Bat Damage Management

Wildlife Damage Management February 15, 2008|Print

Bats | Bat Overview | Bat Damage Assessment | Bat Damage Management | Bat Resources | Bat Acknowledgments | ICWDM | Wildlife Species Information


Contents

Damage Prevention and Control Methods

Pre-management Considerations

Little brown bat, Myotis lucifugus
Little brown bat, Myotis lucifugus

Bat Watch for Infestation Confirmation. To confirm that bats are actually roosting in or on a building, look for bats flying in and out of a site and/or for signs of infestation. A bat watch can be conducted by two people (more may be necessary to observe large or complex sites) posted at opposite corners of a structure. An evening watch begins about 30 minutes before dark and a morning watch begins about 1 hour before dawn. Observations should continue for approximately 1 hour.

Such observations can indicate exit/entry points and the number of bats. With practice, distinguishing some bat species may also be possible. For example, compared to the big brown bat, the little brown bat is noticeably smaller in size, and its flight has more rapid wing beats, and more rapid turning and darting.

It may be necessary to watch for more than one night to compensate for weather conditions, bats’ sensitivity to observers, noisy or inexperienced observers, and improper use of light. Observations can be enhanced with a standard flashlight, but be certain to keep the bright part of the beam as far away from the exit hole being observed as possible. Bright light will increase bats’ reluctance to exit, and may result in an incomplete exit of the colony. A valuable observation aid is a powerful, rechargeable flashlight equipped with a plastic, red pop-off filter (similar to the Kodak Wratten 89B). Also, an electric headlamp supplied with rechargeable batteries and fitted to a climbing or spelunking helmet, allows hands-off illumination outdoors as well as indoors when exploring roost locations. Bats are sensitive to light intensity and can visually discriminate shapes and patterns in extremely low-light situations. They can only see in black and white; hence, the low-contrast illumination and soft shadows produced by red light has little effect on bats.

Locating the Roost(s). It is not always possible or convenient to conduct a bat watch. Thus, a detailed inspection inside the building for bats or bat sign may be necessary to find specific roosts. Daytime is best, especially during the warmer part of the day. Bats roost in the most varied kinds of buildings and in every part from cellar to attic. Some types of buildings appear preferable (older houses, churches, barns, proximity to water) as do certain roost locations therein, especially areas with little disturbance, low illumination, little air circulation, and high temperatures. Often it is easy to locate bats, especially in warm weather in attics or lofts, where they may hang in clusters or side-by-side from the sloping roof lath, beams, and so forth. However, bats have the ability to find crevices and cavities, and if disturbed may rapidly disappear into the angles between converging beams, behind such beams or wallboards, into mortise holes on the underside of beams, and into the multi-layered wall and roof fabrications. If bats cannot be openly observed, usually there are various interior and exterior signs of their presence. Often there are multiple roost sites within or on a single building.

Problem Assessment. Once it has been confirmed that bats are present, one must determine if there is damage, if there is a health risk, and if some intervention is warranted. There are circumstances in which “no action” is the correct remedy because of the beneficial role of bats. In cases where there is risk of contact, damage from excreta accumulations, stains, and so on, intervention may be necessary.

Timing. With the exception of disease treatment and removal of the occasional bat intruder, timing becomes an important planning consideration. Management procedures must not complicate an already existing problem and should emphasize bat conservation. Therefore, all interventions should be initiated before the young are born, or after they are weaned and able to fly. Thus, the annual opportunity extends from about mid-August to mid-May for much of North America. Treatments might otherwise result in the unnecessary death of animals (especially young unable to fly) trapped inside, offensive odors, and attraction of arthropod scavengers.

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Disease Considerations

Rabies — Preventive Measures. It should be noted that newspapers, television, and other mass media some times misrepresent the role of rabid bats as a risk to humans. However, the unfortunate recent (1983 to 1993) deaths of a 22-year-old man in Texas, a 30-year-old bat scientist in Finland, a university student in British Columbia, a 5-year-old girl in Michigan, a man in Arkansas, an 11-year-old girl in New York, and a woman in Georgia, amply underscore the need to pay prompt attention to bat bites and other exposures.

Many rabies exposures could be avoided if people simply refrained from handling bats. Adults and children should be strongly cautioned never to touch bats with bare hands. All necessary measures should be taken to ensure that bats cannot enter living quarters in houses and apartments. Pet cats and dogs should be kept up-to-date in rabies vaccinations. This is also true for pets confined indoors, because contact with bats frequently occurs indoors. Valuable livestock also should be vaccinated if kept in buildings harboring bats or if in a rabies outbreak area (NASPHV 1993). While transmission of rabies from bats to terrestrial mammals apparently is not common, such incidents have been reported (Reid-Sanden et al. 1990, Trimarchi 1987). Dogs, cats, and livestock that have been exposed to a rabid or suspected-rabid animal, but are not currently vaccinated, must be either quarantined or destroyed.

Lastly, pest control technicians, nuisance wildlife control personnel, wildlife biologists, and other individuals at particular risk of contact with rabid bats (or other wildlife) should receive a rabies pre-exposure vaccination. This effective prophylaxis involves only three injections of rabies vaccine, which are administered in the arm during a month’s time.

Rabies — Treatment for Exposure. If a person is bitten or scratched by a bat, or there is any suspicion that bat saliva or nervous tissue has contaminated an open wound or mucous membrane, wash the affected area thoroughly with soap and water, capture the bat without damaging the head, and seek immediate medical attention. The incident should be reported promptly to local health authorities in order to arrange rabies testing of the bat.

If the bat is captured and immediate transportation to the testing laboratory is possible, and if immediate testing can be arranged, postexposure treatment may be delayed several hours until the test results are known. Postexposure prophylaxis must be administered immediately, however, if the bat cannot be captured, if prompt transportation to the laboratory is not possible, if the specimen is not suitable for reliable diagnosis, or if the test results prove positive for rabies.

The prophylaxis has little resemblance to that of many years ago. Today, it consists of one dose of rabies immune globulin (human origin) and one dose of rabies vaccine (human diploid cell) administered preferably on the day of exposure, followed by additional single doses of rabies vaccine on days 3, 7, 14, and 28 following the initial injection. This treatment is normally safe, relatively painless, and very effective.

Histoplasmosis — Preventive Measures. Histoplasmosis can most easily be prevented by avoiding areas that harbor H. capsulatum. Since this is not practical for individuals who must work in and around active/inactive bat roosting sites, other measures can be recommended to reduce the risk of infection during cleaning, field study, demolition, construction, and other activities.

Persons working in areas known or suspected to be contaminated with H. capsulatum should always wear protective masks capable of filtering out particles as small as 2 microns in diameter or use a self-contained breathing apparatus. In areas known to be contaminated, wear protective clothing and gloves that can be removed at the site and placed in a plastic bag for later decontamination via formalin and washing. Also, clean footwear before leaving the site to prevent spore dissemination in cars, the office, at home, and elsewhere.

Guano deposits and guano-enriched soils should not be unnecessarily disturbed. Dampening with water or scheduling outdoor work at a time when the ground is relatively wet will minimize airborne dust. Chemically decontaminate known infective foci with a spray of 3% formalin (see CDC 1977). To protect the environment, decontamination must be conducted in accordance with state and local regulations. Chemical decontamination of an “active” bat roost should be conducted only after the bats have been excluded or after bats have departed for hibernation.

Histoplasmosis — Treatment. Most infections in normally healthy individuals are benign and self-limiting and do not require specific therapy (George and Penn 1986; Rippon 1988). Treatment with an antifungal agent may be prescribed in more severe cases; amphotericin B and/or oral imidazole ketoconazole are typically recommended depending on the specific nature of the infection.

Removal of Occasional Bat Intruders. A bat that has blundered into the living quarters of a house will usually find its way out by detecting air movement. When no bite or contact with people or pets has occurred, the simplest solution for “removing” the bat is to try to confine it to one room, then open windows and doors leading outdoors and allow it to escape. If the bat is present at night, the lights should be dimmed to allow the animal to find open doors and windows. Some light is necessary if an observer is to ensure that the bat finds its way out. If bright lights are kept on, the bat may become confused and may seek refuge behind shelving, curtains, hanging pictures, or under furniture.

Healthy bats normally will not attack people even when chased. Chasing a flying bat with a folded newspaper, tennis racket, or stick will cause the bat to take evasive action, and a bat’s flight reversal to avoid a wall is often misinterpreted as an attack. These flailings, often futile, will cause a bat to seek safety wherever possible, making escape more difficult for the bat and more frustrating for the human.

Figure 9. Using an insect net to remove a bat from a building.
Figure 9. Using an insect net to remove a bat from a building.

If the bat has difficulty escaping, it can be captured in a hand net (for example, an insect net [Fig. 9]). Otherwise, wait for it to come to rest, quickly cover it with a coffee can or similar container, and slide a piece of cardboard or magazine under the can to trap the bat inside (NYSDH 1990). Take the captured bat outdoors and release it away from populated areas, preferably after dark. Note that reasonably thick work gloves should be worn at all times when trying to capture a bat. Also, if a bite or physical contact occurs, capture the bat without damaging its head and immediately contact a physician (see previous section regarding rabies treatment). Management of problems involving bat colonies require more complicated procedures and a greater time commitment.

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Exclusion

Preventive Aspects. The most satisfactory and permanent method of managing nuisance bats is to exclude them from buildings. Locate bats and their points of exit/entry through bat watches or other inspection methods. This is a tedious process to locate all openings in use, and bats may switch to alternate ones when normal routes become unavailable. Thus, consider “potential” as well as “active” points of access.

Often it is apparent where bats might gain entrance even when such openings are not directly observable. By standing in various locations of a darkened attic during daylight hours, one often can find leaks of light at the extreme parts of eaves, in layers of subroofing, and below chimney flashings. Seal all gaps of 1/4 x 1 1/2 inches (0.6 x 3.8 cm) and openings 5/8 x 7/8 inch (1.6 x 2.2 cm) or greater.

Figure 10. Using a clothes hanger/plastic film combination to detect air leaks.
Figure 10. Using a clothes hanger/plastic film combination to detect air leaks.

Bats will also use some of the same obscure holes in buildings through which heat (or cooled air) is lost; thus, bat-proofing often conserves energy. Simple, homemade devices can be used to locate air leaks. Bathroom tissue or very thin plastic film bags can be taped to a clothes hanger. When placed in front of an area with an air leak (for example, around window frames and sashes where caulking or weather stripping are needed), the tissue or plastic will wave and flutter from air movements (Fig. 10). Indoor air leaks can be found easily by the use of an air flow indicator (Fig. 11). Small-volume smoke generators can be used to locate openings in the floor, ceiling, attic, and basement. Obscure openings also may be located from outside the house by activating smoke candles or smoke bombs (as within an attic), which will produce easily observed dense smoke. Be careful of any fire hazards.

Figure 11. Smoke from the Sensidyne Air Indicator makes it possible to visually determine the directional pattern of air currents.
Figure 11. Smoke from the Sensidyne Air Indicator makes it possible to visually determine the directional pattern of air currents.

The easiest time to seal bats out of buildings in northern latitudes is during the cooler part of the year when colonies are not resident. During this period, many homeowners need to be reminded that bats, and bat problems, return each summer. Basic carpentry, masonry, and tinsmith skills are valuable in bat exclusion and other pest proofing interventions.

Devices and Methods. Exclusion becomes “denial of reentry” once the bats have returned to establish maternity colonies (and before the young are born), usually from April through mid-May in the Northeast. Denial of reentry is also appropriate anytime after mid-August when young are capable of flying, as long as bats continue to utilize the roost.

The traditional way to exclude bats from an occupied roost involves five basic steps: (1) identify and close all indoor openings through which bats might gain access to human living quarters; (2) close most confirmed and all unused potential exterior exits, leaving only a few major openings (it’s best to complete this within 1 to 2 days); (3) at night shortly after the bats have departed to feed, temporarily close the few remaining, major exits; (4) check the roost for presence of bats and, if any remain, unplug the temporarily closed exits early the next evening to allow the bats to escape, then temporarily replug the exits (it may be necessary to repeat this step more than once); and (5) when the bats are all out, permanently seal the holes (Frantz and Trimarchi 1984, Greenhall 1982).

Patience and timing are very important in this process. Much of this work can be done during daylight hours except steps 3 and 4, which require climbing on ladders and roofs at night, sometimes with bats flying nearby. The danger of such work is obvious and discouraging.

Some of these difficulties have been overcome by use of the Constantine one-way, valve-like device which is installed in the last exit(s) during the day, and permits bats to leave after dark but prevents their reentry (Constantine 1982). Eventually the valve should be removed and the hole(s) sealed. Another device, the EX-100 Hanks Bat Excluder, consists of a piece of nylon window screening, a wooden plate with a hole in the middle to which is attached a one-way plastic flapper valve, and a rigid plastic mesh cone (Anon. 1983). The screening, to which the wooden plate is attached, is used to cover an opening that bats use to exit a building. Both devices are designed to be used on the last few exit points. Installation instructions are available, and properly applied they will undoubtedly exclude bats from relatively small, discrete openings.

The devices of Constantine and Hanks involve a one-way, self-closing valve feature and can be readily installed during daylight hours. Such devices are not readily adaptable to situations with large, diffuse and/or widely distributed entryways. Also, bats can be inadvertently trapped inside if an important exit hole is mistakenly identified as a minor one and is sealed in an attempt to limit the number of holes requiring an exclusion device.

Figure 12. Bat on birdnetting showing size relationships.
Figure 12. Bat on birdnetting showing size relationships.

To overcome difficulties with exclusion devices, Frantz’ checkvalve was developed using netting made of durable black polypropylene resin (Frantz 1984, 1986). Quality of product is important since the netting should not fray or become misshapen under hot summer conditions. Use only structural grade material that has openings no larger than 1/2 x 1/2 inch (1.3 x 1.3 cm), weighs about 1.3 ounces per square yard (44 g/m2), and is flexible yet stiff enough to maintain the shape of the checkvalve fabricated (Fig. 12). Waterproof duct tape, common staples, and/or wooden lath strips are used to attach the netting to metal, slate, brick, wood, asphalt shingle, or other surfaces. Note that duct tape may stain or discolor painted/enameled surfaces if kept in contact for long periods of time.

Application of check valves follows the same two initial steps as traditional bat exclusion. Close interior openings, then close exterior openings except a few major exits. These latter openings will have been confirmed as important via bat watches, and it is here that check valves will be fitted during the daylight.

Figure 13. Sample configurations for Frantz’ checkvalve (Key: = birdnetting; ......... = attaching to structure; • = exit/entry holes of bats).
Figure 13. Sample configurations for Frantz’ checkvalve (Key: = birdnetting; ......... = attaching to structure; • = exit/entry holes of bats).

The basic design is to attach the netting around an exit hole except at the bottom where the bats will escape (see Frantz 1986, for details). The width and shape of check valves is highly variable so as to embrace the necessary exit point — a single hole, a series of holes, or a long slit-like opening (Fig. 13). Designs must be open enough not to impede the exiting bats. The top can be much larger than the bottom. It is probably best to restrict the bottom opening to no larger than about 1.6 x 1.6 feet (0.5 x 0.5 m). The length of a checkvalve, that is, the distance from the lowest enclosed point of egress to the bottom of the netting, should be about 3.3 feet (1 m).

The above specifications usually are sufficient to abort bats’ reentry attempts. If netting is applied while young are still in the roost, the “evicted” mothers may be motivated to chew holes in the netting to reenter the roost. Applied at the correct time of year, however, netting will allow all bats to exit at dusk and thereafter deny them reentry.

Checkvalves should be kept in place for 3 to 5 days. It is best to verify (conduct a bat watch) that bats no longer exit at dusk before the checkvalves are dismantled and the holes are sealed permanently. As in any exclusion intervention, the excluded animals will go elsewhere. This shift may be to an alternative roost already in use such as a night roost, or one used in previous years.

Supplemental Materials and Methods. While specifications for Frantz’ checkvalve have been provided, additional caulking, flashing, screening, and insulation materials often are needed. The combination of materials used will depend on the location, size, and number of openings, and the need for ventilation. Greenhall (1982) provides many details of bat-proofing methods and materials and is a practical guide. Weather stripping, knitted wire mesh (Guard-All®, Stuffit®), waterproof duct tape, stainless steel wool, and wood lath may be used to block long, narrow openings. Caulking compounds will seal cracks and crevices that develop in a house as it ages, and are best applied during dry periods when wood cracks are widest. Caulks that may be applied with a caulking gun (in gaps up to about 0.4 inch [1 cm] wide) include latex, butyl, and acrylic, which last about 5 years. Elastomeric caulks, such as silicone rubber, will last indefinitely, expand and contract, do not dry or crack, and tolerate temperature extremes. Oakum packs easily and firmly into small cracks. Other fillers include sponge rubber, glass fiber, knitted wire mesh, and quick-setting putty. Self-expanding polyurethane foam applied from pressurized containers can be used for openings larger than 3 inches (>7.5 cm). It must be applied with caution so as to not lift clapboards, shingles, and other surfaces. Exposed surfaces should be sealed with epoxy paint to prevent insect infestation and ultraviolet degradation.

Figure 14. Weather stripping and door sweeps are very useful bat-proofing measures.
Figure 14. Weather stripping and door sweeps are very useful bat-proofing measures.

Conventional draft sweeps (metal, rubber) and other weather stripping supplies (felt, vinyl, metal) will seal the space between a door bottom and the threshold or around windows (Fig. 14). Remember to treat attic and basement doors whenever the gap exceeds 1/4 inch (0.6 cm). Flashing may be used to close gaps wherever joints occur; for example, where the roof meets a chimney. Materials commonly used include galvanized metal, copper, aluminum, and stainless steel. Self-adhesive stainless steel “tape” is also available. Insulation will provide some degree of barrier to bat movements. It is available in a number of forms and types including fiberglass, rock wool, urethane, vermiculite, polystyrene, and extruded polystyrene foam. Inorganic materials are fire and moisture resistant; the safest appear to be fiberglass and rock wool.

The mesh size of screening must be small enough to prevent access of bats and other species, where desired. Hardware cloth with 1/4-inch (0.6-cm) mesh will exclude bats and mice; screening with 16 meshes per inch (2.5 cm) will exclude most insects. Soffits (underside of overhanging eaves) usually have ventilators of various shapes and sizes. Regardless of type, the slots should not exceed 1/4 x 1 inch (0.6 cm x 2.5 cm) and should be covered inside with insect mesh. To prevent bats from entering chimney flues, completely enclose the flue discharge area with rust-resistant spark arresters or pest screens, secured to the top of the chimney. These should not be permanently attached (for example, with screws) in case they must be rapidly removed in the event of a chimney fire. Review fire codes before installing flue covers. Dampers should be kept closed except in the heating season.

Figure 15. Open ends of tile roofs may allow bat entry and provide roosting sites.
Figure 15. Open ends of tile roofs may allow bat entry and provide roosting sites.

Roof Problems. Bats, particularly the Mexican free-tailed bat, often roost under Spanish or concrete tile roofing by entering the open ends at the lowermost row, or where the tiles overlap (Fig. 15). Tight-fitting plugs are difficult to make due to the variation in opening sizes and thermal expansion and contraction. A solution was found by Constantine (1979) in which a layer of coarse fiberglass batting was laid under the tiles so that bats entering holes would contact the fiberglass and be repelled. A layer of knitted wire mesh would undoubtedly work well for this purpose (and would not hold moisture). Bats also may be excluded from the tiles if rain gutters are installed directly under the open ends. Gaps under corrugated and galvanized roofing may be closed with knitted wire mesh, self-expanding foam (avoid causing roofing to lift), or with fiberglass batting (may retain moisture).

Wall Problems. Fiberglass or rock wool insulation blown into wall spaces that are used by bats may be a deterrent, especially when it forms a physical barrier to passage. Such work must be done when bats are absent to avoid their entrapment.

Temporary Roosts. Bats will sometimes temporarily roost on porches and patios, in garages, and behind shutters, shingles, and roof gutters. Roosting behind shutters may also be longterm in duration. Actual control measures may not be necessary unless bat droppings become a problem or the risk of human contact is significant. Coarse fiberglass batting tacked to the surfaces where bats prefer to hang sometimes discourages them. A potentially useful intervention for the wall-ceiling interface is the application of a wide 45-degree molding strip to eliminate the 90-degree angle corner and force the bats to roost in a more exposed area.

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Repellents

While many chemical aromatics and irritants have been proposed and tested for bat repellency, efficacy has been very limited thus far. Naphthalene crystals and flakes are the only repellents registered by the US Environmental Protection Agency (EPA) for indoor bat control and are to be applied in attics or between walls. Sometimes the chemical may be placed in loose-mesh cloth bags and suspended from the rafters. About 2.5 pounds per 1,000 cubic feet (1.2 kg/30 m3) is recommended to chronically repel bats as the chemical vaporizes. Dosages of 5 pounds per 1,000 cubic feet (2.4 kg/30 m3) may dislodge bats in broad daylight. Bats will return, however, when the odor dissipates. The prolonged inhalation of naphthalene vapors may be hazardous to human health.

Illumination has been reported to be an effective repellent. Floodlights strung through an attic to illuminate all roosting sites may cause bats to leave. Large attics may require many 100-watt bulbs or 150-watt spotlights to be effective. Fluorescent bulbs may also be used. In some situations such lighting is difficult, costly, and may result in an electrical hazard. Where possible, the addition of windows to brighten an attic will help to reduce the desirability of the roost site and is not likely to introduce additional problems.

Air drafts have successfully repelled bats in areas where it is possible to open doors, windows, or create strong breezes by use of electric fans. Addition of wall and roof vents will enhance this effort, as well as lower roost temperature. These measures will increase the thermoregulatory burden on the bats, thus making the roost less desirable. In a similar fashion, colonies located in soffits, behind cornices, and other closed-in areas can be discouraged by opening these areas to eliminate dark recesses. Discourage bats from roosting behind shutters by removing the shutters completely, or by adding small blocks at the corners to space them a few inches away from the wall.

Ultrasonic devices have been tested under natural conditions, both indoors and outdoors, to repel little brown and big brown bats either in the roost or as they fly toward an entrance hole (Frantz, unpublished data). The results have not been promising. Numerous ultrasonic devices have been removed from clients’ homes because the bats remained in the roost after the devices were activated. Hurley and Fenton (1980) exposed little brown bats to ultrasound in semi-natural roosts with virtually no effect. Largely because of this lack of known scientific efficacy for ultrasonic devices, the New York State Consumer Protection Board has cautioned against the use of such devices (NYSCPB 1988). Part of the concern is that such devices will provide consumers with a false sense of security and, thus, may prevent them from taking effective preventive actions.

Distress cries of bats recorded on tape and rebroadcast can be used to attract other bats to nets or traps, but they do not serve as an effective repellent. Little brown and big brown bats respond to their own distress cries but not to the cries of other species.

Toxicants

No toxicants are registered for controlling bats. In 1987 the Centers for Disease Control, United States Department of Health and Human Services, voluntarily withdrew the last registration for DDT use against bats in the United States. Thus, DDT is no longer registered for any use in this country.

Although federally registered for rodents, chlorophacinone tracking powder, an anticoagulant, is not registered for bats. Furthermore, it can no longer be registered by individual states for restricted use under Section 24(c) of the Federal Insecticide, Fungicide, and Rodenticide Act D-18 (FIFRA). Lipha Tech, Inc. (the manufacturer) has voluntarily cancelled its registration for “RoZol Tracking Powder for Control of Nuisance Bats” — effective December 16, 1991 (Fed. Reg., 1991).

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Trapping

Kunz and Kurta (1988) reviewed an extensive variety of efficient methods for trapping bats from buildings and other roosting sites or foraging areas. For purposes of wildlife damage control, however, exclusion is less complicated to carry out, less time-consuming, more effective, and requires no handling of bats.

Other Methods

Sanitation and Cleanup. Once bats have been excluded, repelled, or have departed at the end of the summer, measures must be completed to make reinfestation less likely, and to eliminate odor and problematic bioaerosols. As a prelude to such work, it is sometimes useful to apply a pyrethrum-based, total-release aerosol insecticide to eliminate unwanted arthropods.

The safe handling and removal of bat guano has been discussed previously (see the histoplasmosis section in this chapter). In addition to the more bulky accumulations of excreta, there are often diffuse deposits of guano under/ among insulation materials, caked urine and guano on roof beams, and splattered urine on windows. Such clean-up work during hot summer weather may be the least desirable activity of a management program, but it is necessary. All caked, crystallized bat urine and droppings should be scraped and wire-brushed, as necessary, from all roof and attic beams. For this procedure, workers should take the same precautions as outlined for histoplasmosis-related work. Accumulated excreta and contaminated insulation should be sealed in plastic bags and removed for disposal. Remove all remaining droppings and debris with a vacuum cleaner, preferably one that has a water filter to reduce the amount of dust that escapes from the cleaner’s exhaust.

Where possible, wash with soap and water all surfaces contaminated with urine and guano. Allow the surfaces to dry, then disinfect them by misting or swabbing on a solution of 1 part household bleach and 20 parts tap water. Ventilate the roost site to allow odors and moisture to escape. Installation of tight-fitting window screens, roof and/or wall ventilators in attics will enhance this process. Remember, sanitation and cleanup accompanies bat-proofing and exclusion measures, it does not replace them.

Artificial Roosts. For more than 60 years, artificial bat roosts have been used in Europe. Only recently have they gained some popularity in the United States. Though the results are variable, it appears that artificial roosts, if properly constructed and located, can attract bats that are displaced or excluded from a structure. The Missouri Department of Conservation described a successful “bat refuge” that was quickly occupied by a displaced colony of little brown bats (LaVal and LaVal 1980). Bat houses of a similar design have been successfully used in Minnesota, New York, Pennsylvania, and elsewhere (see Fig. 16).

Figure 16. One of five bat houses constructed to provide an alternative roost for bats excluded from nearby structures.
Figure 16. One of five bat houses constructed to provide an alternative roost for bats excluded from nearby structures.

Development of an efficient method to relocate bats into alternative roosts after they have been excluded from buildings could be an important intervention in comprehensive bat management. Frantz (1989) found it helpful to “seed” newly constructed bat houses with several bats, a procedure that later resulted in full-scale colonization without further human interventions. Alternative roosts should be located away from human high-use areas. Thus, people can enjoy the benefits of bats without sharing their dwellings with them and with little risk of direct contact with them.



Bats | Bat Overview | Bat Damage Assessment | Bat Damage Management | Bat Resources | Bat Acknowledgments | ICWDM | Wildlife Species Information


Summary of Damage Prevention and Control Methods

Exclusion

Polypropylene netting check valves simplify getting bats out.

Quality bat-proofing permanently excludes bats.

Initiate control before young are born or after they are able to fly.

Repellents

Naphthalene: limited efficacy. Illumination.

Air drafts/ventilation.

Ultrasonic devices: not effective. Sticky deterrents: limited efficacy.

Toxicants

None are registered.

Trapping

Available, but unnecessarily complicated compared to exclusion and bat-proofing.

Other Methods

Sanitation and cleanup.

Artificial roosts.

Removal of Occasional Bat Intruders

When no bite or contact has occurred, help the bat escape (otherwise submit it for rabies testing).

Conservation and Public Education

Information itself functions as a management technique.
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