The bird is mainly migratory over the northern part of its range; most winter in the south, but some pairs remain in, or not far from, the nesting range. Pairs cling to the territories year after year. They mate for life or until the death of one of the pair, at which time the survivor takes another mate. They prey mostly upon rodents. Prey is consumed whole, and indigestible fur and bones are regurgitated in the form of a “casting” or “Pellet” about 12-18 hours after ingestion. This is a critical self-cleaning function of the digestive tract, and birds fed incorrectly in captivity soon die. The hawk’s eyesight is described as being 10 times as efficient as a human’s.