2 Cooper's Hawk predation - McNicholl

Cooper’s Hawk predation on Northwestern Crow

Martin K. McNicholl

Unit 105, 8752 Centaurus Circle, Burnaby, B.C. V3J 7E7; e-mail: [email protected]

Abstract: A Northwestern Crow (Corvus caurinus) captured by a Cooper’s Hawk (Accipiter cooperii) appears to be the second documented record of predation by Cooper’s Hawks on this corvid species and the first in British Columbia. Other records of large prey of Cooper’s Hawks are reviewed.

Key words: Accipiter cooperii, Cooper’s Hawk, Corvus caurinus, Northwestern Crow, opportunistic predation, predation on large prey.

Introduction prey from considerable heights (Palmer 1988; Rosenfield and Bielefeldt 1993; Stewart 2003; Wheeler 2003; Campbell and On 28 September 1999, Kevin Young and I were walk- Begg 2006; and others). ing along the water’s edge at Crystal Cove, south of Tofino, The gathering of such a large flock of crows in the rela- B.C. (49° 05´ N 125° 51´ W) at about 15:00 Pacific Daylight tively confined space between the shore of Crystal Cove Time, when we noticed an increasingly large flock of North- and the thickly-vegetated island may have provided the hawk western Crows (Corvus caurinus) foraging on tidal flats be- with an opportunity for an ambush. Alternatively, the hawk tween the shore and a nearby high tide island. When their may have caught the crow from a group that were already cawing reached a sudden crescendo and they all grouped mobbing it, as several incidents have been reported of raptors, into a tight flock of about 60 birds, we realized that they had including Cooper’s Hawks, capturing birds that were mob- begun mobbing an adult Cooper’s Hawk (Accipiter cooperii), bing them (Sordahl 1990; Holroyd 2002). As noted by Verbeek judged by size to be a female. The hawk had a crow in its and Butler (1999:9), Cooper’s Hawks are among the species claws. Although it was losing altitude rapidly, the hawk sud- mobbed by Northwestern Crows in “deafening” flocks. How- denly surged upwards into a thick clump of coniferous trees ever, the very short duration between the time that we heard on the island, with the crow still in its talons. The density of the mobbing and saw the struggling crow in the talons of the the trees on the island prevented us from seeing whether or hawk suggests that the predation occurred first and stimu- not the hawk plucked and ate the crow. lated the mobbing. As the hawk in this case was an adult, it was less likely an “inexperienced, hungry individual which pursued inappropriately large prey” as described in Verbeek’s (1985) review. Cooper’s Hawk Diet In Verbeek and Butler’s (1999) review of known preda- tors of Northwestern Crows, the only documented case of Although Cooper’s Hawks, like other members of Accip- Cooper’s Hawk predation was one of 286 food items brought iter, are primarily bird-eating (Bent 1937; Heintzelman 1979; to a nest by a pair of Cooper’s Hawks on Lopez Island, Wash- Kennedy and Johnson 1986; Rosenfield and Bielefeldt 1993; ington (Kennedy and Johnson 1986). I found no additional Wheeler 2003; Roth and Lima 2006), numerous examples of examples of Cooper’s Hawk predation on Northwestern opportunistic predation on less common prey, including in- Crows in other reviews of the biology and life histories of sects, fish, amphibians, reptiles and mammals, have been either species (e.g. Angell 1978; Bent 1937, 1946; Goodwin published (Bent 1937; Palmer 1988; Rosenfield and Bielefeldt 1976; Heintzelman 1979; Palmer 1988). However, in her evalu- 1993). For example, when bird feeders on Canada Way, ation of this manuscript, Mary J. Taitt mentioned finding a Burnaby, attracted the Alexandrian race of Black Rats (Rat- report on the internet of a Cooper’s Hawk eating a crow in tus rattus alexandrinus), a Cooper’s Hawk routinely cap- Beacon Hill Park, Victoria, on an unspecified date. This re- tured both adult and young rats. Other examples of oppor- port was not still available when checked for on 16 February tunistic predation by this species include chasing prey on 2012, and may have involved cleptoparasitism, predation or the ground, predation on birds roosting in shrubs, predation scavenging. Andrew C. Stewart (Pers. comm., 18 November on birds at feeders, predation on nestlings and stooping on 2011) has yet to see such predation after studying Cooper’s

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Hawks for several years, and believes that most records of Blue Jays (Cyanocitta cristata) that were mobbing the hawk crow remains at nests probably involve partially grown near Edmonton. Other large prey, including grebes, bitterns, young. However, he also notes that most studies of Coop- coots, pheasants, grouse, Rock Pigeons (Columba livia) and er’s Hawks to date have been during the breeding period, Burrowing Owls (Athene cunicularia) have been reported when males (the smaller gender) do most of the hunting. (Wedgewood 1978; Rosenfield in Palmer 1988; Rosenfield and This suggests that our knowledge of hunting behaviour Bielefeldt 1993; Zwickel and Bendell 2004; Roth and Lima 2006; outside the breeding season is incomplete. Ryder 2010). Predation on Northwestern Crows by Peregrines Falcons (Falco peregrinus), another similar-sized species has also been documented in both B.C. and Washington (Bishop 2008). The smaller Sharp-shinned Hawk (Accipiter striatus) Relative Sizes of Predator and Prey has also been observed to chase both American and North- western Crows (Verbeek 1985) in apparent attempts by imma- As Northwestern Crows and Cooper’s Hawks overlap in ture hawks to catch inappropriately large prey, in one case of size, these crows would not normally be suitable prey for the which the crows also chased the hawk (Patch 1922). That hawks. The mass of male Cooper’s Hawks in Wisconsin was corvids are desirable prey of accipiters is indicated by their generally less (297–480 g) than that of male Northwestern prevalence in foods brought to nests by Northern Goshawks Crows measured in Washington (389–486 g; n =19), whereas (Accipiter gentilis) in some areas (Meng 1959; Verbeek 1985), mass of female hawks ranged from 460–588 g (n =57) and including in study areas in which no corvids were brought to female crows ranged from 315–421 g (n =8) in the same Cooper’s Hawk nests (Meng 1959). populations (Dunning 1993). In a sample of migrating Coop- Attempted predation by Cooper’s Hawks on such large er’s Hawks from the western United States, mean mass of prey can also endanger the hawk, as exemplified by a female adult males was 281 g (n =177) and that of immature males Cooper’s Hawk that died after being knocked to the ground was 269 g (n =183) (Rosenfield and Bielefeldt 1993: Appendix by two American Crows in Washington (Richardson 1957). 2). Mass of male Cooper’s Hawks on southern Vancouver As also suggested by Andrew Stewart (Pers. comm.), the Island ranged from 275–316 (n =53), whereas females from powerful beaks and feet of corvids may well deter many that population ranged from 480–577 g (n =46) (Rosenfield et Cooper’s Hawks from attempting to prey on them, especially al. 2010). Nine male (378–458 g) and nine female (340–392 g) in combination with the corvids’ mobbing tendencies. As Northwestern Crows measured in B.C. (Verbeek and Butler noted by Robert W. Butler (Pers. comm., 22 November 2011), 1999) fell within the range reported by Dunning (1993). Thus, our observation indicates that the crows perceive Cooper’s assuming that most individuals could not carry weights close Hawks as a threat, which stimulates them to mob the hawks, to their own, some individual Cooper’s Hawks would be un- even though crows are behaviourally and physically formi- able to lift some individual Northwestern Crows and most of dable prey. these crows would represent challenging prey for most Coop- er’s Hawks. However, Cooper’s Hawks have attempted to prey on even larger birds. Mailliard (1908) and a companion observed two Cooper’s Acknowledgements Hawks unsuccessfully attempting to capture an American Crow (C. brachyrhynchos) out of a flock of about 1000 at San Preparation of this note was encouraged by former B.C. Geronimo, California and Sutton (1929) reported the remains Birds editor John B. Sprague and Cooper’s Hawk expert of a crow in the stomach of a Cooper’s Hawk in Pennsylvania. Andrew C. Stewart. The latter also shared his observations The collector of the hawk reported that another Cooper’s Hawk in valuable comments on an earlier version of the manuscript was feeding on the carcass of a crow in the vicinity, causing and reminded me of an additional relevant reference. Phillip Sutton to speculate that the crow may have been killed by S. Henderson kindly located two references for me when an both hawks. He also cited an earlier report of a crow being injury prevented me from doing so. Robert W. Butler and “disabled” by a Cooper’s Hawk in Massachusetts. An obser- referees Mark Phinney and Mary J. Taitt provided additional vation by Baresco (2002) of a Cooper’s Hawk stooping three helpful comments on the manuscript. times on a large flock of crows near Medicine Hat, Alberta, probably represents another case of a Cooper’s Hawk “test- ing” a flock for susceptible individuals. While reviewing this manuscript, Mary J. Taitt found three Literature Cited additional instances temporarily on the internet of Cooper’s Hawks attacking American Crows or crows of unnamed spe- Angell, T. 1978. Ravens, crows, magpies and jays. University cies in Ontario and at unnamed locations. Holroyd (2002) re- of Washington Press, Seattle and London. ported an observation of a Cooper’s Hawk killing a Black- Baresco, D. 2002. “Strange and supremely fascinating.” billed Magpie (Pica hudsonia) from a group of magpies and Alberta Naturalist 32(2):83.

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Bent, A. C. 1937. Life histories of North American birds of Rosenfield, R. N. and J. Bielefeldt. 1993. Accipiter cooperii. prey. Part 1. U.S. National Museum Bulletin 167 No. 75 in A. Poole and F. Gill. (eds.). The birds of North (reprinted by Dover, New York, 1961). America. Academy of Natural Sciences, Philadelphia, Pa., Bent, A. C. 1946. Life histories of North American jays, crows, and American Ornithologists’ Union, Washington, D.C. and titmice. U. S. National Museum Bulletin 191 Rosenfield, R. N., L. J. Rosenfield, J. Bielefeldt, R. K. Murphy, (reprinted by Dover, New York, 1964). A. C. Stewart, W. E. Stout, T. G. Driscoll and M. A. Bozek. Bishop, R. 2008. Peregrine Falcon preys on Northwestern 2010. Comparative morphology of northern populations Crow. Wildlife Afield 5:219–220. of breeding Cooper’s Hawks. Condor 112:347–355. Campbell, R. W. and B. Begg. 2006. Impact of Cooper’s Hawk Roth, T. C. II and S. L. Lima. 2006. Predatory behavior and predation on a nesting colony of Brewer’s Blackbirds on diet of wintering Cooper’s Hawks in a rural habitat. Vancouver Island, British Columbia. Wildlife Afield 3:25–27. Journal of Raptor Research 40:287–290. Dunning, J. B., Jr. (ed.). 1993. CRC handbook of avian body Ryder, J. M. 2010. Small Cooper’s Hawk takes large Rock masses. CRC Press, Boca Raton, Fla. Pigeon. Wandering Tattler 34(4):12. Goodwin, D. 1976. Crows of the World. Cornell University Sordahl, T. A. 1990. The risks of avian mobbing and Press, Ithaca, N.Y. distraction behavior: an anecdotal review. Wilson Heintzelman, D. S. 1979. Hawks and owls of North America. Bulletin 102:349–352. Universe Books, New York. Stewart, A. C. 2003. Observations of nest predation by Holroyd, G. L. 2002. Mobbing Black-billed Magpie, Pica Cooper’s Hawks on Vancouver Island, British Columbia. hudsonia, killed by Cooper’s Hawk, Accipiter cooperii. British Columbia Birds 13:7–8. Canadian Field-Naturalist 116:137-138. Sutton, G. M. 1929. Can the Cooper’s Hawk kill a Crow? Auk Kennedy, P. L. and D. R. Johnson. 1986. Prey-size selection 46:235–236. in nesting male and female Cooper’s Hawks. Wilson Verbeek, N. A. M. 1985. Behavioural interactions between Bulletin 98:110–115. avian predators and their avian prey: play behaviour or Mailliard, J. 1908. Cooper Hawks attacking Crows. mobbing? Zeitschrift fur Tierpsychologie 67:204–214. Condor 10:129. Verbeek, N. A. M. and R. W. Butler. 1999. Northwestern Crow Meng, H. 1959. Food habits of nesting Cooper’s Hawks and Corvus caurinus. No. 407 in A. Poole and F. Gill (eds.). Goshawks in New York and Pennsylvania. Wilson The birds of North America. The Birds of North America, Bulletin 71:169–174. Inc., Philadelphia, Pa. Palmer, R. S. (ed.). 1988. Handbook of North American birds. Wedgewood, J. A. 1978. The status of the Burrowing Owl in Vol. 4. Diurnal raptors (part 1). Yale University Press, Canada. Committee on the Status of Endangered Wildlife New Haven and London. in Canada, Ottawa. Patch, C. H. 1922. A biological reconnaissance on Graham Wheeler, B. K. 2003. Raptors of western North America. Island of the Queen Charlotte group. Canadian Field- Princeton University Press, Princeton, N.J. Naturalist 36:133–136. Zwickel, F. C. and J. F. Bendell. 2004. Blue Grouse: their Richardson, F. 1957. Cooper’s Hawk knocked down by crows. biology and natural history. National Research Council Murrelet 28(3):37. of Canada, Ottawa.

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