Rough-legged form pair bonds that are maintained for at least the duration of the breeding season and possibly longer. Rough-legged hawks are not averse to crossing wide bodies of water, which is unusual for a buteo. In the western part of rough-legged hawk range, spring migration begins in late March or early April, with the largest flights in late April.
Nests tend to be larger in areas where more sticks are available.
Earliest egg dates were May 2 in Labrador and May 18 in arctic Canada and Alaska. Eggs are incubated for 28 to 31 days, mostly by the female. They are fed by both parents. In Finland, rough-legged buzzards were observed active by 4 a.m. in June and July. This hawk tends to avoid the western coastline and the southeastern corner of the United States.