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Method of handling affects post-capture encounter probabilities in male Hypolimnas bolina (L.) (Nymphalidae) PDF

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Preview Method of handling affects post-capture encounter probabilities in male Hypolimnas bolina (L.) (Nymphalidae)

JournaloftheLepidopterists'Society 53(4),1999,138-141 METHOD OF HANDLINGAFFECTS POST-CAPTURE ENCOUNTER PROBABILITIES IN MALE HYPOLIMNAS BOLINA (NYMPHALIDAE) (L.) Darrell Kemp J. SchoolofTropicalBiology,JamesCookUniversity,RO. Box6811Cairns,Queensland,4870,AUSTRALIA AND Myron P. Zalucki DepartmentofZoologyandEntomology,TheUniversityofQueensland,StLucia,Queensland,4072,AUSTRALIA ABSTRACT. Mark-recapturestudiesofbutterflypopulationsareoftenplaguedbylowrecapturerates,whichmakepopulationestimation problematic. Onereasonforlowrecapturesisthatthehandlingprocessofcapture,markingandreleasecontributestolowandunequalcatch- abilityofmarkedindividuals. Herewereporttheresultsofanexperimentconductedtoevaluatethehypothesisthatcoolingindividualspriorto release minimizes handling effects. The post-capture difference in site fidelity of territorial male Hypolimnas bolina (L.) (Lepidoptera: Nymphalidae)wascomparedamongthreegroups:(1)maleshandlednormally,(2)maleschilledpriortorelease,and(3)uncaughtcontrols.Un- chilled malesshowedsignificantlyreducedsitefidelitycomparedtobothcontrol andchilledbutterflies. Furthermore,chilledbutterfliesre- sumedactivityaftercaptureinamannersimilartouncaughtcontrols.Theseresultsindicatethatchillinghasthepotentialtominimizethead- verse effects of handling on subsequent butterfly catchability. Since 'equal catchability' ofcaught and uncaught individuals is a critical assumptionofmark-release-recaptureprograms,thismethodhasthepotentialtogreatlyincreasetheaccuracyofsubsequentpopulationesti- mates.Onthisbasis,inpopulationstudiesonbutterflies,theprecisemethodofhandlingmayproveamoremeaningfulconsiderationthanthe questionofwhetherornottohandle. Additionalkeywords: catchability,mark-release-recapture,censusing,populationestimation. Mark-recapture methods represent apowerful tool Inrecenttimes, manyworkershavetakentocooling for the estimation of animal population parameters, individuals before their release (e.g., Bull et al. 1985, especially those ofinvertebrates (Seber 1973, South- Zalucki & Kitching 1985, Suzuki & Zalucki 1986, Ru- wood 1978, Begon 1979). These methodologies have towski 1992, Zalucki 1993,Wickman &Jansson 1997). often been applied to the study ofbutterfly popula- This technique stems from theideathatincreasedim- tions; however, on manyoccasions, such programs are mobilization ofindividuals immediatelyprior to their plagued by low recapture rates, sometimes in the or- release helps to reduce their subsequent degree of derof1 to 10% (Brussard&Ehrlich 1970, Urquhartet 'panic' (Wickman & Jansson 1997). In this way, indi- al. 1970, Cooketal. 1971, Urquhart& Urquhart 1976, viduals aresupposedlymorelikelytoremainintheim- Wattetal. 1977,Cullenwardetal. 1979).Thismakesthe mediate study area and behave normally, rather than estimationofpopulationsizeandrelatedmeasuresprob- disperse andavoidfurthercapture (asfoundbyLeder- lematic (Rosenberg et al. 1995), and researchers must house 1982). The use of this technique, however, is often resorttolesspowerful methods, such as transect- based on mostly anecdotal information, and little, if based surveys to census theirpopulations (e.g., Pollard any, published research has been conducted to evalu- 1977, Eberhardt 1978,Thomas 1983, Dent 1997). ate its merit. One ofthe manypotential causes oflow recapture The aim ofthis paper is to evaluate the hypothesis rates in the Lepidoptera is that the actual process of that cooling individuals prior to release may increase capture and handling may affect the behaviour of their subsequent catchability relative to individuals markedindividuals, reducingtheirchanceofbeingre- handled in the normal manner. This hypothesis is in- captured (Gall 1984). This effectwould contribute to vestigated using territorial mate-locating males ofthe lowcatchabilityinmarkedindividuals, andleadto sig- nymphalidspecies Hypolimnasbolina (L.). nificant bias in subsequent population estimates (Gall Materials And Methods 1984, Rosenberg et al. 1995). Although crucial to the application of mark-recapture methods, few authors MaleH. bolina inresidentterritorieswerecensused attempttovalidatethe assumptionof'equalcatchabil- along a 1020 m transect (Rutowski 1992) located on ity' (Gall 1984). Severalattemptstoassaytheeffectsof campus atJames Cook Universityin Townsville, Aus- capture in butterflies have indicated that the capture tralia (19°15'S, 146°45'E). Samplingwas conductedin and handling process may have strongly negative ef- two rounds in 1998; from 9-12 February and 16-19 fects on subsequent catchability (Singer & Wedlake April, and once in 1999; from 22-25 February 1999. 1981, Lederhouse 1982, Morton 1984). On each sample round, transects were censused Volume 53, Number4 139 countopportunities (i.e. thenumberoftimeshis terri- tory was passed during transect censuses). Since the ratioofbefore: after-markingcountsineachtreatment group was homogenous between sampling rounds (Chi-squared homogeneity test on before- and after- counts across thethree rounds: %2 < 2.79, p > 0.24for each group), data were pooled across all rounds. Ini- tially, pre- andpost-markingroundcountprobabilities werecomparedforcontrolgroupbutterflies only. This was done to check that the activity ofuntreated but- Control Chilled Unchilled terflies was homogenous and that no other factor, for instance weather, affected the probabilityofcounting Fig. 1. Theaverage (± SE) differenceintheprobabilityofen- countering a male H. bolina between pre- and post-capture cen- butterflies between censuses. Mean differences (pre- suses, as a function ofwhich treatment group hewas assignedto. andpostmarkinground)incountprobabilitiesbetween Control males were not caught, chilled males were caught and butterflies of each treatment group were then com- cooled before release, and unchilled males were caught but not chilled. pared using a one-way analysis ofvariance (ANOVA). Three comparisons were planned prior to analysis; these were (1) between chilled and unchilled butter- hourly for the first two days to identify individuals of flies, (2) between chilled and control group butterflies, high territory site fidelity (for census techniques see and (3) between unchilled and control group butter- Pollard 1977). Notes onsizeandwingwearweretaken flies. These contrastswere evaluatedusingleast signifi- to allow reliable identification ofthese individuals in cant difference (LSD) testforplanned, non-orthogonal subsequent censuses (Rutowski 1992). At 1000 h on comparisons (Sokal & Rohlf1995). Priorto conducting the third day (termed the marking round), each resi- analyses, datasetsweretransformedusingthe angular dentwas randomlyassignedto one ofthree treatment transformation, andKolmogorov-Smirnovgoodnessof groups. 'Unchilled' males were captured at their site, fittestswereusedtoconfirmthatthetransformeddata marked with an identification number on both hind- were normally distributed (Kolmogorov-Smirnov d < wingundersides, andreleasedimmediately(totalhan- 0.24, p > 0.20 for all groups). Levene tests were used dling time of 40-50 seconds). 'Chilled' males were to check homoscedasticity among ANOVA groups; similarly captured and marked, but were held for a these were non-significant in all cases (p > 0.175), further 210 seconds in a paper envelope placed on a which confirmed that datawere homoscedastic. Two- blockoficewrappedin newspaper (Wickman &Jans- tailed probabilities were used, and sample means son 1997), then released directlyback to their perch. throughoutthis paperare given ± 1 standarderror. Notes were taken on the immediate behavior ofindi- Results viduals in these two treatments upon release. Butter- fliesofthethirdgroup, designatedascontrol,werenot Atotalof30primaryterritoryresidentswereidenti- caught. Hourlytransects were then conducted forthe fied during the three sampling occasions, and these remainder ofthe third day and the next dayto deter- were randomlydistributed amongst treatments as fol- mine the behavior ofmales in all three groups. Cen- lows: 11 chilled, 11 unchilled, andeightcontrol. Ofthe suses were conducted no sooner than 0900 h and no total 226 count opportunities before the marking laterthan 1500h, andonlyinthepresence ofsunshine round, 191 counts were registered, and primary resi- before andduringtheentiretransect. Thiswas doneto dents exhibited a mean site fidelity of 0.87 ± 0.02 ensure thatindividualswere censused onlyattimes of (eachbeingpresenton approximately87% ofallcount maximum site fidelity. Duringthe course ofeachtran- opportunities). Mean pre-marking site fidelitydid not sect, individualmaleswere deemedre-countedifthey differ significantly among the three butterfly groups were within 20 meters of their designated territory, (control, chilled, unchilled; ANOVA on angular-trans- and activelyengaged in defense ofthat site. No effort formed data, F227= 0.15, p = 0.86). In addition, the was made to search for individuals that were not im- mean site fidelity ofcontrol group butterflies was not mediately obvious at their sites following marking, significantlydifferent between pre- and post-marking hence the observation technique was kept similarbe- censuses (pairedt-test on angular-transformed data, t fore andaftermarking. = 0.63,df=7,p = 0.55). Anindexofsite fidelitywas calculatedforeach male Post-marking censuses revealed that four marked by dividing his total counts by his total number of individuals (one chilled and three unchilled) had de- 140 Journalofthe Lepidopterists' Society serted their territories. All other males were counted ingbutterflies priorto theirrelease, andit mustbe as- at least once defending theirpre-designated territory sumed that butterflies were simply released immedi- area. The mean difference between pre- and post- ately following marking. The experiment conducted marking round fidelity varied significantly among hereonH bolina corroboratesthe findingthatbutter- . treatment groups (ANOVA on angular-transformed flieshandledinthis mannermaybelesslikelytobere- data, F = 3.97, p < 0.05; Fig. 1). Fidelity was re- captured, butthatthis adverse handlingeffect maybe 2 27 duced to a varying degree in all groups following the mediatedbyachillingtreatmentpriorto release. marking round. The reduction in site fidelity of un- Oneconcernwithcapturingandmarkingbutterflies chilledbutterflieswas significantlygreaterthanthatof isthatindividualswillsufferfrom anincreasedlevelof eithercontrolorchilledgroupbutterflies (LSDtestfor predationowingtothewingmarkandsubsequentloss plannedcomparisons,p < 0.05). Thesignificantdiffer- ofcrypsis or aposematism (Gall 1984, Reynolds et al. ence between the two captured treatment groups 1997). Ifpresent, suchaneffectisoften difficulttodis- demonstratedaneffectduetothe methodofhandling tinguish from any potential effects arising from cap- individual males before their release. Furthermore, ture and handling. Fortunately, in this study, the con- thechangeinfidelityamongchilledbutterflies didnot trasting results between treatment groups allowedthe differ significantly from that shown by control group separation of specific marking effects. Since both butterflies (LSD test, p = 0.85). Hence, relative toun- treatment groups were given similar marks, chilled caught controls, the process ofcapture and marking males provided an adequate control forthe effects of hadnoappreciableeffectonthe subsequentterritorial wing marks in the unchilled group. That onlythe un- fidelity ofbutterflies that were chilled prior to their chilled group ofbutterflies were less likely to be re- release. counted than controls clearlysuggests that, at least in Captured and marked butterflies in each treatment the short term, these were affected bythe method of group showed clear behavioral differences following handling and not by the marks placed upon their theirrelease. Whileallchilledmales remainedperched wings. A similar conclusion was reached by Morton on the substrate where theywere placed, non-chilled (1984),whofoundthatcoloredwingmarksdidnotsig- males either resumed active territory defense (2 nificantly affect recapture ofthe highlycryptic wood- males), roosted on the underside of shaded foliage landbutterflyMelanargiagalathea (L.). Thelimitation nearthesite (2males),orflewquicklyoutofthearea(7 with the current experiment, however, is that post- males). Hence,whileallchilledbutterfliesremainedin markingsite fidelitywas onlymeasuredforaperiodof the vicinity oftheir territory (i.e., less than 20 meters two days. On this basis, the presence ofa longerterm away) in the first instance, only 4 (36.4%) ofthe 11 effect due to wing marks in H. bolina cannotbe com- non-chilledbutterflies did so. pletelydiscounted. The question ofwhy captured butterflies may be Discussion less likelyto be resighted is not specifically addressed Althoughbasedon relativelysmall sample sizes, the bythis study,butsomeinsightis affordedbycasualbe- results ofthis experimentclearlysupportthehypothe- havioral observations made on released individuals. sis that cooling may reduce capture effects and in- Clear differences in behavior were evident between creasepost-handlingcatchabilityofterritorial male H. treatment groups, and this resulted in more unchilled bolina. Not only did the process ofchilling affect the butterflies leaving their immediate area ofcapture in probability of resighting captured males, but chilled the shortterm. This differencealonemayberesponsi- males also resumedactivityinamannersimilartothat ble for differences in encounter probabilities ofun- ofbutterfliesthatwerenevercaught. This resultissig- chilledandchilledindividuals, especiallyinthecaseof nificant, since itshowsthatchillingmaynotsimplyre- a site-tenacious butterfly such as male H. bolina duce or 'manage' the adverse effect ofhandling, but (Rutowski 1992). In unchilledH. bolina, the decision that this process has the potential to actually nullify to leave the territory is more likely to be made as a short-term effects ofcapture. To ourknowledge, this consequence ofimmediate 'panic' upon release. This has notbeen demonstrated previouslyfor anybutter- behaviorappearssimilartothedefensiveorevasivere- flyspecies. sponse of butterflies to failed predatory attacks, or These results contrast with the generally negative failed capture attempts. Chilled butterflies, however, effects ofhandling ofbutterflies obtainedin previous remain in their territory area for quite some time studies, forexample SingerandWedlake (1981), Leder- whilst warming up, and therefore any active decision house (1982), and Morton (1984). In these studies, to abandonthe site mustbe made at some later stage. however, no reference is given to anymethodofchill- On average, the difference between groups after Volume 53,"Number4 141 marking is that unchilled butterflies must decide dae),withacomparisonofdifferentnumericalmethodsthates- whether to return to their former territory, and the timatepopulationsize. Biol.Cons.28:139-154. Lederhouse, R. C. 1982. Factors affecting equal catchability in chilled butterflies must decide whether to leave. If two swallowtail butterflies, Papilio pohjxenes and P.glaucus. boththese decisions are sufficientlyunlikely, then dis- Ecol.Entomol. 7:379-383. crepancies will exist between the recounts ofchilled Morton,A. C. 1984. Theeffects ofmarkingandhandlingonre- capture frequencies ofbutterflies, pp. 55-58. In R. I. Vane- and unchilled group individuals, leadingto the results WrightandP. R. Ackery(eds.),Thebiologyofbutterflies.Aca- observedin this study demicPress,London. In theory (depending on specific post-capture be- Pollard, E. 1977. A method for assessing changes in the abun- danceofbutterflies. Biol.Cons.:115-134. havioural responses), this principle may hold for a Reynolds, D. R., R. Riley, N. Armes, R. Cooter, M. R. wwiiddee vvaarriieettyy ooffbcuitrtceurmfsltyanspceecsi.esInbdeeiendg,sbaomtphleLdedienr-a TmMiuegtcrhkaoteidrosn&,inpJ.pe.cCooJl1.lo1vg1ii-cn1a.4l5a.1n9I9dn7a.Dgr.TiecJRuc..lhtnDuierqnalute,esn&tfooMmro.Jql.uoPa.gnyWt.ailfCytAionBng(Iienndtssee.rc)-t, house (1982) andSingerandWedlake (1981) suggested national,WallingWford. that initial dispersal or displacement from the site of Rosenberg, D. K., S. Overton&R. G. Anthony. 1995. Esti- capture may have accounted for their observed cap- mationofanimalabundancewhencaptureprobabilitiesarelow andheterogeneous. Wild. Mgt.59:252-261. tureeffectsinbutterflieshandledwithoutchilling. The Rutowski, R. L. 1992. JM.alemate-locatingbehaviourinthecom- advantages ofchillingmaytherefore lie inthe preven- mon eggfly, Hypolimnasbolina (Nymphalidae). J. Lepid. Soc. 46:24-38. tion ofearly dispersal immediately following capture, Seber,G.A.F 1973. Theestimationofanimalabundanceandre- asimpliedbyWickmanandJansson (1997). Since'equal latedparameters.2nded. Griffin,London. catchability' of caught and uncaught individuals is a Singer, M. C. & P. Wedlake. 1981. Capture does affect the critical assumption of mark-release-recapture pro- probability ofrecapture in a butterfly species. Ecol. Ento- mol. 6:215-216. gcrreaamsse, tthhiesamcecturhaocdy hoafsstuhbesepqouteennttiaploptuolagtrieaotnlyesitni-- SokalN,ewR.YoRr.k.& F. J. Rohlf. 1995. Biometry. 3rd ed. Freeman, mates. On this basis, in studies that intend to employ Southwood, T. R. E. 1978. Ecological methods with particular referencetothestudyofinsectpopulations. 2nded. Chapman mark-release-recapturetechniques, the actualmethod &Hall,London. ofhandling mayprove a more meaningful considera- Suzuki,Y. &M. P. Zalucki. 1986. Mateacquisitionasafactorin- tionthanthe questionofwhetherornottohandle. fluencing female dispersal in Danaus plexippus (L.). J. Aust. Entomol. Soc.25:31^35. Thomas, A. 1983. Aquickmethodforestimatingbutterflynum- Acknowledgments J. bersduringsurveys. Biol.Cons.27:195-211. gestTihnagntkhseaproetednuteiatlobDern.efCi.tsJ.oHfilclooalnidngPrbouft.teFrf.lSi.esChbeefworfeorrefilresatsseugt-o UrqulhaarrFtl,orFidAa.&popNu.lRa.tiUornqsuhoafrtth.e 1m9o76n.arAchstubudtytoefrftlhyep{eDnainnasuus- Dea.rlJ.ieKr.mParnouf.scRr.ipEt..JoTnheisskriensdelayrocfhfewraesdssuugpgpeosrttieondsbayndancrAituisctirzaeldiaann Urquph.aplretx,ipFpuAs.;,DNa.naRi.dUaer)q.uJh.aLrepti&d.F.SoMc.un30g:e7r3.-871.970. Astudyof PostgraduateResearchAwardtoD. K. a continuously breeding population of Danaus plexippus in J. southernCaliforniacomparedtoamigratorypopulationandits Literature Cited significance in the study ofinsect movement. J. Res. Lepid. 7:169-181. Begon, M. 1979. Investigatinganimalabundance: capture-recap- Watt, W. B., F. S. Chew, L. R. G. Snyder, A. G. Watt & D. E. tureforbiologists. UniversityParkPress,Baltimore. Rothschild. 1977. Populationstructureofpieridbutterflies. Brussard,P.F.&P.R.Ehrlich. 1970. Thepopulationstructureof I. Numbers and movements ofsome montane Colias species. Erebiaepipsodea(Lepidoptera:Satyrinae).Ecology51:119-129. Oecologia27:1-22. Bull,C. M., M. P.Zalucki,Y. Suzuki,D. Mackay&R. L. Kitch- Wickman, P. & P. Jansson. 1997. An estimate of female mate ING. 1985. An experimental investigation ofresource use by searching costs in the lekking butterfly Coenonympha pam- female monarch butterflies, Danaus plexippus (L.). Aust. J. philus. Behav. Ecol.Sociobiol.40:312-328. — Ecol. 10:391-98. Zalucki,M.P. 1993. Sexaroundthemilkweedpatch thesignifi- Cook,L.M.,K.Frank&L.P.Brower. 1971. Experimentsonthe canceofpatchesinhostplantsinmonarchreproduction. In S. demographyoftropicalbutterfliesI.Survivalrateanddensityin B. Malcolm &M. P. Zalucki (eds.),Thebiologyandconserva- Culltewnowsapredci,esMoiJP.a,riPd.eRs.. BEihortlriocpihc,aR3.:1R7.-2W0.hite & C. E. Hol- ttiroinbuotfiotnhsetMooSncairencche,buLttoesrfAlny.geMleuss.eumofNaturalHistoryCon- DREN. 1979. Theecologyandpopulationgeneticsofanalpine Zalucki, M. P. & R. L. Kitching. 1985. The dynamics ofadult checkerspotbutterfly,Euphydryasanica. Oecologia38:1-12. Danausplexippus L. aroundpatchesofitshostplantAsclepias Dent, D. R. 1997. Quantifyinginsectparameters,pp. 57-109. In spp. Lepid. Soc.38:209-19. D. R. Dent& M. P. Walton (eds.), Methods inecologicaland J. agriculturalentomology.CAB International,Wallingford. Eberhardt, L. L. 1978. Transectmethodsforpopulationstudies. 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