, bats cannot create entrances by chewing substrates, therefore, bats must use existing openings. A gap of 1/4" x 1-1/2" (0.6 cm x 3.8 cm) or an opening 5/8" x 7/8" (1.6 cm x 2.2 cm) is sufficient for a bat to squeeze through, but buildings with a well-established roost will probably have larger openings. Watching bats leave the roost at dusk can assist in locating the entry sites. A pair of binoculars and a flashlight (with red filter) may be needed to observe the fast-flying bats.
Any areas that allow air leakage may potentially become a point of entry for bats, such as openings around power lines, water pipes, and television cables; chimneys and louver fans; air intake and exhaust vents; and spaces under doors and around windows. Poorly fitting ridge caps, wooden or slate shingles without full coverage roof sheathing, and other faulty construction may also provide entry.
Once bats have established a roost inside a structure, interior openings that provide access to human occupancy areas must be located. Any opening in the walls or roof can provide access to bats. Common sites include gaps under and over attic doors, gaps around pipes passing into the ceiling, pocket doors which slide into the walls, loose fitting baseboards, and broken plaster. Bats may also enter basements and other rooms through chimneys, hollow walls, pipe chases, etc.
Exclusion measures may be implemented when the risk of trapping bats inside a building is slight. Interior bat proofing will prevent bats from entering the living spaces of a building. In the northern U.S., perform exterior exclusion before May or after mid-August. In the summer months, maternity colonies with flightless young will complicate exclusion efforts. Young animals are not able to leave the roost on their own, and nursing females will be highly motivated to find a way back into the roost. Winter also poses safety concerns while working on the outside of the structure and the possibility of trapping hibernating bats inside. However, since winter will generally be the time of year with the fewest bats inside a building, exclusion, especially from the inside, may be practical. Avoid sealing bats inside a structure, since this is not only an inhumane practice but often results in odor and secondary pest problems.
Bat exclusion can be accomplished with some basic carpentry tools (such as hammers, staple guns, caulking guns) and ladders. Safety ropes for work on roofs are also highly recommended. Except for major (known or suspected) bat entry sites, other gaps and openings on the upper half of the structure must be sealed. Smaller openings can be caulked or stuffed with material such as steel wool or copper gauze. Larger openings can be closed with wood, 1/4" (0.6 cm) mesh hardware cloth, sheet metal, aluminum flashing, foam insulation, or structural-grade polypropylene bird netting. Chimney flues can be capped, but covers must meet fire code standards. Such covers may not provide total exclusion but should reduce bat access through the chimney.
Bats utilize many openings to enter and exit a structure. Some openings, called primary exits, are used more frequently. Exclusion should proceed with the elimination of the minor exit openings with principal openings remaining unsealed. Properly installed checkvalves over these primary exit(s) will allow bats to leave but not re-enter the structure.
Checkvalve devices include: Constantine's one-way, valve-like device, EX- 100 Hank's Bat Excluder; and Frantz polypropylene netting checkvalve. Constantine's device consists of two tubes: a semi-rigid plastic tube which is attached to the entry hole and a collapsible polyethylene tube attached over the free end of the first tube. The polyethylene tube collapses when bats seek re-entry.
The Hank's excluder consists of a wooden plate with a hole drilled in the center. A transparent plastic flapper valve is placed over this central hole that opens up to a plastic mesh cone attached to the board. This system allows the bat to exit but not re-enter. Frantz' checkvalve is adaptable to nearly any architectural configuration; and it can cover any shape and size of a single exit hole or a series of openings. The polypropylene bird netting functions as a checkvalve when it encloses the entry site, allowing the bats to exit 4' to 6' (1.2 m-1.8 m) below the hole (Fig. 3). Behaviorally, the bats will try to re-enter near the hole instead of the open end of the net enclosure. "Stnuctural-grade" bird netting should be utilized because it has stronger strands and narrower mesh size than the standard-grade netting. For details of each of these methods, consult the following:
Constantine's checkvalve--Constantine, D.G. 1982. Bat-proofing of buildings by installation of valve-like devices in entryways. Journal of Wildlife Management 46(2):507-513.
Hank's checkvalve Anonymous. 1983. Wisconsin firm develops bat excluder. Pest Control Technology 11(6): 74.
Polypropylene bird netting checkvalve--Frantz, S. C. 1986. Bat proofing structures with bird-netting checkvalves. Proceedings of the Twelfth Vertebrate Pest Conference, University of California, Davis, pp. 260-268.
Checkvalves, excluders, and screening should remain installed long enough to allow all bats to exit, generally five days. Under rainy conditions, bats do not regularly exit the building, therefore, the checkvalves must remain operative for a longer period of time. The checkvalves should either be closed or removed, and the entry sites repaired. Ensure that the bats were not able to locate an overlooked entryway.
Once a bat colony has been removed, the roosting site may require clean-up to remove guano and urine that have accumulated during the occupancy. Workers should wear dust masks or respirators capable of filtering out a particle size of 2 microns to avoid inhalation of dust or fungal spores (Histoplasrmosis spp.). Uniforms should be disinfected and laundered after service is completed.
Crystallized bat urine and guano may be scraped from surfaces using awire bnush. The droppings should be collected using a vacuum cleaner that filters through water, reducing the amount of dust that may escape from the vacuum cleaner exhaust. After vacuuming, wash nonporous surfaces (e.g., window sills) with soap and water. Disinfect soiled surfaces with a 5% bleach solution while providing adequate ventilation for the service personnel.
Unfortunately, a bat may be trapped inside a building when working with a large bat colony. If this occurs, odor control may be needed. Consult the use of odor masking agents if the carcass cannot be located and removed.
Often a PCO will be requested to remove an individual bat from the human living space of a building. If possible, bats can be guided outside through an open window, door or a chimney with the damper open. Dim interior lights and stay in the room to ensure that the bat flew out of the building. Bats may be transported outside by placing an empty coffee can over the animal and sliding a piece of cardboard under the opening; capturing the animal using an aerial net, or picking up the bat with tongs or thick leather animal-handling gloves.
Bats are often persistent in seeking to re-enter a roost. Returning bats may congregate around sealed entranceways. Follow-up inspections will identify missed access points or new openings. Ongoing maintenance of the building for successful bat exclusion should be emphasized to the customer.
In addition to physically sealing potential entryways, conditions that favor bat habitation should be corrected. Ideal bat roosts reside in environments that offer high temperatures, low air movement, and a lack of light. Modifying these conditions may help in dispersing a colony. For example, the installation of soffit vents, roof vents, and fans will increase airflow. Also, the addition of lighting and less crowded storage of stock help to keep bats out of the lower region of a large warehouse.
Nonlethal control of bats is the most economical and humane method for managing bat populations. Care must be taken not to harm these animals while excluding or removing them from a building. Displaced bats are capable of re- establishing new roosts outside man-made structures where they can continue to play an important ecological role in the environment.
Currently, many retail establishments offer bat houses for purchase. These alternative roosts will be more attractive to displaced bats if the houses are placed as close as possible to the original roosting site, near a water source, and at least 12 feet (3.7 m) off the ground. The entrances to the bat house must not be obstructed, e.g., by tree branches, and should be placed where the house would receive the morning sun. Although, it cannot be guaranteed that the bats will move into a bat house, many customers ask the professional about their installation.
NOTE: Ultrasonic repellers and similar devices will not prevent bats from entering a structure. NPCA does not recommend the use of these devices under any circumstances.
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