J Raptor Res. 28(2):115-117 ¸ 1994 The Raptor ResearchFoundation, Inc.

TRAPS FOR CAPTURING TERRITORIAL OWLS

S. M. REDPATH AND I. WYLLIE Instituteof TerrestrialEcology, Monks WoodExperimental Station, AbbotsRipton, Huntingdon,Cambridgeshire, PEI7 2LS. U.K.

KEY WORDS: lures;Strix aluco;tawny owl; territorial be- Small Modified ChardoneretTraps. Thesetraps op- havior;trapping. erated as for the abovetrap, but this time the lower com- partment was smaller (10 cm high) and containedprey species(house sparrows [Passer domesticus] or laboratory A variety of techniqueshave been usedto capture rap- mice) as lures. The traps were similar in design to the tors (e.g., Berger and Hamerstrom 1962, Meng 1971, falling-lid trap describedby Kenward et al. (1983), based Fuller and Christenson 1976, Kenward et al. 1983, Bull on an originaldesign by Hamilton (Lundberg1933). The 1987). Raptorsare generallyeasier to captureduring the lower compartmenthad a meshsize of 1 cm and contained breedingseason when they can be caught in nest boxes food, water, and shelter for the lure species.Again, the (e.g.,owls) or by placingtraps at or near the nest.Outside traps were set with a perchjust aboveand in front of the open lid. One or two of thesetraps were placed in each the breeding seasonbirds are more difficult to catch as territory just before dusk and checkedat dawn. their positionat any one time is harder to predict. Excep- uons to this are some North American owls which can be RESULTS AND DISCUSSION caughtwith comparativeease (Forsman 1985, Bull 1987). None of the six capture attemptsusing nets was suc- Many owls defend territories,and can be caught by cessful.Owls were twice seento be attracted to the taped exploitingtheir behaviortoward intruders.For example, calls, but flew over or around the net. Due to the length the tawny owl (Strix aluco)vigorously defends territories of time requiredto setup and watchthese nets, this method throughoutthe year (Southern 1970), and can be caught was droppedin favor of the traps. When the successrate usingtape lures to attractbirds to mist nets(Hirons 1976). of the two typesof trap was compared,we found that the Outside the breedingseason tawny owls have also been trap usingthe live owl (11 owls caughtin 32 trap nights) caughtwhile roostingin nestboxes (Baudvin and Dessolin was significantlymore successful(X 2 = 50.3, P < 0.001) 1992) or with the useof live prey as lures (Hardy 1992). than the trap usinglive prey lures (5 owls caughtin 253 trap nights). No more than one owl was ever caught per night per territory. All the owls were fitted with radio- METHODS transmitters and all were found to be territorial birds. During the winters of 1990-91 and 1991-92, three SomeNorth American owls suchas spottedowl (Strix techniqueswere testedin an attempt to capture tawny occidentalis)and great grey owl (Strix nebulosa)appear owlsin woodsin Cambridgeshire,southeast England. Two relatively unafraid of humans and can be caught with of thesetraps rely on the fact that territorialowls defend apparentease (Forsman 1983, Bull 1987). This is not the their territory againstintruders. The third usesprey to casewith tawny owls which invariably fly when humans attract owls to the traps. approachtheir roost sites. Outside the breeding season, Mist Net and Tape Lure. Nets were set up inside tawny owls have previouslybeen caught either in nest knownowl territorieswith a continuoustape of a hooting boxes (Baudvin and Dessolin 1992), with mist net and male placed underneath. These were watched for ap- tape lures (Hirons 1976), or usinglive prey as lures (Har- proximately2 hr. dy 1992). The useof nestboxes for roostingin the winter Large Modified Chardoneret Trap. This trap had appearsto dependon habitattype (Petty 1992), with birds three compartments;a large lower one containinga male lesslikely to useboxes where natural cover(e.g., coniferous tawny owl, andtwo upperones in whichowls were caught trees)is abundant.In the presentstudy owls rarely used (Fig. 1). The lure owl wasprovided with suitableperches boxesto roost in, preferring the cover of plants such as and coverfrom rain. The lid aboveeach of the top com- old man's beard (Clematisvitalba) or ivy (Hedera helix) partmentshad a pieceof stiffwire runningdown its center, The use of nets and tape lures to catch owls also proved which extendedbeyond its baseand, when the trap was ineffectiveand time consuming.The modifiedChardoneret set, restedin a hole in the woodentrigger. The trigger traps had an advantagein that they could be easily was held againstthe wall of the trap by pressurefrom the set and left overnight. Placing a live owl inside a bird's lid wire. The perchwas fixed to the wall of the trap and territory proved more effectiveat attracting owls to the to the trigger. Pressureon the perch pulled the trigger trap than using prey speciesand this techniquepresents down, which releasedthe wire, allowingthe lid to shut. an effective method of capturing territorial owls, which The trap was held shut by two hooksat the end of the lid comparesfavorably to otherdesigns used to captureraptors which snaggedon the wire of the trap. The whole trap outsidethe breedingseason (see Kenward et al. 1983). was constructedof 5 cm weldmesh.The trap was setwith perchesjust aboveand in front of the open lids. It was RESUMEN.--Rapaces,tales comoStrix alucoson a menudo placedin a territory at dusk, and checkedat dawn. dificiles de capturar en la estaci6nno reproductiva.Es-

115 116 SHORT COMMUNICATIONS VOL. 28, NO. 2

hooks

trigger

perch

0.5m

lure

lm

'/ , lm , shelter

5 cm weldmesh Figure 1. Large modifiedChardoneret using a captiveowl as a lure. Owls flew from an externalperch into oneof the top compartments,landing on the internal perchand releasingthe trigger, therebyallowing the lid to close. JUNE 1994 SHORTCOMMUNICATIONS 117 tudiosprevios describen la captufa de avesmientras des- 291-294 in R.W. Nero, R.J. Clark, R.J. Knapton and cansanen nidos caja, o usandoredes de niebla y graba- R.H. H amre lEDS.I,Biology and conservationof north- clonessefiuelo. En este estudio, las aves fueron raramente ern forestowls. Gen. Tech. Rep. RM-142. U.S. Forest encontradasdescansando en nidos caja, de manera que Service, Rocky Mountain Forest and Range Exper. otras tres tgcnicasfueron comparadas.Primero, redesde Sta., Fort Collins, CO U.S.A. niebla fueron levantadassobre una grabaci6nsefiuelo y observadas durante dos horas. Los bfhos fueron atraldos FORSMAN, E.D. 1983. Methods and materials for lo- par la grabaci6npero volaronsobre o alrededorde la red. cating and studyingspotted owls. U.S. Forest Service No hubo captufa en seisintentos. Segundo, una Trampa Gen. Tech. Rep. PNW-162. Portland, OR U.S.A. Chardoneret modificada fue construida, se us6 un macho FULLER, M.R. AND G.S. CHRISTENSON. 1976. An eval- viva de $. aluco como sefiuelo. E1 bfho cautivo se mantuvo uation of techniquesfor capturing raptors in east-cen- en el compartimentoinferior y las captufasse realizaban tral Minnesota. Raptor Res. 10:9-19. en el superior.E1 propiGpeso del bfho aterrizandosobre HARDY,A.R. 1992. Habitat useby farmlandtawny owls una percha en el compartimento superior accionabael Strixaluco. Pages 55-63 in C.A. Galbraith, I.R. Taylor mecanismode cierra de la trampa. En la terceratgcnica and S. Percival lEDS.I, The ecologyand conservation se utiliz6 una pequefiaversi6n de la Trampa de Char- of European owls. UK Nature ConservationNo. 5, doneretmadificada, aunque esta vez se utilizaron especies presacomo sefiuelo y dispuestasen el fondodel compar- Peterborough,Joint Nature ConservationCommittee. umento.De las dostrampas, la primera (conbfihos vivos) HIRONS,G. 1976. A populationstudy of the tawny owl fue mils efectiva(11 bfhos en 32 noches-trampa)que la (Strix aluco)and its main prey speciesin a woodland. trampa que utilizg especiespresas (cinco bfhos en 253 Ph.D. dissertation, Oxford Univ., Oxford, U.K. noches-trampa).La diferenciafue significativa(X 2 = 50.3, KENWARD, R.E., M. KARLBOM AND V. MARCSTROM. P < 0.001). Esta trampa utiliza la conductaagresiva de 1983. The price of successin goshawktrapping. RalO- bfihosterritoriales hacia intrusosy representaun efectivo tor Res. 17:84-91. mgtodopara capturarbfihos territoriales. LUNDBERG,A. 1933. Handbook for jaktvardare. Fahl- [Traducci6n de Ivan Lazo] cranz & Co., Stockholm, Sweden. MENG, H. 1971. The Swedish goshawk trap. J. Id/ildl Manage. 55:832-835. LITERATURE CITED PETTY,S.J. 1992. Ecologyof the tawny owl Strix aluco BAUDVlN,H.AND'J.L. DESSOLIN. 1992. Analyse dela in the spruce forestsof Northumberland and Argyll morphometric de la chouetteshulottes Strix aluco en Ph.D. dissertation,Open Univ., Milton Keynes,U.K. Bourogne.Alauda 60:93-104. SOUTHERN,H.N. 1970. The natural control of a pop- BERGER,D.D. AND F. HAMERSTROM.1962. Protecting ulation of tawny owls (Strix aluco).J. Zool.Lond. 162' a trappingstation from raptor predation.J. Wildl.Man- 197-285. age. 26:203-206. BULL, E.L. 1987. Capture techniquesfor owls. Pages Received11 November 1993; accepted6 February 1994