While many hawk species, such as the most widespread Red-tailed Hawk, breed throughout most of the lower 48 states the Rough-legged Hawk breeds far north in the arctic and boreal forest. So few of us other than those in more northern areas of Alaska and northern Canada see them until winter time when they migrate south. During late fall and winter Rough-legged Hawks are found from the southern sections of Canada to all but the most southern parts of the lower U.S. states.
These hawks, with the unusual exception of dark morph adults, have pale heads as shown in the two photos above. Also shown is one of their diagnostic features, the feathering on their legs not only covers them but goes all the way down to their toes. That feathering helps them keep their legs warm as they do spend a lot of time in very cold locations. The only other raptors found in America that have this full leg feathering are Golden Eagles and Ferruginous Hawks. I like the dark bars shown the leg feathering in the above photos.
The bottom photo shows the long wingspan on Rough-legged Hawks. They use these long wings to hover over prey when they are hunting.
You will most likely find them around farms and other open fields as well as grasslands. You can read more about them on the Hawk Mountain website (they conduct research and they are located where they do raptor counts during migration)
I photographed this Rough-legged Hawk (called a light morph) last week not far from where I live in Colorado. This is an adult bird and I believe it is a female.