TECHNIQUES USEFUL FOR DETERMINING RAPTOR PREY-SPECIES ABUNDANCE* by D. W. R. E. Fitzner, RockyMountain Forestand Range Experiment Station L. E. Rogers, Battelle Battelle Northwest Boulevard Laboratories Uresk U.S. Forest Service South Dakota School of Mines Richland,Washington99352 Campus and Rapid City, SouthDakota 57701 Abstract A workshop washeldby the RaptorResearch Foundation on October27 and28, 1976, in Ithaca, New York, to developstandardizeddata collectionand analytical methodsfor raptor studies.Applicationsof the methodswill ensurecompatibilityand facilitateyear-to-yearand area-to-areacomparisons valuablein environmentalassessment and raptor populationtrend monitoring. We have focusedon one of the workshoptopics,that of methodsappropriatefor measuringprey-species abundance. Emphasisis on techniquesusedin westerngrasslands.The selectionand useof the particulartechniquesdescribedin this paper will dependon the level of quantification desired,the habitattype, and the availabilityof researchtime and money.Long-termstudiesshouldincludemethodsthat will provide quantifieddata, i.e., density(numberof individualsper unit area). Suchdata will enable calculationof prey exploitationratesand prey densities, parametersimportantto our understanding of raptor populationdynamics. Invertebrates SampleCounts Petrusewicz, K., and A. Macfadyen.1970.Productivityof terrestrialanimals,principlesand methods.IBP Handbook13. BlackwellScientificPublications,Oxford.This techniqueis basedon countsof all individualsof the speciesor groupof speciesconsideredin a samplefrom a smallbut representative area.The sizeof the sampleplot dependson the mobility and abundanceof the species.Sampleplots i m2 work well for Coleopteraand Orthoptera.Data obtainable:density. Catch-Mark-R ecatch See above reference.Capture, mark, and releasea number of individualsat the samesite. Later captureagain usingthe samemethodin the samearea and find the marked individuals.The populationcan then be determinedby the Lincoln Index: N=(b)a/a'. This techniqueis usefulfor large, easily capturedinsects,particularly beetles.Data obtainable:relativedensity. QuickTrap and VacuumSampler 1. Turnbull,A., and C. Nicholls.1966. A "quick trap" for area samplingof arthropodsin grasslandcommunities. ]. Econ. Entomol.59:1100-1104.A trap that can be set down quickly over the samplearea to containthe flying insectspresentis used. Material is removedby meansof a D-Vac vacuuminsectnet. Berlesefunnelsare usedto separatemicro-invertebrates from the debris.Widely usedin grasslandstudies.Data obtainable:density. *This work was done for the U.S. EnergyResearchand DevelopmentAdministrationunder contractEY76C061830. 67 68 RAPTOR RESEARCH Vol. 11, No. 3 2. Ahearn,G. A. 1971. Ecologicalfactorsaffectingsamplingof desertTenebrionid beetles. Amer. Midl. Natur. 86:385-406. Discussesthe influence of climatic conditions, activity, populationsize, surfaceillumination,trap density,and trap spacingon the useof the pitfall trappingtechniquein evaluatingpopulationsizeof ground-dwelling beetles. Data obtainable: relative abundance. 3. Greenslade, P. J. M. 1964. Pitfall trappingas a methodfor studyingpopulations of Carabidae.]. Anim. Ecol.33:301-310.Reviewspitfall trappingas a samplingmethod for Carabidae.Considers the effectsof populationsize,locomotoractivity, species' susceptibilityto trapping,and habitat on the total catch. Data obtainable:relative abundance. Malaise Trap 1. Mathews,R. W., and J. R. Matthews.1971. The Malaisetrap: its utility and potential for samplinginsect populations.Mich. Entomol.4:117-122. This method is basedupon the observation that mostflying insectsthat hit an obstaclerespondby flyingor crawlingupwardand thusinto captivity.Thesetrapsare easyto use,canbe placedin almostany habitatat any height,and are cheapto construct,or they can be purchased ready-made.Data obtainable:relative abundance. 2. Townes,H. 1972.A light-weightMalaisetrap. Entomol.News83:239-247. Ocular Census Method 1. Bhatnager,K. E., and R. E. Pfadt. 1973. Growth, density,and biomassof grasshoppersin the shortgrass and mixed-grass association. U.S. IBP GrasslandBiomeTech. Rept. No. 225. ColoradoState Univ., Ft. Collins,CO. This methodpermitsan estimate of the densityof large-sizedinsectsby traversingan area and countingthe numberof individualsin small sampleareas(30.5 cm•). A large numberof sample pointscan be gatheredin a shortwhile, but the methodappliesonly to large,easily recognizedspecies(grasshoppers, beetles,etc.).Data obtainable:density. Vertebrates (Reptilesand Amphibians) Transect Lines Fitzgerald,G. J., and J. R. Rider. 1974. Seasonal activity of the toad Bufo americanus in southernQuebec as revealedby a sand-transecttechnique.Can. ]. Zool. 52(1):1-5.A coveredsandtransectwas usedto collect data on toad movements.The transectwas 225 m long and 46 cm wide. Tracksare recordedand then erasedat leasttwice a day. This techniqueis usefulto measuretrendsin reptile and amphibian populations. Data obtainable:trend data. Drift Fence Gibbons,J. W., and D. H. Bennett.1974. Determinationof anuran terrestrialactivity patternsby a drift fence method.Copeia No. 1, pp. 236-243. Hardware cloth, 0.64-cmmeshand 61 cm high, was usedfor fencing."The fencewas placedin an 810-cm deep ditch, later filled with soil. Metal stakesalongsidethe fence addedextra support.Metal buckets(diameter35 cm; depth41 cm) were placedat 20-m intervals in paired holes on oppositesidesof the fence so the mouth of each can was at groundlevel flushwith the fence."Amphibianswere directedalong the fencingand becameentrappedin sunkenbuckets.This techniqueis widely usedfor amphibians. Data obtainable: relative abundance. Mark-Recapture Rose, F. L., and D. Armentrout. 1974. Populationestimatesof Ambystomatigrinum inhabitingtwo playa lakes.]. Anim. Ecol. 43:671-679.Neotenic salamanders Fall 1977 Fitzner, Rogers& Uresk-- Raptor Prey-Species Abundance 69 were collectedwith a 12.2 m x 1.8 m bag sein.Each animal was toe clipped, and its initial and subsequent datesof capturewere determined.Populationsize was esti- mated by six differentmethods:Lincoln-Peterson (Southwood1966); Bailey triple catch (Bailey 1952); Schnabel(Ricker 1958); Schumacher-Eschmeyer (1943); Jolly (Southwood1966); and Leslie (1952). This techniquewas usedon aquatic organisms, but the principlesalsoapplyto terrestrialorganisms. Data obtainable:density. Grid Trapping 1. Bellis, E. D. 1964. A summersix-linedracerunner(Cnemidophorus sexlineatus) populationin SouthCarolina.Herpetologica 20(1):9-16.Wire-screenfunnel traps (108 cm long; with a 15-cm diameterreceivingcylinder at each end and a cone with a small openingat the apex with a 38-cm base restingon the ground)were used to capture lizards.Each cone was somewhatflattenedwhere it contactedthe ground, thusprovidinga broad receiverfor the lizards.The cylinderswere coveredwith vegetation to protect lizards from excessivesunlight.Traps were systematicallymoved aboutwithin quadrantsto assurethat all habitatswere well trapped.Traps were not baited; their success dependedon movementsof lizards in normal activity. Lizards were individuallymarkedby toe amputationand smallblotchesof posterpaint on their dorsa.Data obtainable:density. 2. Rickard, W. H. 1968. Field observations on the altitudinal distribution of the side-blotchedlizard. NorthwestSci. 42(4):161-164.Five can traps arrangedin a line with 3-m spacingbetweenwere usedto capturelizardsand insects.Data obtainable: relativeabundance;this methodcan alsobe usedto determinedensitywhen coupled with a grid arrangementof traps,the mark-recapturetechnique,and assessment lines. Birds Line Transect Methods 1. Kendeigh,S.C. 1944. Measurementof bird populations.Ecol. Monogr. 14:67106. A simpletally of individualsdetectedper unit of effort. Data obtainable:relative abundanceand speciesdiversity. 2. Rickard,W. H. 1964. Bird surveysin cottonwood-willow communitiesin winter. Murrelet45(2):22-25.A simpletally of individualsdetectedwhile walking along an established path. Data obtainable:relativeabundance and speciesdiversity. 3. Jarvinen,O., and R. A. Vaisanen.1974. Estimatingrelative densitiesof breeding birdsby the line transectmethod.Oikos26(3):316-322.This methodconsiders transectbeltsof two differentwidths."In the line transectcensuses of breedingbirds,all observationsare registered.Observationsmade within 25 m of the transect,about 20% of total, constitutethe 'main belt' recordswhile 'surveybelt' recordsrefer to all observations. This studyshowshow observations outsidethe main belt can be utilized to estimatedensitiesof differentspecies."Data obtainable:relative abundanceand speciesdiversity. 4. Emlen, J. T. 1971. Populationdensitiesof birds derived from transectcounts. Auk 88:323-342. Field transect counts are conducted in which all detections of birds, visualand aural, out of the limit of detectabilityare tallied. The count of each speciesis then multipliedby a conversionfactor (coefficientof detectability)representative of the percentof the populationthat is normallydetectedby theseprocedures. This method is applicablefor all seasons and is more efficientin terms of area covered per unit of effort than nest- or territory-countmethods.Data obtainable:absolute density,whichcanbe usedfor determiningbiomassand energyfunctions. 70 RAPTOR RESEARCH Vol. 11, No. 3 Mammals Mark-Recapture Technique 1. Jolly, G. M. 1965. Explicit estimatesfrom capture-recapture data with low death rates and immigration-Stochastic Model. Biometrika52:315-337.A model is presentedwhichgivesan estimateof the total populationfor eachtrappingperiod. Data obtainable:total populationestimate,movements, and biomassestimates. 2. Smith, M. H., et al. 1971. Determiningdensityfor small mammal populations usinga grid and assessment lines.Acta Theriologica 16(8):105-125.A 16-x-16grid was usedto obtain densityestimates.Eight assessment lines were used to evaluatethe area of effectaroundthe grid. Data obtainable:total population,biomass. 3. Kaufman,D. W., et al. 1971. Useof assessment linesto estimatedensityof small mammals.Acta Theriologica16(9):127-147.Usesan octagoncensusline plus primary and secondaryassessment lines. Linear regression equationswere fitted to accumulative capturesover distancefor primary and secondaryassessment lines to determine the area of effect aroundthe octagoncensuslinesand a selectedportionof the primary assessment lines.Data obtainable:density. 4. Smith, H. D., C. D. Jorgensen,and H. D. Tolley. 1972. Estimationof small mammalusingrecapturemethods:Partitioningof estimatorvariables.Acta Theriologica 17(5):57-66.A modelusinga grid designsurrotmded by a denseline of traps to detect movementof animalsinto and out of the grid. Usefid where permanentand semipermanent grids are established in populationsthat cannotbe disturbedby removalor killing. Data obtainable:density. Area Estimate Flinders,J. T., and R. M. Hansen.1973. Abtmdanceand dispersionof Leporids within a shortgrass ecosystem. J. Mammalogy54(1):287-291.Modifiedbelt or strip method usinga line transectwhich was developedfor grasslands. The number of Leporidssightedwithin the transectarea dividedby the transectarea yieldeda measurementof populationdensity.Data obtainable:densityfor haresand rabbits,coyotes,raccoons,sktmks,badgers,and other medium-sizednight-activemammals;movements. Moundand Earth Plug Census Reid, V. H., R. M. Hanson,and A. L. Ward. 1966. Counting moundsand earth plugsto censusmountaingophers.J. Wildlife Manage.30:327-334.Count moundsand earth plugswhich can be relatedto intensivetrap out of studyarea. Data obtainable: density. Other UsefulReferences Avery,T. E. 1975.Naturalresources measurements. McGraw-Hill, New York. 339 pp. Bailey, N. T. J. 1952. Improvementsin the interpretationof recapturedata.J. Anim. Ecol. 21:120-127. Cochran,W. T. 1963. Samplingtechniq.ues. Wiley, New York. 451 pp. Dixon,W. J., and F. J. Massey,Jr. 1969.Introductionto statisticalanalysis.McGrawHill, New York. 638 pp. Fitzner, R. E., and J. N. Fitzner. 1975.Winter food habitsof short-earedOwls in the PalousePrairie. Murrelet 56(2):2-4. Giles, R. H., Jr.(ed).1971.Wildlife management' techniques. TheWildlife Society, Washington,D.C. 633 pp. Golly, F. B., K. Petrusewicz,and L. Ryszkowski.1975. Smallmammals:their productivity and populationdynamics.CambridgeUniversityPress,New York. 451 pp. Fall 1977 Fitzner,Rogers& Uresk-- RaptorPrey-Species Abundance 71 Guenther,W. C. 1964.Analysisof variance.PrenticeHall, EnglewoodCliffs, N.J. 199 pp. Kovner,J. L., and S. A. Patil. 1974. Propertiesof estimatorsof wildlife population densityfor the line transectmethod.Biometrics 30(2):225-230. Leslie,P. H. 1952. The estimationof populationparametersfrom data obtainedby meansof the capture-recapture method.II. The estimationof total numbers.Biometrika 39:363-388. Ricker,W. E. 1958.Handbookof computations for biologicalstatistics of fishpopulations. Bull. Fish. Res. Bd. Can. 119:1-300. Rogers,L. E., W. T. Hinds,andR. Buschbom. 1976. A generalweightrs. lengthrelationshipfor insects.AnnalsEntomol.Soc.Amer. 69(2):387-389. Rogers,L. E., R. L. Buschbom, and C. R. Watson.1977. Length-weightrelationships of shrub-steppe invertebrates. Annals Entomol.Soc.Amer. 70:51-53. Rotenberry,J. T., and J. A. Wiens. 1976. A methodfor estimatingspeciesdispersion from transectdata.Amer. Midl. Natur. 95(1):64-78. Schumacher, F. X., and R. W. Eschmeyer. 1943.The estimateof fishpopulationin lakesor ponds.]. Tenn.Acad. Sci. 18:228-249. Snedecor, G. W., and W. G. Cochran. 1972. Statistical methods. Iowa State Univ. Press,Ames,Iowa. 593 pp. Southwood, T. R. E. 1966.Ecological methods:with particularreferenceto the study of insects.Methuen,London.391 pp. Woodbury,A.M. 1953.Methodsof fieldstudyin reptiles.Herpetologica 9:87-92. BARBED WIRE IMPALES ANOTHER GREAT HORNED OWL by H. Leroy Anderson U.S. Fish and Wildlife 813 "D" Street Service Anchorage,Alaska99501 At 0900 on 24 May 1976,accompanied by K. Quackenbush, I foundan adult Great Horned Owl (Bubovirginianus)impaledby both wingson the top wire of a fivestrand, barbed-wirefence (fig. 1). The fence was on semiarid rangeland,predominantlymesquite(Prosopis glandulesa)and retama (Parkinsoniaaculeata),near a smallwater tank, approximately20 km NNE of Laredo,Texas. The bird wasalert andactivewhenfound.A setof barbswasentangled in the skin of each wing. Closerexamination showedthat the bird had injuredits right eye, probablyon a barb, duringits attemptto get free. A smallpatchof skinwas lost on eachwing whenthe barbswere removed,but no bleedingoccurred. Becausethe owl was active and did not appear seriouslyiniured,we releasedit, whereuponit hoppedalongthe groundfor 18 m, perchedbrieflyon a smalltree, and then flew 90 m to a mesquitetree. We did not observeit further. The owl was apparentlyflying with wings extendedwhen it hit the barbedwire with enoughforce that it made two completeturns around the wire and became firmlyentangledon the barbs.