Bats - New York State Department of Health · simplify getting bats out. Quality bat-proofing permanently excludes bats. Initiate control before young are born or after they are able

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BATS

PREVENTION AND CONTROL OF WILDLIFE DAMAGE — 1994

Cooperative Extension DivisionInstitute of Agriculture and Natural ResourcesUniversity of Nebraska - Lincoln

United States Department of AgricultureAnimal and Plant Health Inspection ServiceAnimal Damage Control

Great Plains Agricultural CouncilWildlife Committee

Damage Prevention andControl Methods

Exclusion

Polypropylene netting checkvalvessimplify getting bats out.

Quality bat-proofing permanentlyexcludes bats.

Initiate control before young are bornor 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 unnecessarilycomplicated compared to exclusionand bat-proofing.

Other Methods

Sanitation and cleanup.

Artificial roosts.

Important Note: This document is included for information it provides pertinent to bat behavior, exclusion techniques, damage identification, prevention and control measures. However, pages D14 - D18 contain information about rabies and removal of bats from homes that is incomplete with regard to current public health recommendations. For current information see

Guidelines for Managing Bats and Risk of Rabies Transmission at:

Arthur M. GreenhallResearch AssociateDepartment of MammalogyAmerican Museum of Natural HistoryNew York, New York 10024

Stephen C. FrantzVertebrate Vector SpecialistWadsworth Center for Laboratoriesand ResearchNew York State Department of HealthAlbany, New York 12201-0509

Fig. 1. Little brown bat, Myotis lucifugus

www.health.state.ny.us/nysdoh/zoonoses/batmanage.pdf

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Fig. 2. Little brown bat, Myotis lucifugus

Fig. 3. Big brown bat, Eptesicus fuscus

Introduction

Conservation and Public Education

Despite their ecological value, bats arerelentlessly and unjustifiably perse-cuted. Bats are often killed becausethey live near people who needlesslyfear them. These actions emphasize theneed to educate the public on the rea-sons for bat conservation and why it isimportant to use safe, nondestructivemethods to alleviate conflicts betweenpeople and bats. General sources ofinformation on bats include states’Cooperative Extension Services, uni-versities, government environmentalconservation and health departments,and Bat Conservation International(Austin, Texas). Except where controlis necessary, bats should be appreci-ated from a distance — and not dis-turbed.

Identification and Range

Bats, the only mammals that truly fly,belong to the order Chiroptera. Theirability to fly, their secretiveness, andtheir nocturnal habits have contributedto bat folklore, superstition, and fear.They are worldwide in distributionand include about 900 species, secondin number only to Rodentia (therodents) among the mammals.

Among the 40 species of bats foundnorth of Mexico, only a few causeproblems for humans (note that vam-pire bats are not found in the UnitedStates and Canada). Bats congregatingin groups are called colonial bats;those that live a lone existence areknown as solitary bats.

The colonial species most often en-countered in and around humanbuildings in the United States are thelittle brown bat, (Myotis lucifugus, Fig.2), the big brown bat (Eptesicus fuscus,Fig. 3), the Mexican free-tailed bat(Tadarida brasiliensis, Fig. 4), the pallidbat (Antrozous pallidus), the Yumamyotis (Myotis yumanensis), and theevening bat (Nycticeius humeralis).

Solitary bats typically roost in tree foli-age or under bark, but occasionally arefound associated with buildings, someonly as transients during migration.

Fig. 5. Anatomy of a typical bat

Wrist

Ear

Tragus

Upper arm

Forearm

Thumb

Secondfinger

Thirdfinger

Fourth finger

Fifth finger

Wing membrane

Foot

Calcar

Knee

Tailmembrane

Fig. 4. Mexican free-tailed bat, Tadarida brasiliensis

These include Keen’s bat (Myotiskeenii), the red bat (Lasiurus borealis),the silver-haired bat (Lasionycterisnoctivagans), and the hoary bat(Lasiurus cinereus). Excellent illustra-tions of all bats discussed herein can befound in Barbour and Davis (1979),Tuttle (1988), Geluso et al. (1987), andHarvey (1986).

Several species of bats have beenincluded here, with significant inter-specific differences that need to beclarified if well-planned, comprehen-sive management strategies are to bedeveloped. Any problems caused bybats are limited to species distribution;thus animal damage control personnelneed not be concerned with every spe-cies.

Colonial and solitary bats have obvi-ous differences that serve to separatethe species into groups (refer to Fig. 5).Much of the descriptive material thatfollows is adapted from Barbour andDavis (1979).

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Colonial Bats

Little brown bat (Myotis lucifugus)

Recognition

forearm — 1.34 to 1.61 inches (3.4 to4.1 cm)

wingspan — 9.02 to 10.59 inches (22.9to 26.9 cm)

ears — 0.55 to 0.63 inches (1.4 to 1.6cm)

foot — approximately 0.39 inches (1.0cm); long hairs on toes extend be-yond claws.

Distribution (Fig. 6a)

Color

Pale tan through reddish brown todark brown, depending on geo-graphic location. The species is arich dark brown in the easternUnited States and most of the westcoast. Fur is glossy and sleek.

Confusion may occur with a few other“house” bat species. In the East, itmay be confused with Keen’s bat(M. keenii), which has longer ears[0.69 to 0.75 inches (1.7 to 1.9 cm)]and a longer, more pointed tragus(the appendage at the base of theear). In the West, it resembles theYuma myotis (M. yumanensis),which has dull fur and is usuallysmaller. However, the Yuma myotisand little brown may be indistin-guishable in some parts of thenorthwestern United States wherethey may hybridize.

Habits

This is one of the most common batsfound in and near buildings, oftenlocated near a body of water wherethey forage for insect prey. Summercolonies are very gregarious, com-monly roosting in dark, hot atticsand associated roof spaces wherematernity colonies may includehundreds to a few thousand indi-viduals. Colonies may also formbeneath shingles and siding, in treehollows, beneath bridges, and incaves. Litter size is 1 in the North-east; twins occasionally occur insome other areas. The roost is oftenshared with the big brown bat (E.fuscus) though the latter is less toler-

ant of high temperatures; M. keeniimay also share the same site. Sepa-rate groups of males tend to besmaller and choose cooler roostswithin attics, behind shutters, undertree bark, in rock crevices, andwithin caves.

In the winter, little brown bats in theeastern part of their range abandonbuildings to hibernate in caves andmines. Such hibernacula may benear summer roosts or up to a fewhundred miles (km) away. Little isknown of the winter habits of M.lucifugus in the western UnitedStates.

The life span of little brown bats hasbeen established to be as great as 31years. The average life expectancy,however, is probably limited to onlya few years.

Big brown bat (Eptesicus fuscus)

Recognition



ears — with rounded tragus

Distribution (Fig. 6b)

Color

From reddish brown, copper colored,to a dark brown depending on geo-graphic location. This is a large batwithout distinctive markings.

Confusion may occur with the eveningbat (Nycticeius humeralis) though thelatter is much smaller.

Habits

This hardy, rather sedentary speciesappears to favor buildings for roost-ing. Summer maternity coloniesmay include a dozen or so and upto a few hundred individuals, roost-ing behind chimneys, in enclosedeaves, in hollow walls, attics, barns,and behind shutters and unusedsliding doors. They also form colo-nies in rock crevices, beneathbridges, in hollow trees, and underloose bark. Litter size is 2 in the Eastto the Great Plains; from theRockies westward 1 young is born.

E. fuscus frequently shares roostswith M. lucifugus in the East, andwith M. yumanensis, Taderida, andAntrozous in the West. Males typi-cally roost in smaller groups oralone during the summer.

The big brown bat is one of the mostwidely distributed of bats in theUnited States and is probably famil-iar to more people than any otherspecies. This is partially due to itslarge, easy-to-observe size, but alsoto its ability to overwinter in build-ings (attics, wall spaces, and base-ments). Its close proximity tohumans, coupled with its tendencyto move about when temperatureshifts occur, often brings this batinto human living quarters andbasements in summer and winter.Big browns also hibernate in caves,mines, storm sewers, burial vaults,and other underground harborage.While E. fuscus will apparentlytravel as far as 150 miles (241 km) tohibernacula, the winter quarters ofthe bulk of this species are largelyunknown.

Big brown bats may live as long as 18years.

Mexican free-tailed bat (Tadaridabrasiliensis)

Recognition


wingspan — 11.42 to 12.80 inches (29.0to 32.5 cm); long narrow wings

tail (interfemoral) membrane — doesnot enclose the lower one-third toone-half of the tail, hence the namefree-tailed

foot — long, stiff hairs as long as thefoot protrude from the toes.

Distribution (Fig. 6c)

Color

Dark brown or dark gray. Fur of someindividuals may have beenbleached to a pale brown due toammonia fumes from urine and de-composing guano.

Confusion is not likely to occur withother species that commonly inhabithuman buildings.

Habits

T. brasiliensis forms the largest coloniesof any warm-blooded animal, estab-lishing sizable colonies in buildings,particularly on the West Coast andin the Gulf states from Texas east.Hundreds to thousands may befound in buildings or underbridges. It is primarily a cave bat inArizona, New Mexico, Oklahoma,and Texas; buildings are used astemporary roosts during migra-tions. Litter size is 1.

Taderida often share roosts with otherspecies. In the West, for example,they may be found in buildingswith A. pallidus, M. yumanensis, andE. fuscus. Some males are alwayspresent in the large maternity colo-nies, but they tend to segregate inseparate caves.

A few Taderida may overwinter inbuildings as far north as SouthCarolina in the East and Oregon inthe West. Most of this speciesmigrate hundreds of miles towarmer climes (largely to Mexico)for the winter.

Pallid bat (Antrozous pallidus)

Recognition



ears — large; widely separated andmore than half as broad as long.The ears are nearly half as long asthe combined length of the bat’shead and body.

eyes — large

Distribution (Fig. 6d)

Color

pale, upper parts are light yellow, thehairs tipped with brown or gray.Underparts are pale creamy, almostwhite. This large, light-colored batis relatively easy to recognize.

Confusion with other species that com-monly inhabit human buildings isnot likely to occur.

Habits

Maternity colony size ranges fromabout 12 to 100 individuals. Roostsites include buildings, bridges, androck crevices; less frequently, treecavities, caves, and mines. Littersize is most commonly 2. The roostis frequently shared with T.brasiliensis and E. fuscus in the West.While groups of males tend to seg-regate during the nursery period(sometimes in the same building),other males are found within thematernity colony.

An interesting feature of pallid bats isthat they fly close to the ground,may hover, and take most prey onthe ground, not in flight. Preyincludes crickets, grasshoppers,beetles, and scorpions. They willalso forage among tree foliage.

Pallid bats are not known to make longmigrations, though little is knownof their winter habits.

Yuma myotis (Myotis yumanensis)

Recognition


wingspan — about 9.25 inches (23.5cm)

ears — 0.55 to 0.59 inches (1.4 to 1.5 cm)foot — 0.39 inches (1.0 cm)

Distribution (Fig. 6e)

Color

Light tan to dark brown; underside iswhitish to buffy.

Confusion may occur in the West withM. lucifugus, though the latter tendsto have longer, glossier fur, and islarger. In the Northwest, hybridiza-tion occurs with M. lucifugus, mak-ing the species indistinguishable.

Habits

Maternity colonies, up to severalthousand individuals, form in thesummer in attics, belfries, underbridges, and in caves and mines.Litter size is 1. Males typicallysegregate during the nursery periodand roost as solitary individuals inbuildings and other suitable harbor-age.

M. yumanensis is more closely associ-ated with water than is any otherNorth American bat species. Nearlyall roosts have open water nearby.This species is not as tolerant as M.lucifugus of high roost temperaturesand will move to cooler nicheswithin a building when tempera-tures rise much above 100o F(37.8o C).

M. yumanensis abandons maternitycolonies in the fall, but its winterhabitat is not known.

Evening bat (Nycticeius humeralis)

Recognition



ears — with short, curved, androunded tragus

Confusion may occur with the bigbrown bat (E. fuscus), which can bereadily distinguished by its largersize. It bears some resemblance tothe somewhat smaller little brownbat (M. lucifugus) but can be identi-fied by its characteristic blunttragus.

Distribution (Fig. 6f)

Color

Medium brown with some variation toyellow-brown in subtropicalFlorida. No distinctive markings.

Habits

Summer maternity colonies in build-ings may consist of hundreds ofindividuals. Litter size is usually 2.Colonies also form in tree cavitiesand under loose tree bark. In theSoutheast, T. brasiliensis commonlyinhabits the same building with N.humeralis. This is one of the mostcommon bats in towns throughoutthe southern coastal states. Verylittle is known about this species,and virtually nothing is known ofits winter habitat except that italmost never enters caves.

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Solitary Bats

Keen’s bat (Myotis keenii)

Recognition



ears — 0.67 to 0.75 inches (1.7 to 1.9 cm);with a long, narrow, pointed tragus

Distribution (Fig. 6g)

Color

Brown, but not glossy; somewhat palerin the East.

Confusion may occur with M.lucifugus, which has glossy fur,shorter ears, and does not have thelong, pointed tragus.

Habits

Excluding small maternity colonies (upto 30 individuals are on record), M.keenii are generally found singly in theEast. Roosting sites include: behindshutters, under wooden shingles, shel-tered entryways of buildings, in roofspaces, in barns, and beneath treebark. In the West, this bat is known asa solitary species, roosting in tree cavi-ties and cliff crevices. Litter size isprobably 1. The roost is sometimesshared with M. lucifugus. The sexesprobably segregate during the nurs-ery period. In winter, these bats hiber-nate in caves and mines.

Red Bat (Lasiurus borealis)

Recognition


wingspan — 11.42 to 13.07 inches (29.0to 33.2 cm); long, pointed wings

ears — short roundedtail membrane — heavily furred on

upper surface, with a distinctivelong tail.

Distribution (Fig. 6h)

Color

Bright orange to yellow-brown; usu-ally with a distinctive white markon the shoulders.

Confusion may occur with the hoarybat (L. cinereus), which is frosted-gray in appearance and larger.

Habits

Red bats live solitary lives, comingtogether only to mate and migrate.Few people are familiar with this spe-cies. They typically spend summerdays hidden in the foliage of decidu-ous trees. The number of young rangesfrom 1 to 4, averaging 2.3.

These bats often chase insects that areattracted to lights, such as streetlamps. It is this behavior that mostlikely brings them in close proxim-ity to people.

L. borealis is well-adapted for survivingdrastic temperature fluctuations; itdoes not hibernate in caves, butapparently in trees. Some migratelong distances. During migration,red bats have been known to landon high-rise buildings and onships at sea.

Silver-haired bat (Lasionycterisnoctivagans)

Recognition



ears — short, rounded, hairlesstail membrane — upper surface is

sparsely furred on the anterior one-half.

Distribution (Fig. 6i)

Color

Usually black with silver-tipped fur;some individuals with dark brown,yellowish-tipped fur.

Confusion sometimes occurs with thelarger hoary bat (Lasiurus cinereus),which has patches of hair on the earsand wings, heavy fur on the entireupper surface of the tail membrane,and has a distinctive throat “collar.”

Habits

The silver-haired bat roosts in a widevariety of harborages. A typicalroost might be behind loose treebark; other sites include tree hol-lows and bird nests. This species issolitary except when with young.Additionally, there are unconfirmedreports that it is sometimes colonial(Dalquest and Walton 1970) and

may roost in and on buildings. Thelitter size is 2. The sexes segregatethrough much of the summer range.

L. noctivagans hibernates in tree crevices,under loose bark, in buildings(including churches, sky scrapers, andwharf houses), hulls of ships, rockcrevices, silica mines, and non-limestone caves. It also may migrate,during which time it is encounteredin buildings (they favor open sheds,garages, and outbuildings rather thanenclosed attics), in lumber piles,and on ships at sea.

Hoary bat (Lasiurus cinereus)

Recognition



ears — relatively short, rounded,edged with black, and with fur

tail membrane — completely furred onupper surface

Distribution (Fig. 6j)

Color

Dark, but many hairs are tipped inwhite, giving it a frosted appear-ance. This bat also has a yellowishor orangish throat “collar.”

Confusion may sometimes occur withthe much smaller silver-haired bat(Lasionycteris noctivagans), whichlacks the fur patches and markingson the ears, markings on the throat,and has a tail membrane that is onlylightly furred on the upper surface.

Habits

Hoary bats generally spend summerdays concealed in tree foliage (oftenin evergreens), rarely enter houses,and are not commonly encounteredby people. L. cinereus at their dayroosts are usually solitary exceptwhen with young. The litter size is2. The sexes segregate through mostof the summer range.

This is one of the largest bats in NorthAmerica, a powerful flier, and anaccomplished migrant. Recordsindicate that some L. cinereus mayhibernate in northern parts of theirrange.

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j

g h i

Figure 6. Distributions of selected bat species in North America:(a) little brown bat, (b) big brown bat, (c) Mexican free-tailed bat,(d) pallid bat, (e) Yuma myotis, (f) evening bat, (g) Keen’s bat,(h) red bat, (i) silver-haired bat, (j) hoary bat.

b ca

d e f

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Drip edge

Underporchroof

Under siding

Under roofing Ridge cap

Fascia boards

Chimney flue

Between house & chimney

Flashing

Vent Soffits Hollow wallsRafters

Food Habits

Bats in North America are virtually allinsectivorous, feeding on a variety offlying insects (exceptions among housebats were noted previously). Many ofthe insects are harmful to humans.While there must be some limitationsbased on such factors as bats’ bodysize, flight capabilities, and jaw open-ing, insectivorous bats apparently con-sume a wide range of prey (Barbourand Davis 1979). The little brown bat’sdiet includes mayflies, midges, mos-quitoes, caddis flies, moths, andbeetles. It can consume insects equal toone-third of its body weight in 1/2hour of foraging. The big brown batmay fill its stomach in about 1 hour(roughly 0.1 ounce per hour [2.7 g/hr])with prey including beetles, moths, fly-ing ants, true bugs, mayflies, caddisflies, and other insects. The nightlyconsumption of insects by a colony ofbats can be extremely large.

General Biology,Reproduction, andBehavior

Most North American bats emit highfrequency sounds (ultrasound) inau-dible to humans and similar to sonar,in order to avoid obstacles, locate andcapture insect prey, and to communi-cate. Bats also emit audible soundsthat may be used for communicationbetween them.

Bats generally mate in the fall and win-ter, but the female retains the sperm inthe uterus until spring, when ovulationand fertilization take place. Pregnantfemales may congregate in maternitycolonies in buildings, behind chim-neys, beneath bridges, in tree hollows,caves, mines, or other dark retreats.No nests are built. Births typicallyoccur from May through July. Youngbats grow rapidly and are able to flywithin 3 weeks. Weaning occurs inJuly and August, after which thenursery colonies disperse.

Bats prepare for winter around thetime of the first frost. Some species

migrate relatively short distances,whereas certain populations of theMexican free-tailed bat may migrateup to 1,000 miles (1,600 km). Bats inthe northern United States and Canadamay hibernate from Septemberthrough May. Hibernation for thesame species in the southern part oftheir range may be shorter or evensporadic. Some may fly during warmwinter spells (as big brown bats may inthe northeastern part of the UnitedStates). Bats often live more than 10years.

In response to a variety of humanactivities, direct and indirect, severalbat species in the United States havedeclined in number during the pastfew decades. Chemical pesticides (par-ticularly the use of persistent andbioaccumulating organic pesticides)have decreased the insect supply, andcontaminated insects ingested by batshave reduced bat populations. Manybats die when people disturb summermaternity roosts and winter hiber-nacula. Vandals and other irrespon-sible individuals may deliberately killbats in caves and other roosts. Eventhe activities of speleologists or biolo-gists may unintentionally disturbhibernating bats, which depletes fatreserves needed for hibernation.

Fig. 7. Common points of entry and roosting sites o

Modification and destruction of roostsites has also decreased bat numbers.Sealing and flooding of mineshafts andcaves and general quarrying opera-tions may inadvertently ruin bat har-borages. Forestry practices havereduced the number of hollow treesavailable. Some of the elimination ofnatural bat habitat may contribute tobats roosting in buildings.

Damage and DamageIdentification

Bat Presence

Bats often fly about swimming pools,from which they drink or catch insects.White light (with an ultraviolet com-ponent), commonly used for porchlights, building illumination, street andparking-lot lights, may attract flyinginsects, which in turn attract bats.Unfortunately, the mere presence of abat outdoors is sometimes beyond thetolerance of some uninformed people.Information is a good remedy for suchsituations.

Bats commonly enter buildingsthrough openings associated with theroof edge and valleys, eaves, apex ofthe gable, chimney, attic or roof vent,dormers, and siding (see Fig. 7). Other

f house bats.

openings may be found under loose-fitting doors, around windows, gapsaround various conduits (wiring,plumbing, air conditioning) that passthrough walls, and through utilityvents.

Bats are able to squeeze through nar-row slits and cracks. For purposes ofbat management, one should payattention to any gap of approximately1/4 x 1 1/2 inches (0.6 x 3.8 cm) or ahole 5/8 x 7/8 inch (1.6 x 2.2 cm). Suchopenings must be considered potentialentries for at least the smaller species,such as the little brown bat. Thesmaller species require an opening nowider than 3/8 inch (0.95 cm), that is, ahole the diameter of a US 10-cent coin(Greenhall 1982). Openings of thesedimensions are not uncommon inolder wood frame structures whereboards have shrunk, warped, or other-wise become loosened.

The discovery of one or two bats in ahouse is a frequent problem. In theNortheast, big brown bats probablyaccount for most sudden appearances(see Figs. 3 and 8). Common in urbanareas, they often enter homes throughopen windows or unscreened fire-places. If unused chimneys are selectedfor summer roosts, bats may fall orcrawl through the open damper intothe house. Sometimes bats may appearin a room, then disappear by crawlingunder a door to another room, hall-way, or closet. They may also disap-pear behind curtains, wall hangings,bookcases, under beds, into waste bas-kets, and so forth. Locating andremoving individual bats from livingquarters can be laborious but isimportant. If all else fails, wait untildusk when the bat may appear onceagain as it attempts to find an exit.Since big brown bats may hibernate inthe cooler recesses of heated buildings,they may suddenly appear (flyingindoors or outdoors) in midwinterduring a warm spell or a cold snap asthey move about to adjust to the tem-perature shift.

Roosting Sites

Bats use roosting niches that areindoors (human dwellings, outbuild-ings, livestock quarters, warehouses),

semi-enclosed (loading docks, entrancefoyers), partially sheltered (porches,carports, pavilions, highway under-passes, bridges), and open structuralareas (window shutters, signs). Oncethere, active bats in and on buildingscan have several economic and aes-thetic effects, often intertwined withpublic health issues (Frantz, 1988).Unusual roosting areas include wells,sewers, and graveyard crypts. Beforeconsidering control measures, verifythat bats are actually the cause of theproblem.

Rub Marks

Surface areas on walls, under loosewoodwork, between bricks andaround other bat entryways often havea smooth, polished appearance. Thestained area is slightly sticky, may con-tain a few bat hairs, and is yellow-brown to blackish brown in color. Thesmooth gloss of these rub marks is dueto oils from fur and other bodily secre-tions mixed with dust, deposited thereas many animals pass repeatedly for along period over the same surface.Openings marked in this way havebeen used heavily by bats.

Noise

Disturbing sounds may be heard fromvocalizations and grooming, scratch-ing, crawling, or climbing in attics,under eaves, behind walls, andbetween floors. Bats become particu-larly noisy on hot days in attics, beforeleaving the roost at dusk, and uponreturning at dawn. Note that rustlingsounds in chimneys may be caused bybirds or raccoons and scratching andthumping sounds in attics and behindwalls may indicate rats, mice, orsquirrels.

Guano and Urine

Fecal pellets indicate the presence ofanimals and are found on attic floors,in wall recesses, and outside the houseat its base. Fecal pellets along andinside walls may indicate the presenceof mice, rats, or even roaches. Sincemost house bats north of Mexico areinsectivorous, their droppings areeasily distinguished from those ofsmall rodents. Bat droppings tend to

be segmented, elongated, and friable.When crushed, they become powderyand reveal shiny bits of undigestedinsect remains. In contrast, mice andrat droppings tend to taper, areunsegmented, are harder and morefibrous, and do not become powderywhen crushed (unless extremely aged).

The droppings of some birds and liz-ards may occasionally be found alongwith those of bats. However, bat drop-pings never contain the white chalkymaterial characteristic of the feces ofthese other animals.

Bat excrement produces an unpleasantodor as it decomposes in attics, wallspaces, and other voids. The pungent,musty, acrid odor can often bedetected from outside a building con-taining a large or long-term colony.Similar odor problems occur when ani-mals die in inaccessible locations. Theodor also attracts arthropods whichmay later invade other areas of abuilding.

Bat guano may provide a growthmedium for microorganisms, some ofwhich are pathogenic (histoplasmosis,for example) to humans. Guano accu-mulations may fill spaces betweenwalls, floors, and ceilings. It may cre-ate a safety hazard on floors, steps,and ladders, and may even collapseceilings. Accumulations also result inthe staining of ceilings, soffits, and sid-ing, producing unsightly andunsanitary conditions.

Bats also urinate and defecate in flight,causing multiple spotting and stainingon sides of buildings, windows, patiofurniture, automobiles, and otherobjects at and near entry/exit holes orbeneath roosts. Bat excrement mayalso contaminate stored food, commer-cial products, and work surfaces.

Bat urine readily crystallizes at roomtemperature. In warm conditions un-der roofs exposed to sun and on chim-ney walls, the urine evaporates soquickly that it crystallizes in greataccumulations. Boards and beamssaturated with urine acquire a whitishpowderlike coating. With large num-bers of bats, thick and hard stalactitesand stalagmites of crystallized baturine are occasionally formed.

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Fig. 8. Profile of bat species submitted to the New York State Rabies Laboratory, 1981-1992.

Big Brown (R = 6.0%)

Little Brown (R = 1.0%)

Keen’s (R = 1.8%)

Red (R = 5.7%)

Hoary (R = 16.3%)

Silver-haired (R = 8.9%)

Other and Unknown (R = 2.5%)

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Number of Bats

Although the fresh urine of a single batis relatively odorless, that of any mod-erate-sized colony is obvious, and theodor increases during damp weather.Over a long period of time urine maycause mild wood deterioration (Frantzand Trimarchi 1984). As the urine satu-rates the surfaces of dry wood beamsand crystallizes, the wood fibersexpand and separate. These fibers thenare torn loose by the bats crawlingover such surfaces, resulting in woodfibers being mixed with guano accu-mulations underneath.

The close proximity of bat roosts tohuman living quarters can result inexcreta, animal dander, fragments ofarthropods, and various microorgan-isms entering air ducts as well as fall-ing onto the unfortunate residentsbelow. Such contaminants can result inairborne particles of public health sig-nificance (Frantz 1988).

Ectoparasites and otherArthropods

Several arthropods (fungivores, detri-tivores, predators, and bat ectopara-sites) are often associated with coloniesof bats in buildings. Their diversity de-pends on the number of bats, age andquantity of excreta deposits, and sea-son. Arthropods such as dermestidbeetles (Attagenus megatoma) contributeto the decomposition of guano and in-sect remnants, but may also become apest of stored goods and/or a nui-sance within the living quarters. Cock-roaches (for example, Blatta orientalis)attracted to guano may invade otherparts of a building. Bat bugs (Cimexspp.) are sometimes found crawling onthe surface of beams or around holesleading to secluded recesses used bybats. Bat ectoparasites (ticks, mites,fleas, and bugs) rarely attack humansor pets and quickly die in the absenceof bats. Ectoparasites may become anuisance, however, following exclu-sion of large numbers of bats from awell-established roost site. Area fumi-gation with a total release pyrethrum-based aerosol may be an appropriatesolution for arthropod knockdownwithin an enclosed space, but only af-ter bats have departed. For long-termarthropod control, lightly dust appro-

priate surfaces (affected attic beams,soffits) with boric acid powder or dia-tomaceous earth; carefully read allproduct labels before using any pesti-cide. Note that neither rabies norLyme disease is transmitted by anyarthropods associated with bats.

Public Health Issues

Rabies—General Epidemiology.Bats are distinct from most vertebratepests that inhabit human dwellings be-cause of the potential for transmittingrabies — a viral infection of mammalsthat is usually transmitted via the biteof an infected animal. Rabies does notrespond to antibiotic therapy and isnearly always fatal once symptomsoccur. However, because of the longincubation period (from 2 weeks tomany months), prompt vaccinationfollowing exposure can prevent thedisease in humans. Dogs, cats, andlivestock also can be protected byperiodic vaccinations.

Bats are not asymptomatic carriers ofrabies. After an incubation period of 2weeks to 6 months, they become illwith the disease for as long as 10 days.During this latter period, a rabid bat’sbehavior is generally not normal—itmay be found active during the day-time or on the ground incapable of fly-ing. Most human exposures are the

result of accidental or careless han-dling of grounded bats. Even less fre-quently, bats in this stage of illnessmay be involved in unprovokedattacks on people or pets (Brass, pers.commun.; Trimarchi et al. 1979). It isduring this stage that the rabid bat iscapable of transmitting the disease bybiting another mammal. As the diseaseprogresses the bat becomes increas-ingly paralyzed and dies as a result ofthe infection. The virus in the carcass isreported to remain infectious untildecomposition is well advanced.

Significance. Rabies is the mostimportant public health hazard associ-ated with bats. Infection with rabieshas been confirmed in all 40 NorthAmerican species of bats that havebeen adequately sampled in all of thecontiguous United States and in mostprovinces of Canada. Figure 8 showsthe frequency of bat species submittedfor rabies testing in New York Stateover the last 12 years. While not anationwide measure of humanencounters with bats, Figure 8 illus-trates that bat species are not encoun-tered equally. Note that bats submittedfor testing are often ill and/or easilycaptured. The numbers and speciesencountered will vary with the regionof the country; data are generallyavailable from local and state healthauthorities.

Random sampling of bats (healthy andill) indicates an overall infection rate ofless than 1%. Finding a rabid bat in acolony does not imply that the remain-ing animals are rabid. In fact, the prob-ability of immediately finding morethan one additional infected bat in thatcolony is small.

Bats rank third (behind raccoons andskunks) in incidence of wildlife rabiesin the United States (Krebs et al. 1992).In the last 20 years, however, therehave been more human rabies cases ofbat origin in the United States than ofany other wildlife group. Furthermore,the disease in bats is more widely dis-tributed (in all 48 contiguous states in1989) than in any other species. InCanada, bats also rank third (behindfoxes and skunks) in the incidence ofwildlife rabies. Therefore, every batbite or contact must be considered apotential exposure to rabies. Whileaerosol transmission of the rabies virusfrom bats in caves to humans andsome other mammals has beenreported, this is not a likely route ofinfection for humans entering batroosts in buildings in temperate NorthAmerica. Note that vampire bats arenot a threat north of Mexico.

Histoplasmosis—General Epidemi-ology. Histoplasmosis is a very com-mon lung disease of worldwidedistribution caused by a microscopicfungus, Histoplasma capsulatum.Histoplasma exists in nature as a sapro-phytic mold that grows in soil withhigh nitrogen content, generally associ-ated with the guano and debris ofbirds (particularly starlings, Sturnusvulgaris, and chickens) and bats. Windis probably the main agent of dis-persal, but the fungus can survive andbe transmitted from one site to anotherin the intestinal contents of bats, andalso in the dermal appendages of bothbats and birds. The disease can beacquired by the casual inhalation ofwindblown spores, but infections aremore likely to result from visits topoint sources of growth of the fungus.Relative to bats, such sources includebat roosts in caves, barns, attics, andbelfries, and soil enriched with batguano.

Numerous wild and domestic animalsare susceptible to histoplasmosis, butbats (and perhaps the armadillo) arethe only important animal vectors.Unlike bats, birds do not appear tobecome infected with the fungus. Boththe presence of guano and particularenvironmental conditions are neces-sary for H. capsulatum to proliferate. Inavian habitats, the organism appar-ently grows best where the guano is inlarge deposits, rotting and mixed withsoil rather than in nests or in freshdeposits. Specific requirements regard-ing bats have not been described,though bat roosts with long-terminfestation are often mentioned in theliterature.

While histoplasmosis in the UnitedStates is particularly endemic to theOhio-Mississippi Valley region (whichis also an area with the greatest star-ling concentration) and areas along theAppalachian Mountains, it is alsofound in the lake and river valleys ofother states. Outside areas with“appropriate” environmental condi-tions, there also occur scattered fociwith high infection rates usuallyassociated with caves inhabited bybats or birds.

Significance. When soil or guanocontaining H. capsulatum is physicallydisturbed, the spores become airborne.Persons at particular risk of histoplas-mosis of bat origin include spelunkers,bat biologists, pest control technicians,people who clean out or work in areaswhere bats have habitually roosted,and people in contact with guano-enriched soil — such as around thefoundation of a building where guanohas sifted down through the walls.

Infection occurs upon inhalation ofspores and can result in a variety ofclinical manifestations; severity par-tially depends on the quantity ofspores inhaled. The infection mayremain localized in the lungs where itmay resolve uneventfully; this is thecase for about 95% of the 500,000 infec-tions occurring annually in the UnitedStates. Such infections are identifiedonly by the presence of a positivehistoplasmin skin test and/or calcified

lesions on routine radiographs. Otherindividuals may have chronic or pro-gressive lung disease requiring treat-ment. Less severe forms of theseinfections may be accompanied byfever, cough, and generalized symp-toms similar to a prolonged influenza.Resolution of the disease confers adegree of immunity to reinfection. Inaddition, resolution confers varyingdegrees of hypersensitivity to H.capsulatum; as a consequence, massivereinfection in highly sensitized lungsmay result in a fatal acute allergicreaction.

In a small percentage of chronichistoplasmosis cases, the fungus dis-seminates to involve multiple organsystems and may be fatal. This form isusually seen in young children (1 yearor older) and in immunocompromisedadults. In recent years, systemic infec-tions have been increasing in fre-quency globally as an opportunisticinfection of AIDS patients.

Legal Status

The lethal control of bats, even whenthere is a proven potential danger tohumans, often is subjected to carefulscrutiny and interagency coordination.A survey of federal legislative actions,court decisions, and agency interpreta-tions concerning bats can be found inBat Management in the United States(Lera and Fortune 1979).

Some states have laws that specificallymention bats, either providing ordenying protection. Others have legis-lation that applies to bats only byinterpretation, since bats may be con-sidered nongame wildlife or indig-enous state mammals. Some bats haveprotection as either federal or state-listed endangered species, but thesame state may not protect other spe-cies of bats. Enforcement and publiceducation must accompany legislationto accomplish the intended goal ofprotecting the public and savingendangered bats. Familiarity with theappropriate federal and state lawsshould precede any nuisance manage-ment activities.

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Damage Prevention andControl Methods

Premanagement Considerations

Bat Watch for Infestation Confir-mation. To confirm that bats are actu-ally roosting in or on a building, lookfor bats flying in and out of a site and/or for signs of infestation. A bat watchcan be conducted by two people (moremay be necessary to observe large orcomplex sites) posted at opposite cor-ners of a structure. An evening watchbegins about 30 minutes before darkand a morning watch begins about 1hour before dawn. Observationsshould continue for approximately 1hour.

Such observations can indicate exit/entry points and the number of bats.With practice, distinguishing some batspecies may also be possible. Forexample, compared to the big brownbat, the little brown bat is noticeablysmaller in size, and its flight has morerapid wing beats, and more rapidturning and darting.

It may be necessary to watch for morethan one night to compensate forweather conditions, bats’ sensitivity toobservers, noisy or inexperienced ob-servers, and improper use of light. Ob-servations can be enhanced with astandard flashlight, but be certain tokeep the bright part of the beam as faras possible away from the exit hole be-ing observed. Bright light will increasebats’ reluctance to exit and may resultin an incomplete exit of the colony. Avaluable observation aid is a powerful,rechargeable flashlight equipped witha plastic, red pop-off filter (similar tothe Kodak Wratten 89B). Also, an elec-tric headlamp, supplied with recharge-able batteries and fitted to a climbingor spelunking helmet, allows hands-offillumination outdoors as well as in-doors when exploring roost locations.Bats are sensitive to light intensity andcan visually discriminate shapes andpatterns in extremely low light situa-tions. They can only see in black andwhite; hence, the low-contrast illumi-nation and soft shadows produced byred light has little effect on bats.

Locating the Roost(s). It is notalways possible or convenient to con-duct a bat watch. Thus, a detailed in-spection inside the building for bats orbat sign may be necessary to findspecific roosts. Daytime is best, espe-cially during the warmer part of theday. Bats roost in the most variedkinds of buildings and in every partfrom cellar to attic. Some types ofbuildings appear preferable (olderhouses, churches, barns, proximity towater) as do certain roost locationstherein, especially areas with little dis-turbance, low illumination, little air cir-culation, and high temperatures. Oftenit is easy to locate bats, especially inwarm weather in attics or lofts, wherethey may hang in clusters or side-by-side from the sloping roof lath, beams,and so forth. However, bats have theability to find crevices and cavities,and if disturbed may rapidly disap-pear into the angles between converg-ing beams, behind such beams orwallboards, into mortise holes on theunderside of beams, and into the mul-tilayered wall and roof fabrications. Ifbats cannot be openly observed, usu-ally there are various interior and exte-rior signs of their presence. Often thereare multiple roost sites within or on asingle building.

Problem Assessment. Once it hasbeen confirmed that bats are present,one must determine if there is damage,if there is a health risk, and if someintervention is warranted. There arecircumstances in which “no action” isthe correct action because of the bene-ficial role of bats. In cases where thereis risk of contact, damage from excretaaccumulations, stains, and so on, inter-vention may be necessary.

Timing. With the exception of diseasetreatment and removal of the occa-sional bat intruder, timing becomes animportant planning consideration.Management procedures must notcomplicate an already existing prob-lem and should emphasize bat conser-vation. Therefore, all interventionsshould be initiated before the youngare born or after they are weaned andable to fly. Thus, the annual opportu-nity extends from about mid-Augustto mid-May for much of North

America. Treatments might otherwiseresult in the unnecessary death of ani-mals (especially young unable to fly)trapped inside, offensive odors, andattraction of arthropod scavengers.

Disease Considerations

Rabies — Preventive Measures. Itshould be noted that newspapers, tele-vision, and other mass media some-times misrepresent the role of rabidbats as a risk to humans. However, theunfortunate recent (1983 to 1993)deaths of a 22-year-old man in Texas, a30-year-old bat scientist in Finland, auniversity student in British Columbia,a 5-year-old girl in Michigan, a man inArkansas, an 11-year-old girl in NewYork, and a woman in Georgia amplyunderscore the need to pay promptattention to bat bites and otherexposures.

Many rabies exposures could beavoided if people simply refrainedfrom handling bats. Adults and chil-dren should be strongly cautionednever to touch bats with bare hands.All necessary measures should betaken to ensure that bats cannot enterliving quarters in houses and apart-ments. Pet cats and dogs should bekept up-to-date in rabies vaccinations.This is also true for pets confinedindoors, because contact with bats fre-quently occurs indoors. Valuable live-stock also should be vaccinated if keptin buildings harboring bats or if in arabies outbreak area (NASPHV 1993).While transmission of rabies from batsto terrestrial mammals apparently isnot common, such incidents have beenreported (Reid-Sanden et al. 1990,Trimarchi 1987). Dogs, cats, and live-stock that have been exposed to arabid or suspected-rabid animal, butare not currently vaccinated, must beeither quarantined or destroyed.

Lastly, pest control technicians, nui-sance wildlife control personnel, wild-life biologists, and other individuals atparticular risk of contact with rabidbats (or other wildlife) should receive arabies pre-exposure vaccination. Thiseffective prophylaxis involves onlythree injections of rabies vaccine,which are administered in the armduring a month’s time.

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

Rabies — Treatment for Expo-sure. If a person is bitten or scratchedby a bat, or there is any suspicion thatbat saliva or nervous tissue has con-taminated an open wound or mucousmembrane, wash the affected areathoroughly with soap and water, cap-ture the bat without damaging thehead, and seek immediate medicalattention. The incident should bereported promptly to local healthauthorities in order to arrange rabiestesting of the bat.

If the bat is captured and immediatetransportation to the testing laboratoryis possible, and if immediate testingcan be arranged, postexposure treat-ment may be delayed several hoursuntil the test results are known.Postexposure prophylaxis must beadministered immediately, however, ifthe bat cannot be captured, if prompttransportation to the laboratory is notpossible, if the specimen is not suitablefor reliable diagnosis, or if the testresults prove positive for rabies.

The prophylaxis has little resemblanceto that of many years ago. Today, itconsists of one dose of rabies immuneglobulin (human origin) and one doseof rabies vaccine (human diploid cell)administered preferably on the day ofexposure, followed by additionalsingle doses of rabies vaccine on days3, 7, 14, and 28 following the initialinjection. This treatment is normallysafe, relatively painless, and veryeffective.

Histoplasmosis — PreventiveMeasures. Histoplasmosis can mosteasily be prevented by avoiding areasthat harbor H. capsulatum. Since this isnot practical for individuals who mustwork in and around active/inactivebat roosting sites, other measures canbe recommended to reduce the risk ofinfection during cleaning, field study,demolition, construction, and otheractivities.

Persons working in areas known orsuspected to be contaminated with H.capsulatum should always wear protec-tive masks capable of filtering out par-ticles as small as 2 microns in diameteror use a self-contained breathing appa-ratus. In areas known to be contami-

nated, wear protective clothing andgloves that can be removed at the siteand placed in a plastic bag for later de-contamination via formalin and wash-ing. Also, clean footwear beforeleaving the site to prevent spore dis-semination in cars, the office, at home,and elsewhere.

Guano deposits and guano-enrichedsoils should not be unnecessarily dis-turbed. Dampening with water orscheduling outdoor work at a timewhen the ground is relatively wet willminimize airborne dust. Chemicallydecontaminate known infective fociwith a spray of 3% formalin (see CDC1977). To protect the environment,decontamination must be conductedin accordance with state and localregulations. Chemical decontamina-tion of an “active” bat roost should beconducted only after the bats havebeen excluded or after bats havedeparted for hibernation.

Histoplasmosis — Treatment.Most infections in normally healthyindividuals are benign and self-limit-ing and do not require specific therapy(George and Penn 1986; Rippon 1988).Treatment with an antifungal agentmay be prescribed in more severecases; amphotericin B and/or oralimidazole ketoconazole are typicallyrecommended depending on the spe-cific nature of the infection.

Removal of Occasional BatIntruders

A bat that has blundered into the liv-ing quarters of a house will usuallyfind its way out by detecting air move-ment. When no bite or contact withpeople or pets has occurred, the sim-plest solution for “removing” the bat isto try to confine it to one room, thenopen windows and doors leading out-doors and allow it to escape. If the batis present at night, the lights should bedimmed to allow the animal to findopen doors and windows; some lightis necessary if an observer is to insurethat the bat finds its way out. If brightlights are kept on, the bat may becomeconfused and may seek refuge behindshelving, curtains, hanging pictures, orunder furniture.

Healthy bats normally will not attackpeople even when chased. Chasing aflying bat with a folded newspaper,tennis racket, or stick will cause the batto take evasive action, and a bat’sflight reversal to avoid a wall is oftenmisinterpreted as an attack. Theseflailings, often futile, will cause a bat toseek safety wherever possible, makingescape more difficult for the bat andmore frustrating for the human.

If the bat has difficulty escaping, it canbe captured in a hand net (for exam-ple, an insect net [Fig. 9]). Otherwise,

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Fig. 10. Using a clothes hanger/plastic film com-bination to detect air leaks.

Fig. 11. Smoke from the Sensidyne Air Indicator makes it possible to visually determine the direc-tional pattern of air currents.

wait for it to come to rest, quicklycover it with a coffee can or similarcontainer, and slide a piece of card-board or magazine under the can totrap the bat inside (NYSDH 1990).Take the captured bat outdoors andrelease it away from populated areas,preferably after dark. Note thatreasonably thick work gloves shouldbe worn at all times when trying tocapture a bat. Also, if a bite or physicalcontact occurs, capture the bat withoutdamaging its head and immediatelycontact a physician (see previoussection regarding rabies treatment).Management of problems involvingbat colonies require more complicatedprocedures and a greater time commit-ment.

Exclusion

Preventive Aspects. The most satis-factory and permanent method ofmanaging nuisance bats is to excludethem from buildings. Locate bats andtheir points of exit/entry through batwatches or other inspection methods.This is a tedious process to locate allopenings in use, and bats may switchto alternate ones when normal routesbecome unavailable. Thus, consider“potential” as well as “active” pointsof access.

Often it is apparent where bats mightgain entrance even when such open-ings are not directly observable. Bystanding in various locations of a dark-ened attic during daylight hours, oneoften can find leaks of light at theextreme parts of eaves, in layers ofsubroofing, and below chimneyflashings. Seal all gaps of 1/4 x 1 1/2inches (0.6 x 3.8 cm) and openings 5/8x 7/8 inch (1.6 x 2.2 cm) or greater.

Bats will also use some of the sameobscure holes in buildings throughwhich heat (or cooled air) is lost; thus,bat-proofing often conserves energy.Simple, homemade devices can beused to locate air leaks. Bathroom tis-sue or very thin plastic film bags canbe taped to a clothes hanger. Whenplaced in front of an area with an airleak (for example, around windowframes and sashes where caulking orweatherstripping are needed), the tis-

8

sue or plastic will wave and flutterfrom air movements (Fig. 10). Indoorair leaks can be found easily by the useof an air flow indicator (Fig. 11). Small-volume smoke generators can be usedto locate openings in the floor, ceiling,attic, and basement. Obscure openingsalso may be located from outside thehouse by activating smoke candles orsmoke bombs (as within an attic),which will produce easily observeddense smoke. Be careful of any firehazards.

The easiest time to seal bats out ofbuildings in northern latitudes is dur-ing the cooler part of the year whencolonies are not resident. During thisperiod, many homeowners need to bereminded that bats, and bat problems,return each summer. Basic carpentry,masonry, and tinsmith skills are valu-able in bat exclusion and otherpestproofing interventions.

Devices and Methods. Exclusionbecomes “denial of reentry” once thebats have returned to establish mater-nity colonies (and before the young areborn), usually from April throughmid-May in the Northeast. Denial ofreentry is also appropriate anytimeafter mid-August when young arecapable of flying, as long as bats con-tinue to utilize the roost.

The traditional way to exclude batsfrom an occupied roost involves fivebasic steps: (1) identify and close all in-door openings through which batsmight gain access to human livingquarters; (2) close most confirmed andall unused potential exterior exits,leaving only a few major openings (it’sbest to complete this within 1 to 2days); (3) at night shortly after the bats

Fig. 12. Bat on birdnetting showing size relationships.

have departed to feed, temporarilyclose the few remaining, major exits;(4) check the roost for presence of batsand, if any remain, unplug the tempo-rarily closed exits early the nextevening to allow the bats to escape,then temporarily replug the exits (itmay be necessary to repeat this stepmore than once); and (5) when the batsare all out, permanently seal the holes(Frantz and Trimarchi 1984, Greenhall1982).

Patience and timing are very impor-tant in this process. Much of this workcan be done during daylight hoursexcept steps 3 and 4, which requireclimbing on ladders and roofs at night,sometimes with bats flying nearby.The danger of such work is obviousand discouraging.

Some of these difficulties have beenovercome by use of the Constantineone-way valvelike device which isinstalled in the last exit(s) during theday, and permits bats to leave afterdark but prevents their reentry (Con-stantine 1982). Eventually the valveshould be removed and the hole(s)sealed. Another device, the EX-100Hanks Bat Excluder, consists of a pieceof nylon window screening, a woodenplate with a hole in the middle towhich is attached a one-way plasticflappervalve, and a rigid plastic meshcone (Anon. 1983). The screening, towhich the wooden plate is attached, isused to cover an opening that bats useto exit a building. Both devices aredesigned to be used on the last fewexit points. Installation instructions areavailable, and properly applied theywill undoubtedly exclude bats fromrelatively small, discrete openings.

The devices of Constantine and Hanksinvolve a one-way, self-closing valvefeature and can be readily installedduring daylight hours. Such devicesare not readily adaptable to situationswith large, diffuse and/or widely dis-tributed entryways. Also, bats can beinadvertently trapped inside if animportant exit hole is mistakenly iden-tified as a minor one and is sealed inan attempt to limit the number of holesrequiring an exclusion device.

To overcome difficulties with exclus-ion devices, Frantz’ checkvalve wasdeveloped using netting made ofdurable black polypropylene resin(Frantz 1984, 1986). Quality of productis important since the netting shouldnot fray or become misshapen underhot summer conditions. Use onlystructural grade material that hasopenings no larger than 1/2 x 1/2 inch(1.3 x 1.3 cm), weighs about 1.3 ouncesper square yard (44 g/m2) and is flex-ible yet stiff enough to maintain theshape of the checkvalve fabricated(Fig. 12). Waterproof duct tape, com-mon staples, and/or wooden lathstrips are used to attach the netting tometal, slate, brick, wood, asphaltshingle, or other surfaces. Note thatduct tape may stain or discolorpainted/enameled surfaces if kept incontact for long periods of time.

Application of checkvalves follows thesame two initial steps as traditional batexclusion. Close interior openings,then close exterior openings except afew major exits. These latter openingswill have been confirmed as importantvia bat watches, and it is here thatcheckvalves will be fitted during thedaylight.

The basic design is to attach the nettingaround an exit hole except at the bot-tom where the bats will escape (seeFrantz 1986, for details). The widthand shape of checkvalves is highlyvariable so as to embrace the necessary

exit point — a single hole, a series ofholes, or a long slitlike opening (Fig.13). Designs must be open enough notto impede the exiting bats. The top canbe much larger than the bottom. It isprobably best to restrict the bottomopening to no larger than about 1.6 x1.6 feet (0.5 x 0.5 m). The length of acheckvalve, that is, the distance fromthe lowest enclosed point of egress tothe bottom of the netting, should beabout 3.3 feet (1 m).

The above specifications usually aresufficient to abort bats’ reentry at-tempts. If netting is applied whileyoung are still in the roost, the“evicted” mothers may be motivatedto chew holes in the netting to reenterthe roost. Applied at the correct timeof year, however, netting will allow allbats to exit at dusk and thereafter denythem reentry.

Checkvalves should be kept in placefor 3 to 5 days. It is best to verify (con-duct a bat watch) that bats no longerexit at dusk before the checkvalves aredismantled and the holes are sealedpermanently. As in any exclusionintervention, the excluded animals willgo elsewhere. This shift may be to analternative roost already in use such asa night roost, or one used in previousyears.

Supplemental Materials andMethods. While specifications forFrantz’ checkvalve have been

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Sleeve design for bat-proofingfascia board/clapboard inter-face (without roof overhang).

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

Skirt design for bat-proofing ridge cap oftin or tile roof.

Open-bottomed box designs for bat-proofingroof apex, roof corner, and soffit/wall interface.

provided, additional caulking,flashing, screening, and insulationmaterials often are needed. Thecombination of materials used willdepend on the location, size, andnumber of openings, and the need forventilation. Greenhall (1982) providesmany details of bat-proofing methodsand materials and is a practical guide.Weatherstripping, knitted wire mesh(Guard-All®, Stuf-fit®), waterproofduct tape, stainless steel wool, andwood lath may be used to block long,narrow openings. Caulk-ingcompounds will seal cracks and

crevices that develop in a house as itages, and are best applied during dryperiods when wood cracks are widest.Caulks that may be applied with acaulking gun (in gaps up to about 0.4inch [1 cm] wide) include latex, butyl,and acrylic, which last about 5 years.Elastomeric caulks, such as siliconerubber, will last indefinitely, expandand contract, do not dry or crack, andtolerate temperature extremes. Oakumpacks easily and firmly into smallcracks. Other fillers include spongerubber, glass fiber, knitted wire mesh,and quick-setting putty. Self-

expanding polyurethane foam appliedfrom pressurized containers can beused for openings larger than 3 inches(>7.5 cm). It must be applied withcaution so as to not lift clapboards,shingles, and other surfaces. Exposedsurfaces should be sealed with epoxypaint to prevent insect infestation andultraviolet degradation.

Conventional draft sweeps (metal,rubber) and other weatherstrippingsupplies (felt, vinyl, metal) will seal thespace between a door bottom and thethreshold or around windows (Fig.14). Remember to treat attic and base-ment doors whenever the gap exceeds1/4 inch (0.6 cm). Flashing may beused to close gaps wherever jointsoccur; for example, where the roofmeets a chimney. Materials commonlyused include galvanized metal, copper,aluminum, and stainless steel. Self-adhesive stainless steel “tape” is alsoavailable. Insulation will provide somedegree of barrier to bat movements. Itis available in a number of forms andtypes including fiberglass, rock wool,urethane, vermiculite, polystyrene,and extruded polystyrene foam. Inor-ganic materials are fire and moistureresistant; the safest appear to be fiber-glass and rock wool.

The mesh size of screening must besmall enough to prevent access of batsand 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 (2.5cm) will exclude most insects. Soffits(underside of overhanging eaves) usu-ally have ventilators of various shapesand sizes. Regardless of type, the slotsshould not exceed 1/4 x 1 inch (0.6 cmx 2.5 cm) and should be covered insidewith insect mesh. To prevent bats fromentering chimney flues, completelyenclose the flue discharge area withrust-resistant spark arresters or pestscreens, secured to the top of thechimney. These should not be perma-nently attached (for example, withscrews) in case they must be rapidlyremoved in the event of a chimneyfire. Review fire codes before installingflue covers. Dampers should be keptclosed except in the heating season.

Rolled vinyl Adhesive-backed foam rubber

Outside Inside

Window sash

Windowsill

Ouside Inside

Window sash

Windowsill

Inside

Doorjamb

Door

Outside

Inside

Doorjamb

Door

Outside

Door sweepfitted to bottomof door

Inside

Rubber orplastic gasketfitted tobottom ofdoor

Outside

Rubber or plasticgasket fitted tometal doorsill

Inside

Interlockingmetal doorsilland door shoe

Inside

Fig. 14. Weatherstripping and door sweeps are very useful bat-proofing measures.

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

Roof Problems. Bats, particularly theMexican free-tailed bat, often roost un-der Spanish or concrete tile roofing byentering the open ends at the lower-most row or where the tiles overlap(Fig. 15). Tight-fitting plugs are diffi-cult to make due to the variation inopening sizes and thermal expansionand contraction. A solution was foundby Constantine (1979) in which a layerof coarse fiberglass batting was laidunder the tiles so that bats enteringholes would contact the fiberglass andbe repelled. A layer of knitted wiremesh would undoubtedly work wellfor this purpose (and would not holdmoisture). Bats also may be excludedfrom the tiles if rain gutters areinstalled directly under the open ends.Gaps under corrugated and galva-nized roofing may be closed with knit-ted wire mesh, self-expanding foam(avoid causing roofing to lift), or withfiberglass batting (may retain mois-ture).

Wall Problems. Fiberglass or rockwool insulation blown into wall spacesthat are used by bats may be a deter-rent, especially when it forms a physi-cal barrier to passage. Such work mustbe done when bats are absent to avoidtheir entrapment.

Temporary Roosts. Bats will some-times temporarily roost on porchesand patios, in garages, and behindshutters, shingles, and roof gutters.Roosting behind shutters may also belong-term in duration. Actual controlmeasures may not be necessary unlessbat droppings become a problem orthe risk of human contact is significant.Coarse fiberglass batting tacked to thesurfaces where bats prefer to hangsometimes discourages them. A poten-tially useful intervention for the wall-ceiling interface is the application of awide 45o molding strip to eliminate the90o angle corner and force the bats toroost in a more exposed area.

Repellents

While many chemical aromatics andirritants have been proposed andtested for bat repellency, efficacy hasbeen very limited thus far.

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Naphthalene crystals and flakes arethe only repellents registered by theUS Environmental Protection Agency(EPA) for indoor bat control and are tobe applied in attics or between walls.Sometimes the chemical may be placedin loose-mesh cloth bags and sus-pended from the rafters. About 2.5pounds per 1,000 cubic feet (1.2 kg/30m3) is recommended to chronically re-pel bats as the chemical vaporizes.Dosages of 5 pounds per 1,000 cubicfeet (2.4 kg/30 m3) may dislodge batsin broad daylight. Bats will return,however, when the odor dissipates.The prolonged inhalation of naphtha-lene vapors may be hazardous tohuman health.

Illumination has been reported to bean effective repellent. Floodlightsstrung through an attic to illuminateall roosting sites may cause bats toleave. Large attics may require many100-watt bulbs or 150-watt spotlightsto be effective. Fluorescent bulbs mayalso be used. In some situations suchlighting is difficult, costly, and mayresult in an electrical hazard. Wherepossible, the addition of windows tobrighten an attic will help to reducethe desirability of the roost site and isnot likely to introduce additionalproblems.

Air drafts have successfully repelledbats in areas where it is possible toopen doors, windows, or create strongbreezes by use of electric fans. Addi-tion of wall and roof vents willenhance this effort, as well as lowerroost temperature. These measureswill increase the thermoregulatoryburden on the bats, thus making theroost less desirable. In a similar fash-ion, colonies located in soffits, behindcornices, and other closed-in areas canbe discouraged by opening these areasto eliminate dark recesses. Discouragebats from roosting behind shutters byremoving the shutters completely orby adding small blocks at the cornersto space them a few inches away fromthe wall.

Ultrasonic devices have been testedunder natural conditions, both indoorsand outdoors, to repel little brown andbig brown bats either in the roost or as

they fly toward an entrance hole(Frantz, unpublished data). The resultshave not been promising. Numerousultrasonic devices have been removedfrom clients’ homes because the batsremained in the roost after the deviceswere activated. Hurley and Fenton(1980) exposed little brown bats to ul-trasound in seminatural roosts withvirtually no effect. Largely because ofthis lack of known scientific efficacyfor ultrasonic devices, the New YorkState Consumer Protection Board hascautioned against the use of suchdevices (NYSCPB 1988). Part of theconcern is that such devices will pro-vide consumers with a false sense ofsecurity and, thus, may prevent themfrom taking effective preventiveactions.

Distress cries of bats recorded on tapeand rebroadcast can be used to attractother bats to nets or traps, but they donot serve as an effective repellent.Little brown and big brown batsrespond to their own distress cries butnot to the cries of other species.

Contact repellents, such as sticky-typebird repellents and rodent glues, havebeen used successfully in situationswhere roost surfaces and bat accessesmay be coated. Apply masking tape tothe surface first if you desire to removethe repellent after treatment is fin-ished. Replenish contact repellentsoccasionally, since dust accumulationcauses them to lose their tackiness.Also, caution must be exercised so asto apply coatings that will be sticky,but will not entrap the bats.

Toxicants (not recommended)

No toxicants are registered for control-ling bats. In 1987 the Centers forDisease Control, United States Depart-ment of Health and Human Services,voluntarily withdrew the last registra-tion for DDT use against bats in theUnited States. Thus, DDT is no longerregistered for any use in this country.

Although federally registered forrodents, chlorophacinone (RoZol )tracking powder, an anticoagulant, isnot registered for bats. Furthermore, itcan no longer be registered by indi-vidual states for restricted use under

Section 24(c) of the Federal Insecticide,Fungicide, and Rodenticide Act D-18(FIFRA). Lipha Tech, Inc. (the manu-facturer of RoZol ) has voluntarily can-celled its registration for “RoZolTracking Powder for Control of Nui-sance Bats” — effective December 16,1991 (Fed. Reg., 1991).

Trapping

Kunz and Kurta (1988) reviewed anextensive variety of efficient methodsfor trapping bats from buildings andother roosting sites or foraging areas.For purposes of wildlife damagecontrol, however, exclusion is lesscomplicated to carry out, less time-consuming, more effective, andrequires no handling of bats.

Other Methods

Sanitation and Cleanup. Once batshave been excluded, repelled, or havedeparted at the end of the summer,measures must be completed to makereinfestation less likely, and toeliminate odor and problematicbioaerosols. As a prelude to suchwork, it is sometimes useful to apply apyrethrum-based, total-release aerosolinsecticide to eliminate unwantedarthropods.

The safe handling and removal of batguano has been discussed previously(see the histoplasmosis section in thischapter). In addition to the more bulkyaccumulations of excreta, there areoften diffuse deposits of guano under/among insulation materials, cakedurine and guano on roof beams, andsplattered urine on windows. Suchclean-up work during hot summerweather may be the least desirableactivity of a management program, butit is necessary.

All caked, crystallized bat urine anddroppings should be scraped andwire-brushed, as necessary, from allroof and attic beams. For this proce-dure, workers should take the sameprecautions as outlined for histoplas-mosis-related work. Accumulatedexcreta and contaminated insulationshould be sealed in plastic bags andremoved for disposal. Remove allremaining droppings and debris with

Fig. 16. One of five bat houses constructed to provide an alternative roost for bats excluded fromnearby structures.

a vacuum cleaner, preferably one thathas a water filter to reduce the amountof dust that escapes from the cleaner’sexhaust.

Where possible, wash with soap andwater all surfaces contaminated withurine and guano. Allow the surfaces todry, then disinfect them by misting orswabbing on a solution of 1 parthousehold bleach and 20 parts tapwater. Ventilate the roost site to allowodors and moisture to escape. Installa-tion of tight-fitting window screens,roof and/or wall ventilators in atticswill enhance this process. Remember,sanitation and cleanup accompaniesbat-proofing and exclusion measures,it does not replace them.

Artificial Roosts. For more than 60years, artificial bat roosts have beenused in Europe. Only recently havethey gained some popularity in theUnited States. Though the results arevariable, it appears that artificialroosts, if properly constructed andlocated, can attract bats that are dis-placed or excluded from a structure.The Missouri Department of Conser-vation described a successful “bat ref-uge” that was quickly occupied by adisplaced colony of little brown bats(LaVal and LaVal 1980). Bat houses ofa similar design have been successfullyused in Minnesota, New York, andelsewhere (see Fig. 16).

Development of an efficient method torelocate bats into alternative roostsafter they have been excluded frombuildings could be an important inter-vention in comprehensive bat manage-ment. Frantz (1989) found it helpful to“seed” newly constructed bat houseswith several bats, a procedure thatlater resulted in full-scale colonizationwithout further human interventions.Alternative roosts should be locatedaway from human high-use areas.Thus, people can enjoy the benefits ofbats without sharing their dwellingswith them and with little risk of directcontact with them.

Economics of Damageand Control

Virtually all bats are of some economicimportance; those north of Mexico arebeneficial because of their insectivo-rous diet which eliminates many insectpests of humans. The accumulated batdroppings, called guano, is rich innitrogen and is a good organic fertil-izer. At one time, bat guano was com-mercially mined in the Southwest; butits importance has declined due toreduced bat populations and thedevelopment of inorganic fertilizers.Bat guano is still considered a valuablefertilizer resource in some parts of theworld (such as Thailand and Mexico).

No figures are available to determinethe extent of damage caused by nui-sance bats or the cost for their control.The problem is widespread in this andother countries.

Costs for remedial services are highlyvariable, depending on the nature ofthe problem and who will do thework. For example, to fabricate a fewFrantz’ checkvalves on the “average”two-story house would probablyrequire two workers about one-halfday, mostly on stepladders, and lessthan $50 in materials. Much more timewould be required to seal up all theother active and potential bat exit/entry holes. In addition, if a deterio-rated roof, eaves, or other woodworkmust be replaced, the costs canincrease rapidly.

It is often difficult or expensive for thepublic to obtain the services of reliable,licensed pest control operators (PCOs).Many PCOs have limited knowledgeof basic bat biology and are apprehen-sive to work with bats. They may wantto avoid any liabilities should bat-human contact occur. Select a qualifiedprofessional service that concentrateson the exclusion of live bats from astructure rather than on use of lethalchemicals.

Acknowledgments

The authors wish to thank the many people whohave allowed them and other bat researchers towork in and about their homes, and have, thus,contributed to this effort. We give special thanksto Roger W. Barbour and Wayne H. Davis forpermission to reproduce figures from theirexcellent book, Bats of America (University Pressof Kentucky). Charles V. Trimarchi isacknowledged for carefully reviewing thischapter and providing many useful comments.We thank Debra VonZwehl and ChristineBorecki for processing the manuscript.

Figures 2 through 4 from Barbour and Davis(1979).

Figure 5 adapted from Harvey (1986).

Figure 6 adapted from Tuttle (1988), except Yumamyotis and Keen’s bat (from Barbour and Davis1979).

Figure 7 adapted from Trimarchi and Frantz (1985).

Figure 8 by R. Suss.

Figures 12, 15, and 16 by S. C. Frantz.

Figures 9, 10, 11, and 14 from Greenhall (1982)

Figure 13 by S. C. Frantz

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EditorsScott E. HygnstromRobert M. TimmGary E. Larson

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