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Reviewing the evidence on mitigation strategies for bats in buildings: informing best-practice for

policy makers and practitioners

May 2018

Paul Lintott1 & Fiona Mathews2

1 University Of The West Of England And The University Of Exeter2 University Of Sussex And The University Of Exeter

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AcknowledgementsTheauthorsandpublishersofthisreportwouldliketothefollowingAdvisoryGroupmemberswhocontributedtotheproject:BrianKeeley(BatConservationIreland),CarolineWilson(SnowdoniaNationalParkAuthority),CharlotteBell(EDPLtd),DavidTosh(CEDaR),JanCollins(BatConservationTrust),JeanMatthews(NaturalResourcesWales),KatherineWalsh(NaturalEngland),LisaKerslake(SwiftEcology),NickJones(ACDEnvironmental),NikkiTaylor(DorsetCountyCouncil),PaolaReason(Arcadis),PaulWhitby(EcologyCo-Op),PennyLewns(ProtectedSpeciesEcologyLtd)andRobRaynor(ScottishNaturalHeritage).

WearegratefultoNaturalEngland(NE),NaturalResourcesWales(NRW)andalloftheecologicalconsultantswhosubmittedcasestudiesforinclusionintheresearch.

ParticularthanksgotoSophieDavison(UniversityofExeter)forhelpwithsomeofthedataprocessingandLisaKerslake(SwiftEcology),JanCollins(BatConservationTrust),KatherineWalsh(NaturalEngland)andPaolaReason(Arcadis)whohelpedwiththefinalreport.

Thisresearchprojectwassupportedbythefollowingcompaniesandorganisations.

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Reviewingtheevidenceonmitigationstrategiesforbatsinbuildings:informingbest-practicefor

policymakersandpractitioners

EXECUTIVESUMMARY

Aimsandobjectives

Thisstudyaimedtoprovideevidencetoplanners,developersandecologicalpractitionersontheefficacyofbatroostmitigationandcompensationtohelpthemensurethatmitigationapproachesareevidence-basedandbeneficialforbats.

Primaryobjectives

(a) Todeterminetheeffectivenessofmitigationstrategiesforbatswithinbuildings.(b) Toidentifywhichcharacteristicsofmitigationfeaturesareassociatedwiththe

likelihoodofsuccessfulretentionofbatpopulationspost-development.

Secondaryobjectives

(a) Toassesstheextentofbatroostmitigationandpost-constructionmonitoringthatiscurrentlyoccurring.

(b) Todeterminewhatmethodologicalimprovementscouldbemadetothecollectionandreportingofpre-developmentsurveydataandpost-developmentmonitoring.

Rationale

Despitetherelativelywidespreaduseofartificialbatroostsasbothamitigationstrategyandhabitatenhancementtool,relativelylittleresearchhasbeenconductedontheireffectiveness.Mostresearchhasfocusedonpre-andpost-developmentcasestudieswhich,whilstvaluable,arerarelygeneralizable.Giventhattheamountofdatacollectedannuallybyecologicalpractitionersdwarfsthatwhichcouldbecollectedbyresearchscientists,inthisprojectweaimedtoharnessthisresourcetoassesstheeffectivenessofbatmitigationinbuildings.

Methods

1)Licencereportsoutliningi)pre-developmentsurveys,ii)mitigationstrategies,andiii)post-developmentmonitoringwereobtainedfromboththeStatutoryNatureConservationBodies(SNCBs)anddirectlyfromecologicalconsultants.

2)CasestudiesinvolvingMyotisspp.,commonpipistrelles(Pipistrelluspipistrellus),sopranopipistrelles(P.pygmaeus)andbrownlong-earedbats(Plecotusauritus)werespecifically

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requested,asthesespeciesarecommonlyencounteredduringdevelopmentsinvolvingbuildings,andtheyhaveUK-andIreland-widedistributions.

3)Datawasextractedfromthereportsinasystematicmanner,andecologicalpractitionerswerecontactedforadditionalinformationwhenrequired.

4)Batroostpresenceandroostsizeswerecomparedpre-andpost-mitigationtodeterminewhetherbatroostsarebeingretained,andtoassesswhethertheextentofdisturbance(e.g.destructionversusmodification)orthetypeofmitigationfeatureusedcouldpredictsuccess.

5)Featuresofbatlofts,batboxesandreroofingprojectswereidentifiedthatwerelinkedwithagreaterprobabilityofbatoccurrenceandhigherpopulationlevelspost-development.Theprobabilityofbatoccurrencewithincompensatoryroostsovertimewasalsoassessed.

6)Duringdataextraction,thequalityofmonitoringreportswasevaluatedtodeveloprecommendationstofacilitatethetransitiontoarobustandtransparentmonitoringprocess.

Resultsandinterpretation

1)Theprobabilityofretainingbatroostswithinabuildingfollowingmitigationwasstronglydependentonthenatureofthestructuralchangetotheroost.Ifaroostwasdestroyedtherewasalowerprobabilityofbatsreturningtoacompensatoryroostcomparedwithamodifiedroost.Theprovisionofabatloftasmitigationwasusuallymoreeffectivethantheuseofbatboxesatprovidingcompensationforbats.Rooststhatweremodifiedbecauseofreroofingworkwererelativelysuccessfulatretainingsimilarlysizedpopulationspost-development,particularlyforbrownlong-earedbats.

2)Newlycreatedbatloftsattractedbatsatjustoverhalfthenumberofsites,withpost-constructionmonitoringdeterminingthat52%ofloftscontainedbats.Brownlong-earedbatsusednewbatloftsmostfrequently,followedbycommonpipistrellesandthensopranopipistrelles.Theprobabilityofpipistrellesoccupyinganewbatloftwasstronglydependentonthenumberofroostentrancesprovided(whichforpipistrelles,andothercrevice-dwellingspecies,mayalsoactasroostingopportunities).Similarly,therewasamarginallysignificantrelationshipbetweenthenumberofroostentrancesandtheprobabilityofbrownlong-earedbatswithinnewlofts.Althoughtheresultsindicatethatincreasingthenumberofroostentranceswillincreasetheprobabilityofbatsoccurringpost-development,itislikelythatanupperlimitwillexistwherebyadditionalentranceswillcreatedraughtandlightexposuretotheloft.

3)Analysisofbatboxdatawasrestrictedtositeswherebatboxeswereusedastheprimarymitigationorcompensationmeasure.Arelativelylowproportionofsiteswhichusedbatboxesweresuccessfulatretainingbats(31%).Wherebatswerepresentinbatboxespost-

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development,theoverwhelmingmajoritywereidentified(eithervisuallyorthroughtheassessmentofdroppings)aspipistrelles.Increasingthenumberofbatboxesdeployedacrossasiteincreasedtheprobabilityofatleastoneoftheboxesbecomingoccupied.Therewasalsoamarginallysignificantrelationshipbetweenthenumberofbatboxesdeployedandthenumberofbatscontainedwithinthem.

4)Inbuildingsthatweremodifiedduetoreroofingworks,67%ofbuildingsretainedbats.Theprobabilityofpipistrellesreturningtoamodifiedroostwasconsiderablygreaterifroostenhancements(e.g.theprovisionofroughsawntimbercrevices)wereprovidedalongsidereroofingworks.Therewasamarginalbutsignificantrelationshipbetweenthenumberofroostentrancesinstalledandtheprobabilityofallbatspeciesreturningtothemodifiedroostincomparablenumberstothatfoundwithinpre-constructionsurveys.

5)Thelikelihoodofdetectingbatswithincompensatoryroostsincreasedovertimeandwithadditionalsurveys;however,therewasconsiderablevariabilitybetweensitesinthenumberofbatsfoundbetweenmonitoringyears.Monitoringreportswerefoundtovaryconsiderablywithregardstotheextentofkeyinformationcontainedwithinthem.Criticalinformationsuchasthatdetailingwhichmitigationfeatureswereobserved(i.e.the%ofroostentrancesthatwereobservedforbatemergence)waslackinginmostcases.

Conclusions

Evidence-basedmitigationiskeytoconservingbatpopulationsefficientlyandeffectively.Thisstudyhasdemonstratedhowecologicalconsultancydatacouldbeusedtofurtherourunderstandingoftheefficacyofmitigationstrategies.Theconstraintswefacedintermsofaccessingandextractingdatahighlightsthepressingneedforthedevelopmentofanonlinesystem,hostedbytheSNCBs,whichcapturesandsecurelystoresmitigationdata.Thiswillgeneratequantitativedatawhichiscomparablebetweencases,willallowtheSNCBstobetterdetermineiftheyareachievingtheirstatutoryobligations,andwillensurethatinformationcanbesharedwithecologicalconsultantstoinformeffectivemitigationinthefuture.

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Chapter1:Context

1.1Terminology

Inthisreport,theterm‘development’isusedtoencompassarangeofactivitiesthatrelatetotheconstruction,modification,restorationorconversionofbuildings.IncontrasttoMitchell-Jones(2004),thetermdoesnotimplicitlyreferto“operationsthathavethepotentialtoimpactnegativelyonbatsandbatpopulations”butinsteadtakesaneutralstance.

Mitigationrefersspecificallytomeasuresthatreduceand/orminimiseimpactswithinthesiteboundarysuchaschangestotimingtoavoidsensitiveperiodsorreductionstotheextentoftheproject.Compensationreferstothemeasurestakentomakeupforthelossof,orpermanentdamageto,biologicalresourcesthroughtheprovisionofreplacementareas.Anyreplacementareashouldbesimilartoor,withappropriatemanagement,havetheabilitytoreproducetheecologicalfunctionsandconditionsofthosebiologicalresourcesthathavebeenlostordamaged(CIEEM2017).

1.2Overviewofbatmitigation

Despitetherelativelywidespreaduseofartificialbatroostsasbothamitigationstrategyandhabitatenhancementmethod,relativelylittleresearchhasbeenconductedontheireffectiveness.Althoughtherearemanyanecdotalcasestudiesavailabledescribingmitigationsuccess/failure(e.g.MitigationCaseStudiesForum2017),therehavebeenrelativelyfewattemptsatcombiningcasestudiestoproducefindingsthatarestatisticallyrobustandthatcanbegeneralisedtonewsituations(Table1.1andTable2.2).

WiththeexceptionofcasesuploadedtotheBatConservationTrust’s“Roost”website,itisevidentthatmitigationsuccessvariesconsiderablybetweenstudies(Table1.1)1.Thelowlevelofmitigationsuccessfoundinotherstudiesmayreflecttherelativelyshorttimeperiodbetweentheimplementationofamitigationstrategyandpost-developmentmonitoring.Forexample,inMackintosh(2016),mostreplacementroostshadbeeninplaceforlessthan

1TheRoostwebsiteislikelytobeunrepresentativeofmitigationsuccessgiventhatcase-studiesweresubmittedwiththeknowledgethattheywouldbesharedpublicly.

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twosummerspriortomonitoringandtheoldestforthreesummers.Occupancyratesofartificialroostscanbetime-dependent(Flaqueretal.2006);itisthereforepossiblethatbatsmayhavedisplayedahigherdegreeofacceptanceofthemitigationfeaturesoveralongerperiodoftime,whichwasnotcapturedintheMackintosh(2016)study.

Aprevailingthemethroughoutthepreviousstudieswasthattherewasanecessitytoundertakeresearchintothepredictorsofmitigationsuccessandtodeterminehowthisdiffersbetweenspeciesandfordifferentmitigationmeasures(e.g.Stoneetal.2013).Thisstudyaimstoaddresstheuncertaintyintheefficacyofmitigationandtoensurethatmitigationapproachesareevidence-basedandbeneficialforbats.

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Table 1.1. Overview of the current research that has been conducted in the UK assessing the effectiveness of bat mitigation in buildings.

Project Key outcomes Reference

Effect of barn conversion on bat roost sites in Hertfordshire, England

36 barn conversions surveyed for bats following development Only eight of these 36 units were being used by bats, namely Natterer's bat (Myotis nattereri), brown long-eared bat (P. auritus), pipistrelles (Pipistrellus spp.) and serotine bat (Eptesicus serotinus) 13 barns had no bat use with no potential for bats to return.

Briggs (2004)

Snowdonia Bat Mitigation Pilot Project

20 sites which had undergone mitigation inspected Waring (2011) Evidence of bat usage found in 75% of cases

7 projects (35%) were compliant with planning conditions

Bats and Licensing: A report on the success of maternity roost compensation measures

28 maternity roost sites monitored Mackintosh (2016) Compensation installed as described in plan at all sites Evidence of bat usage found in 39% of cases Sites which retained existing access showed least reduction in bat numbers Sites which relied only on boxes showed the greatest reduction in bat numbers

Mitigating the effect of development on bats in England with derogation licensing

Most licensees (67%) failed to submit post-development reports Stone et al. (2013) Information provided by licensees was inadequate and inconsistent

Bat lofts more successful at retaining bats (74%) than bat boxes (13%)

An investigation of the impact of development projects on bat populations

Bats present in 20% of bat boxes used as compensation Aughney (2008)

An additional 30% of boxes showed signs of previous use

Unpublished local authority study

Presence of bats at 45% of post-development sites N/A

Frequent cases involving incorrect installation of mitigation

Mitigation for bats: the National Trust experience

Inconsistencies in the type and quality of monitoring data Hodgkins & Smith (2012)

84% re-occupancy rate post-works for licensed cases Natural fluctuations of some species can obscure meaningful analysis

Roost: The Bat Roost Replacement & Enhancement Resource

24 cases submitted by practitioners outlining successful mitigation practices Bat Conservation Trust (2017a)

A Review of The Success of Bat Boxes in Houses

9 bat roost boxes within roofs were assessed (8 designed for pipistrelles, 1 for brown long-eared bat)

Bat Conservation Trust (2006)

Of the 8 boxes designed for pipistrelles, 7 were occupied by roosting bats. The box designed for the brown long-eared bat was never occupied.

Mitigating the Impact of Bats in Historic Churches

Natterer's bat were not recorded using bat boxes that were provided for them Zeale et al. (2016) Natterer's bat frequently used 'boxed-in' areas that restricted access to main interior of building

Performance of artificial maternity bat roost structures near Bath, UK

Demolition and redevelopment of converted farm house containing Garland et al. (2017) brown long-eared bat and common pipistrelle bat maternity roots Construction of bat house and bat wall structures built in compensation Roosting brown-long eared bats established within 18 months, with observed numbers

Indicating that maternity colony likely re-established. Common pipistrelle maternity roost yet to re-establish after six years

Mitigation Case Studies Forum

Proceedings from the Mitigation Case Studies which was conducted as a first step Bat Conservation Trust in addressing the lack of evidence in the efficacy of bat roost mitigation. (2017) Poll highlighted that majority of attendees thought that monitoring results are

not being analysed and shared, particularly if there was a failure.

The Lesser Horseshoe A wide range of ideas for modifying, enhancing and creating roosts for Schofield (2008) Bat: Conservation Handbook

lesser horseshoe bats, with practical advice on improving and adapting buildings as roosts.

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Table 1.2 Selective overview of current literature assessing the occupancy of bat boxes. Additional literature can be found by consulting the literature reviews in either Rueegger (2016) or Mering & Chambers (2014).

Project Key outcomes Reference The Vincent Wildlife Trust's Irish Bat Box Scheme

Bats present in 20% of bat boxes used as compensation McAney & Hanniffy (2015)

Seasonal occupancy rates; more bats present later in the season Consultants expressed concern regarding lack of post-development monitoring

Managing competition between birds and bats for roost boxes in small woodlands

196 bat boxes inspected for occupancy between 2005 and 2009 (21 sites)

Meddings et al. (2011)

Occupancy does not increase above 30% utilisation with an increasing number of boxes on site after 8 boxes

A comparison of different bat box types by bat occupancy

Bat usage found in 11 - 33% of boxes; dependent on box type Seasonal variation in bat occupancy rate with nesting birds outcompeting bats in spring.

Dodds & Bilston (2013)

An analysis of the usage of bat boxes in England, Wales and Ireland

Bat box occupancy rate varied from 15% in Devon and west Wales, to 4% in the Midlands

Poulton (2006)

Occupancy rates, bat counts and species counts all increased with length of time the boxes were established

Bat box height had a significant effect on occupancy and time to first use by Natterer's bats

Thinking outside the box: A review of artificial roosts for bats

Literature review of 47 publications on creation of artificial boxes Mering & Chambers (2014) Few studies measured height or microclimate in context of attracting bats

Colonisation rates ranged from 7% to 100% Bat Boxes - A Review of Their Use and Application, Past, Present and Future

Literature review of 109 publications Rueegger (2016)

No conclusive evidence was found that bat box installation height is important

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Chapter2:Contextualisingthescaleofbatmitigationandpost-developmentmonitoring

2.1Introduction

EcologicalconsultancyworkintheUKhasrapidlyexpandedoverthelasttwodecades,tomeettherequirementsoftheHabitatsDirective,theEnvironmentalImpactAssessmentDirective,andplanningpolicy.Stoneetal.(2013)estimatedthat,from2003to2005,atotalof£4.13millionwasspentonbatloftsandbatboxesinEnglandascompensation,inadditiontotheassociatedconsultancyfeesandcosts,habitatmitigationandNaturalEngland’sadministration.However,therehasbeennoreviewofthecurrentscaleofmitigation.Inthisproject,theextentofmitigationandpost-developmentmonitoringcurrentlyoccurringintheUKandIrelandwasassessed,andtheperspectivesofecologicalpractitionersonpost-developmentmonitoringwereinvestigated.

2.2Methods

Asemi-structuredquestionnairewasdesignedtoassesstheextenttowhichbatmitigationandpost-developmentmonitoringoccur(Appendix1).ThiswasdistributedinFebruary2017viatheCIEEMmailinglisttoallCIEEMmembers(4,986individuals),mostofwhomarepractisingecologists.Thequestionnairewasprimarilydesignedforecologicalconsultants,butflexibilitywasincorporatedviaopenquestionsthatcouldbeansweredbyarangeofrespondentsincludingecologistsfromlocalplanningauthorities(LPAs)andSNCBs.Thequestionnairewashostedviaonlinesurveysoftware(SurveyGizmo)andwasactivefrom1stFebruary-1stMay2017.

2.3Results

Therewere261respondentstothequestionnaire.Theseincluded228ecologicalconsultants,15LPAecologists,and18otherrespondentsincludingrepresentativesoftheSNCBsandvoluntaryroostvisitors.Thegeographicaldistributionoftherespondentswasasfollows:England80%;Scotland8%;Wales8%;NorthernIreland1%;andRepublicofIreland3%.

Theextentofbat-relatedprojectsundertakenbyecologicalconsultants

Solepractitionersdealwithameanof20(95%ConfidenceInterval(CI):15–25)projectsrelatingtobatsinbuildingsannually,whereaslargerconsultanciescontainingatleasttwostaffmembershandleanaverageof47(95%CI:24–70)casesayear.Overall,ameanof68%(95%CI:64-73)requiremitigation,whilst64%(95%CI:59–69)requireaEuropeanProtectedSpecies(EPS)licence,highlightingthatmostcaseswhichrequiremitigationareundertakenunderlicence.

Only11%ofecologicalpractitionersthoughtthattheevidencebasecurrentlyexiststoenablethemtomakeaninformeddecisiononbest-practicemitigationstrategies.Incontrast,70%thoughttheevidencebasepartiallyexists,whereas19%thoughttheywereunabletomakeinformeddecisionsduetothelackofevidence.Batboxesareusedwidelyasamitigationtool,

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with76%(95%CI:72–80)ofcasesinvolvingtheirdeploymenteitherinisolationorincombinationwithothermitigationstrategies.

Theextentof,andconstraintson,post-developmentmonitoring

Post-developmentmonitoringisrecommendedin51%(95%CI:47–56)ofEPSlicencecases.Justoverathirdofconsultantsreportedthattheyhadencounteredoccasionswheremonitoringhadbeenrecommendedandtheclientwaswillingtopay,butthisactionwasdeemedunnecessarybyanSNCB(29%ofoccasions),aLocalPlanningAuthority(2%),orboth(3%).

Therewasaperceptionamongst34%ofpractitionersthatthissituationhadbecomeincreasinglyfrequentduringthepastfiveyears,incontrastto28%ofpractitionerswhodidnotperceivetheretohavebeenachange.Thepractitionerswhohadobservedachangewereaskedwhytheythoughtthismightbethecase.Theirexplanationscanbebroadlysplitintofourdistinctcategories:

i)Broaderdefinitionof‘lowimpact’(33%ofresponses)

ManyrespondentsfromEnglandstatedthattheintroductionoftheNaturalEnglandLowImpactBatClassLicencehasledtoareductioninmonitoringat‘lowimpact’roosts.Similarly,strongeradherencetotheBatMitigationGuidelines(Mitchell-Jones2004)wasfelttohavereducedthenecessityofconductingmonitoringatroostsoflowerconservationsignificance.Forexample,commentsincluded:

“Relaxationin'policy'tomonitoringoflowimpact/lowstatussites.”

“Becausenon-maternityroostsareconsideredlowimpact”

“Proportionality/stricteradherencetobatmitigationguidelineswhereitstatesmonitoringnotnecessaryforroostsoflowerconservationsignificance.”

ii)Governmental/developerpressure(33%ofresponses)

Manyrespondentsperceivedthattherewasgovernmentalpressuretomakeprotectedspecieslessofanissuefordevelopers.Similarly,othersthoughtthatthepressurefromdeveloperstoreducethecostsofbiodiversitymitigation/compensationwasthemainfactorforareductioninpost-developmentmonitoring.Forexample,commentsincluded:

“Pressurefromgovernmenttoreduceenvironmentalconstraintsondevelopers.”

“Thegovernmentisworriedaboutescalatingcostsforthedeveloperandhasbecomemorelenientwheremonitoringisconcerned.”

“Inabilitytoenforcemonitoringandpressuretoavoiddelaystotheprovisionofhousingsupply.”

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iii)Lackofresources(23%ofresponses)

RespondentsperceivedthatalackofresourcesinbothLPAsandSNCBsmeantthatmonitoringwasoftendeemedunnecessarybecauseitwouldbeimpossibletotrackorenforce.Forexample,commentsincluded:

“Greaterrealisationthatmitigationmeasuresmustbemonitoredandthatthisneedstobeenforced,howevertheresourcesdon’texist.”

“Lackofcouncilstaffresources/timetoexamineplanningapplicationsproperly”

iv)Lackofexperience(11%ofresponses)

RespondentssuggestedthattheconsiderablevariabilityinstaffexperiencewithinbothSNCBsandLPAscontributedtoastrictrelianceonguidanceratherthanincorporatinganunderstandingofthecircumstances.Similarly,differencesinexperiencebetweenLPAstaff(i.e.ifafull-timeecologistwasemployed)resultedinvariablelevelsofmonitoringrequirementsbeingimposed.Forexample,commentsincluded:

“Lossofexpertisefromthestatutorysector.Adviceoftenappearstocomefromabookratherthanempathyorunderstandingofthecircumstances”

“Itseemsverymuchdependentoflatewhosedeskanapplicationlandsonastowhattheyrequireinrespectofmonitoring.”

2.4Discussion

Understandingtheextentofmitigationandpost-constructionmonitoringisimportantasitcontextualisesthescaleofdevelopmentswiththepotentialtoaffectbatsinbuildings.The228consultantsinterviewedinthissurveyhandleover5,000casesayearinvolvingthemitigationofbatswithinbuildings.GiventherespondentstothequestionnairerepresentonlyasubsampleofthenumberofconsultantscurrentlyworkingintheUKandIreland,wecanmakeaconservativeestimatethatthereareaminimumof10,000casesofbatmitigationinbuildingsayear.

Overall,theclearmajorityofrespondentsfelttheyhadinadequateevidenceonwhichtobasetheirdecisionsaboutmitigation;withafifthofthoseperceivingthattheyhadnosoundevidence.Thishighlightsthepressingneedtoestablisharobustevidencebasewhichcaninformbestpractice.

Thisstudyfoundthatbatboxesarefrequentlyusedasamitigationmeasure(in76%ofcases),whichissimilartothatofStoneetal.(2013)whoreportedthatboxeswereusedin67%ofcases.Althoughwedidnotaskconsultantstodistinguishbetweencaseswhereboxesareusedinisolationorincombinationwithothermitigationmeasures,giventhatboxesarefrequentlyusedasinterimmeasures,itislikelythatahighproportionofthecasesdescribedinvolvedtheuseofboxesalongsideadditionalmitigationfeatures.

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Therewasaperceptionamongstmanypractitionersthattherequirementtomonitormitigationhasreducedinfrequencyoverthepastfiveyears;however,thereasonsgivenvariedconsiderably.Therewasabroadconsensusthateithergovernmentalpressureoramovementtobecome‘developer-friendly’wasresponsibleforthedeclineinmonitoring.Reducingthecostimplicationsofdevelopmentwasoftenthoughttobethemaincause.Giventhatpost-developmentmonitoringcanoftenvaryinduration(e.g.additionalsurveyscanberequestedifinitialinspectionsdonotfindsignsofthepresenceofbats),itislikelythatdeveloperswanttoavoidtheuncertaintyofnon-fixedcostsextendingbeyondtheircompletiondate.

ThedifficultythatSNCBsfaceintrackingorenforcingmonitoringrequirementswasoftencitedasacauseofthedeclineinmonitoring.Recentrevisionstolicensingprocedureswerethoughttobeprimarilydesignedtoreducetheiradministrativeburdenratherthanachievehighstandardsandeffectivemitigationpractice.GiventhelimitedresourcesavailabletotheSNCBsthisisunsurprising,andmayalsoexplainwhyconsultantsfeltthatvaryinglevelsofexperienceamongstSNCBstaffmayalsoberesponsibleforvariablemonitoringdemands.

Theoverridingthemerecurrentacrossthequestionnairewasthatmonitoringcouldoftenbeperceivedasanunnecessaryexpenseandwasthereforerelativelyeasytodispensewith.Itisthereforeimportanttoensurethat,onoccasionswherepostdevelopmentmonitoringisconducted,thatitsexplicitpurposeisclear,andthattheresultscontributetobothanunderstandingofmitigationsuccesswithinthesiteandtothewiderunderstandingoftheeffectivenessofmitigation.

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Chapter3:Theeffectivenessofmitigationstrategiesforbatsinbuildings

Theevidencebaseforcurrentmitigationactivitiesislargelycentredonthe2004BatMitigationGuidelines(Mitchell-Jones2004).ThisdocumentplacedtheUKaheadofmostothercountriesgloballyinformalisinganapproachtobatmitigation,andprovidedusefulgenerictechnicaladviceondevelopingmitigationplans.Nevertheless,itwasnecessarilyreliantonpersonalexperience,andonuntested,ifintuitive,recommendationsformitigationstrategies.Formalstatisticalassessmentsofdatacontainedwithinecologicalconsultancyreportshavebeenconductedwithinthisstudyinordertoupdatetheevidencebaseforarangeofwidely-distributedbatspeciesandtohighlightdatagapsforfutureassessment.

3.1Methods

Casestudieswereobtainedfromavarietyofsources.ArequestwasmadeviaemailstotheCIEEMmembers’list,socialmedia,andpersonalcontacts,forcasestudiesinwhichmitigationhadbeenconductedtocompensateforthedamageordestructionofabatroostwithinabuilding.Importantly,informationwasrequestedfromfollow-upmonitoringsothatanassessmentoftheefficacyofmitigationcouldbemade.CasestudiesinvolvingMyotisspp.,commonpipistrelles(P.pipistrellus),sopranopipistrelles(P.pygmaeus)andbrownlong-earedbats(P.auritus)werespecificallyrequested,asthesespeciesarecommonlyencounteredduringdevelopmentsinvolvingbuildings,andtheyhaveUK-andIreland-widedistributions.Horseshoebats(Rhinolophusspp.)werespecificallyexcludedbecause,althoughtheycanformahighproportionofthecase-loadinsomeregions,particularlyinsouth-westEnglandandpartsofWales,itwasconsideredthattheevidencewasmuchmoreestablishedforthesespeciesthanforanyothers(e.g.Rhinolophushipposideros;Schofield2008).

Ecologicalpractitionerssubmittingprojectreportsthatfittedthecriteriaabovewererequestedtoeitheruploadalltheircasestudies,oralternativelytoprovidearandomsubsampleofcases.Thisavoidedthepreferentialselectionofmitigationcaseswhichshowbiastowardseithertheeffectivenessorineffectivenessofcertainmitigationstrategies.Wewere,however,unabletocontrolforwhichecologicalconsultantsprovideduswithdataandtheremaybeanassociationbetweenthelikelihoodofuploadingandmitigationsuccess.

Initially,allofthedocumentationwhichcomprisesaEuropeanProtectedSpecies(EPS)licencewasrequested,namely:licenceapplicationform,licencemethodstatement,workschedule,anyrequestedmodificationstotheapplication,actiontakenunderlicence(e.g.licencesign-offform,monitoringconducted),andanyadditionalfilesthatwererelevant.However,followingfeedbackfromconsultantsthattheprocessofcompilingthesefileswastootime-consuming,subsequentrequestswerechangedtostatethataminimumofthemethodstatementandmonitoringreportswasrequired.Casestudieswereuploadedsecurelyviaafile-hostingservice(Dropbox).Initially,anoptiontoenterdetailsviaanonlinequestionnairewasavailable;however,thiswasrarelyusedbecauseofthetimeconstraintslimitingpractitionerinvolvement,thedifficultiesconsultantsfacedincompilingandextractingdatafromreports,

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andtheextentoftheinformationthatwasneeded.Additionally,werequestedaccessfromSNCBstocasestudiesthathadbeensubmittedaspartofEPSlicenceapplications.TheavailabilityandaccessibilityofthedatavariedbetweentheSNCBs:

DepartmentofAgriculture,EnvironmentandRuralAffairs:MonitoringofmitigationmeasuresisrarelystipulatedinIreland.Consultantswerethereforecontacteddirectlyratherthanobtaininglicencereturns.

NaturalEngland(NE):A‘RestrictedLicenceforreusingNE’sInformationandData’wasobtainedfromNEwhichallowedustoaccesstheir‘TRIM’database.Thisonlycontaineddatafrom2013onwards,asearliercasestudieshavenotbeendigitised.Thisrestrictedthenumberofcasestudieswecouldobtainthroughthismethod,giventhatrelativelyfewcaseshadundergonemitigation,implementation,andmonitoringinthisshorttimeperiod.Wesearched‘TRIM’usinganindexofreferencenumbers,whichlistedcasestudieswherelicencereturnswereexpectedtohavebeensubmitted;however,therewasconsiderablevariabilityintheextenttowhichtheexpectedlicencedocumentswerefoundwithinthedatabase.

NaturalResourcesWales(NRW):CasestudiesreceivedfromNRWconsistedonlyofmonitoringreports.Theirpre-constructionreportsareeitherheldinseparate,individualfolderswithintheNRWdocumentmanagementsystemandaredifficulttoretrieve,orareinpaperformatandwouldrequirehand-searches.NRWdidnotthinkitwasviabletoaccessanyofthesepre-constructionrecordsduetotimepressuresontheirstaffduring2017.

ScottishNaturalHeritage(SNH):MonitoringofcompensationmeasuresisnottypicallysecuredthroughalicenceconditioninScotland.Whenmonitoringisundertaken,theresultsarenotreportedtoSNH(Mackintosh2016).Additionally,itwasconsideredthat,ifpost-developmentmonitoringshowednouptakebybats,thenremedialactionwouldbeextremelydifficulttoimpose(B.Ross,LicensingManager,ScottishNaturalHeritage,pers.comm).Consultantswerethereforecontacteddirectlyforcasestudies.Whererelevant,casestudiesoutlinedinMackintosh(2016)werealsousedtocontributetothemeta-analysis.

Datawasextractedfromcasestudiesusingastandardisedpro-forma.Wherenecessary,ecologicalpractitionerswerecontactedforadditionalinformationtoclarifyanyareasofuncertainty.OurNErestrictedlicenceandassociateddataprotectionlawsmeantwewereunabletocontacteitherhomeownersorconsultantsfromcasestudiesobtained.

Figure3.1showsthedistributionofthecasestudiesthatwerereceivedfromacrosstheUK.AlthoughreplieswerereceivedfrommultipleconsultantsinNorthernIrelandandtheRepublicofIreland,followingindividualrequestsforcases,theconsensuswasthatpost-developmentmonitoringwasveryrarelyconductedintheseareas.

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Figure3.1KerneldensitymapofcasestudysitesacrosstheUK.Mapbasedoncase-studydensitywithin20kmgridsquarezonesacrosstheUK.Darkgreenareasofthemapindicatetheabsenceofsurveysites,whereaslightgreen,yellowandredpatchesindicatetheareaswiththehighestdensitiesofcasestudiesreceived.

Theeffectivenessofmitigationstrategiesforbatswithinbuildingswasassessedinmultiplewaystoensurethatallthedataprovidedwasutilisedfullytoenhancetheevidence-base.Withinthisstudy,anoverviewoftheeffectivenessofavarietyofmitigationstrategiesispresented,thekeymitigationfeatureswhichincreaseoccupancyandre-occupancyratesareidentified,andthemannerofcollectingandreportingmonitoringdataandhowitcouldbeenhancedhasbeenassessed.

3.2Before-afterstudy

Thesimplestwaytoevaluatethesuccessofaninterventionistocomparethenumberofindividualsbeforeandaftermitigationtoassesswhetherbatroostsarebeingretainedwithindevelopments.

Methods

Onlyasubsample(n=90)ofthesubmittedcasestudiesweresuitableforthisanalysis.Theremainderwereexcludedbecausesubstantialmethodologicaldifferencesbetweenthepre-andpost-mitigationsurveysprecludedfaircomparisons.Caseswereincludedonlywhereanassessmentwasmadeoftheroostsize,notjustroostpresence,inbothpre-andpost-developmentsurveys,althoughitshouldbenotedthatestimatesofroostsizecanbesubjective.Thedifferencebetweenthenumberofindividualsbeforeandafterdevelopmentwasformallytestedusingapairedt-testasthedataconformedtoanormaldistribution.Apvalueof<0.05wastakenasanindicationofstatisticalsignificance.Analysiswassplitintocaseswhere:i)roostsweredestroyedandcompensationintheformofeitherbatboxesorbatloftswasprovided,and,ii)caseswhereroostsweremodifiedbecauseofre-roofingactivities.

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Commonandsopranopipistrellebatdatawascombinedduringtheanalysisofmodifiedroostsduetothelimitedsamplesize(26intotal).

Roostdestruction

Incaseswherearoostwasdestroyedandthemitigationstrategyinvolvedtheuseofeitheranewbatloft/houseorbatboxesascompensation,pairedsampledt-testsshowedthattherewasasignificantdifferencebetweenthenumbersofindividualsrecordedpre-andpost-developmentforallbatspecies/genera(Table3.1).

Table3.1Acomparisonofbatpopulationsbeforeandaftermitigationusingapaired-samplet-testforcaseswhereroostdestructionoccurred.

Species/genus Samplesize

t p

Brownlong-earedbat 49 5.06 <0.001Commonpipistrelle 55 6.55 <0.001Sopranopipistrelle 41 3.01 0.005Myotisspp. 12 3.69 0.004

ThetrendsvisibleinFigure3.2demonstratethatrelativelyfewcasestudiesmaintainedorincreasedthenumberofbatspresentfollowingmitigation;forexample,only10%and7%ofcommonpipistrelleandsopranopipistrelleroostsrespectivelymaintainedtheirsizefollowingdevelopment.Intheabsenceofsurveysduringthematernityperiod,itcanbedifficulttodeterminewhetheraroostisusedforbreeding.Nevertheless,itisgenerallytruethatlargerroostsaremorelikelytobeusedasmaternitysites.Forexampleatypicalbrownlong-earedbatnurseryroostcontainsbetween10and30individuals(Greenaway&Hutson1990).Itwasfoundthatonly19%ofpre-constructionroostsabovethisthreshold(10individuals)retainedatleastthisnumberpost-development,and69%oftheseroostsdidnotretainbatsatallfollowingmitigation.

Myotisspp.roostsizesvarydependingonspecies(Dietzetal.2009);however,onlyfoursuchcasestudieswerereceivedwhichcontainedmorethan10individualsinpre-constructionroosts.Noneoftheseroostsretainednursery-levelnumbersofbatsfollowingmitigation(i.e.10individuals),andonlyoneoftheseroostsretainedbats.

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Figure3.2.Acomparisonofthenumberofbatsbeforeandaftermitigationincaseswheretheroostwasdestroyedforcommonpipistrelle(A),sopranopipistrelle(B),brownlong-earedbat(C),andMyotisspp.(D).Theboxplotsrepresentthemedian(boldline),thefirstandthirdquartiles(topandbottomofbox),therange(endofthewhiskers)andoutliers(dots).Thepaireddotplot(centreofthegraph)representsthedifferenceinpopulationsizeforindividualcasestudiesbeforeandafterdevelopment.Anoutlierthatwentfrom180batsinpre-constructionsurveysto200batspost-constructionhasbeenremovedfrom(A)forclarity.

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Roostmodification

Incaseswhereroostsweremodifiedprimarilybecauseofreroofingwork,pairedsampledt-testsshowedthattherewasnosignificantdifferenceinpopulationsizebeforeandafterdevelopmentforeitherpipistrelles(n=26,t=1.13,p=0.27)orbrownlong-earedbats(n=21,t=0.40,p=0.69).Althoughonly12%ofpost-developmentpipistrellebatroostsreachedorexceededpre-developmentsize,overhalf(54%)ofroostsretainedoccupancyofatleastoneindividualfollowingmitigation(Figure3.3A).Incontrast,62%ofcasestudiesinvolvingmodificationtobrownlong-earedbatroostsretainedorincreasedthepopulationsizefollowingmitigation(Figure3.3B).

Forpre-developmentbrownlong-earedbatroostscontaining10ormoreindividuals(whichforthispurposewewillinfertohavebeenamaternityroost;Greenaway&Hutson1990),60%ofpost-developmentroostsretainedatleast10batsafterundergoingreroofing.

Incomparison,pipistrelleroostscouldgenerallybesplitintotwodistinctcategoriesasaconsequenceofthecasestudieswereceived:smallroosts(range1to10bats)andlargerroosts(range=100to876bats).Largepre-developmentroosts(containinggreaterthan100individuals)retainedsimilarnumbersofbatsfollowingmitigationwhereassmallerroosts(i.e.thosecontainingupto10individuals)allfailedtoexceedtenindividualspostdevelopment.Thisappearstohighlightthatlarger,potentiallyimportantroostsfromaconservationperspective,arebeingretainedduringroostmodificationwhereasthesmallerroostswhicharelesslikelytobeofconservationsignificancearenot.

Figure3.3.Acomparisonofthenumberofbatsbeforeandaftermitigationincasestudieswhereroostsweremodifiedprimarilybecauseofreroofingworkforpipistrelles(A),andbrownlong-earedbats(B).Outliers(fourcasestudies)containinggreaterthan100individualswereremovedfrom(A)forclarity(Outlier1:before200,after309;Outlier2:before876,after507;Outlier3:before:100,after0;Outlier4:before300,after300).

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Discussion

Thevastmajorityofcasestudiesinvolvingroostdestructionresultedinadeclineinbatpopulations,whereaspopulationsweremorelikelytoberetainedatbuildingswhereroostsweremodified.Re-roofingcaninvolvearelativelyshortperiodofdisturbanceforbats,particularlyifconductedoveraseasonwhenbatsareseasonallyabsent,meaningbatscanreturntothesameplaceeffectivelywithoutinterruption.Itwouldbeusefultocontrastthelengthoftimebetweensuccessfulandunsuccessfulreroofingworks;however,thisinformationisinfrequentlyreportedinpost-constructionmonitoringreports.

Althoughthereisanevidentnegativetrendacrossstudies,itisimportanttoqualifythesefindingswiththefollowing:

i) Surveyingeffortdifferedbetweenpre-andpost-developmentsurveyswith,onaverage,pre-developmentsurveyingeventsdoublethoseofpost-developmentsurveys(median=2surveys).Althoughonmanyoccasionspre-andpost-mitigationeffortcoulddifferduetofactorsincludingdifferencesinthenumberofroostentrances,therewasalsorelativelylittleconsistencyinthesurveyingmethodologybetweenpre-andpost-developmentsurveys(e.g.timinginthenight,timeofyear).

ii) Observedchangesinpopulationsizemaynotbecausallyrelatedtoanyactivitiesoccurringattheroost,butinsteadbeaconsequenceofchangesinthewiderlandscape.Forexample,femalepipistrellesmaychangetheirroostsbecausetheyareclosertoattractiveforagingsites(e.g.Bartoničkaetal.2008;FeyerabendandSimon2000).Roostuptakewilltherefore,inpart,bedependentonhowthelandscapehasdevelopedduringthemitigationprocess.Giventhatmostcasesconsideredinthisstudywererelativelysmall-scale,itisunlikelythat‘withinthedevelopmentboundary’habitatmodificationswouldhavedramaticallyalteredforagingpreferences;however,wecannotaccountforwiderlandscapemodifications.

Therewerespecies-specificdifferencesintheresponsestomitigation,particularlybetweenbrownlong-earedbatsandpipistrellesinrooststhatunderwentmodification.Brownlong-earedbatsreturnedtomodifiedroostsinsimilarnumberstopre-mitigationlevelsincontrasttopipistrelles,whichrarelyattainedsimilarlevels.Thismayreflectastrongerroostloyaltyinbrownlong-earedbats(Entwistleetal.2000)orlimitedroostingoptionselsewhereforbrownlong-earedbatsincontrasttopipistrelles.Pipistrellesarerelativelyrobusttoexclusionfromroostsinhousesand,intheshorttermatleast,shownosignificantchangeinbehaviourorforagingpatternsfollowingexclusion(Stoneetal.2015).Giventhewidevarietyofalternativerooststhatpipistrellescanuse,rangingfromindividualroostsbehindivyontreestosubstantialcolonyroostsininhabiteddwellings(Stoneetal.2015),itislikelythatpipistrelleswereroost-switchingratherthanreturningtothemodifiedroost.Theprobabilityofdetectingbatsduringpost-constructionmonitoringmaythereforereflectroostavailabilityinthesurroundinglandscapealongsidetheeffectivenessofmitigationandcompensationstrategies.

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3.3Factorsinfluencingwhethernewbatroostsareused

Thecreationofnewormodifiedroostingspaceprovidesroostingopportunitiesnotjustforbatsdisplacedduringdevelopmentbutalsoforthelocalbatpopulationmoregenerally.Thesuccessofnewroostcreationwasassessed,withthecaveatthatitisnotpossibletoknow(intheabsenceofstudiesthatidentifyindividuals)whethertheusageisbydisplacedindividualsorothersinthewiderpopulation.Theuptakeofaroostwillbedependentonawidevarietyoffactorsincludingtheavailabilityofalternativeroostsinthesurroundinglandscape.Similarly,manymitigationstrategiesincludetheprovisionofbothanewbatloftandbatboxes.Inthefollowinganalysis,weassessthesuccessofbatloftsindependentlyofwhetheranyadditionalbatboxeswereused.Analysisofbatboxdataisrestrictedtositeswherebatboxeswereusedastheprimarymitigationorcompensationmeasure.

Methods

Theeffectivenessofmitigationstrategies

Generalizedlinearmodels(GLM)withbinomialerrordistributionswereusedtodeterminetherelativesuccessofdifferenttypesofmitigationstrategiesandwhethertheextentofdisturbance(i.e.destructionversusmodificationtotheroost)couldpredictmitigationsuccess.Thepresenceorabsenceofbatsofanyspecieswasusedastheresponsevariable.Surveyeffortwasincludedasacovariate.

Theresultsofthebinomialmodelsarepresentedbyusingtheoddsratio(OR)whichprovidesanindicationoftherelativeimportanceofeachpredictor.AnORof2.0wouldrepresentadoublingoftherelativeprobabilityofbatoccurrence;anORof0wouldrepresentnochangeinrelativeprobability,andanORof0.5wouldmeantheoddswerehalved.WealsopresentORconfidenceintervals,whichindicatetherangeofvalueswithinwhichtheestimatewouldbeexpectedtofallon95%ofoccasionswheretheworkwasrepeatedmultipletimes.Wheretheconfidenceintervalsexcludeone,theresultisconsideredstatisticallysignificant(p<0.05).Additionally,therelativeimportanceofeachparameterwasassessedbyperforminglikelihoodratiotests(Faraway2005).

Factorsinfluencingwhethernewbatloftsareused

GLMswithabinomialerrordistributionandalogitlink(usedwhenthedependentvariableiscategorical)wereconstructedtodeterminewhichcharacteristicsofabatloftinfluencedtheretentionofbats.Thepresenceorabsenceofi)pipistrelles;andii)brownlong-earedbats,wereusedastheresponsevariableswithineachofthemodels.Similarly,eitherPoissonornegativebinomialmodels(dependentonmodelfit)wereusedtodeterminewhichbatloftcharacteristicsinfluencedthenumberofbatspresentwithinaroost.Themaximumnumberofbats(pipistrellesorbrownlong-earedbats)recordedduringonesurveyingvisitwasusedastheresponsevariablewithineachofthemodels.

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Clearly,largenumbersofcharacteristicshavethepotentialtoaffectthelikelihoodofanewbatroostbeingused.Tokeepthenumberofpotentialpredictorswithinreasonablelimits,thecharacteristicsoutlinedinTable3.2wereselectedforanalysis,basedonrecommendationswithintheBatMitigationGuidelines(Mitchell-Jones2004)andapreliminaryassessmentofthecharacteristicsmostcommonlyreportedwithinthemethodstatementssubmittedbyecologicalpractitioners.

Table3.2.Thecharacteristicsofbatloftsassessedwithinthisstudy.

Characteristic DescriptionLoftvolume(m3) Thelength,widthandheightoftheproposedbatloft.Volumecalculated

followingEntwistleetal.(1997).Numberofcompartments

Thenumberofdistinct(althoughjoined)compartmentswithinaloft(e.g.formedbyinternalbaffles.

Withinloftroostingoptions

Classifiedintodistinctcategories:Boards(e.g.roughtimberboardsmountedonbattensalongtheridgebeam);Box(e.g.squeezeboxestocreateadditionalroostinglocationsinsidetheloft);Crevice(e.g.crevicesonthewallsconstructedofplywoodseparatedby19mmspacers);Multiple(whereacombinationofboxes,boardsand/orcrevicefeaturesareused).

Numberofroostentrances

Thetotalnumberofroostentrancesinstalledtofacilitatebataccessintotheloft.

Numberofroostentrancestypes

Thenumberofdifferentroostentrancetypes(e.g.accessunderridgetilesorbuiltinbattubes).Insufficientdatawasincludedwithinreportstoenableustoassesstheprovisionofflightentrancepoints.

Roostlocation Theprovisionofroostingopportunitieswithineitheri)anewbuilding,orii)thebuildingwheretheidentifiedroostwasoriginallylocated.

Itisimportanttonotethatthe‘Numberofroostentrances’canalsobeinterpretedasthenumberofcrevices/roostingopportunitiesavailableforcrevice-dwellingspecies,whichfrequentlyusethesefeaturesasroostinglocationsaswellasaccessingtheinternalloftstructure.

Surveyeffort(thetotalnumberofsurveyingperiodsincludingroostinspections,dawnanddusksurveys)wasincludedinthemodelsasamaineffect.Allpredictorvariablesweretestedforcollinearity(Pearsoncorrelationcoefficient≤0.6inallcases).Imputationwasusedtoreplacemissingdatawithincasestudiestoavoidlist-wisedeletionofcasesthathadmissingvalues.The‘mice’packageinRStudio(RStudioTeam2016)wasusedtogenerateplausiblevaluesusingpredictivemeanmatchingforcontinuousdataandpolytomouslogisticregressionforunorderedcategoricaldata.

AssessmentofbinomialmodelswasconductedusingOR(theprobabilityofoccurrence),andassessingtherelativeimportanceofeachparameterbyperforminglikelihoodratiotests.ForPoissonornegativebinomialmodels,continuouspredictorvariableswerecentredandstandardisedfollowingSchielzeth(2010)toallowdirectcomparisonofthesizeofestimated

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coefficients.Inferencesontheeffectofeachparameterweremadebycontrastingitsstandardisedestimatetootherpredictorvariablestoassessrelativeimportance,andperforminglikelihoodratioteststocomparemodelsbyexcludingeachparameterinturn(Faraway2005).Simulateddraws(n=2000)wereundertakentoconstructpredictionplotsfromtheestimateddistributionofanexplanatoryvariable,whilstallothermodelparametersweremaintainedattheirmedianobservedvalues.Allmodelswerevalidatedbyvisualexaminationofresiduals(e.g.plottingresidualsversusfittedvaluestocheckforconstantvariance;Crawley2012).

Descriptorsofadditionalvariables(e.g.thepresenceofartificialheating)werealsopresented,whichwerenotreportedinasufficientproportionofreportstoincludewiththeformalmodels,butmayhavebeenimportantindeterminingtheoccurrenceofbatspost-development.Itisimportanttonotethatthedescriptorsareintendedtohighlightmitigationcharacteristicswhich,althoughnotstatisticallyproventobeeffective,mayprovideafocusforfuturedatacollectionandanalysiswhensufficientevidencehasbeenaccumulated.

Factorsinfluencingtheuseofbatboxes

Onlyaverysmallproportionofcasestudiesspecifiedtheexactlocationwherebatboxesshouldbepositionedinpre-developmentmethodstatements,ordetailedwhichboxescontainedbatsduringpost-developmentmonitoring.Allbatboxesatasitewerethereforeconsideredcollectively.Statisticalanalysiswasconductedfollowingthesameprocedureasforbatloftsbutwithdifferentcharacteristicsincluded(Table3.3).

Table3.3.Thecharacteristicsofbatboxesassessedwithinthisstudy.

Characteristic DescriptionLocation Thelocationofboxesona)trees;b)ontheoutsideofbuildings;orc)a

combinationoftheselocations.Meanvolume Themeanvolumeofbatboxesusedatthesite.Numberofboxes Thetotalnumberofbatboxesusedatthesite.Guidance Yes/No–wasguidancetodevelopers(i.e.height/aspectofboxes)

includedwithinmethodstatement?

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Factorsinfluencingtheuseofmodifiedbatroosts

Modificationstobatroostsoccurfrequentlyduringreroofingworkorsimilar.Statisticalanalysiswasconductedfollowingthesameprocedureasforbatloftsbutwithdifferentcharacteristicsincluded(Table3.4).

Table3.4.Thecharacteristicsofmodifiedrooststhatwereassessedwithinthisstudy.

Characteristic DescriptionNumberofroostentrances

Thetotalnumberofroostentrancesretainedorinstalledtofacilitateaccessintotheloft.

Differencesinroostentrances

Differenceinthenumberofroostentrancesbetweenpre-andpost-development.

Roostentrancelocations

Whetherroostentranceswerei)retainedinthesamelocation,orii)movedtoalternativelocations.

Enhancement Theenhancementofthebatroostwhilstreroofingworkwasongoing(e.g.theconstructionofsqueezeboxes)toincreaseroostingoptions.

3.3.1Results

Theeffectivenessofmitigationstrategies

Itwasfoundthattheprobabilityofbatsreoccupyingaroostfollowingmodificationwereconsiderablygreaterthanincaseswhereroostdestructionoccurred.Theprobabilityofbatpresencefollowingmitigationwerejustoverfourtimesgreaterwithinmodifiedbutretainedrooststhanwithindestroyedandnewlyinstalledroostingfeatures(OR4.1,95%CI:1.9,9.4).

Boththetypeofroostalteration(destructionversusmodification;loglikelihood:-143.7,χ²

14.6,p<0.001)andthenumberofpost-constructionsurveys(loglikelihood:-136.5,χ²:6.6,p=0.01)weresignificantpredictorsofthepresenceofbatswithintheroost.

Thepredictedprobabilityofretainingbatswithinamodifiedroostwas0.76(95%CI:0.61,0.87)incontrasttoaprobabilityof0.44(95%CI:0.36,0.52)indestroyedroosts(Figure3.4A).Post-developmentsurveyingeffortwasalsopositivelyrelatedtomitigationsuccess;thepredictedprobabilityofdeterminingbatpresencewithinaroostwas0.72(95%CI:0.56,0.84)whentheroostwassurveyedfivetimesincontrasttoaprobabilityof0.44(95%CI:0.34,0.54)ifonlyonepost-developmentsurveywasconducted.

Similarly,thetypeofmitigationstrategydeployedwassignificantindeterminingoccupancyrate:

• Theprobabilityofretainingbatsafterreroofingwereseventimesgreaterthanifaroostwasdestroyedandonlybatboxeswereinstalled(OR7.0,95%CI:3.0,17.4).

• Thepredictedprobabilityofretainingbatsfollowingbatloftcreationwas0.53(95%CI:0.43,0.62)incontrasttoaprobabilityof0.32ifonlyusingbatboxes(95%CI:0.22,0.44;Figure3.4B).

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Figure3.4Predictionplotsofbatoccurrenceversuslevelofroostimpact(A)andthetypeofmitigationstrategyused(B).

Itisevidentthatthesuccessofmitigationishighlydependentonthestrategyusedandtheextentofdisturbancetoaroostthatoccurs.Inthefollowingsection,species-specificresponsestoeachofthedifferentmitigationstrategiesareassessedandthecharacteristicsofafeaturewhichinfluenceitssuccessaredetermined.

3.4Batlofts

Factorsinfluencingwhethernewbatloftsareused

Thisstudyassessed112mitigationcasestudiesthatincludedtheprovisionofabatloft.Ofthese,71%involvedtheconstructionofabatloftwithinanewbuilding(mostfrequentlyaboveagarage);19%withinthesamebuilding;and10%withinanexistingbutdifferentbuildingfromtheoriginallocationoftheidentifiedroost.Newlycreatedbatloftsweremoderatelysuccessfulatattractingbatswith52%(95%CI:43-61%)ofloftscontainingbatsfollowingdevelopment(Figure3.5).

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Figure3.5.Thepercentageofcaseswhichshowedevidenceofbatsusingpurpose-builtloftsfollowingmitigation.

Thenumberofbatsusingthebatloftsvariedconsiderablybyspecies,withbrownlong-earedbatshavingthehighestmeannumberofindividualswithintheloft(Figure3.6).Thelownumbersofpipistrelles(withtheexceptionofonesopranopipistrelleroost)suggestthatrelativelyfewoftheseloftshavedevelopedintomaternitycolonies.Wealsopresentresultsforthemaximumapproximatenumberofdroppingsfoundinonesurvey;however,itisworthnotingthatitishardtobothi)estimatethenumberofbatsfromthenumberofdroppings,andii)accuratelyestimatethenumberofdroppingsinapile.

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Figure3.6.Themaximumnumberofbatsfoundwithinbatloftsfollowingmitigation(A).Aroostcontaining416sopranopipistrellespost-developmentisnotvisiblewithinthisgraphduetothescale.Themaximumnumberofdroppings(approximate)foundinonesurveyvisitwithinbatloftsfollowingmitigation(B).Tworoostswhichcontainedapproximately3000commonpipistrelledroppingsand1000brownlong-earedbatdroppingsarenotvisiblewithinthegraphduetothescale.

Thecharacteristicsofbatlofts

Table3.5indicatesthecharacteristicsofbatloftsthatwereusedbybrownlong-earedbats,pipistrellesorfailedtobeoccupiedbybats.

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Table3.5Adescriptionofthecharacteristicsofnewbatloftsfollowingmitigation.

Characteristic Metric Descriptionofroosts

Brownlong-earedbat

Pipistrelle Batsnotpresent

Heightofroofspace

Median(range) 2.4m(1.5-4m) 2.18m(0.2-4.6m) 2.5m(0.3-4m)

Volumeofroofspace

Median(range) 37m3(18-264m3) 24m3(0.4-124m3) 75m3(0.3-203m3)

Numberofcompartments

%ofroostswith>1compartment(range)

67%(1-9) 35%(1-9) 49%(1-7)

Numberofroostentrances

Median(range) 2.5(1-9) 4.5(1-12) 3(1-14)

Illuminationintheroofspace

Strategiesdesignedtoensureloftisdark(%)

21% 15% 17%

Presenceofheating

Strategiesdesignedtoheatroost(%)

33%solarheating,6%heater

33%solarheating,6%heater

26%solarheating,7%heater

Otherbatspeciesintheroost

%ofloftsusedbyotherspecies

37%(29%Pipistrellebat;8%Myotisspp.)

27%(Brownlong-eared)

N/A

Alterationoftheroofspace

Strategiesspecifiedtopreventaccesstoloft(%)

34% 15% 13%

ComparableresultstoEntwistleetal.(1997)werefound,inthatbrownlong-earedbatroostsfrequentlycontainmorethanonecompartment(67%ofroostsinourstudyversus73%inEntwistleetal.).Thisislikelytobeaconsequenceofcompartmentsheatingatdifferentrates,therebyprovidingarangeoftemperatureswithintheloft.Pipistrellesweregenerallyfoundinsmallervolumeloftswithlowerheightsthanbrownlong-earedbats,whichisunsurprisinggiventhatinternalflightspaceislessofarequirementforpipistrelles.

Theprobabilityofbatpresencewithinbatloft

Thisstudyfoundthattheprobabilityofpipistrellesoccupyinganewbatloftwasstronglydependentonthenumberofcreatedroostentrances(whichforpipistrellesandothercrevice-dwellingspeciesmayalsoactasroostingopportunities)andmarginallyrelatedtothevolumeofthebatloft.Theoddsofpipistrellebatpresencewithinabatloftincreasedby29%foreveryadditionalbatentranceinstalled(OR1.29,95%CI:1.08,1.57).Theprobabilityofpipistrellebatoccurrenceinaroostcontainingonlyonecreatedentrancewas0.1(95%CI0.04,0.21),whereaswith10createdentrancestheprobabilitywas0.56(95%CI0.26,0.79)(Figure3.7).

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Figure3.7.Thepredictedprobabilityofpipistrellebatoccurrenceatanewbatloftdependingonthenumberofcreatedroostentrances(potentiallyalsoroostingopportunities)available.

Therewasalsoamarginalnegativerelationshipbetweenthevolumeoftheroostandtheprobabilityofpipistrellebatoccurrence.Theoddsofpipistrellebatpresencedecreasedby1%witheachm3increaseinloftvolume(OR0.99,95%CI:0.98,1.00).

Thenumberofroostentranceswasmarginallysignificant(i.e.0.05>p<0.1)inpredictingthepresenceofbrownlong-earedbatswithinlofts(loglikelihood:-54.24,X2:2.87,p=0.09).Theoddsofbrownlong-earedbatpresencewithinaloftincreasedby21%witheachadditionalroostentrance(OR1.21,95%CI:0.97,1.59)added.

Thenumberofroostentranceswasalsoamarginallysignificantpredictorofthenumberofpipistrellesfoundwithinabatloft(loglikelihood:-57.39,X2:14.1,p=0.08).Thesamplesizewasconsiderablyreducedwhenattemptingtopredicthowloftcharacteristicsdeterminethetotalnumberofbats,asthepresenceofbatswasfrequentlydeterminedeitherbydroppingsoremergencesurveyswhichhadconsiderablevariabilityinsurveyingmethodology.

Althoughtheresultsindicatethatincreasingthenumberofcreatedroostentranceswillincreasetheprobabilityofbatsoccurringpost-development,itislikelythatanupperlimitwillexistwherebyadditionalentranceswillcreatedraughtandlightexposuretotheloft.Itwasnotpossibletoassessthismaximalthresholdgiventheconstraintsofnotusinganexperimentalapproach(i.e.veryfewcasesusedmorethansixentrances–thisisevidentbythewideconfidenceintervalsinFigure3.7).Theresultshouldthereforebetreatedwithcautionandattentionshouldbepaidtoensuringanyadditionalentrancesdonotimpacttheconditions(e.g.microclimate)oftheloft.

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Assessmentofsuccessofbatloftsbyecologicalconsultants

Arelativelysmallproportionofbatloftcasestudies(n=35,31%)containedassessmentsofthesuccessofmitigationstrategieswithintheirreport.Theassessmentscouldbebroadlysplitintofourcategories:‘notsuccessful’,‘noconcern’,‘partiallysuccessful’and‘successful’.Thecategoryof‘noconcern’couldbedefinedascaseswherenobatshadbeenfoundbutnoactionwasdeemedtoberequired.

Theonecasestudywhichdefineditselfasunsuccessfulhaddeterminedbatpresencewithintheroost,butstatedthatthiswasinsufficientrelativetothepre-developmentbatpopulation.Incontrast,82%ofcasestudiesthatperceivedtheretobe‘noconcern’hadnotdetectedbatsduringpost-developmentmonitoring.

Thecriteriaonwhichsuccesswasjudgedbyconsultantswereprimarily:

i) mitigationstrategieshavingbeenimplementedcorrectly;ii) activitysurveyshavingrecordedbatsforagingintheareasurroundingtheroost

whichmakeitmorelikelythatbatswouldstartusingtheroost;and/oriii) therehavingbeeninsufficienttimebetweenmitigationandmonitoringforbatsto

havecolonisedtheloft.

Casestudieswhichwereconsideredpartiallysuccessfulhadsmallnumbersofbatspresent,whereasfullysuccessfulcaseshadreachedorexceededpre-developmentlevels.Afewcasestudieshadscenarioswherebatswerestillusingthebuilding,butnottheintendedmitigation:thesewereconsideredsuccessesasthedevelopmentremainedasiteofcontinuedecologicalfunctionality.Itisworthnoting,however,thatretentionofbatsoutsideoftheintendedmitigationmayhaveunforeseenconsequences,suchasthepresenceofbreathableroofingmembraneswithinthenewlyinhabitedarea.Veryfewcasestudiesreportedwhetheramaternityroosthaddevelopedwithinthebatloft;however,onebarncontaining10brownlong-earedbatswasconsideredlikelytobeusedasamaternityroostasthisnumberiswithinthetypicalsizeofabrownlong-earedbatnurseryroost(10-30individuals;GreenawayandHutson1990).

3.5Batboxes

Batboxesarefrequentlydeployedaroundasitewithouttheexpectationforbatstobeusingalltheboxesatanyonetime.Here,theeffectivenessofbatboxesatretainingbatsacrossasiteisassessed.

Factorsinfluencingtheuseofbatboxes

Thisstudyassessed119mitigationcase-studiesthatincludedtheprovisionofbatboxes.Arelativelylowproportionrecordedthattheboxesweresuccessfullyusedbybats(31%,95%CI:24%,40%),withpipistrellespredominantlyusingtheboxes(Figure3.8).Therewasarelatively

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highnumberofcaseswheredroppingswerevisuallyidentifiedaspipistrellebatdroppingswithouttheuseofmolecularverification.

Figure3.8Thepercentageofcaseswhichretainedbatswithinbatboxesfollowingmitigation

Thecharacteristicsofbatboxes

Batswerepresentatsiteswhereamedianaverageoffiveboxeswereinstalled,incontrasttoanaverageofthreeboxesatsiteswhichwerenotoccupied(Table3.6).

Table3.6Adescriptionofthecharacteristicsofbatboxespersitefollowingmitigation.Averagevolumeofboxesisonlyintendedforinformativepurposestoshowtherangeofboxsizesavailableratherthanforanalyticalpurposes.

Characteristic Metric Descriptionofmitigation

Batspresent BatsnotpresentNumberofboxes Median(range) 5(1-32) 3(1-24)Averagevolume(cm3) Median(range) 12,571(5,598-60,000) 11,764(270-

60,000)Height(m) Median(range) 4(3-5) 4(3-5)Aspect %ofboxesfacingbroadly

south63% 54%

Locationofboxes Building(%occupancy) 22%(12-36%) (95%CI) Trees(%occupancy) 39%(28-52%) Mixture(%occupancy) 23%(10-47%)

Therewasnodifferenceintheheightofboxesbetweensiteswhereboxesbecameoccupiedandwheretheydidnot.Giventhatthemajorityofboxesareinstalledatheightsrecommendedincurrentbestpracticeguidelines(BatConservationTrust2017b),therewasrelativelylittle

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rangeofheightsthatboxeswereinstalledat.Siteswhereboxeswereinstalledontreesappeartohaveaslightlyhigher(butnon-significant,seebelow)probabilityofretainingbatsfollowingmitigation.AlthoughthemajorityofbatboxesrecommendedwerecomprisedofWoodcrete(>80%),itwasnotpossibletotesttheeffectivenessofwoodenversusWoodcreteboxesformallygiventhelimitationsofhowthedatawasreported(Chapter4).

Theprobabilityofbatpresencewithinbatboxes

Thisstudyassessedwhichfeaturesofbatboxesdeterminedtheiroccupancybypipistrelles.Otherspecieswerefoundinaninsufficientnumberofsitestobeassessedindividually.

Atthesitelevel,thegreaterthenumberofbatboxesdeployed,thegreatertheprobabilityofatleastoneoftheboxesbecomingoccupied(Figure3.9).Theoddsofbatsoccupyingatleastoneboxincreasedbyapproximately7%(OR1.07,95%CI1.00,1.16)witheachadditionalbatboxthatwasdeployed.

Figure3.9.Therelationshipbetweenthenumbersofbatboxesdeployedwithinamitigationstrategyandtheoccurrenceofpipistrelles.

Additionally,therewasasignificantrelationshipbetweenthenumberofbatboxeswithinadevelopmentandthenumberofbatscontainedwithinthem(coefficientestimate:0.4±0.03,X2=28.9,p=0.04).Despiteitssignificance,therelativelysmalleffectsize(0.4)andtheinfluenceofoneoutlierontheresultindicatesthatthereisonlyaweakbiologicalrelationship.

Theuseofmultiplebatboxes

Giventhevariableexpenseofaddingadditionalbatboxes(costdependentonbatboxmodelused)toamitigationstrategy,itispertinenttoestablishhowtheprobabilityofuptakeincreaseswitheachextraboxinstalled.InFigure3.10thereappearstobeanexponentialrelationshipbetweenthenumberofbatboxesusedaspartofthemitigationstrategyandthenumberofboxeswhichcontainbats.Whenrelativelylownumbersofboxesweredeployed

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(i.e.<20),onlyasmallproportionofthesebecameoccupied,whereaswhenlargernumberofboxeswereinstalled,theoccupancyrateappearstoincrease.However,itisworthnotingthatevenwhenalargenumberofbatboxesweredeployed(i.e.>20boxes),theoccupancyrateremainedrelativelylow(fewerthan50%ofboxeswereused).Giventhewiderangeofboxsizesandmodelsareavailableitislikelythattherelationshipbetweenoccupancyandnumberofboxeswillvarybetweenboxtype.

Figure3.10.Thenumberofbatboxesusedandthenumberofboxeswhichbecameoccupied.Thesizeofthecirclesindicatesthenumberofbatsordroppingsfoundacrossthesite.

Largerclustersofbats(morethan10individualsacrossasite)couldnotbepredictedfromthenumberofbatboxesdeployed.Forexample,siteswhichonlydeployedoneortwoboxesonbuildingsretained14and25batsrespectivelypost-development,whereassiteswhichdeployed30and32boxesontreesretained28and15batspost-development.Therewasnodifferenceinthemakeormodeloftheboxesusedbetweenthesesites.Thishighlightsthatthesitingofindividualboxesatamicro-scale(e.g.alongsidetheedgeofawoodlandcomparedtoinahousingestatewithlittlevegetativecover),alongsidetheavailabilityofalternativeroostsinthesurroundinglandscape,arelikelytobemostimportantindeterminingbatboxuptake.

Discussion

Thenumberofbatboxespresentwithinasitewasthestrongestpredictorofwhetherbatswouldberetainedfollowingmitigation.Additionalbatboxesmayleadtoi)anincreasedprobabilityofabatencounteringabatbox,orii)awidervarietyofmicro-habitats,whichmayattractagreaternumberofbats.Eachadditionalbatboxcomeswiththecostofpurchase,batboxerection,maintenanceandreplacementovertime.

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Giventheextensiveuseofbatboxeswithinmitigation,itisdisappointingthatitwasnotpossibletoassessthepresenceorabsenceofbatsattheindividualboxlevelduetothelackofrecordingofthesedetails(seeChapter4forfurtherdiscussion).

3.6Modifiedbatroosts

Thecharacteristicsofmodifiedbatroosts

Thisstudyassessed52mitigationcasestudieswhereroostsweremodifiedduetoreroofingworks.In67%(95%CI:54–79%)ofcases,batswereretainedfollowingreroofing.

Table3.7indicatesthatthemediannumberofroostentrancesinreroofingcasesisalmostdoublethatofnewbatlofts(Table3.5);thismayexplainthehigherretentionrateofroostswherethereisdisplacementratherthanreplacement.Thismaybebecause,duringreroofingwork,additionaltimeandeffortisfocusedonidentifyingallpreviousentrancessothattheycanberetainedorrecreated.Therewasanecdotalevidence,withinsubmittedcasestudiesandfromTable3.7,thattheretentionoforiginaltimberscontributedtothesuccessofnewbatlofts.However,therewasinsufficientdatatotestthisrelationshipformally.Theinclusionwithinamethodstatementofwhethernewororiginaltimberistobeusedwouldallowtheformaltestingofitsimportanceinretainingbatpopulations.Similarly,airflowortemperaturedatawasrarelyincludedincasestudiesdespiteanecdotalevidencethatthesemaybeimportantindeterminingbatpresence.

Table3.7-Adescriptionofthecharacteristicsofmodifiedbatroostsfollowingmitigation.

Characteristic Metric Descriptionofroosts

Brownlong-earedbat

Pipistrelle Batsnotpresent

Numberofroostentrances

Median(range) 8(1to10) 6(1to22) 3(1to10)

Differenceinnumberofroostentrances(pre-post)

Median(range) 0(0to4) 0(0to4) 1(-2to2)

Locationofroostentrances

%ofsiteswhichinstallednewroostentrances

60 69 67

Retentionofoldtimber %ofroostswhichretainedtimber

33 20 6

Alterationswithinroost %ofroostsalteredtoimproveroostingpotential

31 53 12

Theprobabilityofbatpresencewithinmodifiedbatroosts

Theprobabilityofpipistrellesreturningtoamodifiedroostwerefoundtobeconsiderablygreaterifbatroostswerealteredtoimproveroostingoptionsaspartofthereroofingwork(loglikelihood:-30.4,X2:6.8,p0.009).Althoughtheindividualstrategiesvariedbetweencasestudies,enhancementsincludedthere-instatementoftheroofusinghandmadeclayrooftilestoprovidenumerousnaturalcrevicesandtheprovisionofroughsawntimbercrevicesand

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squeezeboxes.Theoddsofpipistrellebatpresencefollowingmitigationwerejustoversixtimesgreaterwithenhancedrooststhanrooststhatwerenotenhanced(OR6.1,95%CI:1.6,27.7).Thepredictedprobabilityofpipistrellesreturningtoaroostfollowingenhancementwas0.59(95%CI0.3,0.8)incontrasttoaprobabilityof0.19(95%CI0.09,0.37)inroostswithnoenhancements.

Therewasamarginalbutsignificantrelationshipbetweenthenumberofroostentrancesproposedandtheprobabilityofbats(allspecies)returningtothemodifiedroostincomparablenumberstothosefoundwithinpre-constructionsurveys(loglikelihood:-27.3,X2:3.1,p0.079).Theoddsofretainingcomparablenumbersofbatsfollowingmitigationincreasedby16%foreveryadditionalroostentrance(OR1.16,95%CI:0.98,1.42)installed.Thepredictedprobabilityofbatsreturningincomparablenumbersincreasedfrom0.18(95%CI0.06,0.45)whentherewasonlyoneknownentranceincontrasttoaprobabilityof0.53(95%CI0.25,0.79)whentherewere12knownroostentrances.Therewerenosignificantpredictorsofbrownlong-earedbatoccurrencewithinmodifiedbatlofts.

Assessmentofsuccessbyecologicalconsultantsformodifiedbatroosts

Arelativelysmallproportionofreroofingcasestudies(23%)containedassessmentsofthesuccessofmitigationstrategieswithintheirmonitoringreturn.Halfoftheseconcludedthattherewas‘noconcern’.Inallofthesecases,thetargetspecieswasrecordedintheroost,butitisalsonotablethatthenumberofindividualshaddeclinedinallcases.Highforagingactivityrecordedduringmonitoringsurveyswasalsousedasjustificationforthecontinualuseofthesite.Thosecasestudieswhichconsideredthemitigationasasuccessspecificallyhighlightedthatthebatswereusingthesameaccesspointsalongsidereturninginsimilarnumbers.Afewstudiesfoundthatbatswereusingalternativepartsofthebuildingthathadnotundergonedevelopmentwiththepremisethatthewideavailabilityofhigh-qualitybatroostingopportunitiesexplainedthelackofretentionofbatswithinthedevelopedroost.

3.7Theoccurrenceofbatsovertimefrommitigation

Todeterminewhetheri)thepresenceofbatsorii)thenumberofbatsincreasesovertime,siteswereassessedwheresurveyinghadbeenconductedovermultipleyears.Onlysiteswithcomparablelevelsofsurveyingeffortandmonitoringmethods(i.e.emergencesurveys)whichwereundertakenbetweenyearswereincluded,toallowforanaccuratecomparison.Thisconsiderablyreducedthesamplesize(18casestudiesintotal);however,ourresultsmayproveindicativeoftrendsandhighlighttheneedforstandardised,repeatablestudiesovermultipleyears.Therewereinsufficientcasestudiestoassesspopulationchangeovertimeinmaternityroosts.

ItisevidentfromFigure3.11thattheproportionofrooststhatbatsareidentifiedasusingincreasesovertime;however,thereisamarginaldifferencebetweenyears.Figure3.12demonstratesthatthereisconsiderablevariabilitybetweensitesinthetimetakenforrooststoaccumulateeitherdroppingsorbats.Itisimportanttonotethattheseresultsareconstrainedbytherelativelyshortperiodbetweenimplementationandmonitoring.Itwouldbeexpected

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thatthenumberofbatsandthequantityofbatdroppingswouldincreaseincrementallyovertime.Whiletheavailableevidencesupportsthisforbrownlong-earedbatdroppingsandpipistrellebatabundance,therelationshipislessclearforpipistrellebatdroppingsorbrownlong-earedbatabundance(Figure3.12).

Figure3.11.Theproportionofrooststhatshowedevidenceofbatswithinthefouryearsthatfollowedmitigation.Althoughalltheroostsinspectedinthefourthyearcontainedevidenceofbats,thewideconfidenceintervalsindicatetheuncertaintyinthisresultduetothelowsamplesize(n=4).

ThewideconfidenceintervalsinFigure3.12highlightthevariabilitybetweencasestudiesandreflectsite-specificdifferencesinretentionratesandthelengthoftimeitmaytaketorecolonisearoost.Itisimportanttonotethatrelativelyfewreportsindicatedwhetherdroppingswereremovedfromloftsorboxesbetweenyears.Thismakesitdifficulttoascertainifanincreasednumberofdroppingsisasignofgreaterbatuseovertime.Afewstudiesstatedthatsheetsofpaperwereputdownafterasurveytoaccuratelymonitorchangesindroppings;thisisamorequantifiablemethodofmeasuringtheaccumulationofdroppingsandshouldformfuturebest-practiceguidelines.Additionally,batdroppingsmaynotallaccumulatewithintheloftspaceduetotheirroostinghabits(e.g.withinacavityorbetweentileandroofingfelt).

LikeMackintoshetal(2016),mostmonitoringreturnsreceivedwerewithinthreeyearsofmitigation,soitwasnotpossibletoinvestigatelongertime-trendsinroostoccupancy.

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Figure3.12.Roostoccupancyagainstyearsfrommitigation(A).Foreachsite,apercentagewascalculatedbyassessingthenumberofbatsrecordedwithintheroostduringeachpost-constructionsurveyingperiodagainstthepeaknumberofpost-constructionbatsfoundwithintheroost.Similarlyfor(B),apercentagewascalculatedbyassessingthenumberofdroppingsduringeachsurveyagainstthepeaknumberofdroppingsfoundatthesite.Errorbarsindicate95%confidenceintervals.

3.8Detailswithinmonitoringreports

OurmethodofextractingdatafromEPSlicenceapplicationswashighlydependentonreportscontainingsufficientdetailstoallowustoconductstatisticalanalysis.Asub-sampleofmonitoringreports(49casestudies)wereassessedtodeterminewhatkeyinformationhadbeenrecorded(Figure3.13).Thedateofsurvey(93%),personnelinvolved(80%)andweatherconditions(68%)werethemostfrequentlyrecordedwithinreports.

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Figure3.13Thepercentageofcasestudieswhichincludedarangeofsurveyingdetailsinemergencesurveymonitoringreports.‘Mitigationmonitored’referstowhetherthemonitoringreportidentifiedwhichorhowmanymitigationfeatureswerevisibleduringthesurvey(e.g.“allrecentlyinstalledbattileswerevisibleduringthisemergencesurvey”).

Detailsofsurveyeffort,suchasthedurationofemergencecounts(startandendtimes),wereonlyrecordedinjustoverhalfthecases,makingassessmentsofoccupancydifficultgiventhatdetectionratesarelikelytoincreasewithsurveyeffort.Boththelocationofsurvey(i.e.whataspects/extentofthebuildingwerebeingmonitored),andspecificallywhichmitigationfeatureswerebeingobserved,werereportedinfewerthan20%ofcasesdespitebeingcriticalforassessingtheeffectivenessofmitigationstrategies.

Itisunderstandablethatmethodstatementsfrequentlyomitthemakeandmodelofthebatboxes,theirexactlocation,aspectorheightabovetheground,especiallyinlargerdevelopments.Thesedecisionscanoftenbetakenatlaterstagesofthedevelopmentafteralicencehasbeenissued.However,post-developmentmonitoringpresentstheopportunitytorecordthisinformation.Thiswillhelpconsultantsassessifthemitigationstrategyhasbeenimplementedcorrectly,aswellascollectingusefulevidencetoimproveourknowledgeofmitigationefficacy.Similarly,wheremultiplebatboxeshavebeendeployedwithinasite,thereportingofwhichboxescontainedbatsisoftenvague.Itisoftenimpossibletodeterminewhetherboxesretainedbatsacrossseasonsastheidentityofboxesisnotstated.Similaroccurrencescouldbefoundincasestudiesinvolvingthedevelopmentorcreationofmultiplebatloftswithinasite.Whereamethodstatementreferstomultiplelofts,thenitisessentialthatmonitoringreportsusethesamenomenclatureoneachoccasiontoensurethatspecificlocationscanbematchedupwithsurveyresults.

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Caseswerealsoencounteredwherethresholdsofweathervariableswerereported(i.e.“thesurveywasundertakeninconditionssuitableforemergencesurveyssuchastemperaturesabove8°C”)ratherthangivingtheexactmeasurements.Althoughthisconformstothesurveyingrecommendationsforcurrentbest-practiceguidelines(Collins2016),giventhestrongrelationshipbetweenwindspeed,temperatureandbatactivity(Russetal.2003),itiscriticalthatCollins2016isfollowedandtheactualmeasurementsarerecorded.

3.9Theuseofbatactivitytoinferroostuse

Highforagingactivityinthevicinityofroostsmakesitlikelythatamitigationfeatureislikelytobediscoveredandusedbybats.Althoughmostpost-developmentemergencesurveysalsoincludereportsofbatsobserved/recordedforaginginthevicinityofthemitigationstrategy,theseusuallywerenotstandardisedintermsofsurveyeffortorequipmentwiththepre-developmentsurveys,preventingtheformalcomparisonofthetwosurveyperiods.Wherearoostinspectionisnotpossible(e.g.noloftaccessisprovided),oremergencesurveysaredifficult(e.g.multipleexitsacrossabuilding)thanbatactivitysurveysmaybeusedtocompareactivitylevelsbetweenpre-andpost-construction;however,thisisdependentonstringentlyfollowingthesameprotocoltoallowforabefore-aftercomparisontobeconducted.Additionally,whilethereislikelytobearelationshipbetweenthenumberofbatsemergingandthenumberofbatpassesrecorded,thisrelationshipiscurrentlyuntested(andmaybespecies-specific).Thereportingofbatactivityaseither‘low’,‘moderate’,or‘high’byconsultantswithinmonitoringreportsprovidescontexttotheextentofbatactivitythatwasrecorded(butseeLintottetal,inpress);however,thelackofrawdatameantthatitwasnotpossibletoundertakeanyfurtherquantitativeassessment.Enquiriestoconsultantsregardingaccesstodatagenerallyledtodiscussionsaroundthedifficultiesinfindingandcompilingthedatatomakeitaccessibletoothers.Wethereforerecommendthatstandardisingdatacollectionandreportingduringthelicensingprocesswillmaketheprocesseasierforallinvolved(chapter4).

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Chapter4:Barriersandsolutionstothelackofeffectivemonitoring

Althoughthisstudyhasdevelopedourunderstandingoftheeffectivenessofmitigationstrategies,therearestillgapsintheevidencebasewheredatawaseithernotcollectedorwasreportedininsufficientdetailtoallowforanalysis.Recommendationsforimprovementsareoutlinedinthischapteranditisexplainedhowthesecouldfacilitatethetransitiontoarobustandtransparentmonitoringprocess

4.1Thepurposeofpost-developmentmonitoring

Post-developmentmonitoringiscostlytodevelopersandplacesanadministrativeburdenonthoseresponsibleforensuringthatconditionsofplanningconsentandEPSlicensingaremet.Alackofresourceshasthereforefrequentlymeantthatanalysisofmonitoringreturnsrarelyoccurs.Itisthereforevitalthatthereisclarityaboutthepurposeofmonitoringinordertoensurethatthetechniquesusedareproportionate,fitforpurposeanddeliverapositiveresult.Forexample,NaturalEnglandsuggestthatmonitoringmaybeameansof“comparingpopulationtrends”beforeandafterdevelopment(NaturalEngland2015),whereasforpractitionersitmayenhancetheirprofessionaldevelopmentbyprovidingfeedbackontheirdecision-making.

Ifthemainintentionofmonitoringistodeterminetheeffectivenessofmitigation,thenitisvaluabletoconsideri)howsuccessshouldbemeasured,andii)whatadaptivemanagementactions,ifany,shouldbeputinplaceifthemitigationisfoundtobeunsuccessful.Theperceptionofwhatconstitutesmitigationsuccessisopentobroadinterpretationandcouldincludeanyofthefollowingdefinitions:retainingthesamevolumeofroostingspace;maintainingbatforagingactivityaroundtheroost;retainingthepresenceofbatswithinthesamebuilding;theoccupancyofmitigationfeaturesbybats;andmaintainingorincreasingthepopulationsizewithintheroost.Eachofthesemeasureswereusedwithincasestudiesasjustificationthatnofurthermonitoringwasrequiredandthatthedevelopmenthadnotnegativelyimpactedbats.Forexample,therewereseveralcaseswherethediscoveryofbatdroppingsduringaloftinspectionwastakenassufficientevidenceofuseandsoadditionalemergenceandre-entrysurveyswerecancelled.Whilstthismaybepreferabletochargingtheclientextraforadditionalsurveysifthesolepurposewastoconfirmpresence,thesefindingsdonotprovidesufficientlevelsofdetailtoenablecomparisonswithpre-developmentpopulationsizes.Wherethethresholdshouldlieisopentodebate,forexample,inaworkshophostedbytheauthors(MammalSocietyConference2017),itwasarguedbyaudiencemembersthat,giventherelativelyshorttimebetweenmitigationandmonitoring,itwouldbeunrealistictoexpectpopulationstohavereturnedtopre-constructionlevels.Althoughthisviewpointisunderstandable,itisworthquestioningwhetherthetimeframeformonitoringshouldberevisedtoensurethatcomparisonsbetweenpre-andpost-developmentbatnumberscanbedrawn.Itmaybethatifmonitoringisconductedwithinthefirstfewyearsfollowingmitigation,thenthepresenceofthetargetspeciesissufficientasanindicatorofmitigationsuccess;

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whereasinsubsequentyearsattainingcomparablepopulationsizeswouldbeexpected.However,extendingtheperiodofpost-constructionmonitoringwouldbringnewchallenges,suchasobtainingaccesstobuildingsonceownershipchanges,gettingtheclienttopayforthemonitoringandthedifficultiesofcalculatingappropriateratestochargeforvisitsthatmaybe10yearsinthefuture.Irrespectiveofwherethethresholdlies,werecommendthatameasurementofsuccessshouldbedefinedwithinthemethodstatementduringthepre-developmentstageofaproject.

Giventheperceptionthatpressurefromdevelopersandthegovernmentisleadingtoareductioninmonitoring(Chapter2),itmaybethattheexplicitstatementoftheobjectivesofthemonitoringwouldprovideamoretransparentbasisforconductingpost-developmentsurveys.Theinclusionofsuccesscriteriawithinthemethodstatementwouldalsoallowanactionplantobedevelopedifmonitoringhighlightsacauseforconcern.Thisensuresthatremedialworkisoutlinedfromtheoutset,providingbothatransparentcosttotheclientandacoherentpurposeforundertakingpost-developmentmonitoring.

Itisworthnotingthattheoptionsavailableforremedialworkwillvarydependingonthemitigationfeaturesused.Forexample,itisrelativelystraightforwardtorelocateorrepositionabatbox,whereasifabatlofthasbeenconstructedfollowingbest-practiceguidelines,internalconditions(temperature,lightlevelsandhumidity)areacceptable,andtheexternalcontext(lighting,connectivity)iscorrect,theremayberelativelylittlemodificationthatcanusefullybemade.Inthiscase,giventheimportanceofbatloftentrances,itmaybethatremedialactionjustinvolvestheinspectionofroostentrancestoensuretheyhaveremainedclearandunlit.Alternatively,remedialactionmaynotbeconsiderednecessary,regardlessoftheoccurrenceofbats,butbystatingthisatthepre-developmentstage,itgivestheSNCBsandLPAssufficientdetailtoassesstheserecommendations.

4.2Thestandardisationofdatacollectionandreporting

Theextentofanalysesthatwecouldconductwereconstrainedbyi)thenumberofcasestudieswewereabletoobtain,andii)alackofdetailedinformationwithinthecasestudies.Here,weoutlinewhythismighthavebeenthecase,andwhatstrategiescanbeimplementedtohelpbuildtheevidencebaseinthefuture.

Thelackofcasestudies:Consultantsoftencitedalackoftimeanddifficultiesinfindingalltherequiredinformation(e.g.collatingreportsfromdifferentmembersofstaffwhowereinvolvedinvaryingstagesoftheproject;filingsystemsthatmeantthatmethodstatementswereseparatedfromfollow-upmonitoringdata;olderdatabeingarchivedetc.)astheprimaryreasonwhytheywereunabletocontributetotheproject.Itisthereforeevidentthatthemostappropriatetimetocapturethisinformationisduringthelicensingprocessitself,astheSNCBshavetheauthoritytorequiretherelevantdatatobesubmitted.GiventhatmonitoringdataarenotcurrentlyassessedbytheSNCBs(whoalsohavetime-andresource-constraints),thenasatisfactorysolutionmaybetoadaptthecurrentsubmissionsystemtocapturedatamoreeffectively;aprocesswhichshouldalsoassisttheSNCBsindischargingtheirdutiestoreport

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derogationlicencesandtheirconsequencesunderSection17oftheHabitatsRegulations.Themechanismtoenablethisisdiscussedbelow.

Thelackofdetailedinformationwithinlicencereturns:Thisissuehasfrequentlybeenhighlightedasaproblem,forexampleStoneetal.(2013)notedthattheywereunabletodeterminewhethermitigationwaseffectivebecauseof“inadequateandinconsistentpost-developmentdataonlicencereturnforms”.Theirstudyassessedlicencereturnsfrom2003to2005,anditisofconcernthatlittleappearstohavechangedintheinterveningperiod.Thedevelopmentofanintegratedelectronicsubmissionsystemthatlinksdataonthepre-developmentsurveys,proposedmitigationstrategy,implementationandpost-developmentmonitoringisthereforestronglyrecommended.Thissystemwouldcapturequantitativedatathatarecomparablebetweencasesandthatcanbeanalysedandassessedperiodically.

Figure4.1Simpleschematicillustratingtheinformationthatshouldbecollectedandreportedtoprovidecontextforpost-developmentmonitoring.Thisincludescomparableinformationbetweenpre-andpost-constructionsurveys,amethodstatementwhichincludesdetailsofthemonitoringmethodologyandameasureofsuccess,andafeedbackmechanismtoimplementremedialworkifeithermitigationisnotimplementedcorrectlyorthethresholdofsuccessisnotattained.Itshouldbenoted,however,thatsomeprojectswillnotobtainthethresholdofsuccessevenifallmitigationhasbeenimplementedasrecommended;thisshouldbejudgedonacase-by-casebasis.

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Keyrecommendations

1)Pre-constructionmethodstatementsshouldincluderecommendationsforpost-constructionmonitoringstrategiesandadefinitionofwhatwillbeconsideredsuccessful.

2)Wherepossible,assessmentofimplementationasperthemitigation/compensationstrategyshouldbeconductedassoonaspossiblefollowingconstruction.Conversely,delayingpost-constructionmonitoringbyaslongaspossiblewillprovideabetterassessmentofmitigationsuccess.

3)Post-constructionmonitoringshouldreplicatethemethodologyofpre-constructionsurveysasfaraspossible(e.g.surveytype,seasonality,surveyingeffort).

4)Thelevelofdetailcollectedandreportedduringpost-constructionmonitoringshouldmatchorexceedthatofpre-constructionsurveys.

5)Post-constructionmonitoringshouldbeusedtocollectadditionalinformationregardingmitigationstrategiesdeployed,forexamplethemakeandmodelofbatboxesused,theirlocation,aspectandheight.

6)Thedevelopmentofanappropriatelystructuredintegratedelectronicsubmissionsystemthatlinksdataonthepre-developmentsurveys,proposedmitigationstrategy,implementationandpost-developmentmonitoringwillincreasetherobustnessoftheevidence-base.

Conclusion

Batsarefacinganunprecedentedthreatfromrapidurbanisationandthepotentiallooseningofenvironmentalprotectionaffordedtothem.Evidence-basedmitigationisthereforekeytoefficientlybuteffectivelyconservingbatpopulationsatlocal,regionalandnationallevels.Theconstraintsonaccessingorinterrogatingdatatobuildtheevidence-baseshouldbeaddressedasapriority.Anonlinesystem,setuptocaptureandsecurelystoremitigationdatawillbenefitSNCBsbyprovidinganimmediateandclearindicatorofmonitoringsuccess,willcontributetoagreaterunderstandingofhowbesttoundertakemitigation,andwillprovideconsultantswiththeevidencetoundertakeeffectivemitigation.

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Appendix1:Questionnaire

Thisquestionnairewasdistributedtoecologicalpractitionersin2017tofurtherourunderstandingoftheextentthatpost-developmentmonitoringoccurs(Chapter2)

Pleaserestrictyouranswerstoprojectswithinthelast5yearswhichhaveinvolvedbatsroostinginbuildings.Estimatesaresuitableforallanswers.Allanswerswillbetreatedanonymously.

1)Pleaseindicateifyourresponseswillreflect:

i)Casesthatyouhavepersonallyled.

ii)Asummaryofcasesundertakenbyyourcompanyoffice.

iii)Asummaryofcasesundertakenbyyourcompany.

2)What%ofyourprojectsincludedbatmitigation?

3)What%ofthesehadanEPSLicence?

4)Approximatelyhowmanyprojectsrelatingtobatsinbuildingsdoyoudealwithayear?

5)Inyouropinion,doestheevidencebaseexisttoenableyoutomakeinformeddecisionsonbestpracticemitigationstrategies?

Yes,Partly,No

6)Inwhat%ofprojects,hasmitigationspecificallyaddressedconcernsaboutcumulativeimpactsatalandscapescale?

7)What%ofmitigationstrategiesinvolvedbatboxes?

8)Asanestimate,what%ofmitigationprojectshadfollow-upmonitoringrecommendedaspartofanEPSLorplanningapplication?

9)Ifmitigationoccurs,haveyoubeenabletosecurearequirementtomonitorthroughtheEPSlicenceorconditionofplanning?

Yes,No

10)Haveyoueverencounteredasituationwhereyouhaverecommendedmonitoring,andtheclientiswillingtopayforitBUTaStatutoryNatureConservationOrganisationorLocalAuthorityhasdeemeditunnecessary?

No Yes-strippedoutbySNCB Yes-StrippedoutbyLA Yes–Strippedoutbyboth

10a)Doyouthinkthisproblemisgettingworseoverthelast5years?

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