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i� NATURAL HISTORY The Swainson's hawk is a large, broad winged buteo which frequents open county. Approximately the same size as ared- tailed hawk (Buteo jamaicensis) , but trimmer, Swainson's hawks weigh approximately 800 - 1100 g (1 3/4 - 2 lbs) , and have about a 125 cm. . (4+1 ) wingspan. The basic body plumage may be highly variable and is characterized by several color phases - light, dark, and rufous. In dark phase birds, the entire body of the bird may be sooty black. Adult birds generally have dark backs. The ventral or underneath sections may be light with a characteristic dark, wide "bib" from the lower throat down to the upper breast. The tail is gray ventrally with a subterminal dusky band, and narrow, less conspicuous barring proximally. The sexes are similar in appearance; females however, are slightly larger than males, as is the case in most sexually dimorphic raptors. There are no recognized subspecies (Palmer 1988) . The Swainson's hawk is a long distance migrator, leaving nesting grounds in northwestern Canada, the western U.S. and Mexico, most populations migrate to wintering grounds in the open pampas areas of South America (Argentina, Uruguay, southern Brazil) . This round trip journey may exceed 14 , 000 miles. The birds will return to the nesting grounds in early March to establish breeding territories. Swainson's hawks are monogamous and will remain so until the loss of a mate (Palmer 1988) . Nest construction and courtship continues through April. The clutch (commonly 3-4 eggs ) is commonly laid in early-April to early-May. However, may extend significantly later. Incubation lasts 34-35 days, with both parents participating in the brooding of eggs and young. The young leave the nest approximately 42-44 days after hatching. The young remain with their parents and gain hunting practice until they depart on migration in the fall. Large groups (up to 100+ birds) may congregate in holding areas in the fall and may delay migration depending upon forage availability. The specific purpose of these congregation areas is as yet unknown, - but is likely related to the timing of migration, the learning of migration routes for each year's young, and provides a pairing and courtship opportunity for unattached adults. General Reproductive Chronology MAR APR MAY JUN JUL AUG SEPT X---------X ARRIVE FROM WINTERING GROUNDS X----------X COURTSHIP AND NEST CONSTRUCTION X------------------------X EGGS LAID NESTLING STAGE X_______________________________X FLEDGLING X-----------------------X MIGRATION X--------? 3