The nest is about 75 centimeters in diameter and is composed of sticks, bones and other available rigid material, and is lined with grasses, sedges and small twigs. As the season progresses, feathers and fur may be added to the nest. A clutch consists of anywhere from 2 to 7 eggs, but averages from 3 to 5 eggs. In years when rodents are abundant, all eggs may produce fledglings while in years of scarcity only one chick may fledge. Incubation is about 31 days and fledgling as early as 30 days to often longer than 40 days.
Food is principally small mammals, but birds and other vertebrates are taken at times.
On the wintering grounds the Rough-leggeds are able to coexist with other large buteos because of the advantage they get of better insulation from their feathers. A careful observer will notice in these situations that the two species tend to perch in different areas and utilize different hunting techniques. The Rough-leggeds tend to perch more in the open, and use hovering to hunt during the colder months. The fall migration peaks in late October in the Upper Peninsula and in mid-November in the southern Lower Peninsula. The beginning of the spring migration is complicated by the numbers of individuals which overwinter and wander from area to area.