Cooper's Hawk

Accipiter cooperii

Order:
Accipitriformes
Family:
Accipitridae
Sections

Behavior

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Locomotion

Walking, Hopping, Climbing, etc.

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Cooper's Hawk foraging on ground.

Occasionally runs or walks on ground to pursue or retrieve prey, or to gather nesting materials.

© Margaret Viens, Maine, United States, 12 December 2017
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Video: Cooper's Hawk flying.

Several rapid wingbeats alternate with brief glides in usual flight.

© Timothy Barksdale, New Jersey, United States
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Video: Cooper's Hawk flying.

Accipiters, like Cooper's Hawk, have rounded wings and very long tails. In flight, look for Cooper's Hawk's large head that projects out ahead of the wings. The long tail often appears slightly rounded at the tip.

© Larry Arbanas, Arizona, United States, 5 May 2006
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Video: Cooper's Hawk soaring with undertail coverts flared.

Soars frequently in breeding and other seasons. In both sexes, also a high, slow, rocking flight with exaggerated wingbeats, much like nighthawk, often with undertail coverts laterally flared and (at least in male) "kik" calls.

© Timothy Barksdale, Arkansas, United States
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Cooper's Hawk flying in cluttered environment.
© George Ho, Colorado, United States, 29 July 2019
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Cooper's Hawk in flight.

Flying birds use both legs to tuck prey to belly.

© Alan Kneidel, Massachusetts, United States, 11 February 2017

Occasionally runs or walks on ground to pursue (39) or retrieve prey (JB, RNR), or to gather nesting materials (172). Fledglings may run or walk along branches of nest and surrounding trees; may be seen jumping on pine cones during fledging period (26).

Flight

Several rapid wingbeats alternate with brief glides in usual flight, averaging 47 km/h (range 37–88 km/h) in migration (176), but much faster and more highly maneuverable when attacking prey or predators. Flight muscle mass provides reserve power for acceleration during attacks or sustained transport of heavy prey (177). Usually flies close to ground or below tree canopy when hunting or approaching and departing nest, but may carry prey at 30–100 m altitude (106). Soars frequently in breeding (117) and other seasons. In both sexes, also a high, slow, rocking flight with exaggerated wingbeats (similar to nighthawks [Chordeiles]), often with undertail coverts laterally flared and giving (at least in male) "kik" calls (see 178). Such flight has been ascribed to courtship display, but this behavior also occurs in migrants (179) and fledglings (175). Flying birds use both legs to tuck prey to belly.

Self-Maintenance

Preening, Head Scratching, Stretching, Bathing, Anting, etc.

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Video: Cooper's Hawk perching, preening.
© DAVID BROWN, New York, United States
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Cooper's Hawk bathing.

Enjoys bathing in pools of water, as well as in the rain.

© Craig Thayer, Arizona, United States, 2 May 2015
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Cooper's Hawk drying off.

After bathing, birds will often fly to a sunny perch to dry.

© Tom Murray, Massachusetts, United States, 2 November 2017
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Cooper's Hawks interacting.
© Malcolm Gold, Wisconsin, United States, 16 April 2010
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Cooper's Hawks interacting.
© Tom Murray, Massachusetts, United States, 14 October 2016
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Cooper's Hawk courtship display.
© Dan Vickers, Georgia, United States, 6 March 2016
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© Chris Rohrer, Arizona, United States, 17 March 2016
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Figure 8. Bowing display.

Bowing display of the Cooper’s Hawk, usually given by a male in the presence of his mate and before he begins nest building; this is thought to be a signal demonstrating readiness to nest and/or an appeasement display. Drawing by J. Schmitt, after J. M. Papp in Rosenfield and Bielefeldt (1991a).

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Cooper's Hawk copulation.

Male flies to female's tree perch to copulate; female may solicit by tilting to horizontal on perch. Male mounts, usually from flight, and balances with spread wings. One or both sexes give context-specific call while copulating. No post-copulatory displays evident.

© Brian Rusnica, Massachusetts, United States, 22 March 2018
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Young Cooper's Hawk pouncing on stick.

Fledglings have been observed playing with objects during the fledging period.

© Zoe Finney, Wisconsin, United States, 15 April 2017
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Cooper's Hawk being mobbed by Crow sp.
© Lynn Rafferty, Virginia, United States, 20 May 2016
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Cooper's Hawk being mobbed by Scissor-tailed Flycatchers.
© Zach DuFran, Oklahoma, United States, 18 June 2016
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Cooper's Hawk mobbing Great-horned Owl.
© Chris Petrizzo, Colorado, United States, 27 February 2019
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Red-tailed Hawk stealing prey item from Cooper's Hawk.
© Maury Swoveland, California, United States, 18 March 2019
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Northern Goshawk preying upon Juvenile Cooper's Hawk.
© Samuel Paul Galick, New Jersey, United States, 25 November 2012

From Meng (39). Preening typical, 1–20 min on 11 occasions/d in incubating female. Stretches and preens wings to side or overhead, scratches head with toes, stretches leg. May bathe in pools of water, as well as in the rain. After bathing, birds will often fly to a sunny perch to dry (178).

Sleeping and Roosting

Sleeps standing on one leg, head tucked between scapulars and upper back feathers, female roosting near nest after brooding ceases (39). Roosts of 1 male were usually distant (> 120 m) from nest and disproportionately (61%) in pine plantation covering 10% of home range (106). In a study that used radio-telemetry to examine habitat use of of migrant individuals along Kittatinny Ridge in the Appalachians of Pennsylvania, most nocturnal roosts were located in contiguous forest (44%), or in large forest patches (16%), on or near the ridge (87). Fledglings that are well capable of flight have been documented during daylight hours in prone positions, lying with their entire bodies along the axis of tree limbs or on the ground up to 40 m from the nest tree (180). No information on sunbathing.

Daily Time Budget

Diurnal. No information for nonbreeding seasons. In breeding season, male provides nearly all food for female and young from pre-laying to mid-nestling stages, about 90 d. In pre-laying period, male is absent from nest area, presumably hunting, about 20% of day (172). At same stage, male also invests more time in nest building and anti-predator behavior, while female stays near nest and reduces activity in energetically demanding flight (181). Female does most incubation; concurrent male budget unknown. At late nestling and fledgling stages, diurnal activity in adults marked with radio-transmitters (117) included 8.4% (males) and 8.1% (females) soaring flight; 6.4% and 2.8% non-soaring flight; and the remainder of time spent perching, mainly short perching times (median 2 and 6 min) separated by brief flights (median 20 s). A comparable study of adults marked with radio-transmitters reported flight times of 13.7% (males) and 10.7% (females), with the remainder consisting of short perching times (median 1 min for both sexes); median flight duration 20 s (142). At same stages, about half of one male's diurnal time spent in this short-stay perch hunting behavior, with no diel pattern; "inactive" perching bouts 15–40 min, but up to 5 h in extended rain (106).

Fischer (117) estimated energy budgets; see also Kennedy and Gessaman (142).

Agonistic Behavior

Breeding individuals are generally more likely to respond aggressively to conspecific intruders of the same sex. Observations of 11 responses of breeding Cooper's Hawks to heterospecific intruders to the nest area showed that males responded 64%, females 9%, and both members 27% (182). A captive male elicited repeated strikes and threat posture from a wild male (both adults) when tethered near a nest, but only calls and weak threats from the resident female (39). An adult female at the nest showed no defensive reactions to nearby immature conspecifics (183). However, two studies in New Mexico documented frequent aggressive disputes between juvenile females and between between After-Second-Year females and Second-Year females (168, 67). In at least four cases, these disputes resulted in injury or death (67). Presumed threat display is with lowered head, raised "crest" (capital tract), outstretched wings, spread tail, often accompanied by alarm calls.

Spacing

Territoriality

A relatively small area around the nest is defended and intruders are evicted from this territory whenever possible. Adult hunting ranges may be large and could have little, if any, overlap with the breeding territory (178). Minimum distance between nests generally 0.7–1.0 km (170, 117, 184, JB, RNR), but successful pairs as close as 0.16 km and 0.27 km in Albuquerque, New Mexico and Victoria, British Columbia, respectively (1). Female home range may decrease in size with age. Over a 4-year study, home ranges of radio-tagged females decreased from a mean of 932 km2 during the first year to nearly 4 km2 by the fourth year. Most females maintained separate breeding and nonbreeding ranges, but movements within each appeared to become more focused with age and experience (46).

Individual Distance

In mated pairs, female displaces male from prey, perches, and nests, but one male flew at and struck his flying mate when she was off eggs during human disturbance (RNR). Males appear to maintain a minimum perch distance > 1 m from mate (JB, RNR).

Sexual Behavior

Mating System and Sex Ratio

Generally monogamous. Two records of helping at the nest, in which 2 males (1 adult, 1 subadult at both nests) provisioned for a single adult female, and all 3 birds defended each nest (185, 186). Researchers in North Dakota documented a single male successfully fledging young at two urban nests in Grand Forks (187); two fledgling males, one from each of these nests, became successful breeding adults in this city (188). In New Mexico, a single male that was polygynous during 3 consecutive years with the same 2 females, after having been monogamous with one of those females the previous 2 years (B. Millsap and K. Madden, unpublished data). This male was successful at both nests in each year. In a Wisconsin study, 19.3% of nestlings were extra-pair young, and 34% of all broods contained at least 1 extra-pair young (189); sires of 89% of extra-pair young could not be identified and thus male floaters likely important in occurrence and frequency of extra-pair paternity in that population.

Sex ratio skewed towards males (~54–60%) in eggs, nestlings, and fledglings in multi-decade study in territorially saturated, stable population in Wisconsin outside Milwaukee (111, 190). In contrast, during concurrent study years in Wisconsin, offspring sex ratio in rapidly growing population in Milwaukee, Wisconsin was about 1:1 (190). Production of more female young in Milwaukee vs. outside Milwaukee may have been individually adaptive because in a population with a preponderance of males, there might not be enough females for breeding. Raptor offspring ratios often skewed toward males because smaller males cheaper to produce given equal parental investment in young (1). Divergent growth rates in larger female and smaller male nestlings apparently does not lead to skewed nestling sex-ratios through siblicide or male starvation (111, 190); adjustment of sex ratios occurs at conception in Wisconsin Cooper's Hawks (190).

Offspring sex ratio approximately 1:1 in 3 years, but 58% males in one year in Albuquerque, New Mexico (67), and 53% male offspring across 12-year study in Tucson, Arizona (112).

Pair Bond

Courtship Displays and Mate Guarding. Displays generally involve slow, exaggerated wingbeats, alternated by gliding with wings held in a dihedral. During these displays, undertail coverts may be flared laterally (178). An already paired male, less often a female, may give bowing display (Figure 8) to mate before nest building bouts ensue (173). Appeasement and/or symbolic nest building functions have been suggested. See also Flight.

Male leaves nesting area to hunt for himself and mate, but nevertheless remains near nest and female about 80% of day during long prelaying and copulatory period (172); mate guarding inferred. Male brings prey to female 2–3 times/d during month-long prelaying period, providing virtually all the mate's food at this time. Lien et al. (168) monitored brood provisioning throughout one breeding season and documented prey delivery rates ranging from ~0.5–2 prey deliveries per 2-hr period. For Eurasian Sparrowhawk (Accipter nisus), Newton (191) showed experimentally that clutch size varied with food provisioning; if similar in Cooper's Hawk, clutch size should reveal male's hunting ability (18). Lien et al. (168) found that older females fledged 1.6 more offspring and occupied territories where males provisioned at higher rates than did younger females.

Copulation and Copulatory Displays. From Rosenfield (192) and Rosenfield et al. (172), who suggested that patterns are consistent with paternity assurance. In males, building of nest and same-year alternative nest(s) may be precopulatory display; 80% of copulations (n = 102) occurred < 1 min after male visit to nest. Copulation also follows most male prey deliveries. Male flies to female's tree perch to copulate; female may solicit by tilting to horizontal on perch. Male mounts, usually from flight, and balances with spread wings. One or both sexes give context-specific call (see Sounds and Vocal Behavior) while copulating. No postcopulatory displays evident. Brief (mean 4.5 s, range 2–6) but frequent copulations (mean = 0.9/h) throughout the 30 d prelaying period, with no temporal peaks apparent. Copulations throughout day but more frequent in early morning. Total copulations per clutch estimated 372, among highest reported for birds.

Duration of Pair Bond. Few published data on marked birds. Some pairs known to remate and some individuals to have new mates in subsequent years (193, RNR, JB).

Extra-Pair Copulations

Researchers in Grand Forks, North Dakota (188) and in Seattle, Washington (194) observed females make extra-territorial movements during the pre-incubation stage and copulate with extra-pair males. Prevalence of this phenomena across range unknown but these observations and discovery of high rate of extra-pair paternity in Wisconsin nests (195) may suggest this behavior is not uncommon.

Social and Interspecific Behavior

Degree of Sociality

Apparently solitary outside breeding season. Small groups in migration are probably incidental, not social. Sexes roost apart in pre-incubation stage of nesting (JB, RNR). A male roosted once near the nest, but otherwise roosted at a distance of 120–1,980 m (mean 765 m, n = 31) at nestling through fledgling stages (106).

Play

Fledglings may be seen jumping on pine cones during fledging period (26).

Nonpredatory Interspecific Interactions

Mobbed by smaller birds, especially when carrying prey. Calls are often mimicked by Blue Jay (Cyanocitta cristata) and Steller's Jay (C. stelleri), frequent prey items, even near hawks' nest (RNR, JB; P. Kennedy, personal communication). One record of a Cooper's Hawk responded to mobbing by Black-billed Magpies (Pica hudsonia), by killing a bird in the group (196). In Arizona, hummingbirds have been found to prefer nesting in association with hawk nests and have higher reproductive success when nesting near an active hawk nest (197, 198).

Predation

Predation on eggs and nestlings by raccoon (Procyon lotor); on adults, nestlings, and fledglings by Great Horned Owl (Bubo virginianus); perhaps rarely on eggs by American Crow (Corvus brachyrhynchos) (84). Reports of predation on adults by Red-tailed Hawk (Buteo jamaicensis), Northern Goshawk (Accipiter gentilis), and Great Horned Owl (199, 200, 142, 201), and by immature Cooper's Hawks on conspecific nestlings (183).

Adults direct threat postures, alarm calls, attacks, or chases at potential predators near nest, with males assuming most such defense (when both sexes present) in pre-incubation stage (181). Intensity of such responses to human intrusion varies among individuals and probably with stage of nesting, hatch date, and probably prior experience, but individuals rarely strike humans (39, 104, RNR, JB). In New Mexico, 97% of female observations and 63% of male observations during incubation documented no response to human intrusion (104). Breeding pairs in urban areas may be less responsive to human intrusion than those in exurban, or less developed, areas (104). Many breeding pairs are inconspicuous, neither vocalizing nor behaving aggressively in the presence of humans, instead leaving the immediate vicinity of the nest (202, 104). A recurrent intruder to the nest site may elicit increased defensive behaviors (104).

Recommended Citation

Rosenfield, R. N., K. K. Madden, J. Bielefeldt, and O. E. Curtis (2019). Cooper's Hawk (Accipiter cooperii), version 3.0. In The Birds of North America (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.coohaw.03