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3 NATURAL. HISTORY The Swainson's hawk is a large broadwinged buteo which frequents open county. Approximately the same size as a red-tailed hawk (Buteo jamaicensis), but trimmer, Swainson's hawks weigh approximately 800 - 1100 gm. (1 3/4 - 2 lbs)., and have about a 125 cm. (4+') 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 laid in early-April to early-May. 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 (June - July). The young remain with their parents and gain hunting practice until they depart on migration in the fall. Reproductive Chronology * MAR APR MAY JUN JUL AUG SEPT X-----------X ARRIVE FROM WINTERING GROUNDS (3/11 - 4/4) r X----------X COURTSHIP AND NEST CONSTRUCTION X--------------X EGGS LAID (4/1 - 5/1) X------X NESTLINGS FIRST APPEAR (mid-May) X------X NESTLING STAGE (mid to late May - early July) X-----X FLEDGING (July) (late Aug. - mid- Sept) MIGRATION X------X * data from J. Estep 1989.