Let me say this right up front: When identifying Cooper’s and Sharp-shinned Hawks, it’s okay to not have a definitive answer. These two species look almost exactly alike and have very similar habits. Lots of birders—expert birders—have come away shaking their heads and jotting down “Cooper’s/Sharp-shinned” in their notebooks. This is a tough one.
They’re worth the effort, though. Cooper’s and Sharp-shinned Hawks (let’s call them sharpies) are exciting birds and cunning hunters. Along with the Northern Goshawk they make up the North American accipiters—forest hawks with short wings and long tails that help them maneuver through trees in pursuit of songbirds. Have you ever had a hawk terrorize the visitors at your feeders? No matter where you live in the United States, it was most likely a Cooper’s or Sharp-shinned. You should learn to tell the two apart—if you want to be able to curse them out correctly.
For starters, try and figure out if you've got an adult or a juvenile. Both of these accipiters have brown backs and brown stripes on their chests throughout their first year of life. Adults, on the other hand, have blue-gray backs and orange barring on their chests. (Stripes are vertical; barring is horizontal.)
Think you’ve seen an adult? Then read on.
The first difference between the two adults of these species is their size. On average, Cooper’s are about six inches bigger than sharpies. To put it another way: Cooper’s Hawks are around the size of a crow, while Sharp-shinned Hawks are roughly the size of a Blue Jay. That comparison might seem obvious on paper, but size can be deceiving, especially when there's only one bird in sight.
Size is also iffy because it varies greatly between the sexes (they otherwise look similar, though males are a bit more colorful). As is the case with most raptors and owls, female Cooper’s and sharpies are up to a third larger than the males. Since a large female sharpie can come close to the size of a small male Cooper’s, let’s parse out a few more differences.
On perched birds, consider the shape of the head. The Cooper’s Hawk has a big ol’ dome that's sort of like a block stacked on top of its body. It’s the kind that makes you think, “Wow, look at the head on that thing!” Sharpies, on the other hand, have small, smoothly rounded heads—the kind where you’re like, “Oh, that just looks like a normal bird head.” Gut reaction is helpful!
And while you're up there, check out the back of the neck, also known as the nape. The nape feathers on adult Cooper’s Hawks are lighter than the feathers on the top of the head, giving the bird a capped appearance. Adult sharpies have a dark blue-gray tone on both parts.
The head helps with flying birds, too. Both species appear front heavy, with long tails and wide wings, so they resemble a horizontal “T.” Sharpies seem especially unbalanced, with their small heads barely projecting beyond the wings. Cooper’s appear to be a bit more proportional, with their larger heads sticking out in front.
The final tip is literally the tip . . . of the tail. But like size, this one’s not always helpful. The tip of a Cooper’s Hawk’s tail is often rounded, while a sharpie’s is flat. This can be helpful with soaring birds, or when you have a good view on a perched bird. But it can be tough to get a nice, prolonged look at either of these speedy accipiters. Just take all the factors into account (size, geometry, posture while flying, tail shape) and you’ll be one step closer to solving the mystery at your feeder.