May mate for life. In courtship, 2 birds circle high in air, making shallow dives at each other. Display to defend territory includes repeated high flight followed by steep dives, loops, rolls, and other acrobatics. Nest site is most often on cliff ledge, also frequently in large tree, rarely on ground. Sites may be used for many years. A pair may have 2 or more alternate nest sites, using them in different years. Nest (built by both sexes) a bulky platform of sticks, lined with weeds, grass, leaves, moss. New material added each year, and nest may become huge. Eggs: 2, sometimes 1-3, rarely 4. Whitish to buff, marked with brown. Sometimes one egg in the clutch is unmarked. Incubation is by both parents (female does more), 41-45 days. Young: Female remains with young most of the time at first, while male does most hunting, bringing prey to nest. After young are half-grown, female also does much hunting. Age of young at first flight roughly 60-70 days.