Peregrine Falcon

Falco peregrinus


Conservation and Management

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Effects of Human Activity

Disturbance At Eyries

Much as described for Prairie Falcon (Steenhof 1998). Pairs vary greatly in responsiveness to human activities, depending partly on individual characteristics, partly on period of breeding cycle, and partly on environmental circumstances (Cade 1960). Pairs in remote locations most reactive; those in urban areas or frequently visited sites become habituated to close human activities. In past, some historical eyries were abandoned because of human encroachments or increased levels of nearby activity (Hickey Hickey 1942, Hickey 1969; Bond 1946), but not a major factor in population change. Also, temporarily abandoned eyries sometimes reoccupied after disturbance ceased (Bond 1946, Herbert and Herbert 1965), in some cases after many decades (Ratcliffe 1993). Rock-climbing and activity of researchers at eyries not usually detrimental when reasonable precautions taken (Olsen and Olsen 1978, Cade et al. 1996b; see working bib-liography of Porter et al. 1987, for >80 references to effects of disturbances).

Shooting, Trapping, And Egg-Collecting

Before legal protection, these activities accounted for loss of many hundreds of falcons and their eggs. Often shot at famous migration passes (e.g., Fisher's I., NY; Hawk Mountain, PA; Cape May, NJ; Whitefish Point, MI); however, systematic persecution as practiced by European gamekeepers was rare, occasionally done by pigeon fanciers (Bent 1938b). Nonetheless, rein-troduced urban population in greater Los Angeles, CA, area in 1990s received considerable pressure from pigeon fanciers with 14 shot, adults and young, at 1 territory over 4 yr, but with no loss of eyrie occupancy (B. Walton pers. comm.). Small numbers of nestlings/fledglings and first-year migrants also taken by falconers in period 1920s through 1960s before protection under Endangered Species Act in 1970 and Migratory Bird Treaty Act in 1972, and afterward, in case of F. p. pealei . No evidence that losses from these activities depressed number of occupied nesting territories, except in isolated, local circumstances. Reputed cases of impact from taking nestlings include: (1) lower Hudson River, NY (Herbert and Herbert 1965); (2) 40-km stretch of river in Alberta (Dekker 1967); and (3) Langara I., British Columbia (Dekker Dekker 1969, Dekker 1972), but overriding effects of pesticides and/or reduced food supply were operative in these places at same time.

Pesticides And Other Contaminants/Toxins

From late 1940s to early 1970s, massive, continentwide-indeed, nearly global-use of organochlorine pesticides, particularly DDT and HEOD (dieldrin, aldrin) in agriculture and forestry and for human disease control resulted in bioaccumulation of toxic residues in prey species, which in turn contaminated falcons, causing both lethal and sublethal effects (see review papers in Cade et al. 1988). Few fatalities documented in North America (Reichel et al. 1974, Peakall et al. 1990), but HEOD considered important cause of death among British Peregrines in 1950s-1960s and in some other parts of Europe (Ratcliffe 1993); circumstantially implicated as lethal factor in North America (Nisbet 1988). Most significant sublethal effect of DDE (persistent environmental residue of DDT) was repro-ductive malfunction resulting from abnormally thin eggshells. First identified in Great Britain (Ratcliffe 1967), this thin-eggshell syndrome was quickly confirmed as widespread condition of North American Peregrines, coincident with North American use of DDT beginning in late 1940s (Hickey and Anderson 1968; Cade et al. Cade et al. 1971, Cade et al. 1988; Court et al. 1990; Johnstone et al. 1996). Direct correlation exists between concentration of DDE residues in egg contents (reflects circulating levels in laying female) and eggshell thickness, r- values ranging from -0.57 to -0.75 in different geographic samples (Cade et al. 1971, Peakall and Kiff 1988, Newton et al. 1989, Court et al. 1990).

Peregrine population declines in 1950s-1970s associated with population averages for eggshell-thinning of >18% and residue levels of 15-20 ppm wet weight DDE in egg contents (Hickey and Anderson 1968, Peakall et al. 1975), and with associated reduction in breeding success (reviewed by Fyfe et al. 1988).

In arctic Canada from 1981 to 1985, eggs from failed nests had shells averaging 20.2% thinner than normal, while eggs from successful nests averaged 16.1% thinner (Court et al. 1990). Affected populations showing these thinning correlations in North America include e. U.S. (New Jersey, Massachusetts), n. Alaska, interior Alaska, Ungava, n. Quebec, Colorado and Rocky Mtns., and California, as well as others world-wide (Peakall and Kiff 1988). Subsequent population recovery in all these regions following 1980s associated with reduced pesticide residues in prey and in eggs and body tissues of Peregrines, increased eggshell thickness, and increased productivity (Cade et al. 1988, Peakall et al. 1990, Enderson et al. 1995a, Mesta 1999).

PCBs, mercury, and lead are other environmental contaminants often implicated in bird morbidities and fatalities, but none known to have exerted population effects on Peregrines in North America (Dement et al. 1986, Stone and Okoniewski 1988, Peakall et al. 1990). Peregrines occasionally killed by eating birds poisoned by strychnine or other persistent toxic chemicals (see Porter et al. 1987 for specific references).

Collisions With Stationary/Moving Structures Or Objects

Urban-dwelling Peregrines killed or injured by flying into windows or other features of buildings while chasing prey, occasionally by collision with moving vehicles, including aircraft at airports; sometimes strike wires; recently fledged young sometimes fall down chimneys or are killed by air-conditioning equipment or other machinery on tops of buildings; young in nests on bridges often fall into water, significantly reducing productivity at such sites (Barclay and Cade 1983, Cade and Bird 1990, Frank 1994, Bell et al. 1996). In California, electrocutions and wire strikes common in nonurban areas, as well (B. Walton pers. comm.). For other accidental injuries and fatal-ities, see Porter et al. 1987 .

Degradation Of Habitat

Difficult to assess impact on Peregrine because species is so catholic in use of wide range of habitats and landscapes, including those highly modified by humans. Most affected by loss or modification of nesting places, which are limited in number and often nonreplaceable (e.g., cliffs, ledges, special trees, towers, buildings; see Steenhof 1998 for parallel with Prairie Falcon), but has latitude to switch among alternate nesting places in same territory where >1 exists (e.g., from building to stone quarry in Salt Lake City, UT). Unlike Prairie Falcon (Steenhof 1998), agricultural practices not usually detrimental to Peregrine, except use of pesticides, as species readily preys on birds attracted to cultivated landscapes, and owing to hunting style no doubt benefited from conversion of closed-canopy forests to agriculture, as occurred in ne. U.S. in 1700s and 1800s. Migratory and wintering Peregrines, and some breeders, favor wetland areas that support concentrations of waterfowl and shorebirds; loss or degradation of these habitats is no doubt detrimental to the species. Systemic changes in ecosystem functions (e.g., impact of warmer water temperature on marine food web and consequent reduction in plankton and associated seabirds that serve as food for Peregrines in Queen Charlotte Is.; Nelson and Myres 1976) can exert major impact on Peregrine populations (see J. Thiollay 1988 and Ratcliffe 1993 for other examples).

Deleterious Impacts Of Research

Careless methods of field study can result in injury or death of adults and young, or abandonment of eggs (no known case of abandoning young), but such impacts not known to have measurable effect on long-term population stability. Inspection of nest site just before or during laying likely to cause falcons to abandon that site and renest elsewhere on same cliff or in same territory. Sudden appearance of human, or helicopter, near nest can frighten sitting bird to leave so quickly that eggs or recently hatched young may be kicked out of the nest (Cade 1960). Prolonged investigations that keep parents off eggs or downy young for varying periods, depending on climate and age of young, can cause overchilling or overheating and death. Attempts to band young >4-5 wk old can result in premature departure from nest, increasing their vulnerability to predators (Cade et al. 1996b). Trapping adults or flying juveniles sometimes results in injuries; placing identification markers or telemetry transmitters on falcons can reduce survivability. Need for information derived from disturbing procedures must be balanced against risks of injury or fatality resulting from study methods. Fyfe and Olendorff (Fyfe and Olendorff 1976) and Olsen and Olsen (Olsen and Olsen 1978) provide guidelines for minimizing impacts of human disturbance at eyries (see also Cade et al. 1996b).


Legal Protection

No legal protection in North America prior to 1930s. First protected by state law in Massachusetts, New York, and New Jersey in 1934 (Herbert and Herbert 1965, Hagar 1969); most states and Canadian provinces/territories protected Peregrine from unauthorized take by 1950s-1960s. F. p. tundrius and F. p. anatum officially listed as Endangered in 1970 in U.S. under 1969 Endangered Species Conservation Act (Public Law 91-135, 835 Stat. 275) and later transferred to 1973 Endangered Species Act (16 U.S.C. 1531 et seq.); protected with other birds of prey under Migratory Bird Treaty Act (16 U.S.C. 703-712) through agreement with Mexico, but not Canada, in 1972. Also protected from unregulated international trade by inclusion on Appendix I of Convention on International Trade in Endangered Species of Wild Fauna and Flora in 1975.

Management As Endangered Species

Efforts to propagate and release falcons began in late 1960s (Cade et al. 1988, Enderson et al. 1995a) and involved primarily actions by The Peregrine Fund, Inc., Cana-dian Wildlife Service, and several private ventures, followed later by Santa Cruz Predatory Bird Research Group (Univ. of California, Santa Cruz) and the Raptor Center, University of Minnesota. Under the Endan-gered Species Act of 1973, 4 regional-recovery plans were developed for (1) Alaska; (2) California, Oregon, Washington, and Nevada; (3) Rocky Mountain and southwest states; and (4) e. U.S.; Canada also produced nonstatutory plan in 1988 (see Mesta 1999 for sum-maries). These plans established methods and criteria for recovery; all but Alaska plan relied heavily on captive propagation and release of captive-produced birds. All plans emphasized need for reduction in environmental contamination by organochlorine pesticide residues, especially DDT.

Experimental releases of captive-produced falcons by hacking and fostering began in U.S. in 1974 and 1975 (Barclay and Cade 1983) and by fostering in Canada in 1975 (Fyfe 1988). By 1998, nearly 7,000 Peregrines had been released in North America (L. F. Kiff unpubl.), resulting in minimum of 700 re-established breeding territories (pairs in s. Canada, e. and midwestern U.S., Rocky Mtns., and Pacific Coast; TJC based on data in Mesta 1999). Also, as a result of de-creasing organochlorine residues in the environment and strict protection of surviving remnant populations, wild Peregrines began increasing in the late 1970s, first in arctic and boreal regions, but also in Southwest and Baja California and other western locations. Most of this increase resulted from residual pairs that survived the worst effects of organochlorine contamination (Enderson et al. 1995a, Mesta 1999). By 1998 known number of occupied and successful territories in North America indicated practically complete recovery and a demographically viable, continental population (see Demography and populations: population status, above, for details). Annual federal and state costs for recovery of anatum placed at >$5.4 million in the 1990s (Restani and Marzluff 2001), but partly used for law enforcement, habitat improvements, and other peripheral activities. F. p. tundrius down-listed to Threatened in 1984 (49 FR 10520) and delisted 1994 (59 FR 50796) F. p. anatum delisted 1999 (Vol. 64, no. 164: FR 46542-46558).

ESA amendment (section 49 (g) (11)) requires minimum 5-yr post-delisting monitoring in cooper-ation with state agencies to make certain delisted species maintain nonthreatened status. For F. p. tundrius, monitoring focused on breeding populations in following regions: Colville River, AK, and Hope Bay, Coppermine, and Rankin Inlet, Nunavut; also, on number of migrants counted at Assateague I., VA, and Cape May, NJ, and Padre I., TX (Swem and Ambrose 1994). No official report issued, but it is known that these populations either increased or remained stable through 1999. For F. p. anatum, more elaborate system of monitoring developed by ad-hoc committee involves random sampling to detect whether decline in number of breeders occurs over 10-yr period (63 FR 45460).

Management Needs And Objectives For Future

Long-term, continuing objectives under Migratory Bird Treaty Act, state, and Canadian provincial/territorial jurisdictions include: (1) habitat protection, (2) habitat improvements/manipulations, (3) monitoring population trends and productivity, and (4) sustained yield use for falconry. Most important components of habitat requiring special attention are traditional nesting places (eyries), which should be protected from physical alteration or destruction and from excessive human disturbances that might cause abandonment or repeated reproductive failure; also, both coastal and inland wetlands that support abundance of prey species needed, particularly by migrating and wintering falcons, especially barrier islands and associated lagoons. Habitat improvements/manipulations include modifications of nest sites on cliffs, buildings, towers to increase safety from predators and inclement weather; construc-tion of improved, alternate nesting places, including towers or other structures, for safe placement of nest sites. General-habitat improvements that increase the abundance of bird life also beneficial for Peregrines. Detailed guidelines for managing Peregrines include: survey and sampling techniques, banding, observing behavior, collecting tissue samples, aging young, management of specific types of eyries, and manipulations of eggs and young to increase distribution and abun-dance (Cade et al. 1996b).

Once nesting populations stabilize at carrying capacity, little active management should be needed, as Peregrine historically survived for centuries in face of both natural and human-caused losses. Existence of sizable, adult floater surplus (see Demography and populations: population regulation, above) buffers breeding population from annual variations in mortality; also represents potential for further increasing size of breeding population by provision of additional suitable nesting places (e.g., towers; nest sites on buildings, bridges, smokestacks, natural cliffs), and by natural expansion of range into previously un-inhabited regions (e.g., Cuba). This potential far sur-passes the requirements for a secure and viable North American population.

Management Of Hybridization

Breeding with Prairie Falcon in Utah and Canada (Oliphant 1991; both involved Prairie Falcons previously in captivity). Young removed from Canadian nest 3 seasons (ration-ale was to prevent genetic introgression of natural gene pools). Utah mating of male Peregrine and female Prairie Falcon in 1986 produced 4 young; given to falconers; then adult female trapped and relocated. Male Peregrine bred with hybrid Peregrine × Gyrfalcon in Colorado (1996), and 2 infertile eggs were in eyrie; hybrid trapped (J. H. Enderson pers. comm.). Male Peregrine × Prairie Falcon escapee produced young with female Peregrine at nest on church in Washington, D.C., for 5 seasons; young removed and male finally caught and removed (C. Koppie pers. comm.). Hybridization probably not significant because of low hybrid × hybrid fertility.

Recommended Citation

White, C. M., N. J. Clum, T. J. Cade, and W. G. Hunt (2002). Peregrine Falcon (Falco peregrinus), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.