Guest post by Catherine Griset, Spring 2013 Intern
A small hawk hunts quietly from a perch. Watching for smaller birds, it waits until just the right moment to dive down and attack. As it flies back to its post you notice a charcoal gray back, orange barring below, and a long tail. (Or maybe a brown back, with streaking down the front.)
What kind of hawk is this?
From that description, we could be talking about either a Sharp- shinned Hawk or a Cooper’s Hawk. Regardless of age, both hawks have long, barred tails. Adults of these species are gray and orange, with red eyes; immature birds (1st year) are brown and white, with brown streaking on the chest, and yellow eyes.
Differentiating between these similar birds is a notorious ID challenge, puzzling new and seasoned birders alike. While at first it can be frustrating, addressing their similarities and differences is a good place to start. Sharp-shinned (Accipiter striatus) and Cooper’s (Accipiter cooperii) both are small raptors that feed on songbirds—maybe you’ve seen one hunting at your feeder. Along with the Northern Goshawk, these are the only members of the genus Accipiter in North America. Accipiters are typically forest-dwelling hawks that prey on smaller birds, though recently Cooper’s and Sharp-shinned Hawks have ventured into more developed areas.
While both are relatively small for hawks, there is usually a noticeable difference in size between the two. This field mark alone isn’t always reliable. With these birds, one trait alone never is! If the bird is remarkably small you are probably seeing a male Sharpie. Sharp-shinned Hawks (10-14’’) are about the size of a Blue Jay, while Cooper’s Hawks (14-20”) are about the size of an American Crow. Like other raptors, these species show reverse sexual dimorphism, which may compound confusion about size. Reverse sexual dimorphism is a technical way of saying that the females are larger than the males. A small Cooper’s is quite often about the same size as a large female Sharp-shinned. Furthermore, size can be surprisingly hard to judge in the field or from a photograph. When trying to make an identification, look to the surroundings for comparison, such as the size of its perch. If the bird had a successful hunt, take a look at what they’ve caught and go from there to estimate size.
The overall body shape of a Sharp-shinned is distinctly different from that of a Cooper’s. Sharp-shinned Hawks are widest at the shoulders, tapering in toward the waist. Cooper’s Hawks are longer and more barrel-shaped. On a perched Accipiter, the shape and size of the head are good marks to look at. Sharpies have a small, rounded head with barely any visible neck. This sometimes gives them a stout appearance. Cooper’s’ heads are proportionally larger and flat-topped rather than rounded. Head size and projection are also great clues when identifying a bird in flight. A Cooper’s Hawk’s head projects farther out from the wings when seen in flight, along with the varied angle of the wings (held straighter on a Cooper’s, bent slightly at the wrists on a Sharp-shinned).
Oftentimes, these hawks are seen as blurs diving at a feeder area or crashing into a bush. If you’re lucky enough to get good, up-close looks at the bird in question, there are several smaller features you can examine. Does the bird have a small bill, with large eyes centered in the middle (front to back) of its head (Sharpie)? Or is the bill mid-sized, with the eyes closer to the front (Cooper’s)? When visible, the nape or back of the neck is a good indicator. A pale nape that contrasts with a dark cap points to a Cooper’s Hawk. This is why some say that a Cooper’s is “capped”. If the bird has a nape that is the same color as the rest of the head, it is a Sharp-shinned. This gives them a “hooded” appearance.
The legs and feet of these two species are also quite different, seen best when the hawk is perched. Sharp-shinned Hawks have long, very skinny legs, with small feet. Cooper’s Hawks’ have thicker legs and larger, more powerful feet. This difference appears to affect prey choices. Accipiters hunt with their feet and talons out, using them as their primary weapons.
Finally, the tail can offer several distinguishing features. The tail of a Sharp-shinned Hawk often looks squared at the edges and/or notched in the middle. This is because the tail feathers are equal lengths. A Cooper’s Hawk typically has a rounded tail, tipped with white. This can be affected by wear, so be sure to use it in conjunction with other field marks. Unlike those of a Sharpie, the tail feathers of a Cooper’s Hawk are not even; the outer feathers are slightly shorter than the rest. The best times to use this field mark are when the bird has its tail either spread out or folded. In this second position, the outer tail feathers are actually folded into the middle with the longer feathers behind them.
One further resource deserves mention: explore several field guides to prepare your mind with examples. Both detailed paintings (some with live bird models and some from study skin references) and photographs provide at home practice.
So go out, go birding, and watch for hawks!
Catherine Griset was an intern at the Birds of Vermont during the 2013 spring semester, while she was a student at the University of Vermont. She is also an illustrator of birds, created an exhibit poster about birds and climate change, and contributed to our thrice-yearly newsletter, Chip Notes. This article also appeared in the July 2013 issue of the Vermont Great Outdoors Magazine (a digital publication).