Swainson's Hawk

Swainson's Hawk (Buteo swainsoni) is an elegant, long-winged raptor highly characteristic of the open country of western North America. Named after English naturalist William Swainson, this medium-sized Buteo is renowned for its incredible long-distance migration. Each autumn, almost the entire world population of these birds travels up to 10,000 miles to their wintering grounds in the Pampas of Argentina, making it one of the longest migrations of any North American raptor. During the breeding season, they are a common sight in Western prairies and agricultural lands, often seen soaring effortlessly, perching on fence posts, or walking along the ground in search of insects.

Swainson's Hawks are exceptionally slender for Buteo hawks, featuring long, narrow, pointed wings that they hold in a slight dihedral (a shallow V-shape) while soaring.

Plumage Morphs

Swainson's Hawks are highly polymorphic, exhibiting two primary color morphs and intermediates:

• Light Morph (Most Common): Characterized by a crisp white throat, a distinctive dark, reddish-brown breast band (known as a "bib"), and a pale, unmarked belly. From below in flight, the whitish underwing coverts contrast sharply with the dark gray-to-blackish flight feathers.
• Dark Morph: Uniformly dark brown or soot-colored overall. In flight, they still display the characteristic contrast between the dark underwing coverts and even darker flight feathers, though it is less pronounced than in light-morph individuals.

Key Field Marks

• Wing Shape: Long, narrow, and pointed compared to the stubbier, broader wings of Red-tailed Hawks.
• Underwing Pattern: The "two-toned" underwing—light coverts contrasting with dark flight feathers—is a key diagnostic feature for light morphs.
• Face: A white forehead and white patch around the base of the bill are often visible on close inspection.

Breeding Range and Habitat

Swainson's Hawks breed in open habitats of western North America, including native grasslands, prairies, shrubsteppes, and increasingly, agricultural fields like alfalfa, grain, and hayfields. They require scattered trees, windbreaks, or riparian corridors for nesting.

Migration and Wintering Range

These hawks are highly migratory. In late summer and early autumn, they gather in spectacular, swirling flocks called "kettles," sometimes numbering in the thousands, as they make their way down the Central Mesoamerican flyway. They winter primarily in the open pampas of Argentina, southern Brazil, and Uruguay, where they match the open-country habitat of their northern breeding grounds.

Feeding and Diet

The diet of the Swainson's Hawk shifts dramatically between seasons:

• Breeding season: They rely heavily on vertebrate prey to feed their young, hunting small mammals (such as pocket gophers, ground squirrels, and voles), reptiles, and birds.
• Non-breeding season: They become almost exclusively insectivorous, pursuing large grasshoppers, crickets, and dragonflies. It is common to see dozens of these hawks walking on the ground behind tractors, feeding on insects stirred up by agricultural machinery.

Flight and Soaring

Swainson's Hawks fly with a light, buoyant style. They soar with wings held in a slight dihedral (tilted upward in a V-shape), rocking gently from side to side.

Vocalization

Their primary call is a long, plaintive, down-slurred scream: kearrrrrr or kearr, softer and more nasal than the harsh, raspy scream of a Red-tailed Hawk.

Nesting

They build flat, bulky stick nests in isolated trees, small groves, agricultural windbreaks, or occasionally on utility poles. The female typically lays 2 to 3 eggs, which she incubates for about 34 to 35 days.