The Swainson's Hawk, (Buteo swainsoni), is a large hawk.

Their breeding habitat is prairie and dry grasslands in western North America. They build a stick nest in a tree, shrub or on a cliff edge. This species is a long distance migrant, wintering in Argentina.

This bird was named after William Swainson, a British naturalist. In flight, they hold their wings in a slight dihedral; they tip back and forth slightly while soaring.

They are declining in some parts of their range due to loss of habitat. Although the use of DDT has been banned in the United States, the Swainson's Hawk still encounters pesticide use when it migrates in the winter to Argentina (Goldstein et al., 1996). Known as the locust hawk, the hawks will eat numerous amounts of these insects and in turn ingest a high amount of toxin, which causes thinning of egg shells.

This species or its immediate predecessor is the ancestor of the Galápagos Hawk, as demonstrated by recent research. The latter diverged from the mainland birds perhaps 300.000 years ago, a very short time in evolution (Bollmer et al., 2005).

The Swainson's Hawk is a common bird of the western plains of North America. It is one of the most highly migratory of all North American hawks, leaving its breeding grounds in the fall to winter in the pampas of South America. In a life span of seven or eight years, a Swainson's hawk might cover as much as 15,000 miles (24,000 km) during its migrations north and south. See the migration route map of Swainson's Hawks below.

The Swainson's Hawk is a slender raptor slightly smaller in size than a Red-tailed Hawk. However, the Swainson's Hawk has a slightly longer wingspan and slimmer wings than other soaring hawks. A common color pattern for the adult Swainson's Hawk is dark brown plumage with a brown chest and a pale belly.

In flight, the Swainson's Hawk holds its wings in a shallow "V" dihedral and teeters in flight a little like a Turkey Vulture. The long, slim, pointed wings are diagnostic when they show the two-toned effect of pale wing linings and dark flight feathers. No other buteo shows such consistently dark flight feathers.

The habitat of the Swainson's Hawk consists of open and semi-open country in both its breeding and wintering ranges. In North America, it is found in the southwest deserts, grasslands and prairies of the intermountain states and provinces, and the grasslands of the Great Plains. Swainson's require trees for nesting and is found around aspen groves, riparian areas, and farmlands.

It favors wild prairie, hayfields, and pastures over wheat fields and alfalfa fields which may offer its prey too much cover. It requires elevated perches for hunting and a supply of small mammals such as young ground squirrels as prey for its nestlings. The breeding distribution of the Swainson's hawk is tied very closely to the distribution of various small mammals for this reason. In Saskatchewan, for example, the distribution of Richardson's ground squirrel and the Swainson's hawk are precisely the same.

The winter migration of the Swainson's Hawk is an incredible sight. They migrate overland in vast flocks that fill the skies with birds and the viewer with awe. From North America through Mexico and Central America to wintering grounds in Argentina, this annual trip is may range from 11,000 to 17,000 miles. The wintering grounds are the open pampas of southern South America where immatures nomadically follow hordes of migratory dragonflies.