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HowdJInformationCompall)' JOONonh Zccb Rmd, ADnArbor MI4II06- 1J.46USA3l3l761~700 1OOI.521~
St.John's
Relative Abunda nces of Birds of Pre y in Different Forest Habitats in the Western Newfound la nd Model Forest
By
JohnW.Gosse,B.Sc.
Athesis submitted to the School of Graduate Studies in partialfulfilment of therequirements for the degreeof
Masterof Science
BiopsychologyProgramme Memorial Universityof Newfoundland
September 1997
Newfoundland
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Theauthor hasgranted a non- exclusive licenceallowingthe Natiooal Libraryof Canada to reprod uce, loan.distnbute orsell copies of thisthesisinmicroform, paper orelectronicformats.
Theauthor retains ownership of the copyrightinthisthesis.Neither the thesisnor substantial extracts fromit maybeprinted orotherwise repro ducedwithout the author"s permission.
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a
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Abstnd
Balsamfirforests inwesternNewfoundlandare intensive ly manag ed for pulpwood production resultinginafragmentedlandsca pe of different-agedforests and clearcu ts.Priorto thisresearch,the ecologyof woodlandbirdsofpreyhad been unstudied on insular Newfoundland.,and knowledge regarding consequencesoffo restry practices on aspects of their biolo gywas lacking.Astop-levelcarnivores.raprcrs are susceptibletoboth natural andhuman induced perturbationand mayeffectivelybeusedas indicatorspeciesof environmentalhealthin boreal forestecosystems.
Duringthe breeding seasons of 1993and 1994,thediversityand relativeabundances of birdsof preywereinvesti gated in the WesternNewfoundland Model Forest(WNMF).The primary researchobjectiveswereto;I)develop reliable.standardized techniques withwhichto censusbirds of preyin different-aged forestsand clearcutsinthe WNMF.2)determine the speciesdiversityand relativeabundancesofbirds ofprey in uncutoldgrowth,seco nd growth forest,clearcuts and pre-co mmerciallythinnedareas,3) deve lopdensityestima tesofselected speciesofbirdsof prey,4) ide ntify nest-sites ofbirdsof preyand quantifyhabitatcharacteristics atthese sites, 5)identify knowledgegapswith respecttoNewfoundland birds of prey,andin doing sotodeve lop researchobj ectives andmanagem entstrategiesforfuturestudies.
Surveysusingconspecific vocal izationplaybackswere conductedalongforestaccess roads and lakeshorelines thattransected differentforesthabitats.Groundsearchesweremadefor raptoractivity sites(l.e.nests,roost s, prey- plucking-sites),and habitatmeasurementsat the se sitesandunused controlsiteswere obtain ed.The vocalizationplayback method usedwas reasonably effective forloca ting owlsbut less effective forotherwoodlan d raptors.
Nine species of birdsof prey were recordedinthe area: Merlin. AmericanKestre l,Osprey Rough-legged Hawk, Sharp-shinned Hawk. NorthernGoshawk. Boreal Ow l.GreatHom ed Owl, andNorthern Hawk-Owl. Uncutoldgrowthforests contain ed mo re speciesthan seco ndgrowth forests and cleerc uts,however abundancesinall foresttypeswerelow .BorealOwls and NorthernGoshawks were found exclusive lyinuncut oldgrowth.andSharp-shinned.Ha wks mainly in this habitattype.Three species of birdsof preywere recorded in secondgrowth
forests in me studyarea.one of which.theGreatHomedOwl.wasfoundonly in thishabitat type.Clearcutareas were utilized by four species of raprcrsand NorthernHawk-Owl sand American Kestrelsusedclearcuts extensively.Merlins werethemost commonlydetectedbird of prey andunlike any otherspecieswerefoundinallforest habitats .
Predator-prey relations hipsinfluencethe occurre ncesof birds ofpreyin diffe rent habita ts.A comparisonof avian -dependent birds ofprey(i.e. Sharp-sh inned Hawks.Merlins ) and small mammalspeci alists (i.e.BorealOwls.Northe rn Hawk-Owls.Rough-leggedHawks) indicated thatbetween1993 and1994.thenumbersof avian predators remained identical whereas the numbersof rodent predatorsdeclinedsigni fican tly.Thispopulationdecreaseis likelya result of thesim ultaneo us decline in small mammalsinthisregionandreflectsthe impo rtance of food resources ininfluencing population dynamics ofbirds of preyindifferent habita ts.
Densitycomparisonsmade between westernNewfound landanda rangeoflocations throughoutboreal forestsystems in North America and Scandinaviaindicatethatraptor populatio nsareextre me lyvari able.Althoughlacking rigorousempirical analysis.such compari sonsprovideanindex of raptorpopulations at differentspatialandtemporalscales. In weste rnNewfoundland. thelow diversityand numbersofsmal l manunalslike lylimits the densiti esofbirds of preydependentonthisfood resource. (Boreal Owl,Northern Hawk-Owl.
Rough-leggedHawk).Great HomedOwlsandNorthe rnGoshawksmay alsohavebeen food limitedas theirmajor preyspecies (Snowshoe Hare , RuffedGrouse) were uncommon in this region. Thesepredator-preyrelatio nshipsmaybe responsible for thelow densitiesof birds of preyfoun d intheboreal forests of westernNewfoundland.
Habitat selectio ntheorypostulatesthatspecies are preferentially associatedwith panicular habitatsin which they can optimall ysurviveand reproduce.For birds of prey,the mechanismsthatelicitselectionof habitats are notwellunderstood yetthisinformationis needed in order toeffectivelyman ageforeststo maintainthenaturalbiod ivers ityand abund ance ofbirds of prey.Samplesizes of raproractivitysites were small.howevertrendsofhabitat selection were apparent andconsistent with research conducted elsewh ere.
In recentyears.the management of non-gamewildlife has becomean imponantissuein
iii
light of approaches to preserving forest ecosystemsthatgo beyondtheprimaryobjective offibre and timber production.InNo rthAmerica.birds of prey areprotect edunder governmental legislation, andconse rvatio n measures forthem havebeenimple mented inforestman agement stra tegi es . InNewfo und land. however,a previouslackofknowledge regard in g the distributions andabundancesof woodlandraptorshas resultedin minimalanentionwithrespec tto forestry planning.Based.on censusresults ofthispresentstudy,[suggestthatlarge tractsofremaining uncut oldgrowth forests bepreservedfromtimberharvestingandthatthe existence ofthis habitattypebeensured ata landscapelevel in futureyears. Furthermore.researchandsystematic monitoring of woodlandrapto rpopulat ionssho uldcontin ueinan attempt tobetterunderstan d impacts of forestharvesting operations.
iv
Acknowledgements
This researchwas supportedbytheWesternNewfoundlandModel ForestCorporation andbyMemorial UniversityofNe wfoundland.SpecialthankstoDr.W.A .Monrevecchi.
thesissupervisor.for designing the studymethodologyandsuppoltingtheresearch throughout.Drs.R.KnoechelandD.Schneiderprovided statistical counse lling.andother helpful advice. Dr.D.H Steele.I.Brazil.K.Knox.T.WellicomeandD.Butlerprovided valuable feedback.commentaryandassistancethroughoutthestudy.Igratefully thank each of theseindividuals for fieldassistanceandsupport.D.Whitaker.M.Mayo.D.Fillier,L.
Mayo. B.Greene. M.Setteringtonand B.Mactavish.Ialso thank theNe wfoundland and Labrador WildlifeDivision(Departme nt ofNatural Resourc es)for accommodationsat their researchcabinatLittle Grand Lake.andfor use of fieldequipment duringthestudy.
Table cf Ccnte nts Abstract
Acknowledge ments ListofTables ListofFigures ChapterI·Introduction 1.1 Introduction 1.2Study Area
Chapter2· Asunoeyof woodla nd birdsofpreyin theWestern Newfou nd landModelForest
2.1 Introduct ion 2.1.1Raptor censusingmethods 2.2 Methods
2.2.1Surveyprotocol 2.2.2Sta tisti calanalyses 2.2 .3Comp arative dens ities 2.3Results
2.3.1Effectiveness ofconspecificbroadcasts 2.3.2Species compositionofbirdsof prey
2.3.3Habitat associations andrelativeabundancesofbirds ofprey 2.3.4 Breed ing Chronology
2.4Discussion 2.4.1Comparative Densities 2.4.2BreedingChrono lo gy
vi
viii ix
10 II II 11 12 12 14 18 20 22
Cha pter-J -Habitat characteristicsof raptor activity sitesin western
Newfound la nd 23
3.1lntroduction 23
3.2 Methods 25
3.3Results 26
3.4Discussion 39
3.4.1 Recommendationsforthe managementofbirds ofprey 41 in westernNewfoundland
Literature Cited 44
Append ix1•Illustration sand coordinatesofthe seven surv eyroutes nearLittleGrand Lake.George ' s La ke andCook'sPond. 52 Appendix 2 - Compositi on of Merlin.Rough-leggedHawkand Northern S6 Hawk-Ow lpreyremain sfound nearnest-sites in west ern Newfoundla nd , 1993-1 994.
vii
ListofTablcs
Table2.1.Surveytransectspec ifications forthe fourforesttypesintheWestern Newfoundland ModelForestin1993-94.Eachtransectwas surveyedthree times durin g eachbreeding seaso n.
Table2.2Sightin gs of adult birdsof prey in theWest ern Newfoundland ModelForest. 1993- 1994.Numbersofsightings includemultiplesightingsofindividuals.but do not include nestlingsorfled glings.Thesenumbers alsoinclude birdsofpreyrecordedinareas outsideof the survey routesbut intheWNMF region (see Figure1.1).
Table 2.3 Dens ities of raptorsdetected along surveyroutes indifferentbalsam firforesttypesin theWesternNewfoundlandModel Forest, 1993-1994.Numbers inparenthe sesareindivid ual adult raptors and donot incl uderepeat sightin gs.
Tabl e3.1.Factoranalysis ofstruetural and vegetative characteristics at rapto rnest sites.roosts, preyplucking sitesandunused sitesinsecond anduncutoldgrowth.forests.Correlationsof log andarcsine transformed data are reportedwiththefirstthreeextractedfac tors.Onlysignificant corre latio ns(>0 .6) areshown.
viii
ListofFigures
Figu re1.1The Western NewfoundlandModelForest Study area (shadedregion).Study sites are indicat edbynumbers 1-7.
Figur e3.1Sharp-shinnedHawkprey- pluckin g-sitesandunused sitesinuncutoldgrowthbalsam fir forestinreference to factorsI and3.
Figu re 3.2 Merlin nest-sites and unusedsitesinsecondgrowthbalsamfirforestsinreferenceto factors I and 2.
Figure3.3 The distributio nofnests,roosts,prey-plucking-sitesandunusedsitesinsecond and uncut oldgrowthbalsam firforestsinwesternNewfoundlandinreferenceto factors I and2.
Figure3.4The distri butio nof nests,roosts.prey-plucking-sites andunused sitesinsecond and uncutoldgrowthbalsamfirforests in western NewfoundlandInreference to (actorsI and3.
ix
Cha pter1 1.1 In trod uction
Studyofthediversity and abundancesofbirds ofpreyindifferent-aged forestsin western Newfoundlandisan important componentof understanding wildlife-forestryinteractions.
Preservationoftoplevel carnivores offers adirect means with which to understand andmaintain biodiversityin terrestrialecosy ste ms(e.g.Soule'and Wilcox1980;Frankeland Soule' 1981). If foresthabitats and associated communitiesof these wide-rangingtop-levelcarnivorescanbe ensur ed.then theprotection of many othe r wildlife species atlowertrophiclevelswillalsobe promoted. Raptorsare susceptibleto bothnaturalandhuman-induced perturbatio n(e.g.Newt on 1979.Poole1989.Careyand Peeler 1995) and can beusedasindicatorspecies of boreal forest ecosyst em integrity ( seeLandreset of.1988) .Asan example.the Northern Goshawk(Accipiler genii/is)was selected as a managementindica torspeciesinnortheasternCalifornia.becauseitwas designatedas a sensitivespecies andan ecologicalindicator for matureandold-gro wthforests (McCarthyetal.1989).Birds of prey arealsooften featuredinconservationstra teg iesbecause of their positioninfood.websandoftheirpublicattractiveness(Noss1990 ).In additionto their value asecological indicatorspecies.birdsofpreyare alsoconsideredaestheticallyimportant, and this perceptionisreflectedinthe change of publicattitudestowardthisgroupof species.Govenunental legislationnowprotects allspecies of raptors. whereasinpastdecades.birds ofpreywere considered harmfulpredators andpests and wereoftendirectlypersecutedbyhwnans (Johns gard1988).
Extensive researc h describingcaptordistri butions andhabitatassociations has been conductedinNorth AmericaandEurope (Titus and Mosher1981. Armstrong and Euler 1982.
Reynoldsel at.198 2.Haywardetal.1993.Solonen1994).Though patternsof habitatusehave emerged,resultsare oftensite-specific and vary greatlyacross the geographic ranges of some species.The borealforest ofinsularNewfoundlandconstitutes the extremeeastern limitofthe range ofmanyNorthAmericanwoodland raptcrs.andisecologicallyuniqueinthat episodicinsect events functionastheprimarymechanismfor forest successionundernatural conditions(Thompson1994).
The requirement forresearchon forest birds ofpreyinthis regionis furtheraecentuatedsince the west ernNewfoundlandlandscape has been drasticallyaltered by forest harvesting since1924
(Horwood 1986). This hasresultedinextensivefragmentationanda shi ft intheage-class distributionafforestsinthis region. Knowledgeof deleteriouseffectsof these activitieson bird and other wild lifepopulatio ns has notbeen documented. For these reasons,research objectivesofthis studywere aimed atbasicaspectsofraptorsurveytechniquesand ecology,andwere:
I.Tode velopreliable,standardizedtechniqueswithwhichtosurveybirdsof preyindifferent-aged fo restsandc1earcutsinthe WesternNewfoun dland Mode lFo rest(WNMF).
2.Todeterminethespeciesdiversityandrelativeabundancesofbirds of prey in uncutold growth.
second growth forest, clearcutsand pre -commercially thinned areas.
3.To developdensityestimatesofselectedspecies ofbirds of prey.
4.To iden tifynest sites ofbirds ofpreyandquantifyhabitatcharacteristi cs atthese sites. 5.Toiden tify knowled gegapswithrespect toNewfo undl an d birdsof prey, andindoingsoto develo p researchobjec tivesand manag em en tstrategiesforfuturestudies.
1.2Study Are a
The WNMFstudyareafallswithin theComer Brook subregio n(Damm an 198 3)andis characterizedbyhilly terrain with altitud es of upto600m.Forestsare primaril yDryopterts• balsam fir(Abies ba/same a)mixed occasional lywithwhitespruce(Piceaglauca), blacksp ruce(P.
mariana)andwhitebirch(Betula papyriftra; NOd.For.Serv.1992).Thehwnidclimateminimizes firesfrom thisregion(Damman 1983),and undernatwal conditionsinfestation sof hemlocklooper (Lam bdinajisce flaria)orsprucebudworm(Choristoneura fil miferana) arerespo nsib le fo rfore st renewal (BazukisandHansen 1965). Defoliatedpatchesofforestinconjunc tio nwithclearings from timberremovalhasresultedinaveryfragmentedlandscape inthis region.
InthefoUowin gstudyIhaveclassified"uncutold-gro wth"forests as 8G-100 year old uncut stands.Small forestopenings (100 x 100m).resultingfrom insect defoliation ,andan abundance of snags andcoarse woody debrisare typical.Tree heightsinthisforest type oftenreach upto 20-24 m(Ntld. For.Servo1992).Second.growthstandsin westernNewfo undland areregeneratedstan ds followin g timber harvestingearlierinthecentury.Comparedwith uncutolder forests. thesestands are40-60years oldandare characterized by smallertree:diameters,more stemslha. higher shrub diversityandlesswoodydebris(Thompsonand Curran 1995).Clearcu tsites resulting from fore st
harvesting have had mostof the woodvo lwne removed, though some deciduousandotherwise unmerchantabl etreesremain onthesesites. Herbaceousgroundvegetatio n consistingof raspberry (Ru.busspp.)and.alder(Alma spp.)isdense;however.clearc utsnearCock'sPondaredevoidof most groundvegetatio n because of prio r treatmentwiththeherbicideglyphosphate.Clearc utsites rangedfrom5-l5years old.Pre-commerciallythinnedareaswerefound throughou t the studyarea and ranged from 10-30 years old.These wereregenerating sitesthat had been artificiallythinned topromotemore efficienttreegrowth and were almostexclus ively compose dofbalsamfir.My
study sitesrepresentedanarea of approxim ately400Ian' within the WNMF.
Themainstudyareadurin g the 1993 fieldseason (24Mayto14 August ) waslocated near LittleGrand Lake withintheEnvironm ental AssessmentAreawhere cuttinghasbeensuspended.
Much of thisarea is uncut balsam fir forest, though5.3km!washarvestedprior to protection of this area.July8 -14was spentin the Cook'sPond area.Researchtrips werealsomadetositesnear
DeerLake(1. 4,5June.13 July),Victoria Lake (3-5July),andStephenvi lle Crossing (20July,2
August).
Research in 1994wasconducted near LimeGrand Lakealmostentirelyin the area from the TransCanadaHighway (TCH)easttoLittleGrand Lake.the secondary roadfrom the TCH west to George's Lake.andat Cock'sPond(15 - 21 March.. IJune toISAugust ).Thesesiteswerelarg ely locatedwithinuncutoldgrowth(80+ yr).secondgrowth(40-60yr),andclearcut areas respectively. Siteswere also surveyed at Pasadena(27June,17.22July),DeerLake (12 July.3August)andat StephenvilleCrossing (8-11 Augu st;see Figure1.1).
Figu re 1.1TheWest ern Newfo un dla nd ModelForestStu dy area (sha d edregion).Studysites areindicatedbynumbers1·7.
4
50 IOOkm
Legend: IUttJeGnndbke 2 GeorJll'SLake 3 Cook'sPond .aPasadella 5 Deeru.ke 6VictoriaLake 7Ste p b tll Yille C rvuillC
Chapter 2
A survey of woodland birds ofpreyintheWestern Newfoundland Model Forest
2.1Introduction
Forestsinwestern Newfoundland are intensively managedfor pulpwood production.and clearcuningistheprimary harvesting method.Consequently.the landscapeiscomposed largely ofvariousaged c1earcuts,regeneratedsecondgrowth forest,andremnantstandsofuncutold growthbalsam fir forest.Habitat lossfrom timber harvesting is recognizedasa seriousthreatto populations ofsomewoodlandraptors(ArmstrongandEuler1982.McCarthy etaL.1989.Carey et al,1990.Crocker-Bedford 1990).Consequently.management guide lineshavebeen imposed insome regionsinan effort to offset the potential adverse affects that forestharvesting may have on birds ofpreyas wellasotherwildlifespecies (NelsonandTitus 1987). On insular Newfoundland.however.managementguidelinesforwoodlandraprorsare lacking .andpriorto thisresearch.theconsequencesofforestremoval onraptor ecology had notbeenconsidered.
Timber harvestingisscheduledtocontinueinthisregion.so itisimportant to investigatethe species compositionandrelative abuodances of birdsof preyindifferenthabitatstoassesshow forestrypracticeswillinfluenceraptordiversity.abundanceandhabitatassociations.Systematic surveyswereconductedin different-agedbalsam firforestsinan efforttoachie vethese objectives.
Breedingdensities of birds of preyare generallyassumedtobe limitedbyeitherthenumber anddistributionof suitable nestingsites, an adequate food sourceorsomecombination of thesetwo facto rs (Newton1979). Furthermore,thesefactorslikely varywithinandbetween speciesand across differenttemporal andspatialscales. Monitoringthedensities of wildlife populations (numberof individuals or pairs/area) is ofinteresttoecologistsand managers whenassessingthepotential impacts of land-usepractices onthe environment Habitat quality canbeassessedpartiallyby detenninin gthenumber ofindividuals that inhabit anarea.althoughthevalidity of using breeding densityas theonly ormost importantindicato rof habitat qualityhasbeenquestioned (VanHom e
19 83).RaptorsurveyshavebeenconductedthroughoutmuchofNorthAmerica(Ruschet0/.19n, Schm utz 1984, Andersenand Rongstad1989);however.density estimatesare difficult to obtain for woodlandspeciesduring thebreedingseason becausetheyaretypicallywide-rang ing,secretive and oftennest ininaccessibleareas.particularlyinnorthern borealforests (Fullerand Mosher198 7).
EstimatesofraptordensitiesarepresentedandIspeculateonthemainfaetor(s)whichmay limit raptordensitiesinthisregion.In addition.I compared estimated breedingdensitiesof woodland birdsofprey inwesternNewfoundland withdensities recorded inotherNorthAmerican and Europe an boreal forestecosystems.Thiswill provide some insigbtinto raptor populationsin the studyarea,
2.1.1Raptor censusing methods
Compared with birds at lowertrophic levels,most forest-dwellingbirdsofpreynestat relativelylowdensities,arewid e ranging,secret iveandaretherefo re difficulttocensus (Fuller and Mosher1981,MillsapandLefranc 1988,KennedyandStahlecker 199 3, Solonen1994).In recent decades,however ,theincreasedinterestof biologistsa1XI.teed -useplannersinrecording thenumbersand distributions ofraptorsbasledtothenecessityof de velopingeffic ientand accurate censusing techniques. Asagroup,captors occupya widerange of habitats,differ beha viourall yandtherefore differ in theirdetectabilitytoobservers.Consequently, modifications totraditi onalmethods ofcou nting raptors aswellasnew censustechniqueshave evolvedthat are suitableforspecificbirdsofprey ,habita ttypesandthestudyobjectivesof researchers.
Perha ps themostcommo nlyusedmethodfor censusingbirdsofpreyhas beentheroad count(e. g.AndersenandRongstad1989,Donazarnat.199 3,Smallwood (995). Thismethod involvesdriving an auto mobilealong roadwaysataconstantspeed andrecordingthespeciesand numbe rs ofraptorsencountered.Despiteinherent biases suchasdifferencesinobservercapability andseasonalandclimaticvaria bles that mayaffect detectionratesofraprors(Morrellet at.1991), thistechniquehasbeen wide lyemployedsincethe19305 (Leopold1942)becauseofits suitability forcensusingextensive areasand targeting multiple species.Datacollectedfromroadcounts havebeenusedtoprovideanindexintotherelativeabundancesandpopulations of birdsof prey
in a specific area (Fulle randMoshe r198 1).
Nestsearcheshave alsobeenhistoricallyusedto count birds ofpreyanddevelop breeding andpopulatio nestima tes(Fulle r and Mosher1981) .Depend ing on the resourcesavailableand thestud y objectives oftheinvestigator.nestsearches maybe conductedon foot,byground vehicle or aircra ft. Thistechnique hasbeenparticularly effectivefor censusing largerbirdsof prey suchas Bald Eagles(Halia~etuskucocephalus)andOsprey(Pandionnatiaeua;wetmore andGilles pie1976 . CaU 197 8).These speciestypically have prominentstick nests thatoften exte ndabove the tree canopyandareoftenconsp icuo us. Nest searchesforsmal ler woodland raptors are generally moredifftcult.particularly inthedense coniferousdomina ted regions ofthe boreal forestwhere nests are highly concealed(Devaul1988).
Another method that has traditionall ybeen used forcensusing birdsof prey.as wellas otheravianspecies(Marion~Ial,198 1).hasbeentolisten for vocalizationsof territorialadults andtorecordtheirestimatedlocations.Withinthe past two decades.researchershavealsobegun broadcasting recordedvocalizationsatvaryingintervals along surveytransects.The objectiveof thistechniqueistoimprovedetection rates of breedingraptorsinforestedhabitatsthat are typicallydifficulttocensus (Bondrup-Nielsen1978.Devaul1988.Mosheretal.1990.Solonen 1994). To date.thismethod has proveneffectiveforincreasingthedetectionrates ofseveral speciesofhawksandowls.includingSpottedOwls(Strixocctaouaus, Forsmanetal.19TI), Ferrug inousPygmy-owls(Glaucidiumgnoma; Proudfoo t and Beasom1996).BarredOwls(Srrb:
varia;Moshera al.1990) , Cooper'sHawks(Accipitercooperii ,Red-shouldere d Hawks(Buteo uneaua:RosenfieldetaJ.1988.Mosheraal. 1990 )andNorthernGoshawks <Kennedyand Stahleck er1993).
Intheprese nt study.Iusedsystematic pointcounts inconjunct ion withvocalization playbacks(MosheretaI.(990)andnestsearchesto intensivelycensus woodland birds ofpreyin four forest habitats;uncutoldgrowthbalsamfirfores ts.secondgrowthforests. pre-co mmerci ally thinned areasandclearcuts.
2.2Methods 2.2.1Surveyprotocol
Seventransects passingthroughuocutoldgrowthforest (total transect distance
=
15kIn), secondgrowthfores t(9km),pre-commerciallythinnedareas (18kIn)andc1earcuts(16 km)were established alongfores troadsin1993andweresurveyedthreetimesforeachtargetspecies during thebreeding seaso n(fable2.1) . Transects varied inlength(dependingonroads in different-agedforests)from 4.8 to11.2kIDandcomprisedanum ber of broadcastStations at800 mintervals measured usinga vehicleodometer. Inareas inaccessiblebytruck.an all-terrain vehicleorboatwasusedandbroadcast stations wereassigned using1:50,000 scaletopograp hi c maps(see Appendix 1 forlocations of survey routes).Surveysforwoodlandbirdsof preywere conductedalong thetransectsbybroadcastingconspecificterrit orial vocalizationsat each ofthe stations (MosheraaJ.1990).Thesevocal izations wereintendedto elicitaggressiveresponses from territorial adultsmat may occurinthearea,thus improvingdetection ratesof birds. In 1993.thetargetspeciesweretheSharp-shinnedHawk(Accipiur slriQlUS).NonheroGoshawk.Merlin(Fa/co columbari us),BorealOwl(Aegoliusjunereus)andGreatHomed Owl(Bubo Virginianus). Equipmen tusedforplaybacks includeda batterypoweredRealistic vsc-2001 cassetterecorderand2 RealisticportableMinimus-Q.6speakers(83db/1m).Recordingswere obta ined fromtheCornell Laboratory of OrnithologyandfromthePetersonFieldGuide Series (MyerandPeterson1990),lhough onlyonerecording wasusedforany one species. Survey s werenot conducted duringperiodsof inclementweather,t.e.heavyfog,prolongedrainorwinds greaterthanBeaufon3(l3- 191cm1h; Mosherer al.1990).
Upon arriving ateachbroadcas tstatio n,theobserverwould listenandlookforbirds of preyfor 1min.Aseriesofsix 20 secplaybacksofasinglespecies'vocalizations,separatedby 30secsilentintervals ,were then madeovera5minperiod.Threevocalizationsegments were broadcast towardan arbitrarilyselectedside of theroad(detennined by coin toss)followedby three broadcastsegmentstotheothe rside. 1beobserve rwouldthen rema in atthesite foran additional5 min rolistenandlookfor birdsofprey.Only onetarget specieswassurveyedonany morning ornight.Playbac ks fortheremaining targetspecies were broadcas ton successive mo rningsandnights. Each route wassurveyedthreetimesdurin gthebreeding season.
Noctuma1surveysweredo ne each nightfrom.10:30 p.mto2:00a.m,andmorning surveys from 6:QO..I0: 00 a.m.The surveyperiodwas24 May ro14 Augustin1993 .15·21March.and1 June toIS August.1994.
In1994.survey routeswerere-establishedtoensurethat distances surveyedineach habitat typewere comparable.Thedistancessurveyedinuncutoldgrowth.secondgrowthandc1earcut areas were 18.L6and16kmrespectively(fable2.0.andanequalnumber of surveys (n=3) wereagain conductedalong each route.Pre-eommerciallythinnedareas were DOtsurveyedin 1994sincethetotalareaof thishabitattypeintheWNMFis essential lyneglig ible and the refore oflessinterest.Playba cks for Merlins were not broadcastin1994 because resu ltsfrom 1993 ind ica ted thattheydid notrespondtobroad castvocalizatio ns.VocalizationsofSharp-shinned Haw k.Northern Goshawk.BorealOwl.Great HomedOwl and NonhernHawk-Owl(Sumi a ulula)commenced on1June.1994.Incontrasttothemethodsusedin1993.individualsurveys involvedplaybacksformultipl e species.That is.nocturnalsurveysinvolved broad cast ing playbacksfor eachow lspeciesat every second800 minterval alon gthesurvey rout e.Potential behaviouralsuppressionofsmall erspeciesasa resultofbroadcastingthecallsof lar gerraprors wasunknown butwas expected tobeminimal. Lack. ofresponsedue tohabituat ion tothe playbackswasalso considered minimaJsinceonly3visitswere madetoeachpointcount during the season.
Playbacks for individualdiurnalspecieswere broadcastat every third800mintervalalong surveyrout es.Thismethodcontrolledforvariationsinweather condit ions thatmight otherwise influencederecrabitiryofthedifferentspec ies when individualspeci es broadcastswererun on success ivedays.Further.surveys were initiatedatalternatingends ofsurveyroutes on successive visitstobalancethepotential effectof varying broadcasttimes.
InMarch.1995.26Ianofuncut old-growthforestwassurveyed forBore al andGreat Homed Owlsusingconspeci fic vocalizatio ns .Broadcast stationswere 800 mapartandaccesswas bysnowmobile.
Thearea surveyedineach habitattypewascalculated bymultiplyingthekmsurveyed by theestimateddistance on each side oftheroadforwhich broadcasts wereaudibl e .Moshe r eraI.
(l990) found that broadcastswere audi bleto humans at 750 m away fromthe sourceina
10 hardwoodstandinMaryland. Inthisstudy,lhedistance thatbroadcasts werestillaud ibleto researcherswas estimatedto be 600mfor foresthabitats and 800mfor clearcuts and pre- commerciallythinnedareas.
Inadditionto thepointcountmethodusing vocalizationbroadcasts.areasadj ace nt(0the transectswere systematicallysearchedby fOOlthroughout rbestudyperiod inan attempttolocate sites of rapeoractivity (i.e.nests,roostsandAccipiterpre y-pl ucking-sites).Thisinvolvedtaking a compassbearingperpendiculartothetransectandwalkingan estimateddistance of500to 800 mon eachsideoftheroad.Any signs indicativeofraptor activity(l.e. neststructures.territ orial behaviour,preyremains) werenoted.Birdssightedwhile driving betweenbroadcaststations werealsorecorded.
2.2.2Statisti cal analyses
A two-samp ler-test(SakalandRohlf 1981)wasused to comparethe mean abundanceof woodland birdsofprey(speciesand years combined)amongthe four foresthabitats.Specieswere com bined becauseoftheexceedinglysmallsamplesizes ofindividualspecies.Bylump ingspecies together.validstatisticalcomparisonsofspecies assemblages between fore sthabitats couldbe:
performed.Ifdistributions oftheresiduals fornormality (a-score probabilityplots ) indicatedlhat theres idual s werenotnormallydistr ibuted .thenanon -param etricrand o miza tiontechniq ue (Manly 1991) was emp loyed.The randomizationtestis a re-sampling proc edu re whichcreates itsown frequencydistributionbasedontheorig inaldata. thuseliminatinganyassumpdons of nonnalily(AdamsandAnthony 1996).Theteststatisticusedfortheamonghabitat comparisons wasthenumber ofraprorsrb roedcasrstatio navera ged overallvis itsto thatstation.In theinitial step of the randomization test. the differencebetwee n the observed mean values of raptorslb road cast statio n betweenthetwohabitats being comparedwas calculated.Afrequency distribu tionof 3000 possib leoutcomes of differencesbetweenthemeanvalues was then nndomly generatedwith replacement fromtheoriginaldata."The habitats are significantlydifferentwith respect tothenumberof raptorslbroadcaststationiftheobserved differenceof meanvalues betweenthe twohabitatslies outsidethe9S%confidenceintervalsetaroundthe distribution of
II 3000possible mean outcomes .
2.2.3 Comparative densiti es
Thebreeding densitiesof birds of preywere compared betweenwesternNewfoundlan d and a range oflocatio nsinboreal forestsystems (coniferousdominated)throughout theirdistributions.
In thepresentstudy,birds wereconside redtobebreed ingif: I) activenestswere located.or2) territorial behaviourwasrecordedatthesame location overmultiplevisits.Densityestimatesfound in the literaturewere prese ntedinvaryingscales and werestandardized (pairsIlOOkm~to permit moremeaningful comparisons .However.Iemphasizethatdue to discrepanci es insurvey methods and habitattypesbetweenstudies. such comparisonsbetweendistantpopulationsmustbeconsidered withcaution.Abundancedatainboreal forests ecosystemswere not found for Ospreys.American KestrelsandRough-legged.Hawks thus density comparisonswere notmade forthese species.
2.3Results
2.3.1 Effectivenessorconspecific broadcasts
Seven transects totalling58and50Ian(habitats combined)were surveyedforwood land birdsof preyin199 3and1994,respectively(seeTable 2.1). Altho ugh respo nses of raptorsto the broadcastvocalizatio nswere elicited on occasion.mos t sigh tingsoccurredwhile driving between broad cas t stationsor beforethecallswerebroadcast. In1993. onlythree of94 birds detected(3.2%)wereinresponsetobroadcastvocalizations.Two ofthesewereBorealOwlsand the other a Sharp-shinnedHawk. In1994.eight of me 105raptorsdetected (7.6%)werein response tobroadcastvocaliza tions.tbese inc ludedSharp-shinned Hawks(2),BorealOwl(l contac t),Great-Ho medOwls(2),andNorthernHawk-Owl s(3).Forbothyears combi ned.the pro po rt ionof individualsthat res po nded to broadcastvocalizationsversus the total number of detectionsforeach ofthesespecies were: Sharp-shinnedHawk (60%),BorealOwl (60%) .Great HomedOwl(66%).andNorthern Hawk -owl (60%). Noraprorswere detected during winter 1994 alon g 30kmof unuet balsamfirforest. Itisnotabledlat for each encount er .positive
12 respo nsestobroadcastswere madeduringthe5minbroadcastingperiod.
2.3.2Species com positio nof birdsofprey
Ninespecies of raprors were recordedwithinthestudyarea berween24 MayandII August1993,andbetwee n1 Juneand14 August 1994:Merlin.American Kestrel(Fa/co sparvenusi,Osprey,Rough-leggedHawk(Buteolagopus),Sharp- shinned Hawk.Northern Goshawk.Boreal Owl,GreatHomed Owl.and NorthernHawk-Owl (seeTable2.2),
2.3.3Hab ita t associations and relatj yc abundances ofbirds ofprey
Uncutbalsamfirforests nearLittleGrandLakewere util izedbySharp-shinnedHawks, Merli ns,BorealOwlsandOspreysin 1993and1994,andaNorthern Goshawk: in 1994.The number of adultraptcrs(notpairs) andmenumberofdetections/Ianfor each spec iesbyhabitat andyear aregiveninTable2.3.Althoughnumbersarelow,anindex oftheirrelativeabundances isattained. In1993.Sharp-shinnedHawlesandBoreal Owls werethe mostabundantspecies (dcteetio nslkm forthesespecies were 0.27and0.33,respectively).Mert insandOspreyswere less abundantalong surveyroutes lhroughthis habitatandwererecorded at0.0 7and0.13 deteetionslkm, respective ly.In 1994.thenumbers ofSharp-shinnedHawks.MertinsandOspreys were similartothosein1993;however, onlyoneBor ealOwlwasdetect edincompariso n with fivethepreviousyear.Inadd ition.theonlygoshawk recorded duringthisstudyoccurredinuncut forestin1994.
Threespeciesofwoodlandraptorswereidentifiedalong surveyroutestransectingsecond growthforestsnearVictoriaLakeandGeorge'sLake:Sharp-shinnedHawk.MerlinandGreat HomedOwl. In 1993.9Ianofthishabitat wassurveyedresultinginonlyone sightingof each ofthesespecies. In1994.vocalizatio nsbroadcastalong16kmofsecondgrowthforestnear George'sLakeresultedinfourMerlinsandtwoGreatHomedOwlsbeingdetected (Table 2.3).
Inadditionrothefocalraptorspecies.secondgrowthforestsinvarious successionalstages were utilizedbyanestimated 20nestingpairsofOspreyintheStepbenville Crossingarea(p.St.Croix.
13 pers.camm .).
Clearc uts prov ided nestingandforaging habitatforbothNorthernHawk-Owlsand AmericanKestr els as wellasfo ragingsitesforMerl insandRough-legged Hawks. In1993, detectionslkmranged from 0.13forRough-leggedHawks (twoindividuals)to0.19detectionslkm forMerlinsandNonheroHawk-Owls(threeindividualseach).In1994.Rough-leggedHawks were not sighted inctearcu rs: however.twoAmerican Kestrels were recorded (0.13 deteetionslkm).Merlinnumbers wen: identical to thosefound in1993(Table 2.3).
In1993.surveys conductedalong18Ianofapre-commercially thinnedarea indicatedthat onlyRough-leggedHawks (O.17/km)and Merlins(O.06/km) were associatedwiththis habitat (fable 2.3). Noowls were detectedalong26bnofuncutold-growthforest in March.1995.
Old-gro wth balsamfitforests were utilized bymorespecies comparedwithsecondgrowth forests.c1earcutsandpre-conunerciallythinned areas.Statisticalcomparisonswere made between thetotal numberof birdsof preylbroadcan station(spec ies andyears combined)recordedalong surveyroutes passingthroughold-growthbalsamfir forest,secondgrowthandclearcuts.A two- samplet-rest(SokalandRohlf1981)wasfirstusedfOI"eachpairwisecomparison(e.g. old-growth vs.second growth),however examination oftheresidualsarx1normalscoresof theorig inal data indicatedthattheresidualswere non-normallydistributed,thuswarrantingtheuse of non- parametric methods. Subsequentanalysis usingarandomization procedure (Manly1991) indicatedthathabitatsdidnotdiffersignificantlywith respect[Qthemeannumberofraptors (speciesandyears combined)/b roadcaststation recorded alongthesurvey routes.
An analysiswas alsoperformedto investigatechangesinthenumbersof avianpredators (t.e.Sharp-shinnedHawks,Mertins )andsmall rcdenrpredators(i.e.Rough-leggedHawks,Boreal Owls,NorthernHawk-owls) between the 1993and1994 breeding seasons.Theabund anceof raptorsprimari ly dependent on passenne swas similarbetweenyears (fable2.3),however,the numberofrodentspecialists (particularlyRough-legged Hawks) decreased significantlyfrom 1993 to 1994 (randomizati ontest,P<0.(01).
14 2.3.4BrttdiDg Cbro no logy
Specific infonnationon thebreeing biologyof woodland birdsofprey on insular Newfoundllandislacking.However.estimat esof egg-layingdates canbe derived byback-datin g fromthe periodswhen nestlingsorfleglingsarefirstobserved...Sharp-shinnedHawkfledglingswere firstsighted near anestsiteon20 July,199 3.The birds at thistime appearedtobenearadult size.
Assumingthathatching0CCW'l'ed inthe firstweekofJuly,egg-layingwouldhaveoccurredonI June since incu batio ntypicallylasts30day s(Johnsgard1990).ThreeRoug h-leggedHawknests were monitoredforbreedingchronologyand hatchin gwasnotedtooccur between18-25June.1993.
The incubatio ntimeforthisspeciesis28 days (Johnsgard 1990) soegg-layingwas estimatedfor 17·
24May.TwonestlingHawk-Owlswere observedona neston 20June.1994and hatchingwas estima ted.tohave occurredaround 10 June.Egg-layingwasestimatedon 13May.ThreeMerlin nestlin gswerefirstobservedon25July,1994,andhatchin gwasestim ated to have occurredon 20 July.Merlins incubate forapproximately30days(Johnsgard1990 ) so egg-layin g would have occurredinlateJune.
15 Table2.1. Surveytransectspecificationsfor the fourforesttypesintheWestern Newfoundland ModelForest in 1993-94.Eachtransectwas surveyedthreetimesduring each breeding season.
Hab itatType Num ber Total TotalNof Area
of transect bre adea st Surveyed rrausects L<ngtb(Ion) sta tio os (km') 1993
Uncut oldgrowth 2 IS 19 IS
Second growth I 9 \I 10.8
Pre-commercially 2 18 22 28.8
thinned
Cleareut 2 16 20 25.6
Total 7 S8
n
83.21994
Uncutoldgrowth 3 IS 22 21.6
Secondgrowth 2 16 20 19.2
Cleareut 2 16 20 25.6
Total 7 SO 62 66.4
16 Ta ble 2.2 Sigh tings of adultbirdsofpreyintheWesternNewfoWKiland Model Fo rest. 1993- 1994.
Numbersofsightings include multiplesightings of individuals.butdonotinclud enestlings or fled glin gs.Thesenumbers alsoincludebirds of prey recordedinareasouts ideof the survey routes butin the WNMF regio n(seeFigure 1.1).
Number orSigbtings
Species (estimated#ofind ivid uals) Fore stHabitat
1993 1994 Total
Merl in 25 (14) 22(16) 47(30) Clearcuts.old andyoung
Falco columbarius second growth. uncut old
growth
AmericanKestrel 9(8) 4(4) 13(12) Clearcuts
Falco sparverius
Osprey 5 (4) 35 (24) 40 (28) Young secondgro wth and
Pondion hal iaetus uncut old growthDearlar ge
water bodies.
Rough-leggedHawk 22(1 8) O{O) 22(18) Barre nground. clearcuts.cliff
Buteo lagop us faces
Sharp-shinn ed.Hawk 13 (6) IS(8) 28(1 4) Uncutoldgrowthandold
Accipiterstria /us second growthbalsamfir
North ernGoshaw k 0(0) 4(1) 4(1) Uncut oldgrowth Accip itergeruilis
Borea10wl 8(S ) 1(1) 9(6) Uncutoldgrowth
Aego/iusfunereus
Great Hom ed Owl 2 (2) 8(4) 10(6) Oldseco ndgrowth
Bubo virgin/anus
Northe rnHawk-Owl 10(5) 14(7) 24(12) Cleerc urs Surniaulula
17 Table2..lDensitiesofraprors(rapeorszkm) detected along surveyroutesindifferent balsamfirforesttypes inthe WesternNewfoundland ModelForest.1993-1994. Numbersinparenthesesareindividualadultraptors (notpairs)and do notinclude repeatsightings.
/HabitatType Km iIaIll=lkm
1993 urveyed M K 0 RLH SSO GO 80 GOO NHO TotallIofS PI
luncut oldgrowth IS 0.07 0 0.13 0 0.27 0 0.3] 0 0 0.80 4
(I ) (2) (4) (S) (12)
~<eondgrowth 9 0.11 0 0 0 0.11 0 0 0.11 0 03] ]
(I) (I) (I) (])
learcut 16 0.19 0 0 0.13 0 0 0 0 0.19 0.51 ]
m
(2) (]) (8)minDed 18 0.06 0 0 0.17 0 0 0 0 0 0.23 2
(I) (]) (4)
1994
~ncutoldgrowth 18 0.17 0 0.11 0 022 0.06 0.06 0 0 0.62 S
(]) (2) (4) (I) (I) (II)
fseeondgrowth 10 02S 0 0 0 0 0 0 0.13 0 038 2
(4) (2) (0)
learc ur 10 0.19 0.13 0 0 0 0 0 0 0.19 0.51 ]
(3) (2) (]) (8)
1993-94 c:ombi oc:d)
Uncut oldgrowth 18 0.22 0 0.22 0 0.22 0.06 03 ] 0 0 1.01 S
(4) (4) (4) (I ) (0) (19)
Secondgrowth 2S 020 0 0 0 0.04 0 0 0.12 0 030 ]
(S) (I ) (] ) (9)
lean::ut 10 0.25 0.13 0 0.13 0 0 0 0 037 0.82 4
(4) (2) (2) (0) (14 )
Snecies name ab b rev iations"
M=Merlin RLH"" Rough-leggedHawk K::AmericanKestrel 55H=Sharp-shinn edHawk
o
=Osprey GH-NorthernGoshawkBO-BorealOwl GHO-Great Homed Owl NHO=Northern Hawk-O wl
18 2.4Discussion
Pos itiveresponses to vocalization playbackswereelicited byfour speciesofbirdsofpreyinthe swdy(threeof whichwere owls). Broadcastingvocalizationsaccountedfor66%oftheGreatHomed Owl detectionsand60% of BorealOwl.NonhemHawk OwlandSharp--shinnedHawks detections. However.
the playbackmethod accountedfor only3.2and7.6%ofthetotaldetections in1993and1994.
respectively.Woodlandbirds of prey general ly occurinlowdensities .aresecretive.wide-rangingand theref oredifficu lttocensus (Fulle randMosher1981). Inlightofthis.broadcastingtaped callsof conspecificsas a meansof improving detectionrateshasbecome anincreasingly prevalent method for locating forestcaptorsand hasbeenshown to increase detectionrates of SpelledOwls(Forsman eral, 1977),Red-shouldered Hawks,Cooper'sHawks.Barred Owls (Mosheretat.1990) andNorthern Goshawks(Kennedy and Stahlecker 1993).We testedthehypo thesis[hatresponses tovocalizationsmight behigherin latewinterorear ly spring(lMarch-ISApril ), particularly forBorealandGreat Homed Owlswhen territoriesare being established (Morrellaat.1991.Haywardaal.1993).Broadcast surveys forthesetwo owl species were conductedin uncutold-growthforest from 15-21 March.1995. thoughno owls weredetectedalo ng26kmofthishabitat.Withrespect tothebreed ing stage.otherstudies have shown that woodland birdsofprey. includ ing Red-shoulderedHawks.Cooper'sHawksandSpottedOWls.
responded read ily tocallsthroughouttheentire spring-summer period (Forsmanetal,1977.Kimmeland Yahner1990andMosheretat.1990).Thelack of BorealOwl detectionsmay have been attributab leto decreasedensities ofsmal l mammalsinthestudy area atthis time(W.Adair.pers. comm.).BorealOwls areassumedtobe nomadicinresponseto preyfluctuations(lundberg1979.HaywardandHayward(993) andmay have relocatedinsearch of more favoura ble breed ing conditions.oralternatively,mayhave been presentyet sus pe ndedtheonsetofthecouru hipritual (i.e.remainedron-voca l) inresponseto low prey abundance.Great -HomedOwlswere likelyabsent fromthisstudyareadueto thescarcity oftheir primary prey.i.e .SnowshoeHare(Lepus americanus)andRuffe dGrouse(Bonasa umbellus:Ruschet at.1972).
Lundberg (1979inHaywarderal.1993) found that "terri torial and breeding pairsofBorealOwls were moresilent than non-territ orial individuals .· so censusesusing playbacksmaygive biased esti mates ofowl abundances.Hayward~ral.(199 3)contended thata lackofanunderstanding of the factorsthat affectBorealOwl singingratesmakesthevocalizationmethodan inapprop ria temonitorin gtool.Overall,
I! censusing birdsof preyinforestedhabitatsremains problemati c. Furtherresearchshould becoeductec to develop more reliable censusingtechniquesforwoodlandraptors.
Surveys forbirds ofprey conductedduringthe1993 and 1994 breeding seasonsindica te d tha:
uncutoldgrowth fores tscontainedbamthemostindividualsandthemost speci es. Overall.the denst nee of birds ofprey weregenerally low,anddiffere nt-agedbalsam.firforestsand clearcutswere utilizedb) a broadassemblageofspecies.Forestsinadvancedstages of naturalsuccessioninwestern Newfo undland aretypifiedbyextensi vesnag retention (Sturtevan t 1996)andstands aceof various ages,thus allo win g a potentiallywiderrangeof species toinhabitthis habitat type. Forexample.Boreal Owlsare dependent uponthepresence oftreecavitiesfornesting(Haywardaat.1993)andwererestricted touncutold growth balsamfirforests . Sharp-shinnedHawks prefera densecanopy coverfor nesting(platt 1976 .Call1978) anda relatively open underst ory for huntingandwere found mainlyinoldgrowthforests.
SecondgrowthforestsinNewfoundland. aretypically youngereven-aged forests (Thompso nand Curran 1995) with les s stru cturaldiversitythanuncut oldgrowthforests . Species withmorerestricted nesting requirements (i.e .BorealOwls.Hayward andHayward1993)areunl ikelytoselect suchforests for breeding.which mayhelpexplain the decrease inspeciesnumbers incomparisonwith WlCUtoldgrowth forests.Surveysinsecondgrowthforests indica ted mepresence ofonly I:hreespeciesof birds of prey.one ofwhich,meGreat-Homed Owl.is considereda habitat genera lis twithawide ecologicaltolerance (Bosakowskietat.1989).
C1earcuts providedbreeding habitat forboth NonheroHawk-O wls and AmericanKestrels. Large hardwoodsnags have beenleft intact throughoutthese areaspro vidin gbothnestingstru cturesandperchin g sites forforaging. Mert inswere also frequentlyobserved huntin ginthis habitatas wereRough-l egged Hawksin1993. The latterspeciesisan aerialpredator which prefersopen ground. althou ghtypicall y at more northe r ly tundra habitats (PooleandBromley1988.Whitakeretat.1996).
An apparentlink: ofrap tor densitiesto food supply stres ses that forest managementshouldalso consider the impactof timber harvesting operations onspecies atlower trophiclevelsand shouldnot concentratesole lyon predatorsor theirnesting habitat.Thesignificant decline ofmicronne-dependent birdsofprey. t.e.BorealOwls.Northem Hawk-OwlsandRough-leggedHawks.from 1993 to1994 suggests thatsmall mammalpopulations mayhave declinedinthisregionbetweenyears.InFennoscandia.
juvenileandfemaleBoreal Owls dispersewhen volepopulations crash.but mostold males stayon their
20 territoriesthroughouttheyear(Korpimaki1994).whereas Northe rn Hawk-Owlsleadanessentially nomadic life.breedinginareaswithtemporarily high microtineabundance(Nybo an:!.Sonerud1990).The abundanceofavian-dependen t birdsofprey.Le.Sharp-shinnedHawksandMertins.remainedsimilar between years suggestin g thatfoodresou rcesweremorestable forthese spec ies. Thispheno menonhas beenpreviouslydocumentedbyNewton(1979) whostatedthat"raprorpopulationsthatdepend onfairly stable (often varied)food sources sbowfairlystable densities overmany years, whereas populations that depend on fluctuating (often restricted) food sourcesshowfluctuatingdensities,inaccordancewithprey cycles."
2.4.1Compa ra tiv eDensities
Breedingdensities ofbirdsof prey aregenerally assumed to be limited by either thenwnberand distri bution ofnesting sites,an adequatefoodsupplyor somecombinatio nof these two factors (Newton 19 79). TwobreedingpairsofSharp-shinned Hawkswerefoundinuncut balsamfirforestsin1993and1994.
anda pairinolder second growth forestin1994.Adensity estimate of breeding Sharp-shinned Hawks for thesetwoforesttypescombinedbasedonsurvey resultsis 6 pairslloolan2.This approximatesthebreeding density of4 pairs/loo lan2reportedbyReyncldseral.(1982)inOregon. but is amuch lowe:rdensitythanthat recordedinthe coniferousforests of interiorAlaskaby Clarke(1984),wherea density of24pairsllOOkm~
wasfound.Thisfour-folddifferencein breeding densitymaybedueto amor eabundantfoodsupply in comparison with insularNewfoundland.Sharp-shinned hawks prey primari lyonsongbirds(Storer1966, Reynoldset al.1982.Reynolds and Meslow1984) whichare generallyconsidered.tobemore abundanton continental North America (Montevecchi and Tuck 1987).Regional variationinbreedingdensity inrelation to songbird abundancehasalso been noted for theEuropeanSparrowhawk (Accipiternisus';Newton 1979).
One NorthernGoshawk (assumed unpaired) was recordedinthe studyareaduring 1993·1994.
DensitiesofNonhernGoshawks recordedelsewhereinNorthAmericanconi ferous forests are 7.5pairs/IOO km!inColorado(Shuster1977), 3.4 pairs/tOOkm2in Oregon(Reynoldsetal. 1982)and2pairs/IOOkm2at a site ininterior Alaska(McGowan 1975). NorthernGoshawks preyhea vily on SnowshoeHare ,Ruffed GrouseandRedSquirrels (Tamiasciurushudsonicus)all ofwhichwere uncommoninwesternNewfoundland during this study(pets.observ.),andthe abundance of this speciesisagainlikely limited by the availability of adequatefoodresources.
2\ BorealOwlswererecordedinuncutoldgrowthforests at a moderatedensityin1993.low densityin 1994and were not recorded duringlatewinter surveysin1995.Densityestimatesextrapolatedfromroadsi de surveysin uncut oldgrowthwere17and5pairsll OO lan2 for 1993and 1994,res pecti vely.Otherstu dies reportBorealOwl breeding dens ities of 3 pairs/tOO kInlduring a5-year study inMinnesota (Lane.unpub l.
data},9.1pairsllOOkm1at two study sitesinOntarioandAlberta (Bondrup-Nielsen1978).12pairsllOOkm1 recordedintheRockyMountainsof the United States (HaywardttaI.199 3)and22 pairsllOOkm2at a study locationinFinland (Korpimaki 1981). Thevariationinbreedingdensity recordedinthisstudymay reflect fluctuatingrodent numbersbetween yearsand maymore general lyresul t from thelow small mammal pre y base typical of insularNewfoundlandwhereonlyonespecies of smaHmammal.the meadow vole (Microtus pennsylvanieus )isendemicandoccursinanyabundance(Bateman 1986).Smallmammals.particularly voles. arc theprimaryprey ofBorealOwls throughouttheirgeographic range (Haywardet al.1993).and.in northern regionswithpronouncedfluctuations ofvo le numbers, BorealOwlsare microtinespec ialistsand exhi bit extremefluctuationsinbre edi ngparam eters (Korp im aki 19 86).
Grea t Hom ed Owls apparently inha bitsecondgrowthbalsamfirforestsinwestern Newfo und land inlow densitycomparedwith mainlandpopulations. Theestimat ed breed ingdensity for western Newfoundlandis2pairsllOOkm2whereas studies conductedinSaskatchewan(Ho uston 1975).Alberta (RuschelaJ.1972)and Michigan(Crnighead and Craighead(956) ,found densiti eswere12.5and7 pairsllOO km2,respectively.Food resourceslikelylimitsthe breeding densityof Great HomedOwls.Snowshoe Hare oftenforma majo rcompon entof theirdiets(Ruschet al.19 72 ), andperiod ic fluctu ation s orinvas ion s of GreatHom ed Owlsinnorthern forestsoccurinrelation to the varying abundanceofharesandgrouse (Rusch et al,1972. Bosakowskietal.19 89 ).Durin g this study,SnowshoeHare and Ruffed Grousenum bersin western Newfoundlandwere low (P.St. Croix.pers.comm.1994).
North ernHawk-Owlswererelativel ycommon in clearcutsinboth199 3 and 1994(see Table2.3 ) where breedingdensitie swereestima ted at 4pairs/IOO km",TILis is similarto thebreedingdensities of approxim ate ly3 pairsllOOkm2(range 0-6) reportedinthe Yukon byRohneret of.(1995)and2 pairs/IOOkmz in Norwa y (Hage n 1956),but is muc hlessthanthatrecordedfor Sweden (Cramp 19 85) whereameanoflO pairsllOOkm2(range 0.2-20)hasbeendocumented.Northern Hawk-Owlsarean irruptive spec iesthatlead a nomadiclife,occurring atplaceswithtemporarily high microtinedens ities (Mikkola1983inJohns gard 1988,NyboandSonerud1990).Analysisof regurgitated owl pelletscollectedduring 1993from anestsite in the study area indicatedthat MeadowVoleswereimportantprey as all 7 pelletswereexclusivelycomprised
of Meadow Voteremains(seeappendix2).Volesmadeupatleast 93%oftheidentifiedpreyanimalsatnest- sites in Norwa y.Finland and Russia(Mikkola 1983).ItislikelythatsmaJImammalabundanceisthemail factor limi tin g thebreeding dens ity of NorthernHawk-Owlsin western Newfoundland.
Merlinswere the mo st commonwoodlandraptorrecordedinwesternNewfoundlandforboth yean andhabitats combined(16pairsli00kml).Comparative breedingdensiti esfor this speciesinetherconiferous forestsyste ms are lacking ,however.The abundanceof Merlinsmay bemorestablethanother woodland birds ofprey sincetheyareastrongly bird-adapted pmlator(Sherrod1978)anddonotrely onfluctua ting01
cyclic prey such as voles orbaresas doBorealOwls,Great HomedOwlsandNorthernGoshawks..However, it mayaJsobethatMertins are easier todetectby observerssincethisspeciesistypically more vocalthan other wood lan draprors(pers. observ.).
2.4.2BreedingChronology
Obtainingprec ise dates onreprod uctivestages of raptcrs is problema tic.Birdsof prey occur in low dens itiesandare difficulttoloca teandmonit or. Furthermore,breedingchro no logy mayvary betweenseasons.individual pairs.andacross geograp hicareas. Breeding cbrocology ofraptors oninsulae NewfoundlandbasDOtbeenadequa tely documented.Some insight maybegained by comparin gestimated clutch initia tiondatesfromthisstudy with those documented elsewhereinNonhAmerica.
The egg-layingperiodforSharp-shinnedHawksin westernNewfoundland was estimatedtobe1 June.In Alaska,Clar ke(1984) foundthat thisperiod ranged from22May -4 June.andinOregon.from 11 Mayto 19June (Reynolds1978). Rough-leggedHawksinthis studywereestimatedtocomme nceegg- layingfrom 17-24May.Similarly,Rough-leggedHawks inUngav a Bay begin layinginthelast wee k of Mayaodfirst CWO weeksofJune (1.WeaverandD.M.Bird. pers.comm .).Clutchinitia tionforNorthe rn Hawk-owl swasestimatedtooccur on 13May.Insouthwestern Yukon.egg-lay ing ranged from19 Apri l
[011 May(Rohneraal.1995) ,andin DenaliNationalPark.Alaska.KerteU(1986)reporteda rangefrom 13·24 April.Merlinsin westernNewfound landwe reestimatedto beginegg-layinginlateJune.Thisis amucb later datethan reco rdedbyLaing(19 85) ininteriorAlas ka whe re Merli ns were estima ted to commenceincubation duringthethird weekofMay.
23 Chapter 3
Habi tatcha racteristi cs ofnapto ractivitysitesin westernNewfo und la ad 3.1 l ntrod uctioD
Hab itat selectio n theo ry slatesthatspecies arcpreferentiall y associa tedwithaparti cular habitat in whichthey can optimallyfunctionand reproduce (Cody1985).Forbirds of prey ,the importance ofspecifichabitatattrib utesforprovidinglife bistory requirementshasbeen documentedand.includes selection of suitable nesting (Titus and Mosher 1981.Reynoldsetal, 1982.SpeiserandBosakowski19 88. Bosakowskiet al.1989),roosting (Barrows1981, Hayward andGarton 1984)andhuntingsites(Bec hard1982.Widen 1994).Nest-sitefeature sthat influence selection are manyandvaried.andincludestand age (Reynoldset al.1982),tree density and size {Branning1983.MorrisandLemon1983.Selas 1996), topograp hy(Speiser and Bosakowski1988)andproximi tytophysiograp hicfea tures such as water andforest ope nin gs (Titusand Mosher 1981).likewise.roost-site selectionhas been attributedto factorssuch as treedens ity,percent canopycoverand the aspectofslo pes where roostsoccur(Barrows 1981.
Haywardet al,(993).Foraging areas arc also subjecttopatternsof selectionandmaybe influe nced byprey availabilityaswellas structuralfeaturesof habitats .Forexample.Sonerud (1986)suggestedthatBor ealOwlsinNorwayshifted hun tingareasearlyin thespri nginrelation tosnowcond itionsand the accessibilityof prey,andinSweden, Widen(1994)determinedthat the presenceor absenceofsuitableperchesinfluencedtheuseof c1earcutsby foragingraptors thatuse the pause-traveltactic.
Because ofthehabitatspecificityof manyrapto rs, alteration of thephysicaland vegetative structureoftheir habitatsthrough forestharvesting, agriculture and humanhabitation hasledto ageneraldeclinein the populationsof many woodlandraptors througho utmuc hof NorthAmerica(Mos her198 7).More vulnerablespecies includethosethathavenarro w ecologicaltolerances.particular lyif depe nden t onolde rsera!stages suchas NorthernGoshawks (McCarthyetaf.1989,Crocker-Bedford1990).Boreal Owls (Haywardet ai.1993)andSpotted Owls(Forsmanetal.19 77).Conversely.other raptorspec iesthatprefer open oredge habitats
24 suchas Northern Hawk-Owlsand AmericanKestrelsmay benefit fromforest fragmentation . Alteration offoreststructuremayalsoinfluence the availab ilityandaccessibilityof food resourceswhichcan ultimately influencepopulations of birds of prey(Bec hard 1982.Bakerand Brooks1981,Widen1994).Attem pting to manage for the protectionofpopulations ofbirds of prey at thecomm unitylevel necessitate sdeterminingthe habitat requirementsfor anassemb lage of species . andassessing the availa bilityofthis habitatatalandscapelevel.This information may thenbe implementedintoforest managementstrategiesand coordinatedwith wild life objectives.
Informati onon the structuralandvegetativecharacteristics of rapto r activity areas has been describedelsewhereinNorth America. particularlyinthe Northeast and RockyMountai ns of theUnited States(TitusandMosher 1981.Reynoldsetal.1982,Siders andKennedy1996).
How ever.theapplicability of this site-specific infonn at ioninpredi cting ordescribing rapto r habitat inlheinsec t-drive n balsam fir forests ofwesternNewfoundlandis unknown.Itis thereforenecessarytoinvesti gatethe habitatfeaturesof sitesutilizedby woodland birds ofprey inthe extremeeastern pottionoftheir rangeinorder to more fully understand thehabitat requirem ents of these species asawhole.
In thischapter.anexplorato ry approachisusedin an attemptto identi fy the struc tural featuresthat mayinfluencerapto rhabitat selectionat amicro-habitatscale.Irecogni zeand caution. howe ver.thatsamplesizesare smal l and the subsequentanalysesarenot conclus ive.
Howeve r.thisapproachis usefulfor generatingnewhypo thesesthat warrant further investigation. Management recommendationsfor birds ofprey in western Newfoundlandare alsopropo sed.
25
3.2 Metbods
Habitat datarelati ngtofore st stand structure and compo sitionwerecollected at raptor activity sites(i,e.nests,roosts,prey-p lucking -sites)and atcorrespo nd ingunusedsitesat distances of50and400rn.Unusedsites wereinvesti gatedforsignsofactivityseveraltimes throughoutthebreedin gseasonto ensurethatraptorsdidnot utilize these sites.Unused sites were selectedbyhaphazardlyturningthehousing on a compass andwalkingthe appropri ate distanceinlinewiththecompassdirection arrowfromthe centreof the activitysite. Additional habitatdata werealsocollec tedateach800m interval alongthe1994surveyroutes (n=58).
These sites were50 mfromarandomly selectedsideoftheroad(detenni ned by cointo ss)and will hereaft erbereferredtoas roadside sites. Where survey routesfollowedlake shorelines.
habitatmeasurementsweremadeata distance of 50 m from the shoreline.Forallsites.stand levelattributesincludingthe num ber,species,diame teratbreast height (DBH), and vigour (live.
dead)of trees were recordedwithinan 11.3mradius (0.04ba)fixedplot Othermeasureme nts includedanvisualestimationofthe percentofground vegetation andcanopycover.thenumbe r andDBHof snagsand a tally ofcoarsewoodydebris abundance (CWO.i.e.dead fallentreesand lim bs witha diam eterof>4cm ) alonga 22.6m randomtransectthroug h thecentreoftheplot.
A princ ipal com pon entsanalysis (PCA) wasemployed todeterminethe mostimportant habitatfactorsatthenest-sites.roostsand prey-plucki ng-s itesofwoodlandbirds ofprey.This multivariateprocedure reduces alargenumber of variablesinto a smallersubset of related.factors which may be usefulinidentifyingsignificantfeatures of selectedhabitats(Bosakows kietai.
1992).[1shouldbenoted.howe ver. thatthe factoranalysisusedhere isanexploratorytechnique toidentifypotentialmultivari atepatternsinthedata fromwhichspec ific hypothesesmaybe developed.Itisnotusedtoconfirm or testanypre-existinghypothese sregardingrapto r habitat utilizatio n.Habitatvariablesusedin thisanalysisinclu de:I)treedensity.2)numberoflive balsamfir (BF»1 5em DBH.3) liveBF<15 emDBH.4) dead SF>15 em DBH.5)deadBF<
15em DBH. 6)% liveSF.7}%deadBF.8)liveblack.spruce(BS)>15 emDBH. 9)dead
as
<15emDBH.10) live whitebirch>15 em DBH.II)%deadtrees(speciescombined.). 12)%live
26
trees(species combined).13) total number ofsnags.14)snags >15 emDBH.,IS}snags<15 em DBll 16)%coniferous.17)%deciduous. (8)%canopy cover,19)%ground vegeta tion cover, 20)CWO.Significant factors(l.e.eigenvalues>I) were retainedinthe analysis.Followingthe reduction of allhabita t variables into facto rs. eachfac torwas plottedagainst the habitatvariable most stronglycorrelatedwithittoensure thatthe datadistributi on wasnotskewed (Knoec hel andCampbell L988).Scarterp tc ts werethenexaminedto investig ate the distri butio nof raptor activity siteswithrandomSOm,400m,and roadside plotsinrelationtothefactors.
Differences inhabitatstructureandcompositionwere compared amongraptoractivity sites andrando msitesatdistancesof 50 and 400 m forthe variables listedabove using the Mann-Whitney U statistic.nusnonp aram etrictestwasusedsince theunderly ingdistrib ution s of the habitatdata wereunknown and nonnality could notbeassumed(Manly199 1).The level of signific ance for allcomparisonswasa.-o.05. Allcom putationswereperformedusing the SPSS statisticalpackage atMemori al Universityof Newfoundland.Thedatacollected attwo Nonhero Hawk-Owland American Kestrelnestswerenotincluded. sincethisfactoranalysis is specificto forested sites and i.nclusionof thedatawouldprod uce misleadingresults.Qualitative descriptions of thesespec ies andof Ospreys are presented.however.
3.3Resu lts
Factor analysis resultedina reductio nfrom 20 originalhabitat variab lestosixfactors that describe thestru ctural andvegetati ve componentsatnests,roosts andprey-pluckin g-sit es and accountedforapproximately76%of the variancein the originaldata. However.onlythree factors describing53%of thevariance wereusedbecause theotherswerediffi culttointerpretin an ecolog icalcontext(see Tab le3.t).Factors are describedbasedonthe measured habitat vari ablesmoststrongly corre lated with them andaregivena subjectivenameindicativeof this relations hip.Factor I (stand health)re presentsagradient from avigouro us,late successional balsam firstand to an older de generating forest stage dominated by large(>IS emDBH) senescentbalsamfirtrees.Factor2 (snags) describes an increasein the densityof snags that haveresulted from previ ousHeml oc kLooperinfestations.Factor3(youngtreedensity)is
27 definedbyanincreaseintreedensity,particularlylive balsamfirwith small
«
IS em DBH)treediameters.
The distri butionofSharp-s hinned Hawkprey-pluckin g-sites(n=3)andunused sites(0=6) in relationto fac tors 1 and3is illustratedin Figure3.1.Factor I (standhealth) didnot discriminatebetween these siteswhencons ideredsole ly; however. when plottedwith factor 3 (youngtreedensi ty ),the used andunused siteswere reasona blysegregated.Factor2 (snags) did notprovide any further discriminatorypower whenplotted with eitherofthe othertwofactors.
Merlinnest -sites(D""3)and unusedsites (0=5)are plotted in relationtofactorsIand 2 (seeFigure3.2). Nests and unused siteswere separated entirelyalong factorI(standhealth).
howevertheirdistributions overlappedwithrespec t to factor2.Factor3didno t contri bute any addit ional disc rimin atory power.
Figure3.3shows aplot ofthedistribution of rapt ornests,roo sts.prey-pluckin g-sites and unusedsites(SO m,400 m,roadside)insecond anduncut oldgrowth forest.Therewasno separation between the Sharp-shinnedHawk.plucking-sites and theBorealOwl roost along facto r I,however,Merlinnest-sitesshowed a strong positiverelationship with stand health and Osprey nestssites were slightlynegative alongthis gradient.Along thex-axi s (factor2),tbeBoreal Owl roostrelated toan increasing abundanceof snags,whereasSharp-shinned Hawk plucking-sites and Ospre ynests were neutralalongthis facto r.Merlin nest-sitesfellout atthelower end of this distrib ution andwerenegat ively associatedwith snagabundance.Whenthese sites areplott edin referenceto fac torsI and 3 (young treedens ity ),the Boreal Owl roostandOspreynest- sites show a strong positive relationshipwith factor3, whereas Sharp-shinnedHawk plucking-sites andMerlin nest-sitesare neutral alongthis gradient (Figure 3.4).
All comparisons of habitat structure made betweenactivitysites(i.e.nest-sites,roosts, prey-plucking-sites )andthe50and 400munused sites usingtheMann-Whitneytest were non- significant.Thisislikely attributable tolowsample sizes(range1-4 ) of raptoractivi tysites and unusedsites comparedin the test.
Two active NorthernHawk-Owl nests were foundin the studyarea. One near Deer Lake wasloca tedin anextens iveclearcutthathad alsobeendamagedbyfire.Largesnags(>I0em DBH)were presentoutside ofthe immediate 11.3m plot.and ground vegetation. composed
28 mainlyofalders .wasdense.Thenestwassituated at the top of asnag (DBH=29 em) at aheigh t of 6rn.The secondnest-site neatLittle Grand Lake wasalsoina largeclearcct, thou ghthere werefewsnagsin theimmediate nestingarea.Groundvegetation wasalsodenseat this site exceeding about80%ofcover.Thenestwasalso ontop of abroken snag (DBH=6 1em).Both nests wereon relativel ylevelground (slope<5 degrees )andwithinapproximately200 mof a forestaccess road.
Two AmericanKestrel nesting cavities werefoundinc1earcuts that were characterizedby numero us snagsnear thenestin gtree. Bothnestswerein whitebirch(DBH"38.5and31 em) which werelarger than themajorityof the residual treesinthe 11.3m plots.CWO andground covervegetationwas high atthefirstsiteandlowatthe second.
Habitat characteristicswere measuredatfour Osprey nest -sites within 2kmof StephenvilleCrossing.The forestinthisareawas predominandydense.30-60yr secondgrowth balsam firwithan approximately25%deciduous component,All nest-sitesmeasuredwere within1-2kmofa large water bod y.Nesting trees at threeofthese siteswere>15emDBH (range:18-43 em DBR)and extendedabove the canopylayer.The mean heightofthese trees (twoblackspruce.oneyellow birch)was11 m(Standard deviaticne4.3m,n-3).Thefourth nestwasontop ofawooden platform spannin gtwotelephonepoles.
29 Table3.1. Factor analysis ofstructuralandvegetative characteristicsatraptor nest-sites.roosts, prey-pluckin g-sitesand unused sitesinsecond and uncutoldgrowth forests.Correlationsoflog and arcsine transfonned data arereportedwiththe firstthree extractedfactors.Onlysigni ficant corre lations(>0.6)are shown.
YaJ:iahI< futu..l
u =
~Density of dead balsamfir>IS em DBH 0.69 Density oflive balsamfir<15emDBH 0.8 1
Densityof trees (spec iescomb ined ) 0.93
Totaldensityofsnags 0.94
Densityoflivebalsamf1C<ISem DB H 0.84
PercentageoflivebalsamfIC .Q.78
Percentage ofdeadtrees 0.82
Percentage ofl ivetrees -0.87
Dens ityof snags<15emDBH 0.69
Density ofmags>15emDBH 0.83
Cumulative 26.9010 40.7% 53.2%
Explainedvariance
Figure I&2fod
1,2,3 Activity site (i.e.nest, roost, prey-plucking-sire) S Sharp-shinned Hawk prey-pluekmg-site
M Merlin nest
B Boreal Owl roost
o
Ospreynestt)
Unused site (50 m)• Unused site (400 m)
• Unused site(roadside)
30
31
Figure3.1Sharp-shinned Hawkprey-plucking-sites andunused sitesinuncutold growth balsam firforestinreference to {actors1and3.
12 2.0
15j
-. o
1.0
~ o
.5
~
0.0'" o
!!:. ~
•
E
-.5'"'"
I -1.0
-ee S -1.5
rJl 1\
I
-2.0-2.0 -1.5 -1.0 -.5 0.0 .5 1.0 1.5 2.0
- >Densityof youngtrees(Factor 3)
33
Figure3.2Merlinnest-sitesandunused sites insecond growthbaJsam firforestsinreferenceto factorsIand 2.
i . "
'.5
2
1.0
~
()()
~
co .5()
!!:.
E m
0.0:r
."
e -.5
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aJ
Ai
·1.0·2.5 ·2.0 ·1.5 -'.0•
-.5 00Snags(Factor 2)
Figu re3.3 Thedistributionof nests,roosts,prey-pluckin g-sites and unused sitesinsecondand uncut old growthbalsamfirforestsinwestern Newfoundlandinreference to factorsIand 2.
3S
~
o. .
o
B
00
o
o:- - .
o
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. ,
,
o •. .
o¥
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Snags (Factor2)
•All unused sites (roadside.,50m and400 m) arerepresentedbya smalldOL
