Peregrine Falcon (Falco peregrinus)

Status in WI: endangered 1991 numbers in WI: 2 pair Length: female 18-21 inches, male 15-18 inches Wingspan: female 45 inches, male 40 inches Weight: female 32-40 ounces, male 20-25 ounces

Description || Food || Breeding Biology || Distribution || History in Wisconsin || Current Status || Research and Management || What You Can Do || Further Reading || Excerpt from the Animal Guide || Endangered Resources Reports

Description

Peregrine falcons are sleek, crow-sized birds of prey, famous for their speed and beauty. For hundreds of years, peregrines have been prized for the sport of falconry. Recently, however, they have become well known as a species endangered due to pesticide contamination. These magnificent birds are now making a comeback in many parts of their former range.

The peregrine’s bluish upperparts, black cap, black moustache below the eye, white chin and buffy under-parts barred with brown give it a striking appearance. It has dark brown eyes with yellow eye rings, a slate-blue beak and yellow feet and legs. Large, strong feet and a powerful, hooked beak enable the peregrine to carry and eat its prey. Peregrines are compact, fast birds with pointed wings.

As with most birds of prey, male peregrines are smaller than females. Male falcons are called tiercels, which means "one-third"; they are one-third smaller than females.

An immature peregrine falcon is similar to the adult, but has brown upperparts, a heavily streaked breast and a blue-gray beak, legs and feet.

Food

Peregrine falcons eat small to medium-sized birds. They were formerly called "duck hawks" because they occasionally prey on ducks. Those living in urban areas eat large numbers of pigeons and starlings. Peregrines will eat a great variety of species, however, depending on what is available.

Peregrines hunt primarily at dawn and dusk, when their prey is most active. They strike and capture birds in mid-air, a strategy that requires open space. Thus, they often hunt over open water, marshes, valleys, fields and tundras.

A peregrine hunts from the wing or from a high perch. It spots prey with keen eyes and begins its stoop, a streamlined dive with tail and wings folded and feet lying back. The falcon hits its prey with its foot, stunning or killing it, then swoops back around to catch it in mid-air. If the prey is too heavy to carry, the peregrine will let it fall to the ground and eat it there. Peregrines pluck their prey before eating it. Despite their reputation as able predators, peregrines often miss their strike and the prey escapes.

During a stoop, peregrines may reach speeds of 200 mph. The air pressure from this bullet-like plunge might burst an ordinary bird’s lungs. It’s thought that the series of baffles in a peregrine’s nostrils slow the wind velocity, enabling the bird to breathe while diving.

Breeding Biology

Peregrines first breed when two or three years old. The male selects a nesting ledge and courts the female with aerobatics and a "wichew" call. The pair will return year after year to use the same nesting ledge, called an eyrie, which they defend from predators and other peregrines. Eyries are usually at least a mile apart. Lack of suitable nesting sites formerly limited the peregrine population. The same site may be used by successive pairs for many years. One ledge on an island off Wales has been used since at least 1243.

Peregrines nest mainly on high cliffs, although some birds have taken up residence on ledges of skyscrapers in large cities. The nest is a scrape, usually in loose soil, sand or vegetation, with no added nesting material. The female lays 3-5 creamy-white eggs with red-brown speckles. If the eggs are lost early in the nesting season, she may lay another clutch. The female does most of the incubating. After 32 days, the eggs hatch.

Newly hatched chicks are covered with creamy-white down and their feet are noticeably large. The male peregrine does most of the hunting, bringing food to the female and nestlings, which are called eyases. The eyases are fed by the female, who plucks feathers from the prey before giving it to them. The young fledge when 35-45 days old and stay with their parents for several weeks. The adults capture prey for the fledglings, who learn to snatch it from them in mid-air. The young peregrines then begin to capture birds and large insects on their own.

On average, two eyases successfully fledge per nest. Infertile eggs and natural losses of eyases account for this success rate. If the birds survive their first year, their chances for survival are good. Some peregrines have been known to live 18-20 years, but the average lifespan is probably shorter (2-8 years).

Distribution

The Latin name "peregrinus" means "wandering" or "coming from foreign parts." Peregrine falcons are distributed worldwide, occurring on every continent except Antarctica. Some northern populations migrate long distances.

There are three subspecies of peregrines in North America. They differ slightly in appearance, breed in distinct regions and migrate different distances. Peale’s peregrine (F. p. pealei) nests and winters along the coasts of Alaska and British Columbia. The tundra peregrine (F. p. tundrius) breeds in the Canadian arctic south to treeline and migrates as far south as Argentina. The subspecies F. p. anatum, native to North America south of treeline (including Wisconsin), tends to overwinter in the southern U.S., Central America and the Caribbean. This subspecies no longer exists east of the Mississippi.

Historically, peregrines nested in Wisconsin on cliffs along the Wisconsin and upper Mississippi rivers and in Door County. Between 1965 and 1985, however, no peregrines nested in the state. Birds breeding in Canada have continued to migrate through Wisconsin in the spring and fall, following age-old migration routes along the Mississippi River and shore of the Great Lakes.

A map outlining Pre-1977 and 1997 to Present Distribution is available.

History in Wisconsin

At least 24 peregrine eyries were active in Wisconsin until the mid-1950s. Following World War II, however, this previously stable peregrine population began to decline. It took almost 20 years before reasons for the decline became clear. Evidence mounted that there was a direct connection between peregrine declines and the widespread use of pesticides like DDT. During this time, peregrines disappeared from Wisconsin and many other regions of the world.

By the late 1960s, research had begun to show that organochlorine pesticides like DDT caused physiological changes in peregrine falcons and other species of animals that fed high on the food chain. (Dr. Joseph Hickey at the University of Wisconsin-Madison coordinated several key meetings which addressed this problem.) Studies showed that pesticides became more highly concentrated with each link in the food chain (e.g., from plants, to plant-eating insects, to insect-eating birds, to bird-eating peregrine falcons).

Researchers found that high DDT concentrations caused a peregrine’s liver to change the production of an enzyme essential to maintaining levels of the female sex hormone, estrogen. Estrogen levels declined, reducing the amount of calcium in the female’s body and causing her to lay eggs with thin shells. When adults incubated the eggs, the eggs broke under their weight. In addition, parental behavior was influenced by the pesticides; even if the eggs hatched, adults often would not care for the chicks, which soon died. With few chicks surviving, peregrine populations dwindled. Of 300 pairs known to nest in the eastern U.S., none remained by the early 1970s.

Wisconsin banned the use of DDT in 1971; it was one of the first states to do so. In 1972, the federal government banned the use of DDT and other organochlorine pesticides in the U.S. However, residues still remain in the environment. Peregrines and other affected species have begun a slow recovery, but populations have yet to reach pre-pesticide numbers. In addition, these pesticides are still manufactured in the U.S. and sold for use in other countries. Many countries in Central and South America, where peregrine falcons overwinter, still use DDT. Thus, some falcons continue to be exposed to the pesticides and their adverse effects.

In some places, peregrines also have had to cope with habitat loss and human disturbance. For example, egg collecting was a popular hobby during the 1800s and peregrine eggs were gathered in large numbers; some chicks were taken from the nest for use by falconers; and peregrines were shot by owners of homing pigeons, who feared the falcons would kill their birds. However, pesticide contamination has by far been the main cause of peregrine declines.

In an effort to produce birds for falconry, falconers began breeding peregrines in captivity. Using techniques developed by falconers, biologists also began to breed them, with the hope of eventually reintroducing birds to the wild. Breeding programs at Cornell University and other places have been successful and many chicks have been reintroduced to traditional peregrine habitat.

Reintroduction involves more than just turning birds loose at a site. The birds are "hacked," a technique by which chicks are maintained (provided with food and shelter) at a release site until they are acclimated to it and old enough to fledge and hunt on their own. The hope is that the fledged birds will eventually return to the area and take up residence. Hacking, like rearing chicks in the wild, is not foolproof; some chicks have died, often due to predation by great horned owls and raccoons. But many states (e.g., New York, Massachusetts, New Jersey, Minnesota) have had great success. Peregrine falcons are nesting again in many places east of the Mississippi.

In 1976, University of Minnesota biologists brought five peregrine chicks from Cornell University to Wisconsin. The birds were hacked successfully at a traditional eyrie on the upper Mississippi River. None returned to breed in Wisconsin, however. Of three chicks hacked in 1977, two were killed by great horned owls; the third was then returned to Cornell. In 1986, captive-bred peregrines, several hacked in Minnesota, bred in Wisconsin. The DNR’s Bureau of Endangered Resources (BER) began releases of peregrines in Wisconsin in 1987.

Current Status

Peregrine falcons were placed on the Wisconsin Endangered and Threatened Species List in 1975. Although peregrines can be seen in Wisconsin, most are birds migrating through the state between breeding sites in Canada and southern wintering grounds. In 1986, however, peregrines bred in Wisconsin for the first time in 22 years. Several of the adults were captive-bred birds that had been released in Minnesota. As many as three nesting attempts continued along the Mississippi River until 1989. Unfortunately, the young produced each year were killed by predators—great horned owls and/or raccoons. Endangered Resources biologists were pleasantly surprised in 1988 when two one-year old peregrines occupied the release box as a nest site in Milwaukee. They produced two young—another surprise as they usually don’t produce young until two years of age. The site has continued to be occupied since 1988 even though the individuals in the pair have changed. Twelve young (eight wild-produced, four captive-bred) have fledged from this nest.

A pair of peregrines attempted to nest on the State Capitol Building in Madison in 1991. They ignored the nest box we provided and chose a very narrow ledge. At least one egg was found broken below the ledge. No young were produced at the site. Releases started in Milwaukee in 1987 with fourteen young. Thirty-three peregrines were released in Madison between 1988 and 1990. In 1991 La Crosse was the release site for 15 peregrines. Releases will continue for at least another year. More sightings of peregrines continue to be reported. Hopefully, more will come back to Wisconsin to nest.

Research and Management

The federal government has drafted a national peregrine falcon recovery plan and the BER is enacting a Peregrine Falcon Recovery Plan for Wisconsin. The BER’s goal is to establish at least 10 breeding pairs of peregrines in the state by the year 2000, and eventually 18-24 pairs. In 1987, a reintroduction program was started. In addition, the BER recovery plan calls for inventory and protection of existing and potential nesting habitat, and peregrine falcon protection through law enforcement, education and public information.

What You Can Do

The BER can’t "do it all" when it comes to ensuring the future of peregrine falcons in Wisconsin. You can help by: becoming a BER volunteer; reporting peregrine sightings to the BER; supporting legislation banning harmful pesticides; and contributing to the Endangered Resources Fund on your Wisconsin income tax form.

If you’d like to learn more about falcons and hawks—and even see them—consider attending a fall hawk watch. A number of Wisconsin organizations lead hawk watches during fall migration (early September—early October) to Wisconsin’s hawk watching "hotspots" (Wyalusing State Park, Harrington Beach State Park, etc.). For information about these birding trips, watch for news releases or contact: the BER; Wisconsin Society for Ornithology, c/o Thomas Schultz, Field Trip Coordinator, Rt. 2, Box 23, Green Lake, WI 54941, (414) 294-3021; your local Audubon Society chapter; or other birding and environmental organizations.

The future of Wisconsin’s peregrines depends on continued support by Wisconsin’s citizens.

Further Reading

Bent, A.C. 1938. Life Histories of North American Birds of Prey, Part II. U.S. Nat. Mus. Bull. 170:1-482.

Blood, D. 1973. Peregrine Falcon. Can. Wild. Serv., Hinter-land Who’s Who. 3 pp.

Brown, Leslie. 1976. Birds of Prey: Their Biology and Ecology. A & W Publishers, Inc., NY. 256 pp.

Cade, Tom. 1982 The Falcons of the World. Comstock Publishing Assoc., Ithaca, NY. 192 pp.

Gieck, C. 1991. Peregrine Falcons: A Native Returns to Wisconsin. Activity Guide. WDNR-BER 30 pp.

Hickey, J.J. (ed.). 1969. Peregrine Falcon Populations, Their Biology and Decline. The Univ. Wis. Press, Madison.

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

Snow, C. 1972. American Peregrine Falcon and Arctic Peregrine Falcon. Habitat management series for endangered species, Report No. 1. Bur. of Land Management, U.S. Dept. of the Interior. 35 pp.

Excerpt from THE ENDANGERED AND THREATENED VERTEBRATE SPECIES OF WISCONSIN

Status: State Endangered (1975). Federally Endangered.

Occurrence: Uncommon migrant. Rare summer visitor; rare winter visitor south and central. Recently reintroduced. Between 1940 and 1960 these birds were found along the Wisconsin side of the Mississippi River, along the lower Wisconsin River, in Door County, and along the St. Croix River. They disappeared for more than 20 years in Wisconsin. Efforts to reintroduce the Peregrine began in the 1970s. Breeding territories have been established in or near the cities of Milwaukee, Sheboygan, Madison, and La Crosse. A map outlining Pre-1977 and 1997 to Present Distribution is available.

Aid to ID: Adult peregrine falcons have a black cap and a characteristic black moustache below the eye. Throat and underparts are white. Back and upper wings are slate colored. They have dark brown eyes with yellow eye rings. Feet and legs are yellow.

Habitat: Commonly place nests on open ledges, holes, or recesses of either igneous or sedimentary rock. Reintroduction efforts have resulted in them utilizing nesting structures on tall buildings or smoke stacks in cities. High ledges near open water are preferred for nesting.

Food Habits: Majority of diet consists of small to medium sized birds - such as flickers, robins, pigeons, sparrows, and meadowlarks. They occasionally prey on ducks.

Natural History:

Breeding: Nest at 3 years old. Clutch size: 3-4 cream or buff eggs with red-brown markings; laid from March to June. Incubation: 28-29 days. Young fledge 35-42 days after hatching.
Nest: Peregrines do not build nests. They nest on cliffs and bluffs, scraping shallow hollows in the soil, or rarely in hollows of old trees 50-90 feet up.

Management Considerations: A major factor in the decline of the peregrine falcon has been the widespread use of organochlorine pesticides. Eggshell thinning due to the use of DDT reduced reproductive success. Suitable habitat still exists in Wisconsin and efforts to reintroduce the peregrine falcon through captive breeding and restocking has experienced some success, particularly in the Milwaukee area. Great horned owls, which prefer large wooded habitats, have been primarily responsible for impeding peregrine recruitment along the Mississippi River.