Thirty thousand years ago, many peregrines began roaming the skies of the present-day United States east of the Mississippi River and in the Rocky Mountains. In the 1930s, there were approximately 1,000 nesting pairs of peregrines, 300–400 of which nested east of the Mississippi River. But in the early 1950s, the breeding population began to disappear.
In 1970, the peregrine falcon was listed as an endangered species. By 1975, the peregrine population east of the Mississippi had vanished, and only 20 percent of the breeding pairs remained.
Widespread use of the pesticide DDT, which was used to protect trees and crops from insects, nearly annihilated the bird in the United States. Smaller birds, on which the peregrines fed, were being contaminated by eating insects sprayed with DDT. The pesticide weakened the birds’ reproductive capability by making them produce thin-shelled eggs that broke when incubated by the adults.
Today, there are an estimated 1,650 breeding pairs of Peregrine Falcons in the United States and Canada. On Aug. 25, 1999, the U.S. Fish and Wildlife Service officially removed the American peregrine falcon from the Federal List of Endangered and Threatened Wildlife.