The Swainson's Hawk is slightly smaller than the average Red-tailed Hawk and generally has slimmer wings than many other buteos. In flight, the Swainson's Hawk shows a distinctive soaring style, holding its wings above the horizon in a shallow V and teetering 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 White-tailed and Swainson's hawk are the only two North American buteos to have a subadult plumage.
The Swainson's Hawk is a common bird of the western plains breeding in shelter belts, riparian growth, and in isolated prairie trees. It is also common along the edge of the plains where it meets the aspen parklands. It is one of the most highly migratory of all North American hawks, leaving its breeding grounds to winter in southern South America. In a life span of seven or eight years, a Swainson's Hawk might cover as many as 150,000 miles (24,000 kilometers) during its migrations north and south.
SIZE
The Swainson's Hawk is a large buteo. Females are larger than males but measurements overlap considerably. Lengths average 20 to 22 inches (51 to 56 centimeters) for females and 19 to 20 inches (48 to 51 centimeters) for males. Wingspans are up to 54 inches (137 centimeters) for females and up to 49 inches (124 centimeters) for males. Weights average 2.4 pounds (1,100 grams) for females and 1.8 pounds (800 grams) for males.
MORPHS
The Swainson's Hawk displays a wide variety of colors, from completely black to white underneath. It also exhibits all degrees of intermediate colors between light birds and dark birds. Although commonly referred to as color morphs, they are really individual plumage variations, referred to here as "light-morph", "rufous-morph", and "dark-morph." This hawk is the only North American buteo with a true full continuum of plumages.
SPECIFIC DESCRIPTION
Adult Dark-morph - Perched
- darkest birds lack the white forehead but darker intermediates may show it
- yellow cere
- uniform dark brown-black body
- undertail coverts are pale
- gray-brown tail with about six narrow dark bands and one wider subterminal band
- wing tips reach tip of tail or beyond
Immature Dark-morph - Perched
- buffy forehead, buffy eyebrow line, yellow cere
- often a pale patch on chin
- heavy streaking on underparts starting with mustache
- dark brown-black upperparts with some pale feather edges
- light undertail coverts
- wing tips reach tip of tail or beyond
SIMILAR SPECIES
The Swainson's Hawk is superficially similar to the other buteos, including the Red-tailed Hawk, Rough-legged Hawk, Red-shouldered Hawk, Broad-winged Hawk, White-tailed Hawk, Short-tailed Hawk, and Ferruginous Hawk; but in most adult and immature plumage variations, the Swainson's Hawk generally has diagnostic pale underwing linings contrasting with dark primaries and secondaries. The other species usually show an underwing pattern reverse to this. Some dark-morph Swainson's Hawks show completely dark underwings with no contrast between linings and flight feathers. This general darkness is again different from most other dark-morph buteos which generally show a very pale background color on the flight feathers. Also, the Swainson's Hawk has relatively long wings for its size and has narrower, more pointed wings than other buteos, held in a soar above the horizontal like a soaring Turkey Vulture. It often shows a white area at base of tail (but not as broad as the white upper tail coverts of the Northern Harrier), unlike other buteos.
Dark-morph "Harlan's" Red-tailed Hawks are quite similar to dark Swainson's Hawks but have dark undertail coverts, and a different wing shape. The Red-tailed Hawk, with light underwings, will show a dark patagial mark along the leading edge of the inner wing. The Swainson's Hawk never shows such a mark. A dark-morph Rough-legged Hawk shows dark underwing linings and light, contrasting flight feathers. A dark-morph Swainson's Hawk shows an all dark underwing, or light brownish wing linings, that contrast with the dark flight feathers. Light-morph Rough-legged Hawks show a conspicuous square black patch near the bend of each underwing, a mark not present on the Swainson's Hawk. An immature dark-morph White-tailed Hawk has the same dark body coloration and the white rump crescent as a dark Swainson's Hawk but shows a large pale chest patch and much whitish or silver in the flight feathers. Dark-morph adult and immature Short-tailed Hawks show silver on their outer primaries and have generally dark undertail coverts.
A dark immature Peregrine Falcon shows gray spots and bars across its underwings. A dark Gyrfalcon shows spotted underwing linings and paler flight feathers than wing linings. A perched Prairie Falcon could be mistaken for an immature light-morph Swainson's Hawk but has a large black eye, a dark patch behind the eye and its wing tips do not reach the tip of its tail.
OTHER NAMES
The Swainson's Hawk has also been known as "Black Hawk", "Brown Hawk", and "Grasshopper Hawk."
ETYMOLOGY
The scientific name Buteo swainsoni translates into "hawk or falcon" ( Buteo - Latin) named after William Swainson (swainsoni).
MYTHOLOGY
No mythology has been found for this species in North America.
VOICE
Outside the breeding season, the Swainson's Hawk is a rather silent species. During summer the most common vocalization is a shrill, aggravated-sounding "kearrrrrrr", weaker than the similar call of a Red-tailed Hawk. The voice of the females is lower pitched than the males. This call is given when people approach the nest and in other aggressive encounters. It may be followed by a series of whistled "tsip tsip tsip ..." Various other plaintive whistles have been reported as given by hungry or "lonely" young birds.
PELLETS
Although this species forms pellets, dimensions and a description of their appearance is not available. In Argentina, pellets of immatures following flocks of migratory dragonflies were made up of various parts of dragonfly exoskeletons.
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