A Comparison of Acoustic and Capture Methods as Means of Assessing Bat Diversity and Activity in Honduras Claire Hopkins Supervisor: Prof. John Altringham M.Sc. Thesis University of Leeds August 2004 2Contents Abstract3 Introduction 4 Echolocation in microchiropteran bats4 Call frequency5 Intensity and effective range5 Echolocation and foraging behaviour6 Call flexibility 7 Sampling and detection methods8 Aims and objectives 9 Materials and Methods10 Study area10 Site selection 10 Capture survey11 Acoustic survey12 Sound analysis13 Bat activity13 Results15 Capture data 15 Species accumulation curves17 Capture times19 Sonar reference library analysis19 Indices of bat activity23 Discussion25 Interspecific echolocation call properties of Neotropical bats25 Intraspecific sonar characteristics 26 Timing of capture28 Measures of bat diversity in the Neotropics29 Indices of relative bat activity30 Future studies32 Conclusion33 Acknowledgements34 References35 3Abstract Theuseofbatdetectorsinconjunctionwithtraditionalcapturemethodsfor creating inventories of microchiropteran communities is becoming increasingly widespread.Howevertheextenttowhichbatscanbedistinguishedbythe propertiesoftheirecholocationcallsisstillindispute.Thecurrentstudy compares two techniques for detecting bats and evaluates their effectiveness incontributingtowardspecieslistsandelucidatingactivitypatternsina previously unstudied area.Mistnetsweredeployedatanumberofsitesinthreelocationsinthe Merendon Mountains of northern Honduras (Base Camp, Buenos Aires and El Paraiso).Atotalof266batsof28specieswerecapturedoverthe6-week study period and successfully recorded calls formed the basis of a reference library. An acoustic survey based on the number of bat passes detected with a Tranquility detector along a 250m transect was also carried out.Interspecific variability in sonar properties was found to be low in relation to intraspecificvariationandnostatisticaldifferenceswerefoundbetweencall parametersofbatsrepresentingsimilarguilds.Whilethisnegatesthe reliability of acoustic methods to carry out accurate biodiversity assessments it highlights potential for recognition of bats according to their foraging guild.Mist netting remains the most reliable way of identifying bats in the field but tendstobebiasedtowardPhyllostomidbatsforagingintheunderstorey. Acousticmonitoringisfoundtobeaconvenientmethodofassessingbat activity in an area but is sensitive to small scale variations in bat abundance, foragingpatternsandhabitatconfigurations.Futureresearchshouldaimto supplement the call reference library with bats from different guilds and further elucidate ways of recognizing bats acoustically. Patterns of bat activity should also be established in order to maximize the effectiveness of surveys carried out in limited time periods.4Introduction BatsareoneofthemajortaxonomicgroupsinHondurascomprising the most species-rich and ecologically diverse mammalian taxon at the local communitylevelintheNeotropics(Pattersonetal.2001,Kalko1995).The ecological importance of bats in tropical forest ecosystems as seed dispersal andpollinationagentsandtheircontributiontothediversityofvertebrate communitiesisbecomingincreasinglyrecognized.Around98speciesof microchiropteranbatsarecurrentlyrecognisedinHonduras(IUCN,1994). This is dominated by the family Phyllostomidae (New World leaf-nosed bats) which represents a diverse radiation that is endemic to the Neotropics (Kalko &Handley2001).Patternsofdiversityandabundanceinlocalbat communitiesreflectdifferencesinecologicalconditionssuchaslevelsof disturbance(Medellinetal.2000)andtheavailabilityofroostsitesand foraginghabitats(Wunder&Carey1996).Attemptingtounderstandthe factorswhichunderliesuchpatternshaspresentedimportantpractical problems for conservation. As such Honduras has been identified as an area ofpriorityfortheinvestigationofrainforestmammaliandiversityinthe Neotropicalregion(VossandEmmons1996).Thisisareflectionofthe current paucity of data collected in the area and the increasingly fragmentary nature of prime habitats. Echolocation in microchiropteran bats Flight and echolocation are two attributes of microchiropteran bats that helptoexplainthediversityofformandfunctionalniches,havingallowed adaptationtopursuepreviouslyinaccessibleresources(Fenton1995). Researchhasthereforecentredoninvestigatingtheaspectsofflightand echolocation which correlate best with patterns of diversity. All microchiropterans use echolocation - vocalisations produced in the larynx and emitted through the mouth or nose - to orientate, and some use it to detect insect prey. Time comparisons between pulse and echo are vital for acquiring information about the presence, location and structure of prey, and onchangesinpositioninrelationtothesurroundings(Dearetal.1993). 5Thereareanumberofessentialacousticfeaturesofbatsonarsignals. Signals are typically brief to save energy and avoid pulse-echo overlap, and vary in duration from 0.2 to 50ms and in frequency from 12 to 200kHz (Fenton 1995). Call frequency Ultrasonicorientationsoundsmaybeeitherbroad-ornarrowband. Broadbandsignalscoverarangeoffrequencieswhilenarrowbandsignals focus most energy into a smaller range of frequencies (Fenton etal. 1995). Soundsemittedshouldhaveasimilarwavelengthtothedimensionsofthe targetobjectinordertogiveinformationabouttargetrange,direction,size, texture and velocity (Altringham 1996). Calls therefore vary widely according tothespeciesandtheinterestsofthebatinfrequencycompositionand amplitude,andmaycontainfrequencymodulated(FM)componentsor constantfrequency(CF)components.Patternsoffrequency-timestructure basedonCFandFMcomponentshavebeendescribedforsome microchiropteranspecies.Forexample,Phyllostomusspp.usemultiple-harmonicsoundswithrelativelybroadFMsweepsandalargeoverall bandwidthwhichgiveshighresolutioninformationabouttargetsincomplex habitats (Simmons & Stein 1980). The Mormoopid Pteronotus davyi produces high-intensity sounds with short CF component at around 68kHz, a downward FMsweepandshortterminalCFcomponentataround58kHz(OFarrell& Miller 1997). Intensity and effective range Inadditiontofrequency,callsalsovaryintheirintensity.Aerial insectivoresincludingbatsintheEmballonuridae,Mormoopidaeand Vespertilionidaefamiliesuseintense(>110dBSPL)echolocationcallsto detect,trackandassessmovingtargets(Bogdanowiczetal1999)and separatepulseandechointimewithlowdutycycles.Whisperingbats including many Phyllostomids, use directional calls of lower intensity (