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Swainson's Hawk Head © Peter Llewellyn

Swainson's hawks are in decline because of habitat loss and pesticide use.

Traveling from western North America to the pampas of Argentina, Swainson’s hawks travel one of the longest migrations made by raptors.

Swainson’s hawks, named for nineteenth century English naturalist William Swainson, are found throughout western North America during the summer breeding season. Scientists estimate that nearly 20 percent of the world’s population of Swainson’s hawks breed in the boreal forest.

These hawks are notable for both their long migrations and their unusual diet. Each year, Swainson’s hawks migrate in great flocks – called kettles – that contain thousands of birds. Their spring and fall journeys take them on a 17,000 mile roundtrip from their breeding grounds in North America to their wintering grounds in one relatively small area of Argentina’s pampas.

The diet of Swainson’s hawks is unusual among raptors. When breeding and raising young, these hawks, like most other raptors, feed primarily on small mammals, but during migration and wintering, they eat insects, such as grasshoppers, moths, butterflies and leaf beetles almost exclusively.

Because these raptors ride warm air currents (known as thermals) for most of their flights, they must stay close to land where thermals are common. For a few days each fall, virtually the entire population of Swainson’s hawks darkens the skies above Panama, as they follow the curve of the land along the narrowest point between North and South America.

Today, Swainson’s hawks are in decline because of habitat loss and pesticide use, which affects the birds directly and also eliminates many of the insects that they rely on during the winter.

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