Cooper's Hawk

Accipiter cooperii

Order:
Accipitriformes
Family:
Accipitridae
Sections

Systematics

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Geographic Variation

Color and body size vary substantially across North American range (Appendix 2; 47, 42, 2). Using museum specimens often of unknown breeding status and geographic origin, Whaley and White (47) reported that the largest birds occur in the southwest, the smallest in northwest, and eastern birds were intermediate in size. They also indicated that eastern birds had longer toes perhaps due to a greater proportion of avian prey in the diet. Based on large samples of known breeding birds from northern populations in British Columbia, western and eastern North Dakota, and southern Wisconsin, Rosenfield et al. (2) found that British Columbia and western North Dakota birds were similar in size (i.e., body mass), eastern North Dakota birds were larger than birds in these two populations and the largest hawks of these four populations occurred in Wisconsin (Wisconsin birds were similar in size to the 'large' southwestern birds reported by Whaley and White [47]). Indices of size dimorphism between sexes did not vary among these four northern populations (2). Although genetic differences were found between birds in British Columbia versus the three other northern populations (16), body size differences among these four populations were attributed to the principle that smaller size is favored for hunting smaller, agile prey (predominately birds) that comprised the diet of British Columbia and western North Dakota birds versus the larger hawks in eastern North Dakota and Wisconsin that hunted larger prey (birds and mammals such as chipmunks; 2, 16). In contrast to the study by Whaley and White (47), which lacked comprehensive diet data for sampling sites, Rosenfield (48) found that toe length (as indexed by middle-toe length) was longer in proportion to body size in British Columbia versus Wisconsin, in accord with enhancing the reach of British Columbia hawks hunting mostly agile, small avian prey versus likely less agile larger (often mammalian) prey of Wisconsin hawks (49, 50).

Rosenfield et al. (2) also found that wing chords were longer in more migratory northern populations than in nonmigratory adults in British Columbia (longer wings provide more efficient flight at lower energetic costs).

Cooper's Hawks in British Columbia and North Dakota acquire darker orange or red irides more frequently and more quickly than their counterparts at known and relative ages in Wisconsin birds (42). Females in all three study sites were slower and less likely than males to acquire darkest eye colors (dark orange and red; 42).

The underparts of adults in northwestern populations average darker red than that of their eastern counterparts.

Subspecies

No subspecies, following Palmer (28). Populations in the Pacific Northwest historically were treated as Accipter cooperii mexicanus Swainson, 1831, on the basis of size differences, but size varies too inconsistently to diagnosis individuals consistently (51). Hence, that name is a junior synonym of Accipiter cooperii (Bonaparte, 1828). Additional synonyms of the specific name are Falco stanleii Audubon, 1831, and Astur fuscus Giraud, 1844.

Related Species

Within the family Accipitridae, the namesake genus, Accipiter, is sister to, albeit distantly so, the genus Circus, the harriers (52, 53), although how the morphologically similar Harpagus (which contains 2 species of kites from the Neotropics) fits into the mix has been questioned (54). Ultimately, Harpagus may be only distantly related to the clade of Accipiter + Circus (53).

A century ago, Accipiter gundlachi, the Gundlach’s Hawk of Cuba, was classified as a subspecies of A. cooperii, but its phenotype was deemed consistently different enough to warrant recognition as a separate species. These 2 species, along with A. bicolor, the Bicolored Hawk of the lowland Neotropics, and A. chilensis, the Chilean Hawk of southern South America, constitute a superspecies (55, 56). These species form a distinct clade, although A. cooperii and A. gundlachi are not separable at the barcode level, a finding that may mean that either A. gundlachi is not a species or that migratory A. cooperii occasional remain in Cuba to hybridize with A. gundlachi (57), a situation that may lead to the same conclusion.

Haughey et al. (58) recently genetically confirmed that a juvenile female accipiter caught during fall migration at Cape May, New Jersey, was the first report of a natural hybrid between a female Northern Goshawk (female) and a male Cooper's Hawk. The hybrid showed features of both Northern Goshawk and Cooper's Hawk (e.g., a white-line above eyes as in goshawk and intermediate in size between these two species). Rosenfield (1) speculated that range shifts associated with climate change, whereby Cooper's Hawks may now be more prevalent in the northern continental breeding distribution of the Northern Goshawk, may have contributed to this hybrid event.

Recommended Citation

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