Frequently Asked Questions - Peregrine Falcons

What is a Peregrine Falcon?

The Peregrine Falcon (Falco peregrinus; "wandering falcon") is a sleek, crow-sized bird of prey. It grows between 15 and 21 inches long with a wingspan of up to 40 inches. Males are about a third smaller than females. Fluffy white as eyasses (chicks), their down is replaced by brown feathers in three to five weeks. It is arguably the most famous and admired raptor in the world because of its beauty, speed and agility. The Peregrine is one of six falcons found in the United States. The others are Gyrfalcon, Prairie Falcon, Merlin, American Kestrel, and the Aplomado Falcon.

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Where do Peregrines live?

Peregrine Falcons are found virtually worldwide on every continent except Antarctica (from the Arctic to South America), but they are not considered "common" in any specific areas. In Wisconsin, Peregrines are once again nesting in suitable habitat along the bluffs of the Mississippi River. While they typically migrate to the tropics for the winter, some urban-nesting Peregrines are becoming permanent year-round Wisconsin residents.

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What do Peregrines eat?

Peregrines hunt prey while perched on high vantage points or while in flight. Striking in midair, they most often catch a wide variety of small- to medium-sized birds. On occasion, they capture larger, heavier prey species. Instead of taking the heavier species back to their nest or another perch, Peregrines often drop this prey to safe ground to eat. In the Upper Midwest, a total of 107 different bird species have been identified as prey.

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Where do Peregrines nest?

These raptors typically nest on high cliffs or nearly inaccessible ledges. These nesting sites, known as aeries, provide safety and vantage points from which Peregrines can survey their territory and hunt. Used for generations, aeries often have different annual inhabitants because several birds typically find and compete for the same suitable nest. Today, Peregrines in Wisconsin primarily are using tall buildings, power plant stacks, and bridges for nesting. But they also are beginning to recolonize historical sites on Mississippi River cliffs. Falcon mates often remain paired for life, and renew their bond with courtship in late winter or early spring.

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How did the Peregrine Falcon become an endangered species?

Like many threatened and endangered species, Peregrine Falcon populations have suffered from habitat loss and human intrusion. But chlorinated hydrocarbon pesticides like dichloro-diphenyl-trichloroethane (DDT) are the primary reason Peregrines and other raptors experienced dramatic reproductive failure beginning in the 1950s. DDT and other persistent chemicals originally used on grain crops, made their way up the food chain (bioaccumulation). As a carnivore that feeds high on the food chain, Peregrines ingested large doses of pesticides from its prey that ultimately concentrated in the fatty tissues of the falcons. These chemicals caused eggshells to thin. Unable to support the weight of incubating females, the thin-shelled eggs began to break and populations of Peregrine Falcons and other raptors plummeted. Peregrines ultimately disappeared from the entire eastern United States, prompting their placement on the U.S. Endangered Species List in 1973. Although it was delisted in 1999, Peregrine Falcons remain on Wisconsin's threatened and endangered species list.

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How has the Peregrine Falcon reclaimed its spot in Wisconsin's skies?

Wisconsin banned the use of DDT in 1971. Concurrently, several falcon recovery programs were created. Using several different techniques, falcons were bred and raised in captivity, then released into the wild. Ideally, chicks were reintroduced into traditional nest sites in natural habitat. Yet, in the late 1980s, a technique called hacking started to be used in urban settings such as Milwaukee, Madison and Racine. When existing nests were unavailable or when scientists wanted to reintroduce Peregrines to a specific area, four-week old captive-produced chicks were placed in a specially designed box that was positioned on a cliff or rooftop.

To avoid imprinting, the young falcons were fed in a manner that prevented them from associating food with humans. After a few weeks, the front of the box was removed, and the birds were set free to try their wings. Scientists continued to feed them for about five more weeks, until they became self-sufficient. Tall buildings and structures have been used successfully as substitutes for the traditional cliff nesting sites. In 2004, 17 Peregrine nest sites in Wisconsin produced a total of 51 young.

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