Swainson's Hawk IV
A major cause of Swainson's Hawk population decline was pesticide use in its wintering grounds of Argentina. Farmers there were using pesticides (such as DDT) to control grasshopper and locust infestations. The Swainson's Hawks were ingesting these pesticides through gorging themselves on the insects as they lay dying.
The U.S. has worked with Argentinian farmers to resolve this problem, and this bird is currently out of danger.