Cooper's hawk
Cooper's hawk is a medium-sized hawk native to the North American continent and found from southern Canada to Mexico. This species was formerly placed in the genus Accipiter.
As in many birds of prey, the male is smaller than the female. The birds found east of the Mississippi River tend to be larger on average than the birds found to the west. It is easily confused with the smaller but similar sharp-shinned hawk.
The species was named in 1828 by Charles Lucien Bonaparte in honor of his friend and fellow ornithologist, William Cooper. Other common names for Cooper's hawk include: big blue darter, chicken hawk, flying cross, hen hawk, quail hawk, striker, and swift hawk. Many of the names applied to Cooper's hawks refer to their ability to hunt large and evasive prey using extremely well-developed agility.
This species primarily hunts small-to-medium-sized birds, but will also commonly take small mammals and sometimes reptiles.
Like most related hawks, Cooper's hawks prefer to nest in tall trees with extensive canopy cover and can commonly produce up to two to four fledglings depending on conditions.
Breeding attempts may be compromised by poor weather, predators and anthropogenic causes, in particular the use of industrial pesticides and other chemical pollution in the 20th century. Despite declines due to manmade causes, the bird remains a stable species.
Taxonomy
Cooper's hawk was formally described by the French naturalist Charles Lucien Bonaparte in 1828 from a specimen collected near Bordentown, New Jersey. He coined the binomial name Falco cooperii. The specific epithet and the common name were chosen to honour the naturalist William Cooper, one of the founders of the New York Lyceum of Natural History in New York City. Other common names include the big blue darter and the chicken hawk. Cooper's hawk was formerly placed in the genus Accipiter. In 2024 a comprehensive molecular phylogenetic study of the Accipitridae confirmed earlier work that had shown that the genus was polyphyletic. To resolve the non-monophyly, Accipiter was divided into six separate genera. The genus Astur had been introduced in 1828 by the French naturalist Charles Lucien Bonaparte with the Eurasian goshawk later designated as the type species. The genus was resurrected to accommodate Cooper's hawk together with 8 other species that had previously been placed in Accipiter.It appears that Cooper's hawk was the earliest Astur known to colonize North America with a well-defined fossil record dating back perhaps 0.5-1 million years. Fossil evidence shows then that the goshawk came second. Despite the considerably wider range of the sharp-shinned hawk, still considered a member of the Accipiter genus unlike the prior species, the ancestors of the sharp-shinned hawk came over the Bering Land Bridge last. Genetic testing has indicated that Cooper's hawk is quite closely related to the American goshawk, unlike the similar superficial characteristics of Cooper's to the sharp-shinned hawk, a close relative of the Eurasian sparrowhawk, which were likely obtained through convergent evolution. A natural hybrid of a Cooper's hawk and an American goshawk with intermediate physical characteristics was verified via genetic testing of a migrant juvenile in Cape May and was thought to indicate a northward expansion of Cooper's range into historic goshawk haunts.
No subspecies are recognized of Cooper's hawk. A previously described subspecies, A. c. mexicanus, was discounted due to being weakly differentiated. However, evidence based on genetic markers shows that westerly birds such those in British Columbia populations are genetically differentiated from those in the Upper Midwest, indicating that Cooper's hawk were restricted to at least two Pleistocene glacial refugia with the Rocky mountains acting as a natural barrier to gene flow between hawks on either side while breeding.
Several of the other similar largish Astur species in the Americas appear to be closely related, possibly within a species complex, to Cooper's hawk, namely the bicolored hawk, widely distributed from southern Mexico to Central and northern South America, and the Chilean hawk. While there is some degree of obvious differentiation from these species in appearance, distribution and behavior, In particular, Cooper's hawk is now often considered sister to Gundlach's hawk that is endemic to Cuba and together these two species are sister to the bicolored hawk.
more nebulous is the relationship of Cooper's hawk to the very similar Gundlach's hawk of Cuba. In general the relationship of Cooper's and Gundlach's hawk is muddled and genetic testing indicated that it is possible that Gundlach's may even be insufficiently distinct to qualify as a separate species. It is almost certain that Cooper's hawk would at least qualify as the paraspecies for the Gundlach's and data has indicated fairly recent colonization and hybridization between the two hawks.
Description
Cooper's hawk is a medium-sized hawk as well as roughly average to small-sized for an Astur species. Compared to related species, they tend to have moderate-length wings, a long, often graduated or even wedge-shaped tail and long though moderately thick legs and toes. Their eyes tend to be set well forward in the sides of the relatively large and squarish-looking head and a relatively short but robust bill. They have hooked bills that are well-adapted for tearing the flesh of prey, as is typical of raptorial birds.Generally, Cooper's hawks can be considered secretive, often perching within the canopy, but can use more open perches, especially in the western part of the range or in winter when they may use leafless or isolated trees, utility poles or exposed stumps. On perched hawks, the wing-tips tend to appear to cover less than one third of the tail, sometimes seeming to barely cover the covert feathers.
As adults, they may be a solid blue-gray or brown-gray color above. Adults usually have a well-defined crown of blackish-brown feathers above a paler nape and hindneck offset against their streaked rufous cheeks. Their tail is blue-gray on top and pale underneath, barred with three black bands in a rather even pattern and ending in a rather conspicuous white tip. The adult's underside shows a bit of whitish base color overlaid heavily with coarse, irregular rufous to cinnamon bands, though these narrow into marginal shaft streaks around the throat. Against the rich color on the rest of the underside, the pure white on adults is conspicuous. Adult females may average slightly more brownish or grayish above, while some adult males can range rarely into almost a powder blue color.
Although little regional variation is known in the plumage, adult coloring in the Pacific Northwest averages slightly darker overall. Aberrant pale plumage was recorded in at least four total birds of both sexes, all of which were almost completely white and lacked any underside streaking. These birds had faded back color and lacking strong barring on the tail. An aberrant dark female was also recorded. As a juvenile, she had a blackish-brown back and dark inky feathers below with grayish ground color barely showing. Later she produced an aberrant male with similar characteristics that successfully fledged. The latter two were possible cases of melanism and such dark variations are virtually unprecedented in any Astur or Accipiter species.
Juveniles of the species are generally dark brown above, though the feathers are not infrequently edged with rufous to cinnamon and have a variable whitish mottling about the back, wing coverts and, mainly, the scapulars. Juvenile Cooper's tend to have streaking or washing of tawny on the cheeks, ending in a light nuchal strip, giving them a hooded appearance unlike the capped appearance of adults. The crown is brown on juveniles rather than blackish as in adults. The tail is similar to that of the adult but more brownish and sometimes shows an additional fourth band. The juvenile has more pale white to cream base color showing than older birds, with variable dusky throat striping and mid-brown streaks, which appear as sharply defined from about the lower throat to the lower breast. The juvenile may have brown to black spots or bars on the thighs with thin black streaks mostly ending at the belly and conspicuous white crissum and undertail coverts. Juveniles can tend to appear more "disheveled" and less compact than adults in feather composition.
In flight, though usually considered medium-sized, Cooper's hawks can appear fairly small. This effect is emphasized by the short wings relative to the elongated tail. The species tends to have rounded wings, a long rounded tail and long legs, much like other Astur and Accipiter species. Cooper's hawks have a strong flight with stiff beats and short glides, tending to do so on quite level wings with wrist thrust forward yet the head consistently projects. The 5 outer functional primaries are notched on their inner webs, the outermost is the longest, the next outermost nearly as long. When soaring, these hawks do so on flattish or, more commonly, slightly raised wings, with fairly straight leading edges. Against the barred underbody on adults, the wings are more or less flecked in similar color, with pale greyish flight feathers and a broadly white-tipped tail correspondingly barred with dark gray. Meanwhile, the upperside of adults is essentially all blue-grey. Juvenile are mostly dark above though manifest a hooded effect on the head and a rufous-buff edges and especially whitish mottling, the latter can be fairly apparent. Juveniles are mainly whitish below with neatly dark streaks about the wing linings, breast, flanks and thighs, with bars on the axillaries and flight feathers. The tail of the juvenile has a broadly white tip and bars like adults but the ground color is a paler shade of gray.
Adults have eyes ranging from light orange to red, with males averaging darker in eye color, while those of juveniles are yellow. Among 370 breeding hawks from different parts of the range, 1-year-old males usually had light orange eyes and 1-year-old females usually yellow eyes. Meanwhile, males of 2 or more years old always had consistently darker eyes than the eyes of females of the same relative age, with most males of the age having largely either orange or dark orange eyes, while female eyes at this stage were light orange or lighter. From the second year, the eyes of Cooper's hawks may grow darker still but stop darkening shortly thereafter. 3-year or older males were found to have predominantly dark orange, red or mid-orange. For unclear reasons, far more adults in British Columbia and North Dakota had dark orange or red eyes than mature hawks in Wisconsin. Most females over 2 years old in Wisconsin were found to have light orange eyes. The purpose of bright eye color in the hawks may be correlated to feeding stimulation of nestling hawks. The eyes of this hawk, as in most predatory birds, face forward, enabling good depth perception for hunting and catching prey while flying at top speeds. Adults have greenish yellow ceres and have legs of orangish to yellow while these parts on juveniles are a paler hue, yellow-green to yellow.
The prebasic molt begins in late April–May and takes about 4 months. The female usually begins to molt about 7–10 days sooner than the male. Molts occur inward towards the body on the wing feathers. Tail molt may generally start with the middle tail feathers, proceeding posteriorly to the upper tail coverts, also starting with the median feathers on the scapulars. Up to 36% of juvenile feathers may be retained in the second pre-basic molt. Arrested molt has been recorded in the late nesting period, often pausing after the third primary is molted. Molts tend to be halted especially when food supplies are down during the brooding stage, and may be resumed after the stress of feeding the brooding diminishes.