While instantly striking fear into neighborhood feeder birds, a perched Cooper’s hawk also can bring a sense of awe to a yard observer.
Many neighborhoods have their local “Coop,” but as common as this hawk species might seem today that hasn’t always been the case.
Several historical reports show Cooper’s hawk used to be less common in Iowa. Perhaps like the range expansion of northern cardinal into the Upper Midwest, urbanization over the past two centuries has brought more people along with more bird feeders. With an ongoing supply of yard birds as food, Cooper’s hawk has become a staple visitor in many urban spaces across the Midwest.
An adult Cooper’s hawk sits with an upright posture, like other members of its genus, Accipiter. A perched adult will show a densely barred, reddish breast and belly. The backside is a grayish-blue color. The head has a distinct dark cap and the eye is red. Juveniles have brown streaks on white from the throat down to the belly. The backside is brown with white mottling often seen along the shoulders. The eye coloration of a juvenile is yellow. As you may surmise, eye coloration in accipiters changes from juvenile to adult, usually from a yellowish or orangish to red.
Making an ID can sometimes be difficult because of another closely related Iowa hawk known as the sharp-shinned. The “sharpie” is a smaller, more compact version of the Cooper’s. There are several subtle differences in field marks, one of the best being the differences in head structure and eye proportions. The Cooper’s hawk often shows a larger, flat crown (or skullcap) while the sharp-shinned has a smaller head and more rounded crown.
Due to the smaller head, a sharp-shinned Hawk’s eyes will appear to take up more space, making them seem larger. In flight, the Cooper’s overall size will look larger and longer, with wings held straight and a longer tail. A sharp-shinned should look tiny, with wings held forward and a shorter tail. In terms of coloration, adults and juveniles of both species are similar.
Another critical reason it can be difficult to separate these two species in flight or perched is due to sexual dimorphism. A female Cooper’s hawk is larger than a male. The same is true in sharp-shinned hawk. A male Cooper’s hawk and female sharp-shinned hawk may approach similar sizes. Therefore, many birders will often leave accipiters unidentified in the field, noting them as Accipiter sp.
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Look for Cooper’s hawk year-round. Sharp-shinned hawk, however, tends to only winter in Iowa, breeding farther north. In the fall, especially in September, look for large migratory pulses of each species heading south.
One great place to see these two species during migration is at the Grammer Grove Hawk Watch, located near Liscomb in Marshall County. This hawk watch runs September through December.
OTHER BIRDS TO LOOK FOR IN DECEMBER
— Yard birds should become more plentiful as temperatures drop, especially right before and during winter storms. Look for finch diversity to increase with the possibility of less common finches, such as pine siskin and purple finch. If you are lucky you might draw in something rarer, like a crossbill.
— Mixed flocks of Lapland longspur, snow bunting and horned lark may be found in ag lands, especially near and around farms that have open piles of corn. Corn spills along country roads also can be a hot spot for this mix of field birds.
— Where open water persists, looks for a good diversity of waterfowl in November. Keep your eyes peeled for cackling geese, the smaller version of the Canada, in large flocks. Often, flocks assemble where there are wide open fields of Kentucky bluegrass near open ponds.
— Raptors will be setting up winter territories. Red-tailed and rough-legged should be seen along back roads and highways. Look for rough-legged hawks to be hovering in place or “kiting” when they look for food. Red-tailed hawk and American kestrel also may display this behavior. Look for Cooper’s hawk just about anywhere. Look for northern harriers along expanses of grassland and marshland.
DECEMBER BIRDING CALENDAR
— Dec. 15 — Iowa City Christmas bird count. To participate contact Chris Edwards at email@example.com or (319) 430-4732. Visit https://iowabirds.org/Connections/CBC.aspx to see Christmas bird count information for the entire state of Iowa, including many in Eastern Iowa. The list will continue to populate as mid-December approaches, so keep checking back for updates.
Brandon Caswell has undergraduate degrees in biology, anthropology and geology. His graduate degree centered on dating continental collisions within the Precambrian Canada Shield. Bird-watching and nature photography are among his favorite hobbies. Email firstname.lastname@example.org with birding-related questions.