A bird of open country, breeding as far north as the Arctic Circle, the Northern Harrier can be found throughout the West and Great Plains as a year-round resident. During fall migration, birds from the far north appear to leapfrog over the central United States and continue on to winter through Mexico and Central America and into parts of northern South America. This species is recorded annually at nearly every U.S. hawkwatch site, the greatest numbers coming from East and West Coast flyways, the Florida Keys, and the Texas coast.
Harriers usually migrate at relatively low elevations and hunt as they go. The timing of the migration is quite variable; their departure from breeding areas is influenced by both prey availability and onset of first freeze. Because they hunt during migration, their passage rate is also mediated by prey availability. During migration and through the winter, large numbers of Northern Harriers may aggregate and roost communally in areas with high populations of voles and other diurnal rodents.