— , J Raptor Res. 33(2):123-127 © 1999 The Raptor Research Foundation, Inc. COOPERATIVE HUNTING OF JACKDAWS BY THE LANNER FALCON (FALCO BIARMICUS) Giovanni Leonardi^ Avian Science and Conservation Centre, Macdonald Campus ofMcGill University, 21,111 Lakeshore Road, Ste. Anne de Bellevue, Quebec, H9X 3V9 Canada — Abstract. Cooperative hunting has been recorded for several subspecies of Tanner Falcon (Falco biar- micus). On average, the success rate for pairs is higher than for single birds. During 1988-90, 1 collected data on the success of five Tanner Falcon pairs that cooperatively huntedJackdaws {Corvus monedula) in western Sicily. Fifty-three percent of attacks were aimed at larger groups ofJackdaws. Males made most of the initial attacks (74%) but prey captures were mainly made by females (87%). Pairs tended not to share prey and used visual contact to coordinate chases. Most attacks were by partial surprise (60.8%), followed by nonsurprise (21.6%), and surprise attacks (17.6%). Surprise attacks tended to involve small flocks ofJackdaws, whereas partial surprise tended to involve large flocks. Key Words: LannerFalcon] Falco biarmicus; cooperative hunting, Sicily;Jackdaw; prey group size. Caza cooperativa de Corvus monedula por Falco biarmicus Resumen. Ta caza cooperativa de Falco biarmicus ha sido registrada para varias subespecies a lo largo de su distribucion. En promedio la tasa de exito por pareja es mas alta que la individual. Durante 1988- 90 recolecte datos sobre el exito de la caza cooperativa de Corvus monedula de cinco parejas en el oeste de Sicilia. Cincuenta y tres porciento de los ataques fueron dirigidos a grandes grupos de Corvus monedula. Tos machos efectuaron los ataques iniciales (74%) pero la captura de presas fue efectuada por las hembras (87%). Tas parejas tendian a no compartir la presa y utilizaron contactos visuales para coordinar las persecusiones (60.8%), seguidas de ataques sin sorpresa (21.6%), y ataques sorpresivos (17.6%). Tos ataques por sorpresa involucraron pequenas parvadas de Corvus monedula, mientras que los parcialmente sorpresivos involucraron parvadas mas grandes. [Traduccion de Cesar Marquez] Cooperative hunting is a social foraging behav- Hector 1986). Southern Mediterranean Peregrine ior where predators coordinate their movements to Falcons {F. peregrinus hrookei) hunt cooperatively in increase efficiency of capture (Ellis et al. 1993), areas where prey density is low (Thiollay 1988). Prey may be shared among members according to Cooperative hunting in Lanner Falcons has been social organization, prey size and individual func- recorded for several subspecies throughout the tional role (Bednarz 1988, Ellis et al. 1993). Pair species’ geographic range (Cramp and Simmons hunting is cooperative when participants perform 1980, Tarboton and Allan 1984, Leonard! et al. separate roles. In certain species and under certain 1992) Lanner Falcon pairs pursue swift flying prey . circumstances, cooperative hunting is more suc- (e.g., swifts [AjbM.s spp,]) along parallel paths (Mir- cessful than solitary foraging (Hector 1986, Thiol- abelli 1982, Bijlsma 1990) They hunt flocks ofgre- . lay 1988, Yosef 1991, Ellis et al. 1993). garious small birds (e.g., swallows spp.]) Cooperative hunting in the genus Falco seems to working together with repeated stoops upon the be restricted to bird-eating species, such as Lanner same individual (Mirabelli 1982). In contrast, for Falcons {Falco biarmicus), Aplomado Falcons {F. fe- larger perched prey (e.g., shorebirds and pigeons moralis), and Red-headed Falcons {F. chicquera), [Columbasp.]) one falcon flushes the quarrywhile which inhabit semi-open savannas and desert and it is taken by the mate (Mebs 1959, Massa et al. Mediterranean scrub (Mebs 1959, Osborne 1981, 1991, Yosef 1988). Partners have distinct roles. Males usually attack and direct prey toward females ^ Present address: Via Santagelo Fulci, 28, 1-95127 Ca- (Yosef 1991) and females tend to pursue large prey tania, Italy. (Brossett 1961, Tree 1963, Kemp 1993). Success 123 124 Leonardi VoL. 33, No. 2 rates when hunting in pairs (20-25%) are higher tempted to flush prey (Mebs 1959, Massa et al. 1991, Kemp 1993,Jenkins 1995). than that of single birds hunting alone (15-40%) Kemp I observed Tanner Falcons cooperatively hunting both (Bijlsma 1990, Yosef 1991, 1993). Rock Pigeons {Columba livia) and Jackdaw flocks near This paper describes my observations of coop- their nests. Both prey species nest on cliffs 100-300 m erative hunting in Tanner Falcons nesting in west- from Tanner Falcon nests (Sodhi et al. 1990, Suhonen et ern Sicily. In this region, pairs frequently attack co- al. 1994). For evaluating the importance of cooperative hunting, I only investigated hunts ofJackdaws. Prelimi- lonial nesting Jackdaws {Corvus monedula). This nary observations indicated that single female Tanner provided an opportunity to compare success rates Falcons initiated nearly all pursuits ofpigeons. Also, <5% among attacks on different sized flocks, as it relat- of the total attempts on pigeons (N = 32) were per- ed to sex of pursuers and attack strategies utilized. formed by males. Cooperative hunting, and necessarily, participation by males, was more common in hunts of StudyArea Jackdaws. In addition, Jackdaws consistently comprised a I studied Tanner Falcons on the island of Sicily in the large percentage of dietary biomass for lanners in Sicily central Mediterranean. I observed five pairs during the (Massa et al. 1991, Leonardi et al. 1992, Leonardi 1994) Finally, Jackdaws responded to attacking falcons with in- breeding season: two breeding pairs near the northern periphery of the Sicilian distribution and three pairs in tricate forms of mobbing behavior. This provided an op- portunity to investigate interactions between cooperative a southern area where the species was studied previously hunting and antipredator defense behavior (Kenward by Mascara (1986). The climate of the northern study area is temperate- 1978, Caraco et al. 1980, Turner and Pitcher 1986, Cres- mm swell 1994). wet with 600-800 of rainfall and an average annual temperature of 12-14°C. The southern study area has a The number ofJackdaws present was estimated daily mm by counting the maximum number of birds seen simul- subarid climate (<600 of rainfall and temperature >16°C) (Instituto Geografico De Agostini 1987). taneously. Jackdaw colonies typically contained 20-70 in- Land use in the study areas was predominatelyfarming dividuals. During an attack, I estimated the size of each and pasture. Cereal farming and pasturelands covered by flock attacmked by assuming the members to be all birds within 25 of each other (Cresswell 1994, 1996). At olive (Olea europaea) and prickly pear {Opuntia ficus- mdica) cultivation dominated northern open spaces. The times entire colonies behaved as a single flock. Under southern study area was largely in a wheat monoculture these circumstances, I counted the number ofindividuals with interposing spots ofxeric Mediterranean vegetation in the group first attacked (Kenward 1978). For statistical and small Eucalyptusplantations. Within both studyareas, comparisons, I placedJackdaw flocks into three size cat- lanners nested on clay-sand and calcareous cliffs with egories according to previous studies of predation on m prey groups (Kenward 1978, Cresswell 1994, 1996): 2-10, heights of 50-1150 (Massa et al. 1991). 11-30 and 31-50 individuals. I assessed the validity ofthe Methods above flock size classes for this study through preliminary observations of flocking reactions measured for single I visited breeding sites 21 times during two prerepro- and paired Tanner Falcons (Leonardi 1991, Leonardiun- ductive periods (November-January 1988-90). Each publ. data). breeding site was visited 10 times for 55 total H. 1 I compared F-frequencies of hunting strategies and wmatwcihtehd8TXann40eranFadlc1o0nsXh4u0ntbiinngociunlaprasi.rsAgferoamnd20s0e-x60o0f success rates among different flock sizes and strategies using chi-squared tests and Gtests (Zar 1984). I used observed falcons was recorded for each sighting accord- Cochran’s corrected chi-square test for differences be- ing to criteria in Cramp and Simmons (1980) and Porter tween males and females using a 2 X 2 contingency table et al. (1981). (Zar 1984). Attacks were defined as very rapid flights or stoops to- ward one or more clearly observed prey (an individual Results or group ofspecific prey species) (Cresswell 1994, 1996). First attacks were defined as the first, fast approach by In 52 cooperative hunts, I detected no vocaliza- falcons toward potential prey. During each attack, 1 re- tions which might have functioned to coordinate corded the following data: position and sex of each fal- con at the start of the attack, size of the prey flock, and pursuits. Females alone ate 70% of prey captured N type ofattack strategy. placed attack strategies into three in cooperative hunts (captures = 10). In only 2 1 categories: surprise attacks, partial surprise attacks, and of 16 cases (12%), males fed on prey captured in nonsurprise attacks. In surprise attacks, Tanner Falcons cooperative hunts after the departure of females. first approached close to Jackdaws from behind rock cliffs. In partial surprise attacks, one of the two attacking Although Tanner Falcons preferred to attack larg- = = P < falcons was visible to preywhile the other falcon attacked er flocks (Table 1; 12.33, df 2; 0.001), by surprise. In partial surprise attacks, two perched fal- hunting success was inversely proportional to flock cons would depart at different times (Yosef 1991, Kemp size (G = 10.7, df = 2; P < 0.005). 1993). In nonsurprise attacks, both falcons were visible Female Tanner Falcons initiated attacks less of- at the onset ofattacks, then they tried to encircleJackdaw flocks (Cresswell 1994, 1996). In nonsiirprise attacks, one ten than did males (26% vs. 74%). Although males falcon stooped on prey after soaring while the other at- preferred to pursue larger prey (87% of 52 pur- June 1999 Cooperative Hunting by Lanner Falcons 125 Table 1. Distribution ofLanner Falcon attacks on flocks Table 2. Capture success (%) from first attacks of Lan- ofJackdaw by cooperative hunting in Sicily. ner Falcons cooperatively hunting flocks ofJackdaws in Sicily. Jackdaw Flock Size Class Jackdaw Flock Size Class 2-10 11-30 31-50 2-10 11-30 31-50 Total Attempts 10 14 27 Kills 2 5 9 Males Total 12 19 36 First attack 2 12 24 38 Captures (%) 20 35.7 33.3 Kills 0 1 1 2 Captures (%) 0 0.08 0.04 Females suits) and larger flocks more often than did fe- First attack 8 2 3 13 males (Table 2; G = 13.9; df = 2; P< 0.001), male Kills 2 5 7 14 hunting success rates tended to be lower than Captures (%) 0.25 2.5 2.3 those of females (Table 2; ~ 2.86, df = 2; P < 0 10 . ). ence. In partial surprise attacks, flying Lanner Fal- banners attacked Jackdaws by partial surprise (60.8%) much more frequently than they did by con males from outside the colony area would suddenly stoop on Jackdaws. nonsurprise (21.6%) and surprise attacks (17.6%) {N — 52). Although degree of surprise is one of Prey capture percentage of this study was lower (31%) than that observed for other lanner subspe- the most important factors in improving the suc- cies (50%; Yosef 1991, Kemp 1993) and Aplomado cess of raptor attacks, lanners used this technique in only nine of 52 attempts. Also, open attacks give Falcons (45%; Hector 1986). Sicilian lanners pur- sued small- and medium-sized prey with solitary time for antipredatory behavior by prey. Neverthe- less, partial surprise was used significantly more of- hunting strategies and used cooperative hunting ten (x^ = 17.40, df — 2; P < 0.001). In addition, for large-size prey like Jackdaws. Nevertheless, this lanner pairs captured more prey using nonsurprise low percentage may have been due to Jackdaw an- attCaocokpse(rTaatbilvee 3h;uxn^ti=ng11t.e90c,hndifqu=es2;wPer<e 0n.o0t1)u.ni- ltyipurseeddatomrobbebhianvigor(.4L3a%r,geNJa=ck5d8a)wafglaoicnksstfrleaqnuneernst.- formly distributed among prey flock classes. Hunt- This active defense, combined with the dilution ef- fect ofindividuals in a flock, can improve predator ing success in relation to prey flock size was signif- icant for partial surprise on larger groups (22%; avoidance by prey. The dilution effect is an advan- Table 3; P 0.01) and nonsurprise attacks on me- tage because individuals are less likely to be taken dium flocks (27%; x^ = 14.40, df = 2; P < 0.01). by predators when in a flock (Turner and Pitcher 1986). Morgan and Godin (1985) reported that Discussion the rate of predator attack per individual prey is Evidence of coordinative signaling among hunt- inversely proportional to group size. Although examples of role reversal are known ing predators is indicative that hunts are coopera- tive (Hector 1986, Ellis et al. 1993). Male Aplo- (Mebs 1959, Mirabelli 1982, Massa et al. 1991), the mado Falcons initiate attacks and then vocalize a “chip” call (Keddy-Hector pers. comm.). Although Table 3. Percent hunting successes (kills/attempts; total I detected no vocalizations among hunting lan- of 52 attempts, 16 kills) by Lanner Falcons hunting co- ners, Thomsett (1987) reported that pairs of lan- operatively on flocks ofJackdaws in Sicily. ners hunting bats gave chupping calls. Mebs (1959), however, failed to mention any calls given Jackdaw Flock Size Class by cooperative hunting lanners in Sicily. Partici- Attack Type 2-10 11-30 31-50 pants in hunts, however, can coordinate pursuits without vocal signals. Massa et al. (1991) suggested Partial 0 6 22 that partners monitor their movements by visual surprise contact. Predators should avoid vocalizations dur- Surprise 11 11 0 Nonsurprise 9 27 9 ing surprise attacks, which would reveal their pres- . 126 Leonardi VoL. 33, No. 2 male success rate of <1% was irrelevant in com- co columbarius) hunting success when pursuing small parison to the 50% reported. This was probably flocks of birds (Cresswell 1996). In this study, sur- because of the strong reversed sexual dimorphism prise attacks were less successful than were other (RSD) of this species and its tendency not to share strategies (17.6%) and were employed mostly for prey. In other words, females physically dominated attacks ofpigeons. In South Africa, surprise attacks males during hunts and feedings. RSD may also from fast, low coursing flight were principally account for divergences in hunting and prey aimed at small birds and doves {Streptopelia spp.; choice. Males of F. b. feldeggi weigh 69% that of Kemp 1993). In my study in Sicily, surprise attacks females and capture prey which average 45% the on Jackdaws caused intense confusion inside size of the female’s prey (Leonardi et al. 1992). It flocks. This confusion, and the dilution effect, pro- is likely that RSD favors cooperative hunting, since duced an abatement effect; Tanner Falcons had it allows the hunting of a wide range of prey and difficulty attacking the group repeatedly, decreas- also the use of different hunting strategies. ing capture chances (Leonardi 1991, Turner and Data on flock size choice showed that lanners Pitcher 1986, Krause and Godin 1995). prefer to attack larger groups. In previous studies Acknowledgments of flocking behavior and hunting, hunting success has been shown to be inversely proportional to Special thanks are due to Alan Kemp, C.M. White, and R. Yoseffor their invaluable suggestions and critical read- flock size (Kenward 1978, Turner and Pitcher 1986, ing of the manuscript. Dean P. Keddy-Hector, Steve Sher- Cresswell 1994, Krause and Godin 1995). 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Received 6 August 1997; accepted 30January 1999