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Peregrine Falcon

The peregrine falcon (Falco peregrinus) is a bird of prey in the family Falconidae. It is one of the most wide-ranging birds in the world with populations in both the Eastern and Western Hemispheres, and occurring on all continents except Antarctica. It is also the world's fastest-flying bird. Unfortunately, beginning in the 1940s, many populations of the peregrine falcon were decimated by the ecotoxicological effects of pesticide use, particularly DDT and other organochlorines. The concentrations of these chemicals become amplified in the ecological food web, severely affecting top predators such as the peregrine falcon. The organochlorines cause falcons to lay eggs with thin, fragile shells, as well as other physiological problems that led to reproductive failure and population decline.

By the 1960s the peregrine falcon was extirpated from the eastern half of the United States. Prior to the organochlorine-induced losses, there were about 400 breeding pairs of these falcons in that region. Similarly, during the early 1970s there were over 300 breeding pairs in the western states, but that dropped to 200 within a decade. (Populations in Alaska and northern Canada involve a different subspecies of the falcon, which was less affected by organochlorines.)

The peregrine falcon has benefited from programs of captive-breeding and release. Due to reintroduction efforts the species once again breeds in the eastern United States In 1985, for example, 260 captive-raised young falcons were released to the wild, 125 in the eastern states and 135 in the west. By 1991, more than 100 breeding pairs were found in the eastern United States and 400 pairs in the west.

The recovery success of the peregrine falcon is due largely to the efforts of two groups, the Peregrine Fund based at Cornell University in Ithaca, New York, and the Canadian Wildlife in Alberta. Much of their work centered on captive breeding for release into the wild, and finding ways to induce the falcons to nest and raise young in their former range. With great patience, and limited early success, the projects eventually paid off.

The restoration projects yielded much valuable information about peregrine falcons, as well as determining innovative approaches for re-establishing wild populations. For captive breeding, wild falcons trapped as nestlings stood a much better chance of reproducing in captivity than those trapped as flying immatures or as adults. In addition, researchers found that window ledges of tall buildings in cities were a useful site for releasing young falcons. These locations mimic the natural nest sites of peregrines on cliffs, and the birds have abundant prey in the urban ecosystem, particularly rock doves. Many people regarded this as a "service" to the cities, because the "pigeons" tend to be a nuisance species.

Since it began in the 1970s, the captive-breeding program has resulted in more than 3,000 young peregrine falcons being released to the wild. Because the widespread use of organochlorines is no longer allowed in North America, the habitat of the falcons has improved. In combination, these circumstances have allowed a substantial population recovery of peregrine falcons in North America. In 1998, there were at least 1,600 breeding pairs. Because of the population recovery, in 1998 the U.S. Fish and Wildlife Service removed the peregrine falcon from its list of endangered species. It appears that this magnificent falcon is back from the brink of extinction in the continental United States.



Ehrlich, P., D. Dobkin, and D. Wheye. Birds in Jeopardy. Stanford, CA: Stanford University Press, 1992.

Ratcliffe, D.A. The Peregrine Falcon. Vermillion, SD: Buteo Books, 1980.

Sibley, David Allen. The Sibley Guide to Birds. New York: Knopf, 2000.

Eugene C. Beckham

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Science EncyclopediaScience & Philosophy: Pebi- to History of Philosophy - Indifferentism