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THE <I>DHO&Hyphen;GAZA</I> with GREAT HORNED OWL LURE: AN ]. RaptorRes. 26(3):167-178 ¸ 1992 The Raptor ResearchFoundation, Inc. THE DHO-GAZA WITH GREAT HORNED OWL LURE: AN ANALYSIS OF ITS EFFECTIVENESS IN CAPTURING RAPTORS PETERH. BLOOM,JUDITH L. HENCKELAND EDMUND H. HENCKEL WesternFoundation of VertebrateZoology, d39 CalleSan Pablo, Camarillo, CA 93010 JOSEFK. SCHMUTZ Departmentof Biology, University of Saskatchewan,Saskatoon, SK, CanadaS7N OWO BRIAN WOODBRIDGE GoosenestRanger District, U.S. Forest Service, 37805 Hwy 97, Macdoel,CA 96058 JAMESR. BRYAN P.O. Box 861, Silverado, CA 92676 RICHARD L. ANDERSON CaliforniaEnergy Commission, 1516 Ninth Street,Sacramento, CA 95825 PHILLIP J. DETRICH U.S.Fish and WildlifeService, 2800 CottageWay, Sacramento, CA 95825 THOMASL. MAECHTLEAND JAMESO. MCKINLEY GreenfalkConsultants, 8210 Gantz,Boise, ID 83709 MICHAEL D. MCCRARY ZoologyDepartment, California State University, Long Beach, CA 908d0 KIMBERLY TITUS AlaskaDepartment of Fish and Game, Division of WildlifeConservation, P.O. Box 240020, Douglas,AK 99824 PHILIP F. SCHEMPF U.S.Fish and WildlifeService, P.O. Box 021287,Juneau, AK 99802 ABSTR•CT.--Trapeffectiveness and potential factors affecting success of thedho-gaza with GreatHorned Owl (Bubovirginianus) when used as a lurewere examined for 11 speciesof diurnalraptors and 3 species of owls:Black-shouldered Kite (Elanuscaeruleus), Northern Harrier (Circuscyaneus), Cooper's Hawk (Accipitercooperil), Northern Goshawk (A. gentills), Red-tailed Hawk (Buteojamaicensis), Red-shouldered Hawk (B. lineatus),Swainson's Hawk (B. swainsoni),Ferruginous Hawk (B. regalis),Prairie Falcon (Falcomexicanus), Merlin (F. columbarius),American Kestrel (F. sparverius),Spotted Owl (Strixocciden- talis),Great Gray Owl (S. nebulosa),and Great HornedOwl. The techniquewas successfulfor most specieswhen targeting a territorialpair duringthe reproductivecycle. Important conditions necessary for goodtrapping success were placement of the lureowl in an obviouslocation, shade for lureowl and net, shrubsor treesin whichto hide net polesand channelthe raptors,short distance between observer andnet, site preparation, small number of observers,and low wind.Play-back of audio-tapedrecordings of Great HornedOwls or conspecificsusually reduced the amountof time necessaryto facilitatecapture. Swainson'sHawks and FerruginousHawks showedno increasedaggression toward the lure owl that mightbe relatedto ageof young,brood size, presence of foodin the nest,or time of day. 167 168 BLOOM ET AL. VOL. 26, NO. 3 La Dho-gazacon Bfiho CornadoAmericano como sefiuelo: un anfilisisde su efectividaden la capturade aves rapaces EXTR^CTO.--La efectividadde la trampa y los factorespotenciales que afectanel 6xito de la Dho-gaza, cuandorapaces de la especieBubo virginianaus fueron usadascomo sefiuelo, han sidoexaminados para 11 especiesde raptoresdiurnas y 3 especiesde b6hos:Elanus caeruleus, Circus cyaneus, Accipiter cooperii, A. gentilis, Buteojamaicensis, B. lineatus,B. swainsoni,B. regalis,Falco mexicanus,F. colurnba•us,F. sparverius,Strix occidentalis, S. nebulosa, y Bubo virginianus. La tficnicadio buen resultado para la mayorla de las especiescuando tuvo comoblanco una pareja de avesrapaces en su territorio yen su ciclo reproductivo.Importantes condiciones necesarias para una exitosatrampa fueron: la colocaci6ndel bfiho- sefiueloen una ubicaci6nobvia, sombrapara el bfiho-sefiueloy la red, arbustoso/•rboles para ocultar los palosde la red y encaminarlas raptorashacia la trampa, cortasdistancias entre observadory red, preparaci6ndel sitio,pocos observadores, y viento leve. Reproducciones de grabacionesdel ulular de los bfihos(B. virginianus)o de su especieusualmente redujeron el tiempo necesariopara facilitar la captura. Las raptorasB. swainsoniy losB. regalisno demostraronun aumentode agresi6nhacia el bfiho-sefiuelo que pudieraser relacionadacon la edadde losj6venes, el tamafiode la nidada,la presenciade alimentos en el nido, o lo hora del dia. [Traducci6n de Eudoxio Paredes-Ruiz] A variety of traps have been applied to capture the poleswith clothes-pinsand smoothtape tabs (Bloom raptors (Bloom 1987). Few traps equal the success 1987) or a small piece of limp wire (Hamerstrom 1963) of a dho-gazawith a live Great Horned Owl (Bubo sothat the net detachedas the bird struckit. The degree of "hair triggering"necessary is dictatedby wind condi- vzrginianus)lure. The technique,first developedby tionsand size of the raptor. Placingmore tape insidethe Arab and Persian falconers (Meredith 1943), was clothes-pingenerally requires more mass,or a stronger first used extensivelyin North America by Fran wind to pull the net down. JKS used whole mist nets, Hamerstrom (1963, Bub 1991). The Hamerstroms handtied nets,or netsmade from gill nettingwith a border added. The smaller handmade nets (ca. 1.5 x 3 m) were usedthe trap with great effectivenessin their study attachedto wooden poleswith clips;the larger mist nets of Northern Harrier (Circus cyaneus)ecology in remainedattached to polesthat collapsedfully or partially Wisconsin.A minimum of 18 species,including both on capture. For Merlins (F. columbarius),KT and PFS nocturnaland diurnal raptors,have been caught us- used a single five-tiered mist net 2.1 m x 9.1 m (6.1 cm mesh)attached to three poleswith rubber shockabsorbers ing this technique(Bloom 1987). While designand to form a "V" shapednet. This modifiedmist net did not generaluse of the dho-gazawith Great Horned Owl break away or slide (Clark 1981) like a dho-gazaso as to have been well described(Meredith 1943, Hamer- avoid repeatednet damageand repairs from tanglement strom 1963, Bloom 1987) its successrate and ap- in low brushyvegetation. TLM andJOM madea V-shape using two handtied nets 1.2 m by 1.8 m (10.2 cm mesh) plication have not. In this paper we describethe for Prairie Falcons. overallsuccess and applicabilityof the dho-gazawhen The lure owl was centeredjust out of reach of the net, usedon 14 speciesof raptors. tethered with a swivel and leash to the ground, a 0.3 m tall log or a portable ring perch 0.5 m abovethe ground. STUDY AREAS AND METHODS Observerswere in a blind < 15 m away, concealedunder Trapping tookplace in four of the westernUnited States camouflage5-100 m away or in a vehicle 0.1->1 km. and one Canadianprovince. Most studieswere unrelated, Many territories were trapped at repeatedly; hence conductedover multiple years (1981-92), and conducted trapping the sameterritory for 3 yr equaledthree terri- by the co-authors working independently or in various tories. However, multiple trapping attemptsat the same combinations.As a result, somedifferences in trap design territory in the sameyear were consideredas one territory and applicationexist. In generalthey follow a blend of When possible,we evaluatedthe successof our trapping designsand proceduresoutlined in Hamerstrom (1963) effortsusing two techniques.We defined"territory trap- and Bloom (1987). With the exceptionof Prairie Falcons ping success"for a speciesas the total number of individ- (Falcomexicanus) in Idaho trappedduring incubation,most uals captureddivided by the total numberof possibilities, trapping boutswere conductedafter hatching,but before where possibilitiesequaled both individualsof a pair at a dispersalof young. territory. "Raptor trapping success"was the number of PHB, EHH, JLH, BW, PJD, JRB, RLA and MDM individualscaptured, divided by the number of birds that used a standard 2.1 m x 5.5 m mist net (210 denier, 2 made contactwith the net. Raptor trapping successdoes ply, 10.2 cm mesh;Avinet Inc., Dryden, NY), occasionally not reflect instanceswhen a raptor made a passover or two netsin V-shape. Mist netshave the advantageof being arounda net, was vocalbut made no pass,or was present, large placingpoles far apart and can be purchasedready- but engagedin other activitiessuch as copulation,incu- made (Bloom 1987). The mist net was lightly attachedto bation, or territorial defensefrom other avian competitors. SEPTEMBER 1992 OHO-GAZA WITH GREAT HORNED OWL LURE 169 The sexof raptorswas determinedby wing length,body was capturedfirst within 30 rain of trap placement. mass,brood patch evaluation, behavior, relative size com- Males were caught within 1 hr of the time the net pared to their mates,and the literature (Clark and Whee- was reset. ler 1987). Trapping of Black-shoulderedKites (Elanuscaeruleus; Cooper'sHawk. Gooper'sHawks are aggressive EHH, JLH, PHB, MDM, RLA), Cooper'sHawks (Ac- accipitersthat nest in oak woodlandsin southern cipitercooperi; PHB, EHH, JLH), Northern Goshawks Galifornia. Their smaller size contributes to their (A. gentilis;PHB, BW, PJD, RLA, EHH, JLH), North- speedand agility giving them the ability to dodge ern Harriers (PHB, EHH, JLH), Red-tailedHawks (Bu- teojamaicensis;EHH, JLH, PHB), Red-shoulderedHawks some nets or escapewhen a net gets entangledin (B. lineatus;PHB, EHH, JLH, MDM), American Kes- understoryvegetation. The oddsof captureare bal- trels (F. sparverius;JRB), Great Horned Owls (PHB, ancedby their persistentaggressiveness. EHH, JLH EHH, JLH), SpottedOwls (Strixoccidentalis; PHB, PJD) and PHB trapped at 31 territories yielding a ter- and Great Gray Owls (S. nebulosa;PHB) occurred in ritory trapping successof 52% (32) and a raptor California. Swainson'sHawks (B. swainsoni)were trapped in California (PHB, BW, PJD, RLA, EHH, JLH) and trapping successof 76%. Twenty-two females and Alberta (JKS). Ferruginous Hawks (B. regalis) were 10 maleswere capturedincluding 5 pairs; of which trapped in Alberta (JKS). Prairie Falconswere trapped the female was caughtfirst in 4 of the pairs. There
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