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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 (conchologist), 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 (biology), canopy cover and can commonly produce up to two to four Fledge, fledglings depending on conditions. Breeding attempts may be compromised by poor weather, predators and Human impact on the environment, anthropogenic causes, in particular the use of industrial pesticides and other Organochloride, 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.
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 beak, 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 (biology), 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 Tree stump, 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 Molting, 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.
''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 Southwestern United States, 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 (biology), 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 Tibiotarsus, tarsus length, males may vary from , with an average of in museum specimens, and females from , with an average of in museum specimens. The Beak, culmen may measure from in males, averaging about , and from in females, averaging about . The Claw, 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.
''Accipiter'' species in North America are arguably the most vexing raptor to identify in the continent.Crossley, R., Liguori, J., & Sullivan, B. L. (2013). ''The Crossley ID Guide: Raptors''. Princeton University Press.Liguori, J. (2005). ''Hawks from every angle: how to identify raptors in flight''. Princeton University Press.Clark. W.S. (1984). ''Field identification of Accipiters in North America''. Birding, 16: 251–263. The other two species in North America are the smaller sharp-shinned hawk (''Accipiter striatus'') and the larger northern goshawk (''Accipiter gentilis''). Compared to the other two ''Accipiters'', Cooper's have an intermediate amount of feathering at top of the tarsus, as well as intermediate relative middle toe length and eye proportions, but have relatively the longest tail and the shortest wings of the three. The Cooper's and sharp-shinned hawk are very similar (sometimes considered almost identical) in plumage characteristics at all stages of development. Most Cooper's hawks are considerably larger than most sharp-shinned hawks. Generally, the Cooper's species is crow-sized, with the males about the size of a Fish crow, small crow and the females the size of a American crow, large crow, while most sharp-shinned hawks are about the size of a large Steller's jay, jay. Also in the hand, Cooper's hawks and sharp-shinned hawks may be fairly reliably distinguished by their sizes, with the smallest male Cooper's always being heavier and larger clawed than the largest female sharp-shinned hawk (with a 97–98% difference in dimensions of the wing and tail). However, in the field, especially when hawks must be identified in at a distance or at unfavorable angles (such as when migrating) or at a brief glance (such as when hunting), even experienced birdwatchers may not always be able to certainly distinguish the two species, especially female sharp-shins against the nearly similarly sized male Cooper's. The sharp-shinned hawk usually evidences a slimmer, slighter look, with more dainty features, and has relatively longer wings and a shorter and more squared tail with a much thinner white tip. Other slight difference may be noted in plumage via the sharp-shins lacking the capped appearance of adult Cooper's (being more hooded) and being generally slightly darker above. Juvenile sharp-shins, upon relatively leisurely study, can be seen to differ from juvenile Cooper's by having clearer supercilia, browner cheeks and less extensive whitish mottling above and also coarser streaking below extending more to belly. Bare parts, mostly distinguishable as well at close range, differ by the more centered and clearly relatively larger eyes and notably stick-like legs of the sharp-shins. However, often these features can often be difficult to impossible to discern when the hawks are seen in the wild. More distinctive in the field is the larger, more protruding head of the flying Cooper's hawks rather than the compact, rounded head of the sharp-shins which barely appear to exceed the leading edge of the wings in flight.Dunne, P., Sibley, D., & Sutton, C. (1988). ''Hawks in flight: the flight identification of North American migrant raptors''. Houghton Mifflin Harcourt (HMH). Sometimes Cooper's is considered to look like a "flying cross" in comparison to the sharp-shins. ''Accipiter'' hawks of all species are seen mostly flying with quick, consecutive wing beats and a short glide (sometimes abbreviated as “flap-flap-glide”), though the species may also soar as well. However, the sharp-shinned hawk has a more buoyant flight with faster wing beats than the Cooper's and soars with flatter wings (although again variations in the field make these characteristics far from foolproof).
As for the northern goshawk, the smallest male is still usually "clearly" larger than most large female Cooper's hawks. In the Goshutes mountains, migrant male goshawks overlapped with female Cooper's hawks only in the length of the tail and the tarsus, with the body mass especially being quite distinct. In Oregon, male goshawks averaged no less than 34% more massive than female Cooper's hawks, however the footpad of the Cooper's females was almost the same size (7% larger on average in the latter) as the male goshawks (these may be features adapted to procuring birds as prey more so as bird-hunting raptors tend to have more elongated foot morphology). Proportionately, goshawks have longer, broader wings, shorter tail and a generally more Buteo, ''Buteo''-like form overall. Adult goshawks also have broad supercilia, pale gray color on the underside and a much darker Slate, coloring on the back. Given reasonable views, adult goshawks are very different looking and hard to mistake for any Cooper's hawk. Meanwhile, the juvenile goshawk is much paler edged above than the smaller Cooper's, including a panel formed along larger wing coverts. Below, juvenile goshawks have heavier streaks of a darker brown color than juvenile Cooper's. Also, the banding on the tail is off-set on goshawks, creating a zigzag effect on the tail, unlike the even barring on the juvenile Cooper's. Again, though, female Cooper's and male goshawks can come close to the same size and the not dissimilar juvenile plumage of the two species can lead to regular misidentification, especially to those with less prior experience viewing the more scarce goshawk. The most reliable way to distinguish a large juvenile ''Accipiter'' in the field are the differing proportions of the two species, followed by the heavier streaking below and irregular tail banding of the goshawk. For the Cooper's hawk, there may be a possible and marginal overlap with the bicolored hawk (''Accipiter bicolor'') in southern Mexico and Central America. The latter species of similar form and size but at all ages is generally unmarked with bars or streaks below, also with a more or less uniform mantle. Vagrating migrant Cooper's hawks to Cuba may very rarely occur alongside another close relative, Gundlach's hawk (''Accipiter gundlachi''), which is quite similar in most aspects to Cooper's but is slightly larger with a darker hue about the back and the cap, a gray cheek, more dense and rich rufous color on the underside and wing panel in adults and darker and more heavy streaking in juvenile form.Rodríguez-Santana, F. (2010). ''Reports of Cooper's Hawks (Accipiter cooperii), Swainson's Hawks (Buteo swainsoni), and Short-tailed Hawks (Buteo brachyurus) in Cuba''. Journal of Raptor Research, 44(2), 146–150. More unlikely to be mistaken for a Cooper's hawk are some Buteoninae, buteonine hawks such as gray hawks (''Buteo plagiatus''), roadside hawks (''Rupornis magnirostris'') (in Mexico and points south) and broad-winged hawks (''Buteo platypterus'') which are all similar in size to the Cooper's as well as the slightly larger red-shouldered hawk (''Buteo lineatus''). Even the most similar buteonine hawks have notably different proportions than a Cooper's hawk, possessing relatively much longer wings and a much shorter tail. Given reasonable views, all such species are fairly to extremely different in plumage even in juvenile form.
Species account: Cooper's Hawk Accipiter cooperii
Vagrants have been recorded in Colombia.Henny, C. J. (1990). ''Wintering Localities of Cooper's Hawks Nesting in Northeastern Oregon (Lugares en Donde Pasan el Invierno Individuos de Accipiter cooperii que Anidan en el Noreste de Oregon)''. Journal of Field Ornithology, 104–107. There are several cumulative records of Cooper's hawks also appearing in Cuba at times of migration but generally the species is still considered a vagrant rather than a regularly occurring species there.
''Stopover ecology of autumn-migrating raptors in the central Appalachians''
. PhD dissertation, Pennsylvania State University, State College, PA Similarly, in Tennessee, it was found for wintering Cooper's hawks that forested areas were 73% of the habitats used, which is far more prevalent than woodland available in the environs (with only 46% remaining wooded).Lake, L. A., Buehler, D. A., & Houston, A. E. (2002). ''Cooper's Hawk non-breeding habitat use and home range in southwestern Tennessee''. In ''Proceedings of the Annual Conference of the Southeastern Association of Fish & Wildlife Agencies (SEAFWA)'', Tallahassee (Vol. 56, pp. 229–238).
Cooper's hawk may consume well over 300 prey species from across the range. This predator is known to consume vertebrate prey almost exclusively. Often smallish or medium-sized birds are the preferred food, but also many small mammals and, in more arid vicinities, lizards are regularly taken. Infrequently, frogs may be eaten, as will (rarely) insects and fish in nearly dry watercourse. Birds in general form about 50–85% of diet. One estimate is that globally birds form about 71.1% of the diet, 17.9% mammals, 8.9% reptiles and 2.1% other prey. Cooper's hawks generally prefers birds that inhabit the ground or shrub level within the local habitats. One estimate claims that most prey of Cooper's hawks weighs from , with male and female averages of .Storer, R. W. (1966). ''Sexual dimorphism and food habits in three North American accipiters''. The Auk, 83(3), 423–436. Another estimate was from for typical prey sizes, or about 5–37% the weight of males and 8–22% the weight of females, respectively. However, subsequent studies, such as those in Indiana, found prey weighing up to (such as adult Rock dove, pigeons) can be quite common in the diet of Cooper's hawks. Mean prey weights were roughly .Roth II, T. C., & Lima, S. L. (2003). ''Hunting behavior and diet of Cooper's hawks: an urban view of the small-bird-in-winter paradigm''. The Condor, 105(3), 474–483. In Oregon, the mean prey sizes of Cooper's hawk was , with larger prey was taken than in greater proportion than their occurrence in the ecosystem (indicating that they locally search out relatively large prey).Reynolds, R. T., & Meslow, E. C. (1984). ''Partitioning of food and niche characteristics of coexisting Accipiter during breeding''. The Auk, 101(4), 761–779. In Missouri, mean prey sizes were , averaging between amongst the main prey classes. Prey delivered by males averaged an estimated , while the average estimated size of prey delivered by females was . Overall, in Missouri, prey body masses were estimated to range from . One study unusually found no strong dimorphism in the foods selected by males and females.Kennedy, P. L., & Johnson, D. R. (1986). ''Prey-size selection in nesting male and female Cooper's Hawks''. The Wilson Bulletin, 110–115.
Taxonomy
Cooper's hawk was species description, formally described by the French naturalist Charles Lucien Bonaparte in 1828 from a specimen collected near Bordentown, New Jersey, 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 (conchologist), 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, Chickenhawk (bird), 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 Harrier (bird), ''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 (bird), Harpagus'' and ''Erythrotriorchis'' also appear to bear some relation. Genetic studies of three Asian ''Accipiter'' species showed that they may not be a Monophyly, 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 Eurasian sparrowhawk, 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 Eurasian sparrowhawk, 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 Glacier, 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 America, 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 beak, 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 (biology), 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 Tree stump, 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 Molting, 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 Southwestern United States, 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 (biology), 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 Tibiotarsus, tarsus length, males may vary from , with an average of in museum specimens, and females from , with an average of in museum specimens. The Beak, culmen may measure from in males, averaging about , and from in females, averaging about . The Claw, 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 Arizona do not seem to vocalize less than their rural nesting counterparts.Estes, W. A., & Mannan, R. W. (2003). ''Feeding behavior of Cooper's Hawks at urban and rural nests in southeastern Arizona''. The Condor, 105(1), 107–116. There is perhaps some evidence that individual hawk's voices may become lower pitched with age. When coming with food to the nest or while displaying during courtship, the male may let out a nighthawk-like ''kik'', apparently this call is more prevalent in pairs using thicker woods. Infrequently, females may utter the ''kik'' call as well, apparently when looking for her mate or gathering nesting materials. Many soft calls have been recorded in intimate or "conversational" interactions, exclusively between breeding pairs and between mothers and their broods. The initial call of the young is a ''cheep'' or ''chirrp'', which by the time they are fledgling young alters to a penetrating hunger call, ''eeeeeeee-oo'' or ''tseeeee-ar'' (among different transliterations).Layne, J. N. (1986). ''Observations on Cooper's Hawk nesting in south central Florida''. Florida Field Naturalist, 14:85–112. The higher pitched calls of the young may even extend to females nesting within their first year while still in immature plumage. Females have what is often thought of as their own hunger cry, ''whaaaa'', heard especially in poorer food areas, when the male appears. Nonetheless, the females ''whaaaa'' call has also been uttered in different contexts, such as during nest building and during a "postural bowing" display, and some authors inferred that it may be a means of communicating to the male that it is not dangerous for him to approach her (as female ''Accipiters'' can be dangerous to the much smaller males).Rosenfield, R. N., & Bielefeldt, J. (1991). ''Undescribed bowing display in the Cooper's Hawk''. The Condor, 93(1), 191–193. Generally, Cooper's hawks are silent outside the breeding season. Rarely, though, some males that appear to be isolated from any other hawks of their species have been known to call during winter.Rosenfield, R. N. (2018). ''The Cooper's Hawk: Breeding Ecology & Natural History of a Winged Huntsman''. Hancock House Publishers.Confusion species
''Accipiter'' species in North America are arguably the most vexing raptor to identify in the continent.Crossley, R., Liguori, J., & Sullivan, B. L. (2013). ''The Crossley ID Guide: Raptors''. Princeton University Press.Liguori, J. (2005). ''Hawks from every angle: how to identify raptors in flight''. Princeton University Press.Clark. W.S. (1984). ''Field identification of Accipiters in North America''. Birding, 16: 251–263. The other two species in North America are the smaller sharp-shinned hawk (''Accipiter striatus'') and the larger northern goshawk (''Accipiter gentilis''). Compared to the other two ''Accipiters'', Cooper's have an intermediate amount of feathering at top of the tarsus, as well as intermediate relative middle toe length and eye proportions, but have relatively the longest tail and the shortest wings of the three. The Cooper's and sharp-shinned hawk are very similar (sometimes considered almost identical) in plumage characteristics at all stages of development. Most Cooper's hawks are considerably larger than most sharp-shinned hawks. Generally, the Cooper's species is crow-sized, with the males about the size of a Fish crow, small crow and the females the size of a American crow, large crow, while most sharp-shinned hawks are about the size of a large Steller's jay, jay. Also in the hand, Cooper's hawks and sharp-shinned hawks may be fairly reliably distinguished by their sizes, with the smallest male Cooper's always being heavier and larger clawed than the largest female sharp-shinned hawk (with a 97–98% difference in dimensions of the wing and tail). However, in the field, especially when hawks must be identified in at a distance or at unfavorable angles (such as when migrating) or at a brief glance (such as when hunting), even experienced birdwatchers may not always be able to certainly distinguish the two species, especially female sharp-shins against the nearly similarly sized male Cooper's. The sharp-shinned hawk usually evidences a slimmer, slighter look, with more dainty features, and has relatively longer wings and a shorter and more squared tail with a much thinner white tip. Other slight difference may be noted in plumage via the sharp-shins lacking the capped appearance of adult Cooper's (being more hooded) and being generally slightly darker above. Juvenile sharp-shins, upon relatively leisurely study, can be seen to differ from juvenile Cooper's by having clearer supercilia, browner cheeks and less extensive whitish mottling above and also coarser streaking below extending more to belly. Bare parts, mostly distinguishable as well at close range, differ by the more centered and clearly relatively larger eyes and notably stick-like legs of the sharp-shins. However, often these features can often be difficult to impossible to discern when the hawks are seen in the wild. More distinctive in the field is the larger, more protruding head of the flying Cooper's hawks rather than the compact, rounded head of the sharp-shins which barely appear to exceed the leading edge of the wings in flight.Dunne, P., Sibley, D., & Sutton, C. (1988). ''Hawks in flight: the flight identification of North American migrant raptors''. Houghton Mifflin Harcourt (HMH). Sometimes Cooper's is considered to look like a "flying cross" in comparison to the sharp-shins. ''Accipiter'' hawks of all species are seen mostly flying with quick, consecutive wing beats and a short glide (sometimes abbreviated as “flap-flap-glide”), though the species may also soar as well. However, the sharp-shinned hawk has a more buoyant flight with faster wing beats than the Cooper's and soars with flatter wings (although again variations in the field make these characteristics far from foolproof).
As for the northern goshawk, the smallest male is still usually "clearly" larger than most large female Cooper's hawks. In the Goshutes mountains, migrant male goshawks overlapped with female Cooper's hawks only in the length of the tail and the tarsus, with the body mass especially being quite distinct. In Oregon, male goshawks averaged no less than 34% more massive than female Cooper's hawks, however the footpad of the Cooper's females was almost the same size (7% larger on average in the latter) as the male goshawks (these may be features adapted to procuring birds as prey more so as bird-hunting raptors tend to have more elongated foot morphology). Proportionately, goshawks have longer, broader wings, shorter tail and a generally more Buteo, ''Buteo''-like form overall. Adult goshawks also have broad supercilia, pale gray color on the underside and a much darker Slate, coloring on the back. Given reasonable views, adult goshawks are very different looking and hard to mistake for any Cooper's hawk. Meanwhile, the juvenile goshawk is much paler edged above than the smaller Cooper's, including a panel formed along larger wing coverts. Below, juvenile goshawks have heavier streaks of a darker brown color than juvenile Cooper's. Also, the banding on the tail is off-set on goshawks, creating a zigzag effect on the tail, unlike the even barring on the juvenile Cooper's. Again, though, female Cooper's and male goshawks can come close to the same size and the not dissimilar juvenile plumage of the two species can lead to regular misidentification, especially to those with less prior experience viewing the more scarce goshawk. The most reliable way to distinguish a large juvenile ''Accipiter'' in the field are the differing proportions of the two species, followed by the heavier streaking below and irregular tail banding of the goshawk. For the Cooper's hawk, there may be a possible and marginal overlap with the bicolored hawk (''Accipiter bicolor'') in southern Mexico and Central America. The latter species of similar form and size but at all ages is generally unmarked with bars or streaks below, also with a more or less uniform mantle. Vagrating migrant Cooper's hawks to Cuba may very rarely occur alongside another close relative, Gundlach's hawk (''Accipiter gundlachi''), which is quite similar in most aspects to Cooper's but is slightly larger with a darker hue about the back and the cap, a gray cheek, more dense and rich rufous color on the underside and wing panel in adults and darker and more heavy streaking in juvenile form.Rodríguez-Santana, F. (2010). ''Reports of Cooper's Hawks (Accipiter cooperii), Swainson's Hawks (Buteo swainsoni), and Short-tailed Hawks (Buteo brachyurus) in Cuba''. Journal of Raptor Research, 44(2), 146–150. More unlikely to be mistaken for a Cooper's hawk are some Buteoninae, buteonine hawks such as gray hawks (''Buteo plagiatus''), roadside hawks (''Rupornis magnirostris'') (in Mexico and points south) and broad-winged hawks (''Buteo platypterus'') which are all similar in size to the Cooper's as well as the slightly larger red-shouldered hawk (''Buteo lineatus''). Even the most similar buteonine hawks have notably different proportions than a Cooper's hawk, possessing relatively much longer wings and a much shorter tail. Given reasonable views, all such species are fairly to extremely different in plumage even in juvenile form.
Distribution and habitat
The Cooper's hawk's breeding range extends from southern Canada to northern Mexico. In southern Canada, they breed (but do not normally winter) in the southerly parts of the Provinces and territories of Canada, provinces of British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec to extreme southwestern Nova Scotia. They reach their northerly limits as a breeder roughly in Jasper National Park and Cedar Lake (Manitoba), Cedar Lake, Manitoba. Cooper's hawks live almost throughout the contiguous United States, excepting some parts of the southern Great Plains, as well as perhaps a bit of northwestern Maine and northernmost Montana. Their breeding range terminates just before the southern part of Gulf Coast states, south Florida, the southern tip of Texas and all but inland northwestern Mexico.Sauer, J. R., Link, W. A., Fallon, J. E., Pardieck, K. L., & Ziolkowski Jr, D. J. (2013). ''The North American breeding bird survey 1966–2011: summary analysis and species accounts''. North American Fauna, 79(79), 1–32. Their Mexican breeding range consists of northern Baja California, the mountains from eastern Sonora and Chihuahua (state), Chihuahua to Durango, also recently in northern Coahuila, formerly east into Nuevo Leon and south to Michoacán and possibly still in Guerrero. In Oaxaca, records show that the species has been recorded year-around with the first confirmed breeding reported in 2001. In winter, they are found up to the southern half of Washington (state), Washington, the southern two-thirds of Idaho and Wyoming, southern South Dakota, the southern parts of Minnesota, Wisconsin and Michigan, extreme southwestern Ontario, southwestern and southeastern New York and New England up through all but northwestern Massachusetts and to the southeastern part of New Hampshire. In winter they range regularly throughout the parts of the southern United States where they do not breed, such as all Gulf Coast areas and in south Florida. Wintering Cooper's hawks are common through essentially all parts of Mexico, becoming less regular around Guatemala and isolated spots of the border of Honduras and Nicaragua, where the species is considered "infrequent but regular" as well as in central and southern Costa Rica and perhaps northern Panama.Global Raptor Information Network. (2010)Species account: Cooper's Hawk Accipiter cooperii
Vagrants have been recorded in Colombia.Henny, C. J. (1990). ''Wintering Localities of Cooper's Hawks Nesting in Northeastern Oregon (Lugares en Donde Pasan el Invierno Individuos de Accipiter cooperii que Anidan en el Noreste de Oregon)''. Journal of Field Ornithology, 104–107. There are several cumulative records of Cooper's hawks also appearing in Cuba at times of migration but generally the species is still considered a vagrant rather than a regularly occurring species there.
Habitat
The Cooper's hawk tend to occur in various types of temperate deciduous forest and Temperate broadleaf and mixed forest, mixed forest. They are also adaptable in all seasons to Montane ecosystems, forested mountainous regions, especially foothills. The species may further make itself at home in some pure Pinophyta, conifer forest, including the extreme southern part of the taiga but also in many parts of the west.Garner, H. D. (1999). ''Distribution and habitat use of Sharp-shinned and Cooper's hawks in Arkansas''. Journal of Raptor Research, 33(4), 329–332.Kennedy, P. L. (1988). ''Habitat characteristics of Cooper's Hawks and Northern Goshawks nesting in New Mexico''. In ''Proceedings of the Southwestern Raptor Management Symposium and Workshop'' (R. Glinski, B. G. Pendleton, M. B. Moss, B. A. Millsap, and S. W. Hoffman, Editors). National Wildlife Federation, Washington, DC, USA. pp. 218–227. The species can habituate favorably while breeding to various kinds of open woodlands, including small woodlots, riparian woodlands in Semi-arid climate, dry country, pinyon pine, pinyon woodlands, Agriculture, farmlands and floodplains.Rosenfield, R. N., Bielefeldt, J., Anderson, R. K., & Papp, J. M. (1991). ''Status reports: accipiters''. In ''Proceedings of Midwest Raptor Management Symposium Workshop''. Nat. Wildl. Fed., Washington, DC (pp. 42–49). In fact, some authors felt the species increased locally in wooded parts of the Rocky mountains after human habitat fragmentation of once continuous woodland areas. Adaptability to forest fragmentation has also been reported in other parts of the range. In denser forest areas, these hawks tend to prefer easy access to Woodland edge, edges, Clearing (geography), clearings, Dirt road, roads and Freshwater ecosystem, waterways.Reynolds, R. T., Meslow, E. C., & Wight, H. M. (1982). ''Nesting habitat of coexisting Accipiter in Oregon''. The Journal of Wildlife Management, 124–138. For example, average distance from waterways away from nests in Wisconsin and Utah was , respectively.Rosenfield, R. N., & Anderson, R. K. (1983). ''Status of the Cooper's Hawk in Wisconsin''. Bureau of Endangered Resources, Wisconsin Department of Natural Resources.Hennessy, S. P. (1978). ''Ecological relationships of accipiters in northern Utah-with special emphasis on the effects of human disturbance''. M.S. thesis, Utah State Univ., Logan, Utah. However, in the Appalachians, there seemed to no detectable preference for access to water.Titus, K., & Mosher, J. A. (1981). ''Nest-site habitat selected by woodland hawks in the central Appalachians''. The Auk, 98(2), 270–281. Forest edges, in particular, tend to be key as these are peak hunting grounds for these hawks.Fischer, D. L. (1986). ''Daily activity patterns and habitat use of coexisting Accipiter hawks in Utah''. Ph.D. dissertation, Brigham Young University, Provo, UT, USA. Cooper's hawks usually occur at elevations from sea-level to , more infrequently up to . In the American southwest and northwestern Mexico, they are commonly considered a bird of wooded foothills, often dwelling above . Although they often live in areas where deciduous trees are predominant, almost throughout the range they are often attracted to stands of conifers, which, due to their density, provide more extensive shelter and perhaps a more sturdy nesting site. Therefore, in areas such as Massachusetts and Wisconsin, they most often used stands of Pinus strobus, white pines (''Pinus strobus''). Additional Wisconsin studies showed that exotic conifer stands now support many Cooper's hawks even where native woodland is available.Rosenfield, R. N., Bielefeldt, J., Sonsthagen, S. A., & Booms, T. L. (2000). ''Comparable reproductive success at conifer plantation and non-plantation nest sites for Cooper's Hawks in Wisconsin''. The Wilson Journal of Ornithology, 112(3), 417–421. Tall, native deciduous tree stands may still be used extensively elsewhere, i.e. Fagus grandifolia, American beeches (''Fagus grandifolia'') in New York (nearly 40% of nest trees used) and oaks in Maryland (60% of trees used as nests). This species often prefers fairly mature forest, i.e. in two different areas of Oregon, the Cooper's hawks preferred areas with trees of 30–60 years old (and 656 trees per ha) and 50–70 years old (and 1159 trees per ha), respectively. On average, the number of trees per hectare in Arkansas were found to be 935.7. Canopy coverage is key to nesting Cooper's hawks, needing to be at minimum about 55–70%, averaging 55% in Wisconsin and 69.8% in Arizona.James, R. D. (1984). ''Habitat management guidelines for Ontario's forests nesting accipiters, buteos and eagles''.Boal, C. W., & Mannan, R. W. (1998). ''Nest-site selection by Cooper's Hawks in an urban environment''. The Journal of wildlife management, 864–871. More so than breeding habitat, wintering habitat seems to be highly opportunistic. They may be found in any environment with some trees, including Woodland, open woods, parkland and Shrubland, scrub areas. In Central America, wintering Cooper's hawks have been recorded in unusual habitats such as stunted cloud forest and treeless montane grassland. In most parts of the range, Cooper's hawks have shown to be somewhat adaptive to all gradients of Land development, human development, including urbanized areas and can even nests in many cities.Stahlecker, D. W. & Beach, A. (1979). ''Successful nesting by Cooper's Hawks in an urban environment''. Inland Bird Banding News, 51:56–57.Murphy, R. K., Gratson, M.W., & Rosenfield, R. N. (1988). ''Activity and habitat use by a breeding male Cooper's Hawk in a suburban area''. Journal of Raptor Research, 22:97–100. They were once thought to be averse to cities and towns, but are now fairly common urban and suburban birds even when nesting. The species may even making use of isolated trees in suburbs, industrial parks and Strip mall, strip and shopping malls though large urban parks and other Peri-urbanisation, available wooded habitat is usually preferred in such areas when nesting.Beebe, F. L. (1974). ''Field studies of the Falconiformes of British Columbia: vultures, hawks, falcons, eagles''. Victoria: Occas. Pap. Brit. Columbia Prov. Mus. No. 17.Stout, W. E. & Rosenfield, R.N. (2010). ''Colonization, growth, and density of a pioneer Cooper’s Hawk population in a large metropolitan environment''. Journal of Raptor Research, 44:255–267. The cities provide plenty of prey species such as Columbidae, pigeons and doves and invasive species of bird for the Cooper's hawk to prey on. Evidence from a well-studied population in the city of Tucson, Arizona shows that Cooper's hawks are now considerably more common within the city than elsewhere in the surrounding regions. Despite the success of Cooper's hawks in Tucson, attempts to find breeding activity in Phoenix, Arizona, Phoenix and Casa Grande, Arizona, Casa Grande were unsuccessful, it is thought that the ambient temperature was too high or beyond thermal tolerance levels. Although more adaptable in habitat than the sharp-shinned hawk, studies from Pennsylvania have indicated that the species still more often than not prefers sizeable tracts of woodland for breeding and migrating to fragmented, developed areas.Goodrich, L.J. (2010)''Stopover ecology of autumn-migrating raptors in the central Appalachians''
. PhD dissertation, Pennsylvania State University, State College, PA Similarly, in Tennessee, it was found for wintering Cooper's hawks that forested areas were 73% of the habitats used, which is far more prevalent than woodland available in the environs (with only 46% remaining wooded).Lake, L. A., Buehler, D. A., & Houston, A. E. (2002). ''Cooper's Hawk non-breeding habitat use and home range in southwestern Tennessee''. In ''Proceedings of the Annual Conference of the Southeastern Association of Fish & Wildlife Agencies (SEAFWA)'', Tallahassee (Vol. 56, pp. 229–238).
Behavior
The Cooper's hawk is a typical ''Accipiter'' in all respects. This species tends to be active earlier in the morning than sharp-shinned hawks and Eurasian sparrowhawks (''Accipiter nisus'') and is generally much more likely to be active in the morning than in the afternoon. These hawks may readily take to conifers to Bird#Resting and roosting, roost, generally sleeping with their heads tucked in. During daylight hours, they tend to Preening (bird), preen while sitting on a perch about 11 times a day, and may take about 1–20 minutes to do so. When attaining water to drink, Cooper's hawks appear to prefer to come to relatively secluded waterways. In more arid regions, Cooper's hawks may seek out artificial body of water, bodies of water to drink from (especially in passage). Although a rare behavior, there are now several records of juvenile hawks of the species Prone position, proning wherein they lie on their backs along a branch (or rarely the ground), apparently as a form of Sunning (behaviour), sunning.Rosenfield, R. N. & Sobolik, L.E. (2014). ''Proning behavior in Cooper's Hawks (Accipiter cooperii)''. Journal of Raptor Research, 48:294–297. Cooper's hawks may come to walk on ground to gather nesting materials as well as to hunt.Rosenfield, R. N., Bielefeldt, J. & Cary, J. (1991). ''Copulatory and other pre-incubation behaviors of Cooper's Hawks''. Wilson Bulletin, 103:656–660. Cooper's hawks have a well-developed muscle mass that powers their flight, especially helping with acceleration during hunts and when carrying heavy prey. However, some other non-raptorial birds may have similar muscularity relative to their mass, such as the Canada goose (''Branta canadensis'') and even pied-billed grebes (''Podilymbus podiceps''), and these ample muscle masses may be correlated with Bird migration, migratory (rather than hunting) behavior.Marsh, R. L. & Storer, R.W. (1981). ''Correlations of flight-muscle size and body mass in Cooper's Hawk: a natural analogue of power training''. Journal of Experimental Biology, 91:363–368. Cooper's hawks have been recorded as engaging in an exaggerated, nighthawk-like flight in non-courtship circumstances, such as during migration or by recent fledglings. During the late nesting stage, parent Cooper's hawks were recorded during daylight in Utah to engage in soaring flight 8.4% for males and 8.1% of the time for females with a further 6.4% and 2.8% of the time in different kinds of flights, perching the remainder of the time (about 2–6 minutes at each perch interspersed with brief flights). Another study found 13.7% and 10.7% of daylight at this later breeding stage to be in flight, the rest of time perching, with occasional inactive perching spells of around 15–40 minutes. However, that inactivity could last up to 5 hours during heavy rainfall. Breeding adults generally engage in agonistic behavior when an interloper of their sex is present; 11 responses showed that males responses consisted 64% of the provocations, 9% of the time by females and both members 27% of the time.Boal, C. W. (2001). ''Agonistic behavior of Cooper's Hawks''. Raptor Research 35:253–256. Frequent aggressive interactions were recorded between females, often yearling and second year vs older females.Lien, L. A., Millsap, B. A., Madden, K., & Roemer, G. W. (2015). ''Male brood provisioning rates provide evidence for inter‐age competition for mates in female Cooper's Hawks Accipiter cooperii''. Ibis, 157(4), 860–870. The Cooper's hawk's threat display appears to consist of them lowering their heads, raising their "crest" (capital tract), stretching out their wings, spreading the tail and engaging in vocalizations. Stress levels, as indicated by a study of corticosterone levels, were considered quite high when hawks are being handled by researchers, particularly in males (indicating that they experience higher levels of stress than females). The Cooper's hawk is subject to frequent Mobbing (animal behavior), mobbing by various birds and some mammals, with good cause, but evidence shows that even main prey types like Jay (bird), jays will sometimes shy away from engaging in full-fledged mobbing of a Cooper's, perhaps due to the risk in closely approach this very agile predator, which can in an instant suddenly turn and kill a member of the mob. Therefore, less dangerous hawks such as ''Buteos'' are mobbed more vigorously than the more dangerous Cooper's. Many potential prey will confine their response to a hawk of this species to vocal scolding and/or attempt escape before an attack occurs.Migration
Like a majority of diurnal birds of prey in the Northern Hemisphere, the Cooper's hawk is a Bird migration, partial migrant. They tend to be most migratory in the north and largely to partially sedentary elsewhere. With individual exceptions, hawks of the species largely migrate out of nearly all of their range in southern Canada as well as cooler parts of the Pacific Northwest, essentially all of Montana and northern parts of surrounding states, the Dakotas (but for southern South Dakota), the northern parts of the Great Lakes region, Great Lake states, northern New York and much of New England. Despite being classed as sedentary, banding studies have revealed that many Cooper's hawks south of the typical migratory populations engage in some variety of seasonal winter movements.Goodrich, L. J., Farmer, C.J., Barber, D.R., & Bildstein, K.L. (2012). ''What banding tells us about the movement ecology of raptors''. Journal of Raptor Research, 46: 27–35. Migrants in the Florida Keys were determined via Stable isotope ratio, stable isotopes to have originated from mid-Atlantic states and the southeastern United States both (largely) south of the typical migratory range. While females in the urban areas of Tucson were sedentary (99%), about 6% of the females outside of the urban areas did not remain on their breeding grounds during winter.Millsap, B. A. (2018). ''Female recruitment in an urban subpopulation of Cooper's Hawks (Accipiter cooperii) in central New Mexico''. PhD dissertation, New Mexico State University. Las Cruces, NM, USA. In British Columbia, many adults are non-migratory but juveniles do tend to migrate.Meehan, T. D., Rosenfield, R. N., Atudorei, V. N., Bielefeldt, J., Rosenfield, L. J., Stewart, A. C., Stout, W.E. & Bozek, M. A. (2003). ''Variation in hydrogen stable-isotope ratios between adult and nestling Cooper's Hawks''. The Condor, 105(3), 567–572. From the Great Lakes region in particular, migrants appear to disperse in multiple directions to the south. Multi-directional movements, even to the north as well as potentially any other direction, are more common than previously thought in this and other migratory raptors, which has been previously described as "inefficient and indirect method of 'homing'". However, reaching regions where appropriate habitat and prey is available is probably far more significant in seasonal movements to birds of prey than climatic concerns.Hoffman, S. W., Smith, J. P., & Meehan, T. D. (2002). ''Breeding grounds, winter ranges, and migratory routes of raptors in the mountain west''. Journal of Raptor Research, 36(2), 97–110. Fairly strong evidence has been found of habitual northbound migration by Cooper's hawks from Central California, Central and Southern California, usually over fairly short distances, often less than . However, the three longest distance movements from southern California were all northbound, i.e. .Bloom, P. H., McCrary, M. D., Papp, J. M., & Thomas, S. E. (2017). ''Banding Reveals Potential Northward Migration of Cooper's Hawks from Southern California''. Journal of Raptor Research, 51(4), 409–416. Cooper's hawks originating from Northern California do generally migrate south, mostly wintering in Mexico though sometimes covering up to to Central America. In Lansing, Michigan, evidence has been found of individual Cooper's hawks being annually devoted to the same wintering grounds, presumably due to their high quality. Migratory movements in the autumn are generally between late August to mid-October, peaking at the end of September and beginning of October in the Eastern United States, east, but sometimes migration extend into November.Mueller, H. C., Mueller, N. S., Berger, D. D., Allez, G., Robichaud, W., & Kaspar, J. L. (2000). ''Age and sex differences in the timing of fall migration of hawks and falcons''. The Wilson Bulletin, 214–224. Meanwhile, spring northward migration may be any time from the end of February to May, with the last ones leaving Mexico in April and very late individuals were passing over south Texas in late May. Generally, spring migration is more dispersed and less consistent than fall migration. There is evidence from the Great Lakes region that spring migration is occurring sooner due to Global warming, warming temperatures in recent years. Passage appears to be timed to coincide with that of their main prey, medium-sized birds. In migration, first-year juveniles precede two-year-old hawks which themselves precede adults when moving south in fall. Furthermore, females of all ages tend to migrate sooner and spend longer in winter quarters than like-age males, the latter staying relatively north and traveling back again earlier.Hull, J. M., Pitzer, S., Fish, A. M., Ernest, H. B., & Hull, A. C. (2012). ''Differential migration in five species of raptors in central coastal California''. Journal of Raptor Research, 46(1), 50–56. Interestingly, the sharp-shinned hawk (despite the even more dimorphic migration times between sexes) showed no strong difference in distance on migration between the sexes, unlike female Cooper's which sometimes can move considerably further than males. At regular western migration sites, the average difference of passage timing for Cooper's hawks of the earlier females and later males of like-age was five days.DeLong, J., & Hoffman, S. W. (1999). ''Differential autumn migration of Sharp-shinned and Cooper's hawks in western North America''. The Condor, 101(3), 674–678. In the Marin Headlands, migration of the sexes differed by 6 days in juvenile, first-year females and males and by 11 days in older females and males. Like other ''Accipiters'' (but unlike falcons), Cooper's appear to not start moving until day is warmer and thermals can be used. During migration they favor mountain ridges and coastlines, which coincide with migratory raptors routes in general. This species can seem to cross some bodies of water unlike most sharp-shinned hawks but seldom do so over wide bodies of water. However, they have been seen to turn up in such oceanic vicinities as the Florida Keys and Cuba, and so are capable of crossing larger than usual bodies of water. It is thought that Cooper's hawks also avoid the Great Plains while migrating as well. Like many other raptors, Cooper's hawks favor strong Wind direction, northwesterly winds during autumn passage. At coastal migration sites like Cape May, first year Cooper's hawks are far more regularly encountered than older individuals, with the juvenile Cooper's accounting for 92.7% of recorded individuals of the species (juveniles of various other raptor species also generally seem to favor coastal over montane migration when it is available). In Cape May, Cooper's hawks are the third most commonly recorded raptor species in passage behind the sharp-shinned hawk and the American kestrel (''Falco sparverius'') but are far less than numerous in migration or in winter in the nearby Delaware Bayshore locations of New Jersey than various other raptor species.Sutton, C., & Kerlinger, P. (1997). ''The Delaware bayshore of New Jersey: a raptor migration and wintering site of hemispheric significance''. Journal of Raptor Research, 31, 54–58. Interestingly, in the Manzano Mountains and Goshute Mountains, juvenile sharp-shinned hawks were roughly twice as numerous as juvenile Cooper's hawks but the number of adults seen passing through of the two species was roughly the same. At the Hawkwatching, hawkwatch in Cedar Grove, Wisconsin, the Cooper's hawk was not among the most regular species, being the 6th most frequently most recorded species. In central and southwestern Idaho, Cooper's hawk accounted for relatively few of the recorded raptors, i.e. 3.45% of 748 migrating raptors. A similarly low volume was observed relative to other bird of prey species in Yellowstone National Park, where the Cooper's was only the 9th most frequently observed out of 17 species and averaged only 50 hawks in passage over the course of autumn. Nonetheless, the Cooper's hawk was second only to sharp-shinned hawk as the most frequently recorded species seen migrating at nine major hawkwatchs throughout the western United States (and 1 in Canada) and, unlike the sharp-shinned, has shown a trend of increase in numbers overall in recent decades, despite some declines in numbers at Grand Canyon, Lipan Point and Bridger Range.Smith, J. P., Farmer, C. J., Hoffman, S. W., Kaltenecker, G. S., Woodruff, K. Z., & Sherrington, P. F. (2008). ''Trends in autumn counts of migratory raptors in western North America. State of North America's birds of prey''. Series in Ornithology, 3, 217–251. The Cooper's hawk was the 7th most often recorded raptor at four migration sites along the Gulf Coast, being much more frequently identified in the site at Veracruz, Mexico than the ones in the United States, but showed an annual stability of numbers that many of the more numerous raptors (including sharp-shinned hawks) in passage did not. Along the Blue Mountain (Pennsylvania), Kittatinny Ridge in Pennsylvania, studied Cooper's hawks that were migrating from further north spent only 12% of the day actually migrating, devoting the remainder of their time to perching and hunting along their passage. Adipose tissue, Fat stores were measured to consist of 4–12% of the body mass of migrants, being higher in autumn than in spring, and higher on average in adults over younger hawks and in females over males. Migration speeds appear to be largely similar to those of other raptors, with average speeds of , but one migrating from Colorado was recorded to cover about per day.Broun, M. & Goodwin, B.V. (1943). ''Flight speeds of hawks and crows''. Auk, 60 :487–492. Typically Cooper's hawk migrate singly but sometimes can be seen in groups of two to five. Flock (birds), Flocking is not typically engaged in by raptors who migrate using powered flight, such as ''Accipiters'', falcons and Northern harrier, harriers, but many ''Buteo'' hawks do form loose flocks.Black, R. W., & Borowske, A. (2009). ''The morphology, flight, and flocking behaviour of migrating raptors''. Evolutionary Ecology Research, 11(3), 413–420. 96.3% of 806 observed Cooper's hawk seen migrating in Johnson County, Iowa were solitary, although 30 migrating pairs were seen together.Diet
Hunting methods
Cooper's hawks are known as bold and aggressive predators. Given their dietary habits, these hawks bore a poor reputation well into the 20th century, with one account describing the species as "noxious", an "avian outlaw" and "a relentless tyrant and murderer of small birds". Another describes the species as "bloodthirsty" and a "villain". Early accounts underestimated the opportunistic nature of the Cooper's hawks’ hunting behavior and provided little insight into the actual effect the hawks have on their prey. The maximum hunting range was estimated at in Michigan and in Wyoming.Craighead, J. J. and F. C. Craighead, Jr. (1956). ''Hawks, owls and wildlife''. Stackpole Co. Harrisburg, PA. In another Michigan study, most Cooper's hawks were found to be flying from their wooded nests to hunt on agricultural ground.Hamerstrom Jr, F. N., & Hamerstrom, F. (1951). ''Food of young raptors on the Edwin S. George Reserve''. The Wilson Bulletin, 16–25. Males in New York usually covered more than , sometimes up to , during hunting efforts when flying away from the nest area. Due to scattered prey availability in North Florida, females were nearly nomadic, wandering anywhere where food could be accessed (i.e. Poultry farming, chicken farms, feedlots, bird feeders, etc.), while males were more typically devoted to hunting on their regular home range. During hunts, Cooper's hawks rely on agile, twisting flights between bouts of perching and scanning, their flight suddenly picking up speed upon approach to the prey. Hunting hawks typically use Woodland edge, forest edge, open woodland and fencelines and such while hunting. In southwestern Tennessee, the preferred hunting habitats in the non-breeding season were forest, then woodland edge, then lastly Open terrain, open country.Lake, L. A., Buehler, D. A., & Houston, A. E. (2002). ''Cooper's Hawk non-breeding habitat use and home range in southwestern Tennessee''. In Proceedings of the Annual Conference of the Southeastern Association of Fish & Wildlife Agencies (SEAFWA), Tallahassee (Vol. 56, pp. 229–238). Near Stevens Point in Wisconsin, males prefer to hunt in quiet woods while females preferred to stay within of the nest making males a more common sight. This differed strongly in Tucson where hawks while hunting mostly in manmade environments such as residential areas, regional parks, and golf courses more so than they were prevalent in the environment, though usually where there were large (albeit usually non-native) trees.Boal, C. W., & Mannan, R. W. (2000). ''Cooper's hawks in urban and exurban areas: a reply''. The Journal of Wildlife Management, 601–604.Boggie, M. A., & Mannan, R.W. (2014). ''Examining seasonal patterns of space use to gauge how an accipiter responds to urbanization''. Landscape and Urban Planning, 124: 34–42. The Cooper's hawk does attack birds attracted to bird feeders with a fair amount of frequency. However, data from Indiana showed that birds using bird feeders were at no greater risk of attack than those in random transects, and the effect Cooper's can have on feeder birds may be at times exaggerated.Roth, T. C., Vetter, W. E., & Lima, S. L. (2008). ''Spatial ecology of wintering Accipiter Hawks: Home range, habitat use, and the influence of bird feeders''. The Condor, 110(2), 260–268. If it sees birds when flying, a hunting hawk does not fly directly to them but instead circles around to available trees and bushes often perching for a few moments before launching its attack. If birds become aware of it, the hawk will tend to quickly gain height in hopes of intercepting some prey. It was found compared to some other North American raptors who are more likely to watch for prey on the ground and/or in the open, that the Cooper's hawk had a rather enlarged Visual field, binocular field. During hunts, these hawks may suddenly alight when detecting an available mammal. Sometimes, Cooper's hawks will engage in Pack hunter, tandem hunts with one dashing around after the prey while another waits on the other side of a tree trunk or wooded thicket. Many birds are caught when they inadvertently fly around a tree where a hawk is inconspicuously perched. Young Cooper's are impetuous about crashing into bushes after prey, sometimes even into thorny cover such as barberries, whereas adults are said to be more "prudent". They may chase prey into cover or from bush to bush. The first instance of non-piratical Scavenger, scavenging on carrion was recorded when a Cooper's hawk was seen eating at a white-tailed deer (''Odocoileus virginianus'') carcass. When hunting bats, they can follow all twists and turns, and may succeed in capture in up to 90% of hunts. Much like goshawk, sometimes Cooper's hawks will capture Cottontail rabbit, rabbits by pursuing on the ground, half-running, half-flying. Other on-foot hunting efforts, especially when chasing New World quail, quail, have been detected as well. When hunting House sparrow, sparrows, Cooper's hawks may make multiple passes on a bush before success and the efforts can take up to 45 minutes. During hunts of rock doves (''Columba livia)'' in urban areas, Cooper's hawks have been seen to engage in open air Bird flight, stoops to capture the prey.Mead, R. A. (1963). ''Cooper's Hawk attacks pigeon by stooping''. Condor, 65:167.Clark, R. J. (1977). ''Cooper's Hawk hunting in the city''. Auk, 94:142–143. An unusual Harrier (bird), harrier-like flight was seen in be engaged in by a Cooper's hawk before an attack on Grebe, aquatic prey in a marsh. Most prey is killed by repeatedly kneading the talons, with the kneading sometimes going on even after death, although in some cases birds are plucked while still alive.Jones, S. (1979). ''Habitat management series for unique or endangered species''. Report No. 17, the Accipiters. USDI-BLM Tech. Note 335. Despite its Gracility, gracile appearance, the Cooper's hawk, like the northern goshawk, is extremely powerful for its size and presumably able to capture larger prey relative to its size than other raptors such as falcons and ''Buteos'' (including red-tailed hawks (''Buteo jamaicensis'')) due to its unusually high-speed foot velocity and resulting impact during prey captures.Goslow, G. E. (1971). ''The attack and strike of some North American raptors''. The Auk, 88(4), 815–827. At times, after capture, Cooper's hawk have been seen to hold still living prey underwater, presumably trying to drown it.Forbush, E. H. (1927). ''Birds of Massachusetts and other New England states. Part II''. Land birds from Bobwhites to Grackles. Mass. Dept. Subsequent to the preys’ demise, they may eat the victim head first, followed by the Organ (anatomy), viscera, with the meat eaten lastly. Like other raptors who most regularly take birds, the Cooper's hawk was profiled in a study as an "attacker" rather than a "searcher" (i.e. mammal-hunters such as ''Buteos''). "Attackers" such as ''Accipiters'' and large falcons usually had lower average hunting success rates, which averaged among the attacker species at 27%, due to the difficulty of capturing the prey. 33% of 45 observed hunts in a study in Missouri were successful. In Terre Haute, Indiana, about 23% of attacks by male Cooper's hawks and 20% by females were successful and were far more prone to being carried out in relatively open areas than those of nearby sharp-shinned hawk.Roth II, T. C., & Lima, S. L. (2006). ''Predatory behavior and diet of wintering male Cooper's Hawks in a rural habitat''. Journal of Raptor Research, 40(4), 287–290. Post-fledgling Pack hunter, parties of hawks in Wisconsin were seen to hunt in sibling groups of 2–4, mainly pursuing Eastern chipmunk, chipmunks, and were observed to succeed in 56% of 18 hunting attempts.Nicewander, J., & Rosenfield, R. N. (2006). ''Behavior of a brood of post-fledging Cooper's Hawks: non-independence of sibling movements''. Passenger Pigeon, 68, 321–343. During the first six weeks after the young hatch, in New York, it was estimated that a male Cooper's hawk would need to procure about 66 prey items over the period.Meng, H. (1959). ''Food habits of nesting Cooper's hawks and goshawks in New York and Pennsylvania''. The Wilson Bulletin, 71(2), 169–174. In these first six weeks in California, it was thought a minimum of would be required per nestling per day.Fitch, H. S., Glading, B., & House, V. (1946). ''Observations on Cooper Hawk nesting and predation''. California Fish and Game, 32(3), 144–154.Prey spectrum
Cooper's hawk may consume well over 300 prey species from across the range. This predator is known to consume vertebrate prey almost exclusively. Often smallish or medium-sized birds are the preferred food, but also many small mammals and, in more arid vicinities, lizards are regularly taken. Infrequently, frogs may be eaten, as will (rarely) insects and fish in nearly dry watercourse. Birds in general form about 50–85% of diet. One estimate is that globally birds form about 71.1% of the diet, 17.9% mammals, 8.9% reptiles and 2.1% other prey. Cooper's hawks generally prefers birds that inhabit the ground or shrub level within the local habitats. One estimate claims that most prey of Cooper's hawks weighs from , with male and female averages of .Storer, R. W. (1966). ''Sexual dimorphism and food habits in three North American accipiters''. The Auk, 83(3), 423–436. Another estimate was from for typical prey sizes, or about 5–37% the weight of males and 8–22% the weight of females, respectively. However, subsequent studies, such as those in Indiana, found prey weighing up to (such as adult Rock dove, pigeons) can be quite common in the diet of Cooper's hawks. Mean prey weights were roughly .Roth II, T. C., & Lima, S. L. (2003). ''Hunting behavior and diet of Cooper's hawks: an urban view of the small-bird-in-winter paradigm''. The Condor, 105(3), 474–483. In Oregon, the mean prey sizes of Cooper's hawk was , with larger prey was taken than in greater proportion than their occurrence in the ecosystem (indicating that they locally search out relatively large prey).Reynolds, R. T., & Meslow, E. C. (1984). ''Partitioning of food and niche characteristics of coexisting Accipiter during breeding''. The Auk, 101(4), 761–779. In Missouri, mean prey sizes were , averaging between amongst the main prey classes. Prey delivered by males averaged an estimated , while the average estimated size of prey delivered by females was . Overall, in Missouri, prey body masses were estimated to range from . One study unusually found no strong dimorphism in the foods selected by males and females.Kennedy, P. L., & Johnson, D. R. (1986). ''Prey-size selection in nesting male and female Cooper's Hawks''. The Wilson Bulletin, 110–115.
Birds
Predation rates and passerines
Birds are by far the leading prey for Cooper's hawks in most areas. A wide diversity of birds, considerably over 250 species, are known to be taken, constituting more than three-quarters of known prey species for these hawks. A Cooper's hawk is estimated to kill an average of two birds a day, or 700 birds a year. Although prior data mostly reflected the taking of adult birds, a study in Wisconsin revealed that Cooper's hawks may largely take young of the year, mostly fledglings but also not infrequently nestlings, during the breeding season. 74% of ageable bird prey in this study were young of the year.Bielefeldt, J., Rosenfield, R. N., & Papp, J. M. (1992). ''Unfounded assumptions about diet of the Cooper's Hawk''. The Condor, 94(2), 427–436. Similarly, in Michigan during summer, immature birds were more than 2.5 times more often delivered to Cooper's hawk nests than adult birds. In one case, a Cooper's hawk was seen to fly away with an entire occupied nest of American goldfinches (''Spinus tristis''). One study determined that birds that nest in the canopy (biology), canopy level tended to nest fairly close to this hawk but those with mid-level, shrub level and ground level nests nested farther away, indicating that non-canopy-nesting birds are generally taken during the breeding season. Key to prey selection for Cooper's hawk is the availability and abundance of birds in a given region. Therefore, the extremely numerous American robin (''Turdus migratorius'') appears to be the most widely reported prey species. Robins were the leading prey species in northwestern Oregon, at 19.6% of 281 prey items, Lopez Island, Washington (state), Washington, 23.4% of 107 prey items, in Victoria, British Columbia, at 34.6% of 2896 prey items and prominent but ranked second also in California (Berkeley, California, Berkeley and Albany, California, Albany) food studies, 24.5% of 1057 prey items.Cava, J. A., Stewart, A. C., & Rosenfield, R. N. (2012). ''Introduced species dominate the diet of breeding urban Cooper's Hawks in British Columbia''. The Wilson Journal of Ornithology, 124(4), 775–782. The robin is regularly hunted in all seasons due to its commonality in exurban regions, with both adults, at estimated averages of when taken, and young being relatively easy for them to access. Beyond the common robin, nearly all Thrush (bird), thrushes in North America (excluding one Gray-cheeked thrush, species whose breeding range is largely north of the Cooper's range and one Bicknell's thrush, rare, little-studied species) are opportunistically hunted by Cooper's hawks.Sherrod, S. K. (1978). ''Diets of North American Falconiformes''. Raptor Res, 12(3/4), 49–121.Reynolds, R. T. (1978). ''Food and habitat partitioning in two groups of coexisting Accipiter''. Thesis. Dept of Fish and Wildlife. The closest rival to the robin in being most widely taken as prey for Cooper's hawks may be the common starling (''Sturnus vulgaris''), a Invasive species, non-native bird in North America with mean weights when taken of . The starling was the main food for these hawks in Ithaca, New York, at 28.2% of 857 prey items, and Terre Haute, Indiana, at 56.5% of 57 prey items, and taken in large but somewhat secondary numbers in Missouri, Michigan, and Victoria, British Columbia. In the urban environment of Terre Haute, it was found that starlings were taken in almost the same proportion as starlings were of all birds observed by researchers (i.e. they were 60% of 2146 individual birds seen).