Cooper's hawk

Cooper's hawk (''Accipiter cooperii'') is a medium-sized hawk native to the North American continent and found from southern Canada to Mexico. This species is a member of the genus '' Accipiter'', sometimes referred to as true hawks, which are famously agile, relatively small hawks common to wooded habitats around the world and also the most diverse of all diurnal raptor genera. As in many birds of prey, the male is smaller than the female.Snyder, N. F., & Wiley, J. W. (1976). ''Sexual size dimorphism in hawks and owls of North America (No. 20)''. American Ornithologists' Union. The birds found east of the Mississippi River tend to be larger on average than the birds found to the west.Pearlstine, E. V., & Thompson, D. B. (2004). ''Geographic variation in morphology of four species of migratory raptors''. Journal of Raptor Research, 38(4), 334–342. It is easily confused with the smaller but similar sharp-shinned hawk. (''A. striatus'')

The species was named in 1828 by Charles Lucien Bonaparte in honor of his friend and fellow ornithologist, William Cooper.Palmer, R. S., ed. (1988). ''Handbook of North American birds. Volume 5 Diurnal Raptors (part 2)''. Other common names for the Cooper's hawk include: big blue darter, chicken hawk, flying cross, hen hawk, quail hawk, striker, and swift hawk.Bent, A. C. 1938. ''Life histories of North American birds of prey, Part 1''. U.S. National Museum Bulletin 170:295–357. Many of the names applied to the 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.Rosenfield, R. N., K. K. Madden, J. Bielefeldt & Curtis, O.E. (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.

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.Snyder, N. F. R. (1974). ''Can the Cooper's Hawk survive?'' National Geographic Magazine, 145:432–442. 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 (later the New York Academy of Sciences) in New York City. Other common names have been known to include the big blue darter, chicken hawk, hen hawk, Mexican hawk, quail hawk, striker and swift hawk. The Cooper's hawk is a member of the genus '' Accipiter'', sometimes referred to as "true hawks" (and the members of which are at times commonly referred to as goshawks or sparrowhawks). This genus is the most diverse of all in the species-rich family Accipitridae, with nearly 50 recognized species, and is also the most diverse of all diurnal raptor genera. The genus ''Accipiter'' appeared to diversify in the last few million years due to an increase in accessible avian prey.Griffiths, C. S., Barrowclough, G. F., Groth, J. G., & Mertz, L. A. (2007). ''Phylogeny, diversity, and classification of the Accipitridae based on DNA sequences of the RAG‐1 exon''. Journal of Avian Biology, 38(5), 587–602. They appear to be a sister genera to ''Circus'' or harriers, albeit a distantly related one.Lerner, H. R., & Mindell, D. P. (2005). ''Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA''. Molecular phylogenetics and evolution, 37(2), 327–346. Other smaller genera including ''Harpagus'' and '' Erythrotriorchis'' also appear to bear some relation. Genetic studies of three Asian ''Accipiter'' species showed that they may not be a monophyletic group, with various clades divisions outside traditional subfamily lines, with even the sharp-shinned hawk-like and aptly named tiny hawk (''Accipiter supercilious'') appearing to cluster outside of the genus nearer very dissimilar genera like '' Buteo'' and '' Milvus''. It appears that the Cooper's hawk was the earliest ''Accipiter'' 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 and, despite the considerably wider range of the sharp-shinned hawk compared to the other two species, the ancestors of the sharp-shinned hawk came over the Bering Land Bridge last. Genetic testing has indicated that the Cooper's hawk is quite closely related to the northern goshawk, with the similar superficial characteristics to the Cooper's of the sharp-shinned hawk, a close relative of the Old World sparrowhawk, apparently obtained through convergent evolution.Newton, I. (2010). ''The sparrowhawk''. A&C Black. A natural hybrid of a Cooper's hawk and a northern 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 the Cooper's range into historic goshawk haunts.

No subspecies are recognized of the 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 the 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 ''Accipiter'' species in the Americas appear to be closely related, possibly within a species complex, to the Cooper's hawk, namely the bicolored hawk, widespread through Central and South America, and the Chilean hawk (''Accipiter chilensis'').Breman, F. C., Jordaens, K., Sonet, G., Nagy, Z. T., Van Houdt, J., & Louette, M. (2013). ''DNA barcoding and evolutionary relationships in Accipiter Brisson, 1760 (Aves, Falconiformes: Accipitridae) with a focus on African and Eurasian representatives''. Journal of Ornithology, 154(1), 265–287. While there is some degree of obvious differentiation from these species in appearance, distribution and behavior, more nebulous is the Cooper's hawk relationship to the very similar Gundlach's hawk of Cuba. In general the relationship of the Cooper's and Gundlach's hawk is muddled and genetic testing indicated that it is possible (but not certain) that the Gundlach's may be insufficiently distinct to qualify as a separate species.Reynard, G. B., Short, L. L., Garrido, O. H., & Alayón, G. G. (1987). ''Nesting, Voice, Status, and Relationships of the Endemic Cuban Gundlach's Hawk (Accipiter gundlachi)''. The Wilson Bulletin, 73–77. It is almost certain that the 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 and relatively large for an ''Accipiter''. 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 (though the head can look somewhat rounded if the feathers on the nape are held flush) 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 (rather than mid-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 ''Accipiter'' species.Morrow, J., & Morrow, L. (2015). ''Aberrant plumages in Cooper's Hawks''. Journal of Raptor Research, 49(4), 501–505.

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 (some juveniles, unlike adults, may manifest a slim supercilium as well). 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.Brown, Leslie and Amadon, Dean (1986) ''Eagles, Hawks and Falcons of the World''. The Wellfleet Press. . 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 (unlike unrelated hawks, the wingspan is usually less than twice as broad as the total length). The species tends to have rounded wings, a long rounded tail and long legs, much like other ''Accipiters''. 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 (40.4%) or dark orange (32.3%) 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 (37.3% vs 21.6% of similar age females), red (34.6% vs 3.3% of similar age females) or mid-orange (26.6% vs 55% of similar age females).Rosenfield R. N. & Bielefeldt, S. A. (1992). ''Reanalysis of Relationships among Eye Color, Age and Sex in the Cooper's hawk''. J. Raptor Res, 31(4), 313–316. For unclear reasons, far more adults in British Columbia and North Dakota (83% of males, 63% of females) had dark orange or red eyes (which also manifested at an earlier age in British Columbia) than mature hawks in Wisconsin (49% of males, 14% of females). Most females over 2 years old in Wisconsin were found to have light orange eyes.Rosenfield, R. N., Bielefeldt, J., Rosenfield, L. J., Stewart, A. C., Murphy, R. K., Grosshuesch, D. A., & Bozek, M. A. (2003). ''Comparative relationships among eye color, age, and sex in three North American populations of Cooper's Hawks''. The Wilson Journal of Ornithology, 115(3), 225–230. The purpose of bright eye color in the hawks may be correlated to feeding stimulation of nestling hawks (i.e. darker orange or red objects may be more perceptible and tend to be pecked at more so than duller colors). 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.Henny, C. J., Olson, R. A., & Fleming, T. L. (1985). ''Breeding chronology, molt, and measurements of Accipiter hawks in northeastern Oregon''. Journal of Field Ornithology, 97–112. Up to 36% of juvenile feathers may be retained in the second pre-basic molt.Pyle, P. (2005). ''First-cycle molts in North American Falconiformes''. Journal of Raptor Research, 39:378–385. 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.Howell, S. N. G. (2010). ''Peterson Reference Guide to Molt in North American Birds''. Houghton Mifflin Harcourt Company, Boston, MA, USA.

Size

Cooper's hawks are fairly variable in size. There is usually minimal to no overlap in dimensions between the sexes, with females being considerably larger than males. On average, she may be about 20% larger linearly and around 40% heavier (though can be up to 125% more massive). More westerly Cooper's hawks (roughly west of the Rocky mountains) show slightly less pronounced sexual dimorphism than hawks of the species elsewhere.Smith, J. P., Hoffman, S. W., & Gessaman, J. A. (1990). ''Regional Size Differences among Fall-Migrant Accipiters in North America''. Journal of Field Ornithology, 192–200. Sexual dimorphism in Cooper's hawks is most reliably measured by wing size, talon size, then body mass. Although there is some margin of error, within a given region dimensions of the two sexes never overlap in these regards (but may overlap marginally in tarsal and tail lengths). In general terms, ''Accipiter'' species are among the most sexually dimorphic in size of all raptorial birds.Reynolds, R. T. (1972). ''Sexual dimorphism in accipiter hawks: a new hypothesis''. The Condor, 74(2), 191–197. Sexual dimorphism in ''Accipiters'' may be due to greater male efficiency through smaller size and resulting agility in food gathering for the family group. Meanwhile, the female may be better suited to the rigors of brooding (including perhaps most nest defense) due to her larger size, also allowing the sexes to compete less on the same food sources. Geographic variation in body size has also been found, with more easterly hawks tending to be rather larger on average than those found in western North America.Dewey, T. and V. Perepelyuk. (2000)
''Accipiter cooperii''
Animal Diversity Web. Accessed April 22, 2010.Mueller, H. C., & Berger, D. D. (1981). ''Age, sex, and seasonal differences in size of Cooper's Hawks''. Journal of Field Ornithology, 52(2), 112–126. On the contrary, in the American southwest, the species may reportedly reach its largest sizes but there is little evidence that these birds average distinctly larger than the large bodied individuals measured in the more northeasterly parts of the species’ range in North America, from eastern North Dakota to New Jersey.Whaley, W. H., & White, C. M. (1994). ''Trends in geographic variation of Cooper's hawk and northern goshawk in North America: a multivariate analysis''. Western Foundation of Vertebrate Zoology. The size variation evidenced in Cooper's hawks is apparently the most pronounced of any of the three North American species of ''Accipiter''. However, Cooper's hawks are one of an estimated 25% of studied bird species that do not appear to correspond to Bergmann's rule (i.e. being larger where living farther north) instead varying in size much more so by longitude. Furthermore, juveniles can differ somewhat in size, tending to be slightly lighter and smaller than older birds, but not infrequently averaging longer in tail and especially wing length.Rosenfield, R. N., Rosenfield, L. J., Bielefeldt, J., Murphy, R. K., Stewart, A. C., Stout, W. E., Driscoll, T.G. & Bozek, M. A. (2010). ''Comparative morphology of northern populations of breeding Cooper's Hawks''. The Condor, 112(2), 347–355. Total length of full-grown birds can vary from in males and in females. Wingspan may range from , with an average of around .White, C.M., Boesman, P. & Marks, J.S. (2020). ''Cooper's Hawk (Accipiter cooperii)''. In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.Cartron, J. L. E. (Ed.). (2010). ''Raptors of New Mexico''. UNM Press.

Body mass, along with standard measurements, is much more frequently measured than total length or wingspan in different populations. Museum specimens from the western United States averaged in 48 males and in 20 females, while those sourced from the eastern United States averaged in 16 males and in 31 females.Friedmann, H. (1950). ''Birds of North and Middle America, Part 2''. U.S. National Museum Bulletin no. 50. Average weight of 104 male migrating hawks in Cedar Grove, Wisconsin was (with adults averaging 4% heavier than juveniles), whilst the average of 115 females migrants was (with adult averaging about 5.5% heavier than juveniles). A different sample of Wisconsin Cooper's hawks reportedly averaged in males (sample size 60) and in females (sample size 57). At Cape May Point, New Jersey, weights were similar as in Wisconsin (although only hatching-year juveniles were apparently weighed), with averages of in two samples of males and in the two samples for females. Migrant hawks in the Goshute Mountains of Nevada were significantly lighter than the eastern ones at in 183 first year males and in 177 older males and in 310 first year females and in 416 older females. Weights were similar to the Goshutes in the Marin Headlands, California where 50 males (all first-years) averaged and 117 first-year females averaged .Pitzer, S., Hull, J., Ernest, H. B., & Hull, A. C. (2008). ''Sex determination of three raptor species using morphology and molecular techniques''. Journal of Field Ornithology, 79(1), 71–79. Averaged between early and late summer, the average mass of males in Oregon was and that of females was reported at . The average weights of Cooper's hawks from Oregon was about 19.4% lower in males and 14.5% lower in females than those from Wisconsin but the Oregon hawks evidenced less seasonal variation in weight. In British Columbia, males averaged and females averaged while in western and eastern North Dakota, males averaged and females averaged . In northern Florida, males averaged and females averaged .Millsap, B. A., Breen, T. F., & Phillips, L. M. (2013). ''Ecology of the Cooper's Hawk in north Florida''. North American Fauna, 78(00), 1–58. In general, males may weigh anywhere from and females anywhere from , the lightest hawks generally being juveniles recorded from the Goshutes of Nevada, the heaviest known being adults from Wisconsin.Hoffman, S. W., Smith, J. P., & Gessaman, J. A. (1990). ''Size of Fall-Migrant Accipiters from the Goshute Mountains of Nevada (Tamaño de migrantes otoñales (Accipitrinae) de las Montañas Goshute, Nevada)''. Journal of Field Ornithology, 201–211.Rosenfield, R. N., Bielefeldt, J., Haynes, T. G., Hardin, M. G., Glassen, F. J., & Booms, T. L. (2016). ''Body mass of female Cooper's Hawks is unrelated to longevity and breeding dispersal: Implications for the study of breeding dispersal''. Journal of Raptor Research, 50(3), 305–312.

Among standard measurements, the wing chord may vary from in males and from in females.Rosenfield, L. J. (2006). ''Comparative morphology among three northern populations of breeding Cooper's Hawks'' (Doctoral dissertation, University of Wisconsin—Stevens Point). Wing chord is generally commensurate with body mass, averaging largest in the heavier hawks of eastern North Dakota, where males averaged and females , and in Wisconsin, where males averaged and females (those from Cape May also being similar to those two samples). However, smaller, more westerly hawks such as those in the Goshute mountains, where males measured at a mean of and females at a mean of , and in British Columbia, with a male mean of and female mean of , were proportionately longer winged relative to their other body proportions. The tail of males may vary from and that of females at , consistently over in females and averaging under in males. In tarsus length, males may vary from , with an average of in museum specimens, and females from , with an average of in museum specimens. The culmen may measure from in males, averaging about , and from in females, averaging about . The hallux claw, the enlarged rear talon featured on nearly all accipitrids, may measure from in males, averaging about , and from in females, averaging about . The footpad of Cooper's hawks may measure in males , averaging in 42, and in females , averaging in 23. For unclear reasons, the smaller-bodied hawks found in British Columbia were found to be proportionately larger footed, median toe length between sexes of , than the larger bodied ones in Wisconsin.Rosenfield, R. N., Stewart, A. C., Stout, W. E., Sonsthagen, S. A., & Frater, P. N. (2020). ''Do British Columbia Cooper's Hawks Have Big Feet?'' British Columbia Birds, 30.

Voice

Some authors have claimed that during breeding Cooper's hawks may utter well over 40 call variations, which would rank them as having among the most varied collection of calls recorded for any raptor. However, many such variations are probably quite subtle (marginal differences in harshness, clarity, tempo and volume) and other authors have diagnosed only four overall call types.Meng, H. K. (1951). ''Cooper's Hawk, Accipiter cooperii''. Unpublished thesis, Cornell Univ., Ithaca, New York.Rosenfield, R. N., & Bielefeldt, J. (1991). ''Vocalizations of Cooper's Hawks during the pre-incubation stage''. The Condor, 93(3), 659–665. The typical call of a Cooper's hawk is a harsh, cackling yelp. This call may be translated as ''keh-keh-keh''..., males tending to have a higher pitched, less raspy and faster-paced voice than females. However, some variants uttered by males were surprisingly actually deeper than the female's version of said calls.Fitch, H. S. (1958). ''Home ranges, territories, and seasonal movements of vertebrates of the Natural History Reservation''. University of Kansas Publications Museum of Natural History, 11:63–326. A still more modulated and raucous version is given during the dawn chorus. Some studies have indicated that pairs nesting in more deeply wooded areas may vocalize more frequently due to inferior sight lines. However, hawks nesting in urban areas of