Studying peregrines in the 1970s led scientists to discover the environmental dangers of DDT, not just for birds but for other wildlife and humans as well. The clue was in the eggs. DDE, the main breakdown product of DDT, prevents normal calcium deposition during eggshell formation, resulting in thin-shelled eggs that are susceptible to breakage during incubation. Populations laying eggs with shells that averaged more than 17 percent thinner than before DDT had such high rates of reproductive failure that the number of peregrine pairs declined. West of the 100th meridian, only 33 percent of historical peregrine nest sites in the Rocky Mountains were still occupied by 1965. The U.S. Fish and Wildlife Service listed the peregrine falcon as endangered in 1970, when the population in the eastern United States had completely disappeared and western populations had declined by as much as 80 to 90 percent. By 1975 the population reached an all-time low of 324 nesting pairs in North America, and the United States had banned the use of DDT in 1972.

The recovery was slow. In 1970 there were 39 known pairs of peregrine falcons in the lower 48 states. The Peregrine Fund's first successful hatches in captivity came in 1973, with 20 young produced, and the first release was in 1974. According to its founder, it was not until 1980 that released falcons returned and successfully fledged young. By August 1999 The Peregrine Fund and others had released over 4,000 captive-raised peregrine falcons in 28 states, after 28 years of effort. When the species was delisted in August 1999, the Fish and Wildlife Service said there were at least 1,650 peregrine breeding pairs in the United States and Canada, well above the overall recovery goal of 631 pairs. The 1999 rule removing the American peregrine from the endangered list took effect on August 25, 1999. The Fish and Wildlife Service must monitor a species for at least 5 years after delisting.

In 1999 the peregrine falcon was taken off the United States list of endangered species, after its numbers had grown back, and migrant peregrines are known to accumulate pesticides while wintering in Latin America, so the 1999 delisting rule included a contaminant monitoring component in its post-delisting monitoring plan. Peregrine Fund biologists have studied peregrines on South Padre Island, Texas, banding birds and taking small blood samples to look for signs of oil exposure after the 2010 Gulf of Mexico oil spill. As of November 2026, Audubon says current peregrine falcon populations appear to be stable or increasing. National Geographic says that, in some parts of the globe, there actually may be more peregrines than existed before the 20th-century decline. In Alaska, eggshells were as much as 20-22 percent thinner than before DDT in the mid-1960s, about 14 percent thinner by the early 1980s, and 12.1 percent thinner from 1993 through 1995.

The Peregrine Fund says falcons that nest closer to the equator tend not to migrate, because year-round prey means there is no reason to leave, and farther north, peregrines that nest on Arctic tundra and winter in South America can fly more than 15,000 miles in a year. In a satellite-tracking study of 61 peregrines, the birds migrated an average of 8,624 km southward and 8,247 km northward, travelling at an average of 172 km a day southward and 198 km a day northward, and individual birds in that study stopped migrating anywhere from the U.S. mid-Atlantic coast to central Argentina. Many peregrine falcons migrate, but some stay in one place all year, and home ranges of peregrine falcons have been estimated from 177 to 1508 square kilometers, and males and females regularly hunt up to 5 km from their nest site or territory.

A peregrine's year begins at the nest ledge. Males display at nest ledges to attract females, and before egg-laying the pair engage in aerial displays involving power dives, tight cornering, high soaring and body rolls. Peregrine falcons form pairs that often last through many breeding seasons, and both sexes have a strong attachment to previous nesting sites, and some nest sites are used again and again for many years, and a peregrine falcon does not build a nest. It lays its eggs in a scrape, a small dip in the soil or gravel of a ledge, one egg every 48 hours, for a total of 2 to 6 eggs, and the eggs hatch in 33 to 35 days, and a male brings food to the female and to the young at the nest. Young peregrine falcons are ready to fly about five to six weeks after they hatch.

A peregrine falcon often watches for prey from a high perch, such as a cliff or a tall tree, and then hunts by diving down from high above. About 450 species of birds in North America have been documented as peregrine falcon prey, and the number worldwide may be as many as 2,000. Peregrines hunt birds as large as sandhill cranes and as small as hummingbirds. Trained peregrine falcons are sometimes flown by their trainers at airports to scare off birds that could collide with a plane. In a typical year, most peregrine falcons do not live to be 1 year old, but a healthy falcon that survives lives an average of 13 years. Peregrine falcons like open country, and they are found worldwide except for rainforests and cold, dry Arctic regions. They have also colonized urban areas, and in cities they nest on ledges of tall buildings.

Words to know

• DDT: a pesticide
• delisting: taking off list
• incubation: egg sitting
• contaminant: harmful substance
• colonized: moved into