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.