Cooper’s Hawk (Accipiter cooperii)

Distribution

Breeding: Breeding range extends from southern Alaska along the Pacific Coast to northern Washington; inland from southern Yukon south to western Montana, central Idaho, and Cascade Mountains of central Oregon.

Winter: Winters primarily in highlands of Mexico, south to Nicaragua, and rarely to Costa Rica. A small population winters along Pacific coast from west-central Washington south to southern California.

Breeding habitat

Coniferous, deciduous, and mixed forests. May prefer more open or patchy landscapes such as woodlots, riparian forests, or forested patches in a matrix of farmland. May also prefer open stands of trees rather than dense continuous stands. Often found near forest openings or edges, and near a stream, lake, or other body of water. It is unclear how tolerant the Cooper’s Hawk is of human disturbance, but there are an increasing number of reports of successful nestings in suburban or urban areas.

Conservation status

Being a representative top predator in many parts of North America, the Cooper’s Hawk is of moderate conservation importance and is on the threatened or special concern list for many states. This species seems tolerant of human activity and habitat modification, although the precise habitat and area requirements in many parts of its range are poorly known. Although this species is poorly monitored on its breeding grounds, overall populations appear to be stable, with some increases noted in eastern regions and possible declines in many parts of the West.

Description

Medium-sized (crow or grouse), forest-dwelling accipiter with a long, narrow tail and short rounded wings. Marked reverse sexual size dimorphism, with males weighing about 65% of females. Tail noticeably rounded at tip, with tail feathers progressively shorter, outward from central pair. Tail also has alternating light and dark bands with a wide white terminal band. May soar during mornings, migration, and displays, but most flight is active, with periods of flapping alternating with short glides. In flight, appears to be a “long-necked” accipiter, with head extending forward well beyond the leading edge of wings. Legs appear relatively thick when perched.

Male: Dark-brown to slate-gray back, with a darker gray to black crown that contrasts with the lighter nape. Finely barred rufous underparts. Undertail coverts pure white. Iris color varies from deep reddish- orange to red. Legs and cere yellow.

Female: Same coloration as male, but larger.

Juvenile: Attains adult plumage in second year; hatch-year birds wear juvenal plumage through first winter. Back and upper-wings medium brown, head with dark-brown crown. Underparts creamy white with fine dark-brown streaking, undertail coverts white. Iris color greenish-yellow to yellow; cere yellow; legs greenish-yellow.

Vocalizations

Song: None.

Calls: Does not call frequently, except during breeding season, and has a small repertoire of vocalizations. Most common call is the kek-kek-kek alarm call that may be given by either sex. This call is also sometimes given by both members of a “duetting” pair during breeding season or during displays. Female has two recognized calls: a soft ki or krrr that may serve to indicate the location of female and a louder “wail” call. Juveniles may give a begging call or “hunger shriek,” which sounds like a thinner, higher pitched version of the adult wail call. This call may be given by several juveniles at once, and may also be used by fledglings that have left the nest but are still dependent on parental feeding.

Foraging strategy

Most prey is taken while “still-hunting” from ambush or by stealthy approach flights that take advantage of landscape features to hide the approaching hawk from its prey until the last second. This may entail a twisting, circuitous flight at high speeds and low levels. Cooper’s Hawks are superb and powerful flyers, capable of rapid flight through dense vegetation. Prey may be taken on the ground, in flight, or in trees or bushes. May even pursue prey into dense underbrush on foot.

Diet

Up to 80% of prey taken may be birds, with the remainder mostly mammals. Proportion of mammalian prey may increase during breeding season. Avian prey may range in size from warbler species and House Sparrows to Northern Bobwhites or Northern Flickers. Mammalian prey may include various species of squirrels and young cottontail rabbits. Smaller male takes correspondingly smaller prey, with prey weights averaging around 75% of those taken by female.

Behavior and displays

• Both males and females may engage in “slow flight” territorial displays in which the birds fly with stiff, slow, exaggerated wingbeats while exposing their white undertail coverts. Both sexes may give the kek-kek-kek call during these flights.

• The kek-kek-kek call, or alarm call, is also used to signal the presence of intruders in the vicinity of the nest.

Courtship

• Courtship behavior is not well documented. Male probably obtains and defends a breeding territory and attracts a female by calling and performing display flights. Courtship flights begin with both birds soaring on thermals and end with a slow speed chase of female by male. During slow speed chase, both birds alternate periods of extremely slow, exaggerated wingbeats with short glides.

• Courtship feeding has also been reported, in which male brings the perched female partially or fully plucked prey.

Nesting

Nest Site: Nests built in mature trees against the trunk and supported by one or more large branches. Males may show a high degree of territory fidelity, with several old nests located within a radius as small as 300 feet (90 meters).

Height: 20–90 feet (6–27 meters).

Nest: Substantial platform of large, often fresh, twigs broken from branches. Central cavity lined with bark chips. Males assist in building nest. Old nests of Cooper’s Hawks, crows, and other species may be refurbished and reused.

Eggs: Usually 4, with an interval of about 2 days between the laying of each egg. Earliest egg records from most states are around the middle of April.

Incubation period: Incubation by female (male does not normally incubate) often begins when third egg is laid and may last from 30–35 days. All eggs tend to hatch within a 2–3 day period.

Nestling period: Young remain in nest about 4 weeks, guarded and brooded by female and fed by male who does most of the hunting. During the latter phase of nestling period, female may take an increasingly large part in hunting, leaving young alone in nest. Young normally eject feces over the side of nest; ground and bushes below nest may be liberally splattered with whitewash before young fledge.

Fledgling period: Fledglings remain in vicinity of nest and continue to be fed by parents until they are about eight weeks old.

Broods: Normally single-brooded; may make another breeding attempt if a nest fails early in the season.

Notes

• Adult Cooper’s Hawks do not defecate at or near the nest. The female tends to defecate at a plucking post instead. The plucking post, which may be a fence post, stump or fallen tree, is usually located within about 150–200 feet (46–61 meters) of the nest. It may be recognized by an accumulation of feathers from plucked prey and by whitewash splattered on the surrounding area.

• It appears that most males do not breed until their second year; a small proportion of female breeders may be first-year birds in juvenal plumage.