Peregrine falcons can be found on all continents except Antarctica, and in a variety of habitats from tundra to desert. While they commonly nest on cliffs along mountain ranges, river valleys, and coastlines, many peregrines also reside on skyscrapers and bridges in large cities. Like other raptors, peregrines are well adapted for hunting prey. They possess great vision, powerful talons, and sharp, curved beaks for tearing flesh.

No other bird flies as fast as a peregrine, and it's when hunting for flying prey like pigeons, starlings, and ducks that a peregrine demonstrates its greatest speed. Starting from a high perch or airborne position, it dives and strikes its prey in midair with its feet. During its rapid descent, or "stoop," the peregrine may top 320 kph (200 mph). If the initial high-speed strike is not fatal to the prey, the peregrine catches the stunned animal and kills it with a bite to its neck.

The peregrine's history over the last 50 years is one of sickness, endangerment, and recovery. Beginning in the late 1940s and continuing for 20 years, each of the identified 500 breeding pairs in the eastern U.S. were extinguished, as were nearly all of the 1,000 pairs in the west and Mexico. While human encroachment on habitat was partly to blame, scientists determined that the decreased survivorship resulted from the widespread application of DDT, an insecticide sprayed in an effort to control insect-borne diseases.

Toxins enter the food chain when organisms absorb them from the air or water around them. Near the bottom of the food chain, organisms have relatively low levels of toxins. However, in larger animals, through a process known as biomagnification, toxins accumulate and concentrate in fatty tissue, such that the more tainted prey a predator eats, the more toxins it acquires.

In the case of peregrine falcons, scientists have determined that the high DDT concentrations in female peregrine populations interfered with liver enzymes that helped produce the sex hormone estrogen. As estrogen levels declined, the amount of calcium produced in the female's body also declined. Consequently, females laid eggs with thinner shells, and these eggs broke more readily during incubation. With fewer peregrine chicks than normal surviving to replace dying adults, populations dwindled overall.

In 1972, the federal government banned the use of DDT in the U.S., and two years later, peregrine reintroduction programs began. Captive breeding involved a process called "hacking," in which human caregivers sheltered peregrine chicks in boxes set atop towers or cliff ledges and fed them through a chute. Once the young were ready to hunt on their own, they were released into the wild. While their populations have yet to attain pre-contamination levels, and some are exposed to DDT still in use in their winter havens in Central and South America, peregrines have recovered enough to have been removed from the Endangered Species List in 1999.

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