The Swainson's hawk is a medium-sized hawk with dark brown plumage and a brown breast, pale belly, and a white patch under the bill.1
Habitat: The Swainson's hawk prefers open habitats, such as grasslands with trees and shrubs for perching, irrigated meadows, and edges between two habitat types. The hawk may be found in arid habitats throughout the western United States. It nests in riparian areas, roadside trees and telephone poles, and occasionally near urban areas.2
Range: B. swainsoni is a migratory bird. The hawk's breeding range is restricted to western North America, from Alaska and western Canada south into northern Mexico. The hawk winters in Argentina.3
Diet: The hawk is a versatile and opportunistic predator, feeding on insects, small mammals, birds, and reptiles.4 The Swainson's hawk will take advantage of certain farming activities such as plowing by either perching on the ground or diving down onto prey that has been stirred up by the tractor.2
Reproduction: The Swainson's hawk begins nesting in late March.4 The nest is made with large sticks, twigs, brambles, and grass, and is lined with feathers, fresh bark, leaves, flowers, and down.3 The female lays two to three eggs. Both sexes care for the eggs. The young leave the nest 33 to 37 days after hatching.3
Migration: B. swainsoni travels in large flocks from the nesting areas south to their winter grounds in Argentina.4 The hawk leaves North America by early October and arrives in South America by November. Spring migration usually begins in March.4 The annual trip ranges from 11,000 to 17,000 miles.1
Status: The Swainson's hawk is a Federal Species of Concern, and is protected by the Migratory Bird Treaty Act. It is also an Arizona Wildlife Species of Special Concern. This hawk is considered "forest sensitive" by the Regional Forester.
Swainson's Hawk in Pima Country: Since the 1940s, populations of the Swainson's hawk have declined by ninety percent.2 Key reasons for this decline are loss of native nesting and foraging habitat, and changes in land uses from agricultural to urban. The most critical factor is the loss of many suitable nesting trees within preferred riparian habitat.3 Another reason for decline is the threat from insecticide use in Argentina, a practice killing over 10,000 birds in 1995.2
1. Texas Parks and Wildlife. "Swainson's Hawk. Wildlife Fact Sheet." 12/15/99 Web site
2. Brown, N.L. 1996. "Swainson's Hawk Profile." Endangered Species Recovery Program. Fresno, California. 12/15/99 Web site http//arnica.csustan.edu/esrpp/swainson.htm
3. New Mexico Game and Fish Department. 1997. "Buteo swainsoni." BISON-M Taxonomy.
4. "Buteo swainsoni." 12/17/99 Web site www.wildfire.org/feis/animals/bird/busw/all_frames.htm
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