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J. Raptor Res. 25(4):127-131 ¸ 1991 The Raptor ResearchFoundation, Inc.

HUNTING TECHNIQUES AND SUCCESS RATES OF URBAN (Falco columbarius)

NAVJOT S. SODHI Departmentof Biology,University of Saskatchewan,Saskatoon, SK, CanadaS7N OWO

IAN G. WARKENTIN Departmentof ZoologicalResearch, National ZoologicalPark, SmithsonianInstitution, WashingtonD.C., 20008-2598

LYNN W. OLIPHANT Departmentof VeterinaryAnatomy, Western College of VeterinaryMedicine, University of Saskatchewan, Saskatoon,SK, S7N OWO

ABSTRACT.--Huntingtechniques and successrates are describedfor urban Merlins (Falcocolumbarius). Attack from a perch was the most commontechnique (58% during breeding,95% during winter) and cruisingflights the secondmost common (37% and 5%, respectively).Hunting successof breedingMerlins was significantlyhigher (28%) than winteringbirds (11%).

Modalidadesde caza y susproporciones de •xito en los halconesde la especieFalco columbarius ExTR•CTo.--Describimoslas modalidadesde caza y suscorrespondientes proporciones de •xito en los halconesde la especieFalco columbarius. E1 ataque desdeuna percha fue la modalidadm/rs frecuente (58%durante la •pocade reproducci6n y 95% durante el invierno).En segundolugar se observ6 la caceria al vuelo(37% y 5% respectivamente).Estos halcones tuvieron m/rs •xito en suscacerlas durante la •poca de reproducci6n(28%) que duranteel invierno(11%). [Traducci6n de Eudoxio Paredes-Ruiz]

The hunting techniquesused by raptors depend METHODS upon the of prey, , weather, and char- BreedingMerlins (F. c. richardsonii)were trapped at acteristicsof the hunting such as age, sex and their nests in $askatoon and fitted with radiotransmitters experience(Balgooyen 1976, Wakeley 1978, Cade BetweenMay and July 1987-90, observationsof hunting behavior were made on 16 males and 11 females that were 1982). Merlins (Falcocolumbarius) feed primarily tracked for a total of 1200 hr. Only one bird was tracked on small (Oliphant and McTaggart 1977, at a time, generally for 4-hr periodsduring the first and Becker 1985, James and Smith 1987, Sodhi et al. last four daylighthours. The methodologyemployed in 1990). Most publishedinformation on hunting tech- radio trackingis presentedby Sodhiet al. (1991). niques of this specieshas been obtained from mi- From 1983-88, Merlins were trappedeach winter. Most of the wintering Merlins at Saskatoonare derived from grating or wintering birds (Rudebeck 1951, Page the local breedingpopulation (Warkentin et al. 1990). and Whitacre 1975, Boyce 1985, Buchananet al. Individuals were fitted with radiotransmitters and detailed 1988, Dekker 1988, Warkentin and Oliphant 1990). informationwas gatheredthroughout the day from six Similar data obtainedduring the breeding season femalesand three males during 542 hr of direct visual are generally basedon few observations(Armitage contact.A detaileddescription of methodologyfor the col- lectionof data in winter is presentedby Warkentin and 1932, Craigheadand Craighead1940, Roberts1962, Oliphant (1990). Kermott 1981). Here, we describethe hunting tech- In addition, we presentother observationsof hunting niques and successrates of Merlins from an inten- Merlins, madeon an urban wintering populationof Black sivelystudied urban breedingpopulation in $aska- Merlins (F. c.suckleyi) in Seattle,, from 1968- 70 and on the Saskatoonpopulation (both breedingand toon, Saskatchewan(Oliphant and Haug 1985, wintering) from 1971-90. These observationsare difficult James1988) and make comparisonsto the hunting to quantifyin termsof hoursbut conservativelyrepresent behaviorof Merlins wintering there. about 200 separateattacks on prey. Generally only in-

127 128 SODHIET AL. VOL. 25, NO. 4

Table 1. Hunting techniquesused by breedingMerlins in Saskatoon,Canada. Most data (n -- 73) were collected from 26 radio-taggedadults. Data are presentedas number of hunting attemptsmade. Hunting successrate on on which >-3 attempts were observedis also reported. AP • attack from perch, GF = cruising flights, and OHF = other hunting flights.

SUCCESS- % SrEClES AP CF OHF TOT•, rUL SUCCESSa

House Sparrow (Passerdomesticus) 16 7 -- 23 13 56 American Robin (Turdus rnigratorius) 6 2 -- 8 1 11 Brewer's Blackbird (Euphaguscyanocephalus) 4 -- 1 5 1 20 Horned (Erernophilaalpestris) -- 2 1 3 1 33 Cedar Waxwing (B. cedrorurn) 1 -- 1 2 0 0 Chipping Sparrow (Spizellapasserina) 4 -- -- 4 2 50 ( Tachycinetabicolor) -- 1 -- 1 0 0 Common Grackle (Quiscalusquiscula) 1 -- -- 1 0 0 Eastern Kingbird (Tyrannustyrannus) -- 2 -- 2 0 0 Unidentified 14 16 1 31 3 30 Total 46 30 4 80 21 28

Valuesare basedon huntingattempts of knownoutcome only. stanceswhere kills were observedwere recorded,making in it, about 1 m from the ground. The started it impossibleto generatesuccess rates from these obser- hoppingdown until it chasedthe sparrowsout and vations. Observationswere also recordedof the hunting then it followed them. Out of 45 attacks of known flights of sevenfalconry-trained Merlins. A hunting attemptwas consideredas one or more strikes outcomeinitiated from a perch, 12 (27%) were suc- at potentialprey (Page and Whitacre 1975, Dekker 1988, cessful in summer. In winter, Merlins were suc- Warkentin and Oliphant 1990). Even when the bird dis- cessfulin 30 (11%) of 273 attemptsfrom a perch. appeared from view, radiotracking facilitated, based on Cruisingflights (CF). This was the secondmost radio signal amplitude, in determining whether it had changedthe hunting techniquewhen out of view. commonhunting techniqueused (37% in summer and 5% in winter; Tables 1 and 2). The hunting RESULTS Merlins flew at high speedand at varyingaltitudes, Description of Hunting Techniques. Merlins closeto the groundor just overor belowthe canopy usedthree main huntingtechniques which are listed in woodedareas. Birds alreadyin flight or flushed separatelybelow althoughthey were at times used at the approachof the were attacked.Low in conjunction. fast flights were frequently used while hunting in Attackfrom perch (AP). Merlins often (58% in open country.This behaviorwas efficientin cap- summerand 95% in winter; Tables 1 and 2) initiated turing prey suchas Horned that flushedfrom attacksdirectly from perchessuch as ,utility ground cover. In urban areas, Merlins often used poles,deciduous trees, and even the ground. When streetsas relatively open paths along which they flew hunting from high perches,prey sightedat consid- at highspeed below the archedcanopy of trees.House erabledistances were attackedby strongdirect flights. Sparrowsthat flushedfrom besideor under parked The falcon at times initially glided down to near vehicleswere particularlyvulnerable to attack.Birds groundlevel from the perch,which may allow great- suchas BohemianWaxwings (Bornbycillagarrulus) er accelerationand provideconcealment when ap- and Cedar Waxwings were caught after flushing proachingpotential prey. The final approachtoward aheadof the Merlin, or were takendirectly off their prey was often a fixed-wing glide. perches. Ground percheswere used by Merlins while On one occasion,we observeda flying Merlin hunting in open country. These perchespossibly attacka blackbirdthat had beenflushed by a Swain- made Merlins less detectable and enabled them to son'sHawk (Buteoswainsoni). On anotheroccasion, attackflying birdsfrom below,forcing the prey away a Merlin took a quarry flushedby a dog. We also from cover. On one occasion,we observed a Merlin observedone attack on a nestof an EasternKingbird. landing in a sprucetree that had House Sparrows The Merlin took a nestling from the nest while WINTER 1991 HUNTING BY MERLINS 129

Table 2. Hunting techniquesused by winteringMerlins in Saskatoon,Canada. Data presentedwere collectedfrom radio-taggedbirds. For abbreviationsof hunting techniquessee Table 1.

SPECIES AP CF TOTAL SUCCESSFUL % SUCCESS

House Sparrow 260 11 271 25 9.2 Waxwings 12 2 14 5 35.7 Common Redpoll ( Carduelisfiammea) I 0 1 1 Total 273 13 286 --

passingover, without landing.Of 28 cruisingattacks birds flying at considerabledistance below. Soaring of known outcomeduring the breedingseason, six flightswere observednear the height of spring mi- (21%) were successful.In winter, only one of 13 grationwhen greater numbers of birdspassed through (8%) attemptswere successfulusing this technique. at moderatelyhigh altitudes. Other huntingflights (OHF). Merlins also used Hunting SuccessRates. The successrate of the three other typesof hunting flights (5% in summer AP was slightly, but insignificantlyhigher than CF and 0% in winter; Tables 1 and 2) to capturetheir both in summer (Z = 0.6, P > 0.05) and winter (Z prey. Someof thesebehaviors were not usedby ra- = 0.4, P > 0.05). Merlins were observedto attack dio-tracked birds. nine and three speciesof passerinesduring summer a) Ringing flights. Certain prey species(e.g., and winter, respectively(Tables 1 and 2). The per- Horned Lark and BohemianWaxwing) attempted cent of successfulhunting attemptswas highest on to outfly attackingMerlins resultingin rising aerial HouseSparrows during the breedingseason. During chases.The term "ringing" denotesthe tendencyfor winter, hunting Merlins were more successfulwhen bothprey andpursuer to fly in circlesas they climbed. attackingwaxwings. Overall, 28% (21/75) and 11% Typically, the quarry flew in tighter circlesas was (31/286) of hunting attempts of known outcome describedby Williamson and Williamson (1953). (observedfrom startto finish)were successfulduring Merlins climbed in larger circles,often at such a summerand winter respectively,a significantdif- distancethat it was not always evidentthat it was ference (Z = 5.6, P < 0.05). actuallyin pursuit. If the Merlin succeededin out- climbingits prey, it then stooped;forcing its quarry DISCUSSION to do likewiseto avoidbeing caught. Prey were typ- Both wintering and breedingMerlins most fre- ically taken after one or more stoopsor were able quently attacked prey from a perch. However, to successfullyfind cover.Both flocksand solitary breedingMerlins more frequently attackedprey birds were attackedby this technique. while in cruising flight than wintering Merlins (X2 b) Straight aerial pursuit. Birds suchas swallows = 66.8, P < 0.01). While wintering Merlins made attemptedto outfly the Merlin by sheerspeed and relativelymore attacksfrom a perch. These differ- maneuverability.These flights consistedof a series encesmay be dependentupon seasonaldifferences of rapid, short stoopsand direct aerial chasesover in prey behavior (e.g., flocking), prey speciesat- a relatively long period of time but did not vary tacked, energeticconstraints and habitat used by much in altitude. Merlins. Native sparrows(e.g., the Clay-coloredSparrow, In contrast to our results, it has been documented Spizellapallida) andjuncos that flushedfrom sparse previouslythat while hunting shorebirds,wintering coverwere often capableof dodgingseveral attacks Merlins useaerial attacksmore frequently than oth- by a pursuingMerlin. These attackstook the form er hunting techniques(Page and Whitacre 1975, of a seriesof twisting swoopsin rapid succession, Boyce 1985, Buchanan et al. 1988, Dekker 1988). the Merlin rising lessthan 1 m aboveits quarry. It is possiblethat the urban settingmay have made c) Attack from high soar. Similar to the hunting aerial attacks less feasible or that extended aerial techniquedescribed by Walter (1979) for Eleonora's chasesare more conspicuousin rural settingsand Falcon (F. eleonorae),soaring Merlins stoopedat therefore more often recorded. These differences could 130 SODHI ET AL. VOL. 25, NO. 4 alsobe duethe differentprey species (e.g., shorebirds LITERATURE CITED versuspassetines). ARMITAGE,J. 1932. Merlins taking young from nests. The hunting successof Merlins during the breed- Brit. Birds 25:303-304. ing seasonwas significantlyhigher than duringwin- BALGOOYEN,T.G. 1976. Behaviorand ecologyof the ter in Saskatoon. These differences could be due to American (Falcosparverius) in the Sierra Ne- the fact that radio-taggedbreeding Merlins were vada of California. Univ. Calif. Publ. Zool. 103:1-83. only observedwhen activelyhunting. Other studies BECKER,D.M. 1985. Food habits of Richardson's Mer- lin in southeastern Montana. Wilson Bull. 97:226-230. on wintering or migrating Merlins report hunting BJORKMAN,G. 1978. Hunting associationbetween Mer- successrates between 5-22% for Merlins (Rudebeck lin, Falcocolurnbarius, and , Circuscyaneus. 1951, Page and Whiracre 1975, Buchanan et al. Vat Fagelvarld37:259. 1988, Dekker 1988, Dickson 1988). Dekker (1988) BOYCE,D.A. 1985. Merlins and the behavior of win- reporteda hunting successrate of 40% for breeding tering shorebirds.Raptor Res. 19:94-96. Merlins. Thus, the available information indicates BUCHANAN,J.B., C.T. SCHICK,L.A. BRENNANAND S.G. that hunting successof Merlins during the breeding HERMAN. 1988. Merlin on wintering seasonis higher than in winter or migration. Some Dunlins: hunting successand Dunlin escapetactics. of the possiblereasons for this include:a) only ef- Wilson Bull. 100:108-118. ficient foragersbreed, b) prey vulnerabilitymight CADE,T. 1982. The falconsof the World. Cornell Uni- be higherduring the breedingseason due to an influx versity Press,Ithaca, New York. CRAIGHEAD,J. AND F. CRAIGHEAD.1940. Nesting Pi- of fledgedbirds in prey populations,and c) migrant geon . WilsonBull. 52:241-248. and winter populationsof Merlins include higher CUDWORTH,J. ANDC. MASSINGHAM.1986. Hen Har- numbers of juvenile birds, which may be less ex- rier and Merlin hunting together.Brit. Birds 79:340. perienced hunters. DEKKER,D. 1988. PergerineFalcon and Merlin pre- Most hunting techniquesreported here havebeen dation on small shorebirdsand passetinesin . previouslydocumented (Armitage 1932, de Law- Can. J. Zool. 66:925-928. rence 1949, Rudebeck 1951, Williamson and Wil- DICKSON,R.C. 1988. Habitat preferencesand prey of liamson 1953, Roberts 1962, Sperber and Sperber Merlins in winter. Brit. Birds 81:269-273. 1963, Page and Whiracre 1975, Kermott 1981, Bu- HAUG, E. 1985. Merlin feeding on road-kills. Raptor Res. 19:103. chanan et al. 1988, Dekker 1988). However, Mer- JAMES,P.C. 1988. Urban Merlins in Canada.Brit. Birds lins landing in coverand then flushingand attacking 81:274-277. prey, and attacking from high soar have not been • AND A.R. SMITH. 1987. Food habits of urban- reported earlier. Although Merlins have been ob- nestingMerlins, Falcocolurnbarius, in Edmontonand servedattempting to captureprey flushedby other Fort Saskatchewan, Alberta. Can. Field-Nat. 101:592- objects(both living and nonliving;Jenkins 1972, 594. Bjorkman 1978, Cudworth and Massingham1986, JENKINS,M.A. 1972. Opportunistichunting tactics of Dekker 1988), we documentthe first suchhunting the Merlin. Bird-Banding 8:40-41. with prey flushedby a Swainson'sHawk and a dog. KERMOTT,L.H. 1981. Merlins asnest predators. Raptor Somehunting behaviorspreviously reported in lit- Res. 15:94-95. erature,were not observedby us (e.g., Haug 1985). BE LAWRENCE,L.K. 1949. Notes on nesting Pigeon Hawks on Pimisi Bay, Ontario. WilsonBull. 61:15- ACKNOWLEDGMENTS 25. We thank Paul C. James, Steve K. Sherrod, Marc J. OLIPHANT,L.W. AND E. HAUG. 1985. Productivity, Bechard,Daniel N. Gossett,Joseph B. Buchanan,and R. populationdensity and rate of increaseof an expanding Wayne Nelson for making commentson an earlier draft Merlin population.Raptor Res. 19:56-59. of this manuscript. We also thank Geoff Peat, Joanna -- AND S. MCTAGGART. 1977. Prey utilized by Freeland and Charanjit Sodhifor field assistance.Funding urban Merlins. Can. Field-Nat. 91:190-192. was provided by the Natural Sciencesand Engineering PAGE,G.W. AND D.F. WHITACRE. 1975. Raptor pre- Research Council of Canada (NSERC), the University dation on wintering shorebirds.Condor 77:73-83. ResearchSupport Fund of the Canadian Wildlife Service, ROBERTS,E.L. 1962. Merlins taking newly hatchedpas- the Frank M. Chapman Fund of the American Museum serines. Scot. Birds 2:245. of Natural History, the CanadianPlains Research Centre, andthe Universityof Saskatchewan.I.G.W. helda NSERC RUDEBECK,G. 1951. The choiceof prey and modesof postdoctoralfellowship while this manuscriptwas pre- hunting of predatorybirds with specialreference to pared. their selective effect. Oikos 3:200-231. WINTER 1991 HUNTING BY MERLINS 131

SODHI, N.S., A. DIDIUK AND L.W. OLIPHANT. 1990. WALTER,H. 1979. Eleonora'sFalcon. University of Differencesin bird abundancein relation to proximity ChicagoPress, Chicago, IL. of Merlin nests. Can. ]. Zool. 68:852-854. WARKENTIN,I.G. ANDL.W. OLIPHANT. 1990. Habitat --, I.G. WARKENTIN,P.C. JAMESAND L.W. OLI- use and foragingbehavior of urban Merlins (Falco PHANT. 1991. Effects of radiotaggingon breeding columbarius)in winter. J. Zool.,Lond. 221:539-563. Merlins. J. Wildl. Manage. 55:in press. , P.C. JAMESAND L.W. OLIPHANT.1990. Body SPERBER,I. AND C. SPERBER.1963. Noteson the food morphometrics,age structure, and partial migration of consumptionof Merlins.Zool. Bidrag. Uppsala 35:263- urban Merlins. Auk 107:25-34. 268. WILLIAMSON,K. AND E. WILLIAMSON. 1953. Hoopoe WAKELEY,J.S. 1978. Hunting methodsand factors af- pursuedby a Merlin. Scot.Nat. 65:56-57. fectingtheir use by FerruginousHawk. Condor80: 327-333. Received8 June 1991;accepted 9 September1991