Identity theft is a serious crime. Birds, to my knowledge, rarely bring legal action against one another, but if they did, there is a serious suit brewing amongst the accipiters. Presenting the case of Cooper v. Sharpie!
Sharp-shinned Hawks and Cooper’s Hawks are so alike as to be nearly indistinguishable. These two birds are a fantastic model of parallel evolution. They look the same, follow similar routines, work similar territories, and migrate at the same times. Some expert birders may be able to peg them with reasonable accuracy but hardly any would claim to be right every time.
The similarities of adult Cooper’s and Sharp-shinned Hawks (immatures are equally difficult to differentiate) start with their plumage, dark gray above with rusty streaks below. Both birds boast piercing red eyes and small hooked beaks. They also sport broadly banded grey and black tails. This last mark helps distinguish them from other raptors, as do their distinctive silhouettes. Hawks of the genus Accipiter are characterized by short wings and long tails. Accipiters have rounded wings, whereas falcons have pointed ones. Buteos like Red-tailed, Red-shouldered, and Rough-legged Hawks also have rounded wings but theirs are longer. As far as other raptors go, you’d be hard-pressed to mistake an accipiter for a vulture or an eagle.
Coopers and sharpies can be distinguished in the field, but observers cannot count on one single mark to make the call. Instead, a holistic approach to identification is required. The best place to start is size. Sharp-shinned Hawks are, for the most part, noticeably smaller than their cousins. Averaging 10-14 inches long, they are comparable in size to a Mourning Dove or Blue Jay. Cooper’s are roughly crow-sized, a hefty 14-20 inches long. Usually, size alone is enough to call a bird with confidence. However, as you can see, the upper range of one bird overlaps with the lower range of the other. In those instances where ambiguity exists, look more closely at the bird’s silhouette.
The tail is often a giveaway as to an accipiter’s identity. The Cooper’s has a rounded tail, proportionally longer than the Sharp-shinned, with long middle tail feathers and a broad white band at the tip. I’ve heard the sharpie’s tail likened to a matchstick, long, thin, and squared at the end. Its tail is capped by thin white terminal band which may, next to an adjacent grey band, seem like the broader Cooper’s band.
The Cooper’s is a meatier bird than the sharpie, with a noticeably larger head extending far beyond the wings in flight. Both raptors have broad shoulders but the Cooper’s is thicker throughout. The Sharp-shinned has narrower hips, thinner legs, and a higher apparent center of gravity. Of course, keeping all of these details straight while watching a soaring hawk is a tough task, complicated by the fact that the act of flight changes a bird’s shape. Your last chance for a clean call is to observe the flight style. Cooper’s Hawks follow short glides with slow, regular wingbeats. A sharpie’s flight is both more frenetic and erratic.
With so many details to remember, it is understandable that many birders are intimidated by this accipitrine affinity. As in all matters, practice makes perfect. Once you’ve got a few hawkwatches under your belt, you’ll probably be picking these two birds out with the best of them. Until that day, do what I do and try to stand as close to the best birders possible. Birding tends to be easier that way.