Reviewing the evidence on mitigation strategies for bats ... · Evidence of bat usage found in 75%...
Transcript of Reviewing the evidence on mitigation strategies for bats ... · Evidence of bat usage found in 75%...
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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?