This species is a long-distance migrant, wintering in Argentina; it has been recorded as a vagrant in neighboring Chile, in the island countries of the Dominican Republic, and Trinidad and Tobago, and in Norway.

It broadly overlaps in size with the red-tailed hawk (B. jamaicensis), a related species found as a breeding resident almost throughout North America.

Breeding areas include south-central Alberta, central Saskatchewan, southwestern Manitoba, and west and southern Minnesota.

Breeding continues south through the eastern parts of Washington and Oregon, locally to the central valley of California, Arizona, New Mexico, Colorado, and most of Texas.

Small populations winter in southeastern Florida and along the Texas coast, probably having failed to find the way south around the Gulf of Mexico.

Individuals reported north of these areas in winter (for example, on Christmas Bird Counts) are almost invariably misidentified buteos of other species.

The flight from breeding ground to South American pampas in southern Brazil or Argentina can be as long as 7,100 mi (11,400 km).

The birds gradually head southwards toward Central America where virtually the entire population funnels through the Isthmus of Panama.

But surprisingly, the occasional Swainson's hawk — including birds one or two years of age — has also been recorded in the eastern states of Maranhão, Pará, Pernambuco, Piauí and Tocantins, thousands of kilometers away from their usual migration route and wintering grounds and sometimes in mid-summer.

This suggests that individuals occasionally become lost during migration, and/or that they may spend a whole year in the tropical regions and range about, rather than just overwintering at one site.

The earliest Swainson's hawks arrive in southern Canada in late March, with migration peaking from mid April onwards.

The habitat of Swainson's hawk consists of open and semi-open country – deserts, grasslands and prairies – in both its breeding and wintering ranges.

It requires elevated perches for hunting and a supply of small mammals such as young ground squirrels as prey for its nestlings.

In Uruguay, the species likes largely open but broken (with rocks or woods) plains or low hills, where it can be seen to gather in larger groups.

Flocks of over one hundred birds have been recorded several times, e.g. one that roamed the Cuchilla Marincho region south of Andresito (Flores Department) in mid-late December 2005.

Males that fledged in territories with higher primary productivity had lower natal dispersal in northern California, suggesting they were trying to stay closer to more prey-dense habitat.

Many still-hunt, watching for prey activity from a perch such as a tree, bush, pylon, telephone pole, hummock or other high object.

[3] Others hunt by soaring over open ground with wings held in a dihedral, using their stellar vision to watch for prey activity below.

It hunts insects such as dragonflies or dobsonflies while in flight, flapping little as it rides a wind current and stoops upon a fly, grabbing it with its foot and immediately transferring the prey to its bill.

Also, when dragonfly hordes are grounded by weather, Swainson's hawk will stand near groups sheltering from the wind and pluck at individual insects.

The species commonly follows tractors and other agricultural equipment during haying or ploughing, where rodents are exposed for the hawks to capture, or insects are uncovered after crop cutting.

Swainson's hawks typically nest in isolated trees or bushes, shelterbelts, riparian groves, or around abandoned homesteads.

Nest trees and bushes include ponderosa pine, Douglas-fir, spruce, cottonwood, domestic poplar, aspen, elm, mesquite, willow, saguaro cactus, and soaptree yuccas.

The oldest wild Swainson's hawk on record is 26 years 1 month (Swainson's Hawk 26 years 01 months 07/06/1986 California Local Unknown 07/24/2012 California Saw or photographed neck collar, color band, or other marker (not federal band) while bird was free Alive - Released/Left On Bird).

[16] Swainson's hawks die because of collisions with traffic, illegal shooting, electrocution, and even during severe prairie weather such as hailstorms.

Swainson's hawk has suffered population declines since the first half of the twentieth century and was Blue-listed in the United States from 1972 to 1982.

Swainson's hawk was removed from the active federal list because it was found to be more abundant than previously thought; it is not considered a threatened species by the IUCN.

[17] Swainson's hawk has adapted well to grazing and pastureland and seems to be holding its own over much of its breeding range, from northern Mexico to the southern parts of the prairie provinces.

However, far western populations, like that of Oregon, and southern California, have drastically declined, often due to habitat loss or incompatible agricultural practices.

A possible reason for declines in parts of its range may be agriculturally motivated reductions in populations of both ground squirrels and grasshoppers, major seasonal foods.