184TheRehabilitationandCaptiveCareofInsectivorousBatsThe Rehabilitation and Captive Care of Insectivorous Bats184

CHAPTERTHIRTEEN HIBERNATION,RELEASEANDEUTHANASIA

Hibernation  Duringthewinterinsomepartsoftheworld,ambienttemperaturesdropsignificantlyandadequatefood(i.e., insects)isnotavailableforanextendedperiodoftime.SomespeciesofbatssimplymigratetowarmercliͲ mateswherefoodisavailable.Otherspeciesadapttotemperateconditionsbyenteringhibernation,aphysioͲ logicalstateinwhichmetabolicactivityisdecreasedtominimalsurvivallevels.ManybatsdecreaseenergydeͲ mandsbyenteringadailystateofinactivitycalledtorpor.Byallowingbodytemperaturestoapproximatethe ambienttemperature,theyareabletodecreaseenergydemand.Heartratesofbatsindailytorpormaydrop to40Ͳ80beatsperminute,whileratesaslowas10beatsperminutehavebeenrecordedinsomebatsduring winterhibernationThisisasignificantdecreaseasheartratesof250to450beatsperminutehavebeenreͲ cordedforsomebatsatrest,whileratesinflyingbatscanreach1000beatsperminute.Alittlebrownbat(M. lucifugus)hasadailyenergybudgetof0.89Kcal/g/daywhichmeansthata7glittlebrownbatrequires6.23kcal (6230calories)perday(HillandSmith1984).Becausesmallermammals(suchasbats)havegreatersurfaceͲ areaͲtoͲvolumeratiosthanlargerones,theyrequiremorecaloriespergramofbodyweighttomaintaintherͲ malhomeostasis.  ManyofthebatsofthefamilyVespertilionidaeintheUnitedStatesandCanadaenterhibernationduringwinͲ termonths.Somespeciesmigrateshortdistancestospecifichibernationsitesincavesorabandonedmines wheretemperaturesremainrelativelyconstant.OthersstayinthesamelocationyearroundwhenthetemͲ peraturesdrop.Bigbrownbats(E.fuscus),aspeciesthatcommonlyroostintheatticsofhomes,sometimes hibernatetherethroughoutthewintermonths.  Somebatspecieshibernateintightlypackedclusters.Byclusteringwithoneanothertheyarebetterableto stabilizebodytemperaturesagainstpotentialenvironmentalfluctuations.Otherspecieshibernatesinglyorin smallgroups.Whenambienttemperaturesriseinthespring,hibernatingbatsarouse.Thereisanincreasein boththeheartrateandtherespiratoryrate,andasubsequentincreaseinbodytemperature.Differentspecies ofbatsarousefromhibernationstatesatdifferentrates,soitwilltakesomebatslongertowarmupthanothͲ ers.  Ifawakenedfromhibernation,batsexperienceanincreaseinmetabolicactivity,usingupstoredfatneededto survivetheremainderofthewinter.Althoughhibernatingbatsmayarouseduringwinter,eacharousalleadsto theexpenditureofalmost30daysofbodyfat.HibernatingbatsarethereforeextremelysensitivetodisturͲ bances.Inaddition,becausesomespeciesofbatscomefrommultiͲstateregionsandcongregateingreatnumͲ bers(asmanyastensorevenhundredsofthousandsofindividuals)atasmallnumberofhibernationsites, disruptionanddisturbancesofanykindcanresultinthelossoflargenumbersofbatsimportanttotheagriculͲ turalinterestsoffarmersfarfromthesite.  Somespeciesofbatsmakelongmigrationswhencolderweatherarrives.Thehoarybat(L.cinereus),thered bat(L.borealis),andthesilverͲhairedbat(L.noctivagans)canbefoundasfarnorthasCanadainthesummer butareknowntomakelongmigrationstothesouthernUnitedStatesandMexicointhewinter.Somespecies, suchasthoseinthefamilyMolossidae,arenotabletotoleratecoldtemperaturesforextendedperiodsoftime andmigratetowarmerclimatesduringcoldmonths.IntheUnitedStates,southwesternpopulationsofMexiͲ canfreeͲtailedbatsmakelongmigrationstopartsofMexicowheretheyspendthewinter.AsubͲspeciesofthe BrazilianfreeͲtailedbatremainsinwarmerpartsofthesoutheasternUnitedStatesyearround.Althoughthe Molossidaearenottruehibernators,theyarecapableofenteringdailytorpor.SeeRoostingandHibernating Patternsonpage5foradditionalspeciesinformation.

TheTheRehabilitation Rehabilitationand andCaptive CaptiveCare Careof ofInsectivorous InsectivorousBats Bats 185

 Artificialhibernationallowsabusyrehabilitatortheluxuryofminimizingthetimeneededtocareforhealthy batsthatmustremainincaptivityforseveralmonthsbeforerelease.IfacaretakerreceivesdozensofbatsdisͲ turbedduringhibernation,artificialhibernationallowstheopportunitytomaintainallofthebatsforthereͲ mainderofthewinter,somethingthatmightnotbepossibleifeachindividualrequireddailycare.Hibernation incaptivitydoesnotappeartobenecessaryforthesurvivalofabat.Somebatcarespecialistshibernatebats simplybecausetheyprefertoduplicatenaturalconditionswhenpossible.  ReviewbyWimsatt(1969),hasshownthatspermstorageisonefacetofthecomplexreproductiveadaptations ofbatslivingintemperatelatitudeswhereaperiodofhibernationoccursduringprolongedoestrus.Females thathavematedmaygivebirthduringthewinterorearlyspringiftheyarekeptfromenteringnormalhibernaͲ tion.Normally,fertilizedovaimplantwhenfemalesarousefromhibernation,butartificiallywarmconditions, lowstress,andappropriatenutritionhaveresultedinoutͲofͲseasonbirthsinhibernatingspecies.Malesand females housed together under artificially warm conditions may engage in mating behavior outside normal matingperiods,whichmayalsoaffectseasonalcyclesofmating,fertilization,implantation,andgestation.  NeverattempttohibernateanonͲhibernatingspecies;norabatthatissick,underweightorinjured.TheaniͲ malisunlikelytosurvive,andevenifitdoes,healingofbonesandtissuewillslowsignificantlyifnotaltogether. Onlyahealthybatofaspeciesthatnormallyhibernatesshouldbeartificiallyhibernatedincaptivity.  AbatthatappearshealthybuthasbeendisturbedduringhibernationisapotentialcandidateforartificialhiͲ bernation.(Renovationofbuildingssometimesdisturbshibernatingbats.)Batsshouldberehydratedandfed foratleasttwodaysbeforebeingplacedinartificialhibernation.Ifthebatdoesnotapproachtheupperendof theweightrangeforitsspecies,itshouldnotbeartificiallyhibernated(i.e.,donothibernateathinbat,which isoftenthecasewithjuveniles).  Hibernatingbatsrequireveryspecifictemperaturesandhumiditylevels.Anartificialhibernaculumneedsto duplicatetheseconditionsasmuchaspossible.Olderrefrigeratorshavebeenusedsuccessfullytohibernate bats;however,theuseofmodern,frostͲfreerefrigeratorsisconsideredanunnaturalandinhumanepracticeas thehumiditylevelsaremuchtoolow(Barbosa,1996).  Theambienttemperatureduringthewintermayallowcaretakerstohibernateabatinanunheatedroom, suchasagarage.However,thetemperatureinthisroomshouldnotdropbelow40°Fahrenheit,andinsome partsoftheUnitedStatesandCanada,temperaturesingarageswilldropfarbelowfreezingforextendedperiͲ odsoftime.Manybatsmaynotbeabletosurvivesuchconditions.Ifthisisthecaseinyourarea,unused roomsorbasementsthathavesomeheat,butremainrelativelycool,mayprovidemoreappropriatetemperaͲ tures.Temperaturesinaroomusedtohibernatebatsshouldremainatleastinthelowtomid40°’s.SurprisͲ ingly,somespecies,suchasbigbrownbats(E.fuscus),havebeensuccessfullyhibernatedforthewinterwithͲ outsupplementalfeedingsattemperaturesrangingfromthelower50°’stothemid60°’s.Insomepartsofthe U.S. various species of bats have different temperature preferences in the wild. Variations may even exist withinthesamespeciesfromonegeographicalareatoanother.However,itisnotrecommendedthateither theupperorlowertemperaturerangesexceedthesetemperatures,astheyhaveprovenoptimalforhibernatͲ ing bats in captivity. Do not hibernate bats at freezing temperatures. Bats undergoing artificial hibernation mustalsobeabletomaintainsufficientbodytemperaturewithminimaloutlayofenergy.  Onceanappropriatelocationhasbeenchosen,setupanenclosurewithaheatingpadoverasectionofthetop orononesideoftheenclosureforwarmth.Inthewild,manybatspeciesarousefromhibernationiftemperaͲ turesdropbelowacertainlevel,andmovetoareaswhereconditionsaremorefavorable.Whileaheatingpad willallowabattomoveonorawayfromawarmerspot.RoostingpouchesshouldbeplacedinnumerousposiͲ tionsthroughouttheenclosureforcrevicedwellingspecies.Whenpossible,itisbesttoallowbatstohibernate inclustersofindividualsastheynormallydointhewild.Forexample,ifacaretakerreceivesasmallcolonyof big brown bats that were disturbed during hibernation, it would be best to hibernate them together as a group.  186TheRehabilitationandCaptiveCareofInsectivorousBatsThe Rehabilitation and Captive Care of Insectivorous Bats186

Highhumiditylevelsinanaturalhibernaculumcanresultinthecondensationofwaterdropletsonbat’sfur, thusmakingwateravailabletothebat.Inaddition,relativehumidityinmanyhibernaculaapproaches90%. Bats in the wild sometimes arouse from hibernation to find water and replenish their fluids. In captivity, a small,shallowdishofwatershouldbeplacedinsidetheenclosureandfreshwatershouldbeavailabletohiberͲ natingbatsthroughouttheentirehibernationperiod.  Wecannotperfectlyduplicatenaturalhibernation.BecausebatskeptinartificialhibernationdonothaveacͲ cesstotheirnaturalenvironment,theauthorrecommendsthatbatsbedeliberatelyreawakened(seebelow) andprovidedwithfoodandwaterperiodicallythroughouttheentirehibernationperiod.  Recordtheweightofthebatbeforeinitialhibernationandeachtimeitisawakenedandfed.Thebat’sinitial weightshouldbeintheupperendoftheweightrangeforthisspecies.TheauthorrecommendsthatahiberͲ natingbatbereawakened,weighed,andfedafterthefirstthreedays.Ifthebatappearshealthyandhasnot experiencedasignificantweightloss(i.e.,itisnotatorbelowthelowerendoftheweightrangeforthespeͲ cies),continuetoawakenandcareforitonceeveryonetosixweeksthereafterthroughoutthenormalperiod ofhibernation(i.e.,wintermonths).  Toawakenabatfromhibernation,allowittowarmuptoroomtemperatureslowly.Donotforcetheanimal intoanykindofheatedcontainer.Instead,movetheentireenclosureintoawarmerroom.Allowtheanimalto warmupslowlyonitsown.Itwilltakedifferentspeciesofbatsdifferentperiodsoftimetoarouse,soallowthe batatleastonetotwohourstowarmonitsownbeforehandling.Onceithaswarmed,weighit,andthenoffer itwaterandfood.Thenreturnittotheenclosure(whichshouldhaveremainedatroomtemperature)forthe nightsoitcancompletethedigestionprocess.Ifthebatappearswellandhasmaintainedabodyweightatthe upperendoftheweightrangeforthespecies,itcanbeplacedbackintohibernation.  Ifthebatiskeptoutofhibernationforlongerthan12hours,itshouldbefedagainasmetabolicactivitywill haveincreased.TheprocedureofawakeningandcaringforabatthatishibernatingincaptivityshouldbereͲ peatedonceeveryonetosixweeksthroughoutthehibernationperiod.AlthoughmanyresearchershaveartifiͲ ciallyhibernatedbatsforamatterofmonthswithoutintermittentfeeding,morefrequentfeedingsallowcareͲ takerstoensurethecontinuedgoodhealthofeachindividualwhichwilllikelyresultinhighersurvivalrates.  Ifintendedforrelease,artificiallyhibernatedbatsshouldnotbereleaseduntiloutdoorambienttemperatures havewarmedsufficientlytoallowaninsectpopulation.Itisnotnecessarytohibernatebatskeptinpermanent captivity,eveniftheywouldnormallydosointhewild.HibernationisamethodbywhichbatsinthewildsurͲ viveperiodsofsubͲoptimaltemperaturesandaninsufficientfoodsupply,aproblembatsincaptivitydonot experience.  Again,artificialhibernationisamethodbywhichabusycaretaker,whoisalreadycaringforseveralbats,or whoreceivesdozensofbatsdisturbedduringnaturalhibernationinthewild,canminimizehisorhertime.This allowsacaretakertheopportunitytocareformanymoreindividualsthanwouldbepossibleifeachbatreͲ quireddailycare.Inaddition,artificialhibernationmayalsohelptoensurenormaltimingoffertilization,imͲ plantation,orfetaldevelopmentinfemalesofreproductiveage.Timingofbirthsisimportantbecauserearing youngneedstocoincidewithoptimaltemperaturesandfoodavailabilityinthewild.Itispossiblethatartificial hibernationmayhelptoensurethesurvivalofoffspringoffemalebatsreleasedinthespring.