About 30 years ago pesticides - particularly DDT - spread through the food chain topped by the Peregrines. There were only 39 breeding pairs in the United States, and none east of the Mississippi River when wildlife scientists put them on the endangered species list and worked to bring them back.

As Peregrines disappeared, their natural predator, the Great Horned Owl, took over the falcon's high perches. The Peregrines' rescuers realized that introducing Peregrines into owl-stalked habitats would imperil the already-endangered falcons. So the scientists introduced the Peregrines to new habitats: tall buildings, bridges, and grain elevators - areas that owls usually avoided. Peregrines now live in more than 25 North American cities, feasting primarily on pigeons, starlings, sparrows, and other urban birds.

In 1999, the U.S. government took the Peregrine Falcon off the endangered species list but will continue to monitor Peregrine populations. The Peregrine Falcon remains on the Endangered Species List of most states in the eastern United States.