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American peregrine falcon

The American peregrine falcon (Falco peregrinus anatum) breeds only in North and Central America and occurs throughout much of North America from the subarctic boreal forests of Alaska and Canada south to Mexico [1]. It is estimated that prior to the 1940s, there were approximately 3,875 nesting pairs of peregrines in North America [1]. From the 1940’s through the 1960’s, however, the population of the peregrine, and many other raptors, crashed as a result of the introduction of synthetic organochlorine pesticides to the environment. By 1975, there were only 324 known nesting pairs of American peregrine falcons in the U.S. [2].

Scientists investigating the peregrine's decline, found unusually high concentrations of the pesticide DDT and its breakdown product DDE in peregrine falcons and other birds of prey [1]. Organochlorine pesticides were put into use following World War II. Use peaked in the late 1950’s-early 1960’s and continued through the early 1970s [1]. Organochlorine pesticides cause direct mortality and reduced reproduction in birds of prey who, being at the top of the food chain, ingest high doses of pesticides concentrated and stored in the fatty tissue of prey animals that themselves ingested contaminated food [1]. Heavily contaminated females may fail to lay eggs and organochlorines passed from the female to the egg can kill the embryo before it hatches [1]. Probably the most serious problem resulted from DDE, the principal metabolite of DDT, which prevents normal calcium deposition during eggshell formation, causing eggs to frequently break before hatching [1] During the period of DDT use in North America, eggshell thinning and nesting failures were widespread in peregrine falcons, and in some areas, successful reproduction virtually ceased [1].

The degree of exposure to these pesticides varied among regions, and peregrine falcon numbers in more contaminated areas suffered greater declines [1]. The eastern population plunged from an estimated 350 active nest sites in the 1930's and 1940's to no active breeding birds from 1964 to 1975 [3]. Peregrine falcons in the Great Plains states east of the Rocky Mountains and south of U.S. and Canadian boreal forests were also essentially extirpated [1]. West of the 100th meridian, peregrine falcons were significantly reduced [1]. Local populations were greatly depressed or extirpated and by 1965, fewer than 20 pairs were known west of the U.S. Great Plains [1].

In 1970, the American peregrine was listed as endangered and efforts to recover the species began. The use of DDT was banned in Canada in 1970 and in the United States in 1972 [1]. This was the single most significant action in the recovery of the peregrine falcon [1]. In addition, in the eastern United States, efforts were made to reestablish peregrine falcons by releasing offspring from a variety of wild stocks that were held in captivity by falconers [1]. The first experimental releases of captive-produced young occurred in 1974 and 1975 in the eastern United States [1]. These and future releases demonstrated that “hacking”, the practice of retaining and feeding young captive bred birds in partial captivity until they are able to fend for themselves, was an effective method of introducing captive-bred peregrines to the wild [1]. Since then, over 6,000 falcons have been released in North America [1]. Approximately 3,400 peregrines were released in parts of southwest Canada, the northern Rocky Mountain States, and the Pacific Coast States [1].

In the late 1970s Alaska became the first place American peregrine falcon population growth was documented and, by 1980, populations began to grow in other areas [1]. Not only did the number of peregrine falcons begin to increase, productivity (another important measure of population health) improved [1]. Efforts to reestablish peregrine falcons in the East and Midwest proved largely successful and by 1999 peregrines were found to be nesting in all States within their historical range east of the 100th meridian, except for Rhode Island, West Virginia, and Arkansas [1]. In highly urban areas, peregrine falcons showed great adaptability, and began substituting skyscrapers for natural cliff faces as nesting sites [4]. By 1998, the total known breeding population of peregrine falcons was 1,650 pairs in the United States and Canada (far exceeding the 456 required for delisting) and other recovery goals, including estimates of productivity, egg-shell thickness, and contaminants levels, had been met [1]. The final decision to delist the America Peregrine was made on August 25, 1999. Monitoring of American Peregrine populations has continued, however, under a post-delisitng monitoring plan [5]. Starting in 2003, data has been collected from a subset of American peregrine falcon territories [5]. Data will be collected every 3 years and presented in triennial reports [5]. Monitoring will continue through 2015 [5]. So far, it appears American peregrine populations have continued to increase since delisting [5].

ALASKA: Surveys conducted between 1966 and 1998 along the upper Yukon River demonstrated increases in the number of occupied nesting territories from a low of 11 known pairs in 1973 to 46 pairs in 1998 [1]. Similarly, along the upper Tanana River, the number of occupied nesting territories increased from 2 in 1975 to 33 in 1998 [1]. The recovery objective of 28 occupied nesting territories in the two study areas was first achieved in 1988, with 23 nesting territories on the Yukon River and 12 on the Tanana River [1].

PACIFIC STATES: By 1976, no American peregrine falcons were found at 14 historical nest sites in Washington [1]. Oregon had also lost most of its peregrine falcons and only 1 or 2 pairs remained on the California coast [1]. Surveys conducted from 1991 to 1998 indicated a steadily increasing number of American peregrine falcon pairs breeding in Washington, Oregon, and Nevada [1]. Known pairs in Washington increased from 17 to 45 and in Oregon from 23 to 51 [1]. The number of American peregrine falcons in California increased from an estimated low of 5 to 10 breeding pairs in the early 1970s to a minimum of 167 occupied sites in 1998 [1]. The increase in California was concurrent with the restriction of DDT and included the release of over 750 American peregrine falcons through 1997 [1].

ROCKY MOUNTAINS/SOUTHWEST: The Rocky Mountain/Southwest population of the American peregrine falcon has made a profound comeback since the late 1970s when surveys showed no occupied nest sites in Idaho, Montana, or Wyoming and only a few pairs in Colorado, New Mexico, and the Colorado Plateau, including parts of southern Utah and Arizona [1]. Surveys conducted from 1991 through 1998 indicated that the number of American peregrine falcon pairs in the Rocky Mountain/Southwest area has steadily increased [1]. In 1991, there were 367 known pairs; in 1998 the number of pairs increased to 535 [1].

EASTERN STATES: The eastern peregrine population has a unique history and complex status under the Act [1]. Peregrine falcons were extirpated in the eastern United States and southeastern Canada by the mid-1960s [1]. Releases of young captive bred peregrines have reestablished populations throughout much of their former range in the east [1]. In 1998, there were a total of 193 pairs counted in five designated eastern State recovery units [1]. The number of territorial pairs recorded in the eastern peregrine falcon recovery area increased an average of 10% annually between 1992 and 1998 [1]. Equally important, the productivity of these pairs during the same 7-year period averaged 1.5 young per pair, demonstrating sustained successful nesting [1].

[1] U.S. Fish and Wildlife Service. 1999. Final Rule to Remove the American Peregrine Falcon from the Federal List of Endangered and Threatened Wildlife, and to Remove the Similarity of Appearance Provision for Free-Flying Peregrines in the Conterminous United States. Federal Register (64:46542).
[2] Hoffman, C. 1999. The Peregrine Falcon is Back! New release, U.S. Fish and Wildlife Service, August 20, 1999.
[3] Clark, K. 2005. The Peregrine Falcon in New Jersey, Report for 2005. New Jersey Department of Environmental Protection, Division of Fish and Wildlife, Endangered and Nongame Species Program.
[4] New Jersey Division of Fish and Wildlife. Fact sheet, Peregrine Falcon Falco pereginus. New Jersey Department of Environmental Protection, Division of Fish and Wildlife, Endangered and Nongame Species Program. Website (http://www.njfishandwildlife.com/tandespp.htm) accessed February, 2006.
[5] USFWS. 2003. Monitoring Plan for the American Peregrine Falcon, A Species Recovered Under the Endangered Species Act. U.S. Fish and Wildlife Service, Divisions of Endangered Species and Migratory Birds and State Programs. Pacific Region, Portland Oregon 53pp.

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