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Tucson Audubon Society Sharp-shinned
and Cooper’s Hawks Before getting into the differences between these two birds, a note or two is in order. Sharp-shinned and Cooper’s Hawks are accipiters which is defined to mean agile, short-winged, long-tailed forest raptors. When soaring, they are readily identified by exhibiting several quick wing beats followed by a glide. Three accipiter species occur in North America - our two featured here plus the Northern Goshawk. The adult Goshawk should not be confusing due to its huge size, barrel-shaped chest and distinctive plumage. Immature Goshawks have more pronounced white eyebrows, much heavier breast streaking, and narrower white terminal tail bands than young Cooper’s Hawks. The juvenile plumage bars on the retrices (tail feathers) are nearly aligned in the Cooper’s Hawk, but are offset in Goshawks, yielding a zigzag effect. Goshawks have proportionately longer wings and shorter tails than the other two accipiters. They flap their wings fewer times for a given speed and are fast and powerful fliers. In our area, Goshawks are much more limited in numbers and are usually observed only in or close to montane regions. Determining whether an accipiter is a Sharp-shinned or a Cooper’s Hawk can be more demanding. Size can sometimes make things easy. Female Cooper’s are larger and look it, while male Sharpies are small. The other sexes of the pair do not overlap in size but can appear to in the field. Female Cooper’s Hawks are one-third larger than males, with western birds significantly smaller than eastern. Male Sharp-shinned Hawks average 57% of the body mass of females, the most sexually dimorphic of all North American raptors. In soaring birds, it helps to draw an imaginary line across the leading edge of the wings and to observe how much the head and neck project beyond it. The Cooper’s bulky head and neck protrude noticeably beyond this line, while on the Sharp-shinned they will not. With practice this method seems to work well, aided by the fact that the Sharp-shinned tends to thrust its “wrists” forward. The much touted squareness of the tail can work nicely (Cooper’s have rounded tail corners, while Sharpies have a thin rectangular tail shape), but not when the bird has its tail fanned in certain ways. A rule of thumb might be that a distinctly squared tail will probably allow elimination of a bird from being a Cooper’s, but a rounded tail does not safely eliminate it from being a Sharp-shinned. A good field mark to look for in perched birds is the location of the eye in a profile view. The bulkier neck and head of the Cooper’s Hawk, with feathers often slightly raised at the rear of the crown make the eye appear very close to the bill, while the Sharpie’s eye will appear closer to the center. This particular identification tool seems to be very apparent at times, yet may be ambiguous at others. This same attribute is said to cause the eye to appear small on the Cooper’s, giving it a fierce look. The correspondingly larger appearing eye of the Sharp-shinned gives it a more gentle look. Another perched field mark is the contrast between crown and back in adults. The Cooper’s blackish crown is darker than their backs and shows a sharp line of contrast with the paler nape. The Sharp-shinned has a crown the same color as the back without the line of contrast at the nape. Cooper’s Hawks of all ages have a broader, more defined white terminal band to the tail. Breast streaking on juvenile Cooper’s Hawks is finer and sharper, and does not extend to the belly. The legs of the Cooper’s are stout, while the Sharpie has “sticklike” legs with the tarso-metatarsus laterally compressed, hence the name “Sharp-shinned.” The Cooper’s Hawk derives its name from William C. Cooper, a New York scientist and father of James C. Cooper, for whom the Cooper Ornithological Society is named.
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