This handsome western buteo, which occurs in both light and dark morphs (color variations), was named for British naturalist William Swainson. Some of its folk names-"grasshopper hawk" or "locust hawk"-reflect this bird's tastes in prey. (Read about Ferruginous Hawk, another impressive western buteo.)

Starting in late August, nearly the entire population of Swainson's Hawks migrates south to Argentina and Brazil in huge "kettles" or flocks. Hundreds of thousands of Swainson's Hawks can pass by single hawk-watching sites in Veracruz, Mexico, in a single fall day.

The species' migration is a round trip of more than 12,000 miles-the longest of any North American raptor.

In the 1990s, Swainson's Hawks showed an alarming decline in the western U.S., which was traced to heavy mortality on their wintering grounds. An estimated 35,000 birds had died in Argentina in one season alone, carpeting the ground with dead birds in some places.

This disastrous die-off turned out to be due to the toxic pesticide monocrotophos, which was used to control insects in sunflower fields. The hawks were eating poisoned grasshoppers and dying in huge numbers. Although this pesticide was removed from use in the U.S. in 1991, it was still widely used in Latin America.

In 1996, American Bird Conservancy spearheaded an international campaign to remove monocrotophos from Swainson's Hawk's wintering habitat and to educate Argentinean farmers on safer pest control techniques. We successfully urged Ciba-Geigy (now Novartis) to halt distribution of monocrotophos to Argentina and persuaded the Argentinian government to stop all uses, which was a major international conservation victory.

Since then, Swainson's Hawk numbers have stabilized-an encouraging sign for this neotropical migrant.

More at: www.abcbirds.org