In the winter, bird feeders bring in lots of birds, jostling noisily and chasing each other for the heaviest seed or the best piece of suet or even the highest perch on the birdbath. Suddenly, all of the birds take off in a noticeable “whoosh,” heading in all directions and completely out of sight. Where normally you hear lots of chatter, squawking, and call notes, all is shockingly quiet. You may not see it, but most likely a predator has entered the scene—and for many of us, the most common predator at a bird feeder is a Cooper’s Hawk.
A Cooper’s Hawk is a crow-sized, bowling-pin-shaped hawk in the accipiter family. An adult has a blue-gray back and a horizontally barred rufous chest and belly. A young bird looks quite different, though—a warm brown back with brown vertical streaks on a cream-colored chest. Regardless of its age, a Cooper’s Hawk’s long, narrow tail shows a white band at the end that can be rather conspicuous as the bird flies away from you. Coupled with its short, powerful wings, its rudder-like tail enables skillful maneuverability in areas thick with trees and shrubs, making this hawk well adapted for zipping, zigging, and zagging after forest birds and mammals. Both sexes have the same plumage. However, female Cooper’s Hawks are about 1/3 larger than their male counterparts—the greatest size dimorphism of any of the world’s hawks. This size differential may enable the female to catch larger prey than her more diminutive partner, thereby allowing them to exploit a broader range of prey for feeding the kids.
Cooper’s Hawks (also affectionately known as Coops) forage primarily on ground-feeding birds. Up to 80% of the summer diet consists of small- and medium-sized birds such as finches, thrushes, doves, and jays. But sparrows are a staple, accounting alone for 25% of their summer menu. Coops will also catch and eat rabbits, hares, ground squirrels, and tree squirrels. When hunting, a Coop relies on stealth, watching for long periods, then suddenly dropping down from the perch and zooming low across ground. These surprise attacks allow the raptor to single out sick or more slow-witted birds from the healthier, more alert birds. This sudden burst of speed when hunting also accounts for the challenge we humans have in spotting one as it strafes the ground under feeders. Before you even realize a Coop is around, it’s gone.
In Colorado, you might see 3 members of the accipiter family: in addition to Cooper’s Hawks, Sharp-shinned Hawks and Northern Goshawks may appear. However, Coops are the most common of the accipiters in Colorado. Here, Coops nest in most forest types, from cottonwoods along a creek or river to spruce and fir at 10,000 feet. In the first Colorado Breeding Bird Atlas work, atlasers turned up Coops nesting in pinyon/juniper habitats more than in any other type of habitat. The male does most nest building, gathering nest material within a 500-foot area of the nest. The female lays and incubates a clutch or 3 – 4 eggs that hatch after 34 – 36 days. The female also takes primary responsibility for feeding the young directly until the nestlings reach 18 – 21 days: The male delivers prey nearby, which the female takes to nest and pulls off pieces for the kids. The youngsters leave the nest at about 30 days old, although the parents may continue to bring them food for up to 7 weeks afterward.
Known officially as Accipiter cooperii, the Cooper’s Hawk has a pretty straightforward scientific name. Accipiter is a general term in Latin for a bird of prey, especially a hawk. The species name, cooperii, and the common name honor William C. Cooper (1798-1864), an American zoologist and one of the founders of the New York Lyceum of Natural history (the precursor to the New York Academy of Sciences). The word “hawk” derives from the Anglo-Saxon word hafoc, which was their name for this type of bird.
Confident identification of a Cooper’s Hawk is as much art and luck as it is science. Its major competitor is the nearly identical-looking Sharp-shinned Hawk (which also has an affectionate nickname—Sharpie). Since both species exhibit not only similar plumages but also the same size dimorphism, a male Sharpie—about the size of a Blue Jay—can often be distinguished confidently from a female Coop (about the size of a Common Raven). But size alone presents problems, since these two species have a LOT of overlap. For instance, a big female Sharpie can easily be larger than a small male Coop. Some subtle distinctions exist. For example, Coops have more rounded tails while Sharpies have more squared-off tails. (Good luck with that one.) If you’re looking at one in flight, a Sharpie has practically no head projecting beyond the front edge of its wings, while you can see quite a bit of a Coop’s head beyond its wings. (Yeah, well…) Wingbeats might offer some clues—a Sharpie often has 3 quick flaps and then a glide, while a Coop has 3 slower, steadier flaps before the glide. (Um, okay…) My husband really knows hawks; but of all the raptor species, the Coop/Sharpie distinction often leaves him shrugging and offering only an educated guess too.
You know, sometimes you just have to be happy with calling one of these woodland birds an accipiter—and feeling honored to have this stunning predator keeping the songbird gene pool strong.
You can read more about and see photos of Cooper’s Hawks here.