Swainson's hawks are back from their winter in Argentina. Working on our Littleton, Colorado, farm today, I observed several of these large buteos cavorting overhead, soaring, hovering and stooping, as if to display their pleasure in having completed a long migration. Indeed, making a roundtrip journey of more than 4000 miles each year, Swainson's hawks travel further between breeding and wintering grounds than any other American raptor (with the possible exception of Arctic breeding peregrine falcons).
Monogamous, these hawks are highly territorial during the breeding season and their high-pitched calls are commonly heard from the time of their arrival in spring until their chicks are fledged. Nests are generally constructed in large, solitary trees in open country and may be used repeatedly over the years. The female incubates the eggs and the male brings food during that time; once the chicks hatch, both parents hunt for food, which generally consists of small mammals, reptiles and birds throughout the breeding cycle. During the rest of the year, Swainson's hawks, despite their size, are known to prefer insects, feasting primarily on grasshoppers and dragonflies.
The summer breeding range of Swainson's hawks extends from western Minnesota, Iowa and Missouri to the Pacific Coast and from western Canada to northern Arizona, New Mexico and Texas. Though a bit smaller than red-tailed hawks, their long wings give them an eagle-like appearancer in flight and their plumage pattern (especially in the common white-phase subspecies) aids identification. By August, their territorial instincts have abated and Swainson's hawks begin to congregate in large flocks, drifting southward on their two month journey to the pampas of Argentina; there they have long been threatened by the use of DDT and other pesticides, highlighting the importance of international cooperation in efforts to conserve migratory birds. Fortunately, this practice has diminished and populations of this majestic buteo seem to have stabilized across most of its breeding range.
