Swainson's Hawk (Birds of the Kaibab National Forest)

Swainson's Hawk

Buteo swainsoni

Summary ⁵

Swainson's Hawk (Buteo swainsoni), is a large Buteo hawk of the Falconiformes, sometimes separated in the Accipitriformes like its relatives. This species was named after William Swainson, a British naturalist. It is colloquially known as the Grasshopper Hawk or Locust Hawk, as it is very fond of Acrididae (locusts and grasshoppers) and will voraciously eat these insects whenever they are available.

Taxon biology ⁶

Swainson’s Hawk (Buteo swainsoni) is a medium-sized slender hawk (Crow-sized), with long, pointed wings and a long tail. Measurements include: length 17-22 inches (43-56 cm); wingspan 47-54 inches (120-137 cm); weight 1.3-2.7 lb (595-1240 g). Females slightly larger than males. Plumage extremely variable, but most individuals are recognizable. Adult-sides of the head and entire upper parts dark blackish brown; feathers obscurely edged with paler brown to cinnamon. Tail gray, basally whitish, with a narrow white tip, and several indistinct blackish bars, the last one broader. Primaries blacker than back; becoming paler basally. Throat white; breast brownish chestnut with weak black shaft streaks. Belly and legs dull white; indistinctly mottled and barred with brown to rufous. Under-wings pale with conspicuous dark marks at ends of coverts. Dark phase more or less sooty all over. Wing and tail as in normal phase, except that wing linings are much more marked with blackish. Rufous phase lighter brown below than the dark phase; and somewhat barred and blotched below with rusty brown. Intermediates occur between all the phases. Eye dark brown; cere pale greenish yellow; bill blackish; legs wax yellow (Brown et al 1968).

The immature plumage, which is worn for two years, is similar to that of adults in its two- toned underwing and finely barred tail, but young birds have a spotted and streaked breast that at times shows a hint of a darker pattern, and the head shows a definite buffy streak above the eye and on the cheek, with a dark eye line and malar stripes. This typical pattern occurs on perhaps half the Swainson’s Hawk encountered in Arizona, and if color pattern alone is used for identification, the other half will be mis-identified. (Glinski 1998).

Found only in the New World; it breeds in North America, in the Great Plains and arid regions, north sparingly to interior Alaska, and south to northern Mexico, and winters in South America. The normal winter range is the Pampas of Argentina, and it has been assumed that any found elsewhere at that season are casuals, probably unable to make the long migration (Brown et al 1968).

Gives a descending shrill, plaintive whistle, kreeeeeeer, trailing off at end. In flight, shows profile like that of Turkey Vulture; the wings are held in a dihedral, or "V", position, which promotes aerodynamic stability in open landscapes where wind can interfere with flight close to the ground. Highly migratory, often seen in large flocks on spring and fall flights. During the breeding season, a soaring, open country hunter. Sometimes hunts high in the air, but more frequently courses low over prairie. Rarely observed flying low at high speed as Ferruginous Hawk does. Often hunts from perches such as tree limbs, poles or posts, rocks, and elevated ground.