Swainson’s hawk (Buteo swainsoni) is listed as State-Threatened under the California Endangered Species Act (April 17, 1983). It is considered an uncommon breeding resident and migrant in Northern California, and occurs primarily in the Central Valley and on the Northeastern Plateau. This species was formerly abundant throughout Northern California but numbers have declined throughout the breeding range in part due to conversion of foraging habitat and loss of nesting habitat.
Swainson’s hawk is a medium sized soaring hawk with long, narrow wings, a very small bill, and a fan-shaped tail. Adults range in size from 19 to 22 inches in length and have a wingspan of approximately 52 inches. There are three primary color phases (morphs) of Swainson’s hawk, including a light-morph, dark-morph, and rufous-morph. The light morph has a dark bib, white wing linings that contrast with the dark flight feathers, a white belly, and barred tail. The dark morph is generally dark brown in color with dark wing linings that blend with the brown flight feathers. The rufous-morph is a lighter color brown with rusty barrings on the underparts. Swainson’s hawk soars with its wings held above the horizontal in a “V” shape. When birds are perched, the wings are slightly pointed and extend to or just beyond the tail feathers.
Swainson’s hawk is an open country species that prefers deserts, grassland or agricultural areas containing scattered large trees or small groves. Birds generally begin to arrive in the Central Valley from wintering grounds in Mexico, Central America, and South America during March to breed and nest. Nesting primarily occurs in riparian woodlands and open oak woodlands, often in solitary trees in open fields, somewhat close to water. Some nesting in urban woodland areas has also been recorded. Nests are typically located from six to 30 feet up in a large bush, tree or utility pole, and measure approximately 21 to 28 inches in diameter. The nest consists of a structure of sticks and grasses lined with bark and other plant material, including leaves and lichen. Swainson’s hawks often use abandoned nests of other raptors, crows, ravens or magpies and are known to re-use nests annually. Breeding occurs from late March to late August, with peak activity in late May through July. Usually two eggs are laid and incubation occurs for 25 to 28 days. Eggs and young are tended by both parents and fledging occurs approximately one month after hatching.
Swainson’s hawk forages in agricultural fields, grasslands, and open pasture and have been known to venture as far as 20 miles from their nesting site. Adults dive to the ground for a variety of small rodents including mice, voles, gophers, and occasionally ground squirrels. They are also known to eat large insects, snakes, and small birds.
Swainson’s Hawks occur at the Valley Glen, 3D South, River Ranch, and Silvergate preserves.