THE JOURNAL OF RAPTOR RESEARCH A QUARTERLY PUBLICATION OF THE RAPTOR RESEARCH FOUNDATION, INC. VOL. 25 FALL 1991 NO. 3 J. Raptor Res. 25(3):49-62 ¸ 1991 The Raptor ResearchFoundation, Inc. HUNTING RANGE AND STRATEGIES IN A TUNDRA BREEDING PEREGRINE AND GYRFALCON OBSERVED FROM A HELICOPTER CLAYTON M. WHITE Departmentof Zoology,Brigham YoungUniversity, Provo, UT 84602 R. WAYNE NELSON 4218-65rd Street, Camrose,AB, Canada T4V 2W2 ABSTRACT.--Between6-15 June 1974 an adult male PeregrineFalcon (Falcoperegrinus) from a breeding site on Alaska's North Slope was followed by helicopter and mapped during 21 hunting sorties.His huntingrange was about319 km2 and the greateststraight line distancefrom the eyrie where he stooped at prey was 14.6 km. All parts of the hunting range were not usedequally. An area with sedge-grass marshesand many small lakes was hunted most frequently with 51% of the prey capture attempts occurringthere. A secondarea of similar but drier habitat was usedsecondly with 36% of prey capture attemptsoccurring there. Three different hunting methodswere used:1) low, "ground-effect"flight, 2) high direct/maneuveringflight, and 3) soaring. One flight of long duration and one of short duration from start to finish are described.Seventeen hunts timed from leaving to returning to the eyrie averaged 57 min. The shortesthunting sortie followed by helicopterwas 22 min; when not followed, the shortest sortiewas 23 min. From 2-24 stoopswere required during a hunting foray beforea kill was made. Between27 June and 4 July 1978 near the DempsterHighway, Yukon Territory, Canada, a nesting femaleGyrfalcon (F. rusticotus)was followedby helicopter(on 9 flights)for a total of 4 hr 1 min and a male (on 5 flights) for 3 hr 10 min. The female hunted and patrolledwithin 3.2 km of the eyrie. The male went up to 24 km from the eyrie while hunting. On 1 sortiehe "patrolled" a three-quartercircle, travelinghigh approximatelymid-way betweenhis eyrie and thoseof four neighboringpairs. Hunting methodsare describedand includedsoaring, ridge-sailing, and "forest slalom." We also discussedcautions and advantagesof using the helicopterto study home ranges,habitat use and behavior far from the nest. Areay estrategiasde caza de un Halc6nPeregrino y Gerifaltesde la tundraobservadas desde un helic6ptero EXT•½TO.--Entre el 6 y el 15 de junio de 1974, seguimosen helic6pteroa un ejemplarmacho adulto de Halc6n Peregrino(Falco peregrinus) desde su nido en la vertientenorte de Alaska, y describimossu recorridodurante 21 excursionesde caza. Su firea de acci6ncubri6 319 kms2. La mayor distanciaentre su nido y el puntoen que selanz6 en picadapara atrapar a la presaalcanz6 14.6 kms.E1 halc6nno us6 indistintamentetodas las seccionesdel firea,sino que mostr6preferencia por un fireapantanosa y lacustre. Un 51% de suslances ocurrieron en el fireamencionada. La segundapreferencia result6 ser un firea con un hfibitatsimilar, aunquemils seco,escenario de un 36% de los lances.E1 halc6nutiliz6 tres mgtodos diferentesde caza:1) vuelorasante; 2) vuelo,maniobras y suspensi6nen altura; y 3) planeode altura. Se describendos ruelos completos, uno de larga y uno de corta duraci6n.E1 tiempode duraci6nde 17 excursiones,desde la salidahasta la 11egada,promedi6 los 57 minutos.Las salidasque seguimoscon el helic6pteroduraron un mlnimo de 22 minutos;las salidasque hizo solo, duraron un minimo de 23 minutos.Durante las excursiones,el halc6nse lanz6 en picadaentre 2 y 24 veceshasta matar una presa. Entre el 27 dejunio y el 4 dejulio de 1978, en las proximidadesde la carreteraDempster (Territorio de Yuk6n) seguimosen helic6pteroa una hembra de Gerifalte (F. rusticolus)que estabaincubando. La seguimosen 9 ruelos por un total de 4 horas 1 minuto, y a un macholo seguimosen 5 ruelos por 49 50 CLAYTON M. WHITE AND R. WAYNE NELSON VOL. 25, No. 3 3 horas10 minutos.La hembracaz6 y patrul16en un radio de 3.2 kms.desde el nido. E1 machose alej6, en suscacerlas, hasta 24 kms.del nido.En una excursi6nrealiz6 un "patrullajede altura" recorriendo trescuartas partes de un clrculoentre su propionido y losde 4 vecinos.Se induyeny sedescriben tres m•todosde caza:planeo de altura,aprovechamiento decorriente de aire ascendente, y vuelo ziõzaõueante entre los rirboles('slalom'). Tambi•n secomentan las ventajas y desventajasde usarun helic6pteropara estudiarlos territorios, el usode hribitaty el comportamientode los halconescuando estrin lejos del nido. [Traducci6nde Hugo N. Olaiz] There are few publisheddata on huntingranges Gyrfalconstudy (by R.W.N.) soughtinformation on of the PeregrineFalcon (Falco peregrinus), other than huntingmethods and rangesrelative to neighboring someinformative radio tracking studies such as those eyries,while gatheringpopulation, reproductive, and of Endersonand Kirven (1983), and Mearns (1985). behavioraldata for a subsequentlarger study by N. For the Gyrfalcon (Falco rusticolus)there are no Barichello.White was at first skepticalthat a heli- comparablepublished data. Much of the information coptercould be usedto follow huntingperegrine but on hunting techniquesused by wild falconscomes the techniquesthat evolvedproved to be perhapsthe from observationson the outcomeof specificstoops mostsuitable available for this type of studyat the fortuitouslyobserved from the ground(e.g., Rude- time. White's successwith peregrinesstimulated beck 1951, Campbell 1975, and Dekker 1987) or Nelsonto attemptsimilar observationson Gyrfal- from observationof nestingfalcons that huntedwith- conswhen that opportunityarose. in sight of nestingcliffs (e.g., Monneret 1973, Bird STUDY AREA AND METHODS and Aubry 1982). Becauseour studysites were se- In thispaper a hunt, forayor sortieis definedas a flight lectedon the basisof eyrie locationrelative to in- in which prey captureappeared to be the main objective. tensityof human activities(peregrine) and relative A huntingforay may includeany numberof stoopsor to neighboringeyries (Gyrfalcons)and becauseit capture attemptsof prey. A stoopis any dive during a was necessaryto know the travelsand spaceuse by huntingforay that appearsto be directedtoward a prey thesewide-ranging falcons, the logisticsand prob- item. A chaseis the following,in directflapping flight, of a prey item with apparent intent to capture. lems of using radiotelemetryor ground-basedob- Peregrine Falcons. Peregrineobservations were made servationsprecluded those methods. This paper re- on the SagavanirktokRiver on Alaska'sNorth Slopefrom portson the first successfulattempts to studyhunting 6-15 June 1974, variouslybetween 0600-2300 H, at one behaviorand use of homerange of two raptorsby eyrie ca. 3.2 km from an Alaskan pipeline construction followingthem in a helicopterat closequarters from campof about200 persons.A Bell 206B Jet Rangerhel- icopterwas usedto followthe falcon.Originally the hel- the birds' leavingtheir eyrie'sto their return. icopterwas parked below the eyrieand some180 m distartt. We recognizethat the singlepair of both species The male falcon,doing all the huntingfor the femaleand watchedmay not berepresentative of their respective recentlyhatched young, was watched with binocularsfrom speciesin tundra habitat. We have tried not to draw the waiting helicopteruntil he left the cliff to hunt. The helicopterwas then started.Because of a warm-up time too many generalconclusions from our observations. for the aircraft, the falconusually was out of sight and Becauseemotion regarding raptors frequently runs unlocatableby the time we were airborne.We then tried high, a good deal of prudenceand commonsense waitingon top of the cliff and some180 m away hoping to be ableto keeptrack of him as he flew away.This was must be used when studyingthem (cf. Fyfe and also unsuccessful. Olendorff1976). Althoughhelicopters are routinely Upon arrival at the cliff on 7 June after a refueling usedto locateraptor eyries,use of helicoptersnear stop,we interceptedthe falconas he left to hunt. It became eyriesis still controversial,especially around rarer evidentthat onceboth helicopterand falconwere in the species.Our studiesprovide further information on air it was relativelyeasy to follow him at a distanceof the responsesof 2 raptor speciesto "non-threaten- 150 m as long as he was silhouettedabove the horizon. At that distance, however, he was lost to view as he made ing" helicoptersnearby. his secondstoop. In general,once he was lostto visionand The peregrinestudy (by C.M.W.) was accom- if his directionof flight was unknown,he was impossible plished during the constructionof the Alaska oil to relocateexcept by chance.Because of this problemwe pipeline on Alaska'sNorth Slope.The study was adjusted our distance from the airborne falcon until it became dear that he could be followed from as dose as designedby the U.S. Fish and Wildlife Serviceand 45 m. oil companypersonnel to determine effectsof oil While waitingbelow the eyriewe timedthe male'srest developmenton huntingranges of the peregrine.The intervalsbetween hunting sorties,which were about 1.5 FALL 1991 FOLLOWING FALCONS WITH HELICOPTERS 51 hr. By waiting for this time periodand then flying slowly went unrecorded.Flying the helicopterupward 200-300 past the roostingmale, we found we could flush him into m from the falcon,and then slowly approachingit hori- the air, veer away to let him start a hunting trip, and then zontally, causedneither attack nor avoidance. closethe distanceand follow him through the entire hunt. Usually we followed 30-50 m behind with the falcon It requirespractice and skill on the part of the helicopter at the 1000-1030