During the breeding season, the male performs an elaborate courtship flight consisting of a series of U-shaped maneuvers. The nest is a flimsy structure built of sticks and grass on the ground. It can be found in dense vegetation or situated in a slightly elevated position. The clutch averages 5 eggs. Incubation lasts 30-32 days and begins before the last egg is laid, so the young vary in size.
Clutches are larger and reproductive success is higher during years when vole populations are high.
Northern harriers breed in North America from northern Alaska and Canada south to northern Baja California, Mexico and the southern U.S., except in the southeast. Wintering occurs from southern Canada to northern South America. Communal flocks roost on the ground in agricultural fields, abandoned fields and salt marshes. Breeding occurs in marshes, grasslands, meadows and cultivated fields. It appears that coastal areas are preferred, but inland areas are used when coastal habitats are limited.