Cooper's Hawk

Present in the county throughout the year, but more abundant in the winter months. Along with the similar-looking Sharp-shinned Hawk (Accipiter striatus), Cooper's Hawk is one of the two common Accipiters in Sonoma County and one of only three normally present in North America. The third is the rather rare (in our area) Northern Goshawk (Accipiter gentilis), which has been sighted in Sonoma County only on three or four occasions (most recently, in 1996, according to Bolander and Parmeter). Cooper's Hawk feeds mainly on other birds. Usually seen in forested areas and near forest edges. Occasionally makes appearances in suburban settings near woods. Sometimes hunts for prey at suburban bird feeders. The bird photographed above was about 75 yards from my own house. Known to nest in inland forested areas of the county (mostly the eastern part of the county at higher elevations).

Just about every local birder of experience can relate a story about mixing up Cooper's Hawk and Sharp-shinned Hawk on some occasion. Good birders will make the ID with care and admit that there are many times when a positive ID is simply not possible. The accipiters call for humility and caution. Too often, they are seen momentarily, on the fly, or obscured by branches. With a good look, however, the two birds may be distinguished by a number of traits. A bird with a combination of these traits is probably securely identified, but don't trust one alone. There is much overlap in most of them.

Kenn Kaufman, in his Field Guide to Advanced Birding, points out that size is both the most reliable and the least useful clue. Cooper's Hawk is bigger than Sharp-shinned Hawk. While there is a great deal of size difference between the males and females of both Cooper's and Sharp-shinned Hawks (the females are the bigger birds), all Cooper's Hawks tip to tail are bigger than all Sharp-shinned Hawks (barring aberrations). Unfortunately, size is not of much use unless the birds are side by side, and size is notoriously difficult to judge in the field. With experience, however, a general feel for the sizes of the two birds can be of use (Kaufman, p. 200, has a useful bar graph illustrating Accipiter sizes). Other field marks to look at include head size, shape, and coloration; tail length, shape, and pattern; and leg size. Breast patterns are useful for distinguishing juveniles of the two species (Juvenile Cooper's will have dark brown streaking on a tannish-pale brown breast and belly, while a juvenile Sharp-Shinned Hawk will have muddier, reddish-brown streaking with less of the background color showing through).

Looking at the head may be the best way to tell adult birds apart, if looking at a perched bird. Cooper's Hawk has a proportionately large, squarish head that is very dark on top. Paler areas below the cap (mostly the cheek and nape) make the cap stand out sharply in adults. An adult Cooper's Hawk may look like it's wearing a badly fitting toupé (photo below). Sharp-shinned Hawk has a proportionately small head, it lacks the capped look of Cooper's Hawk, and the line of the back of the head is more flowing, without the slightly notched look of the Cooper's Hawk--and Sharp-shinned Hawk has a lighter, more elegant look generally. An adult Cooper's Hawk will have a reddish-orange eye, as will an adult Sharp-shinned Hawk, but eye color changes with age. Young birds in both species will have paler, yellower eyes, so eye color is not a reliable tool for distinguishing the species. Eye size and placement is useful, however. "Sharp-shinned Hawks have big, buggy, deer-in-the-headlight eyes that look centrally placed in the head. Cooper's Hawks have relatively smaller eyes with a heavy brow that look positioned more toward the beak" (Allen Fish, Director of the Golden Gate Raptor Observatory, private communication).

Pay attention to the tail. If you can get a good view of the tail from underneath or of the tail partially fanned, Cooper's Hawk will show outer tail feathers on average a half inch or more shorter than the central tail feathers. The tail feathers of Sharp-shinned Hawk will be of roughly the same length--although this may be difficult to see in the field, especially from the dorsal view. Overall, Cooper's Hawk has a longer tail than Sharp-shinned Hawk, and the tail usually has a narrow white band at the tip, but this white fringe may become completely worn away on some birds, so the absence of the white does not automatically indicate Sharp-shinned Hawk. Cooper's Hawk has fairly thick yellow legs. Sharp-shinned Hawk has notably thinner yellow legs (often described as "pencil-thin") that can give that bird a very long-legged look.

Finally, many birders and guide books will note that, in flight, the head of a Cooper's Hawk should project well in front of the front edge of the bird's wings, while the smaller head of a Sharp-shinned Hawk will appear to be nestled in the notch created by the "wrists" of the bird's wing. This can be very hard to see, but may be a useful indicator. Experienced birders also point to differences in the way the birds fly. If, in the end, it's not clear, you can safely call your bird an Accipiter and leave it at that.

For current raptor migration information, visit the Golden Gate Raptor Observatory website