Peregrine falcon (pealei and anatum/tundrius) COSEWIC assessment and status report: chapter 3

Species Information

Name and classification

Scientific name:

Falco peregrinus Tunstall 1771

English name:

Peregrine Falcon

French name:

Faucon pèlerin












Current classification follows the American Ornithologists’ Union (AOU 2006). The species was first described in Europe by Tunstall in 1771. Globally, 19 subspecies of Peregrine Falcon are recognized (Hayes and Buchanan 2002; White et al. 2002), three of which are found in North America (Godfrey 1986). They include F. p. anatum (Bonaparte 1838), F. p. tundrius (White 1968a) and F. p. pealei (Ridgway 1871).

Throughout the status report, the three subspecies will be referred to as: Anatum Peregrine Falcon, Tundrius Peregrine Falcon and Pealei Peregrine Falcon.

A recent genetic study shows that Pealei Peregrine Falcons are genetically distinct from Anatum and Tundrius Peregrine Falcons, but that historically (pre-DDT decline) these two subspecies were not genetically distinguishable (Brown et al. 2007). The study also found only weak contemporary differences between Anatum and Tundrius, likely due to anthropogenic causes such as the limited gene pool used in reintroductions (Brown et al.2007). For this reason, and because Anatum and Tundrius subspecies show a clear continuum in terms of distribution and plumage (see below), the two subpsecies will be considered as a single designatable unit. Pealei Peregrine Falcon will be a separate designatable unit.Most available information is reported by subspecies, so we will include information for all three subspecies in the report, combining Anatum and Tundrius information where appropriate (e.g. extent of occurrence, population size).

Morphological description

The Peregrine Falcon is a crow-sized, medium to large falcon with long, pointed wings. Males range in length from 36-49 cm and weigh 650 g on average and females range from 45-58 cm and weigh about 950 g. Sexes are best distinguished by size, with females being 15–20% larger and 40–50% heavier than males. There is little size overlap between sexes within a given subspecies (White 1968b, White et al. 2002).

Adults have bluish-grey or darker upperparts, a variable-width blackish facial stripe extending from the eye across the malar, and paler underparts that are whitish, greyish, or buffy with variable amounts of blackish spotting and barring. Immatures are similar but upperparts vary from pale to slate or chocolate brown and underparts are buffy with blackish streaks. Plumage and morphological differences exist between subspecies. Differences are clinal, however, with paler birds occurring in dry areas and darker birds in wetter areas, and smaller birds in the north and larger birds in the south and west. Tundrius Peregrine Falcons tend to be paler and smaller (White 1968b); Anatum Peregrine Falcons have orange or brownish tinges to underparts; Pealei Peregrine Falcons are darker overall and are the largest peregrines, on average, in North America (White et al. 2002). Plumage variation within local geographic areas can also be large (e.g. northern Hudson Bay; Court et al. 1988a), obscuring differences between subspecies, especially anatum and tundrius.

Genetic description

Genetic diversity and population structure

A comparison of the historical (pre-DDT decline) and current genetics of Peregrine Falcons in Canada is now complete (Brown et al. 2007). The study assessed the level and distribution of neutral genetic variation within and between Canadian populations of the three North American subspecies before and after the DDT-induced population declines. The study addressed the consequences of the population decline and subsequent reintroductions on i) levels of genetic diversity, ii) the validity of the current taxonomy, and iii) genetic structuring across the bottleneck. Contemporary and historical (museum) specimens were genotyped for 11 nuclear microsatellite loci and a 405 nucleotide fragment of the mitochondrial control region. Genetic diversity was low for all populations in both time periods. Neither significant declines in genetic diversity nor consistent bottleneck signatures were found for any subspecies. Contemporary levels of diversity were generally higher than historical levels. The lack of a bottleneck signature was apparently related to the promptness of the recovery and the possible introgression of alleles from non-native individuals (Brown et al. 2007).

In terms of population genetic structuring, only two diagnosable genetic groups were identified in historical samples of Peregrine Falcons in Canada: pealei, and all other individuals (Table 1). Brown et al. (2007) state: “Both mtDNA and microsatellite data show that F. p. anatum and F. p. tundrius were genetically indistinguishable historically and that contemporary samples are weakly, but significantly differentiated.” Microsatellite analyses suggest that the changes in genetic structure between Anatum and Tundrius are largely due to changes within Anatum alone (Table 1) and that this change is localized to northern Ontario and Québec, where reintroduced Anatum individuals, their descendents and possibly also birds from the USA occur. The change in genetic structure of Anatum in this area is most likely due to the limited gene pool associated with the introductions and introgression from non-Anatum birds from the USA (Brown et al. 2007; see below). Breeding Peregrine Falcons of mixed subspecific pedigree, originating from the USA, have been documented in both provinces.

Some individuals from the Strait of Georgia and all samples from the lower Fraser River valley of coastal British Columbia appear to belong to anatum, whereas all samples from the outer British Columbia coast belong to pealei. However, both subspecies apparently occur on at least some of the same Gulf Islands in the Strait of Georgia (J. Brown pers. comm. 2004).

Table 1.  Pairwise estimates of population differentiation derived from mtDNA (ΦST; above diagonal) and microsatellite (FST; below diagonal) data between F. p. anatum, F. p. tundrius and F. p. pealei. Numbers in bold are significantly greater than zero at α= 0.05. (Table modified from Brown et al. 2007 with permission of the author).
Population Historical population:
anatum (n = 24)
Historical population:
tundrius (n = 49)
Historical population:
pealei (n = 15)
Contemporary population:
anatum (n = 109)
Contemporary population:
tundrius (n = 46)
Contemporary population:
pealei (n = 24)
Historical population: anatum
Historical population: tundrius
Historical population:pealei
Contemporary population: anatum
Contemporary population: tundrius
Contemporary population: pealei

Reintroductions and genetic integrity

Captive-bred Peregrine Falcons were reintroduced into Canada and the USA following the collapse of North American populations in the 1950s and 1960s. In Canada, about 1,500 pure Anatum Peregrine Falcons were released during the reintroduction program (G. Holroyd pers. comm. 2006). In the USA, 2500 Peregrine Falcons of seven subspecies, including anatum, tundrius, pealei and four exotics were released in 13 states including several (e.g. New York, North Dakota, Minnesota, Michigan, Wisconsin, Ohio) adjacent to Canada (Tordoff and Redig 2003). The introduction of subspecies from outside North America into the USA raised concerns about the genetic integrity of Anatum Peregrine Falcons breeding in Canada. Although the origin of breeding birds in the recovering populations of Peregrine Falcons in Canada have not been determined absolutely, there are several reasons to expect that the USA introductions have had relatively little influence on the genetic makeup of the re-established populations in Canada. First, Anatum Peregrine Falcons comprise nearly 40% of the gene pool of birds released in the eastern USA, with Tundrius peregrines contributing a further 23% (Tordoff and Redig 2003). If, as the recent genetic evidence suggests, Anatum and Tundrius were not genetically distinguishable historically (see above), then over 60% of the USA gene pool is of native stock. Secondly, the populations most likely to be affected by introgression with non-native birds (i.e. Peregrine Falcons in southern Ontario, Quebec) are a very small portion of the total Canadian breeding population of Anatum. Finally, some pure Anatum birds released in Canada have bred in the USA, further diluting the impact of non-native birds.

Additional genetic information

Peregrine Falcons are capable of hybridization with Prairie Falcons (F. mexicanus) (Oliphant 1991) and Gyrfalcons (F. rusticolus), although this is probably extremely rare in the wild. Modern falconry, however, frequently involves the cross-breeding of full species (Peregrine Falcon crosses with Gyrfalcon, Prairie Falcon, and Merlin (F. columbarius) to produce falconry stock, and some portion of these hybrids are known to be fertile. Such birds are thought to be “sterilized” by imprinting on humans, but falconry hybrid escapees have paired and produced young in the wild. Although the contribution to the genome of the native Peregrine Falcon population from such sources is believed to be insignificant (White et al. 2002), it has not been quantified.

Designatable units

The three subspecies of Peregrine Falcon in Canada have traditionally been assessed separately and treated as three designatable units. For the purposes of this assessment, however, we will consider Anatum and Tundrius as a single designatable unit and Pealei Peregrine Falcon as a separate designatable unit. The rationale for combining the first two subspecies is based on recent genetic evidence showing that historically Anatum and Tundrius Peregrines were not genetically distinguishable and that the weak contemporary differences are likely due to anthropogenic causes, such as the limited gene pool used in reintroductions (Brown et al. 2007). Additionally, Anatum and Tundrius subspecies show a clear continuum in terms of distribution and plumage. Because most available information is reported by subspecies, we will include information for all three subspecies in the report, combining Anatum and Tundrius information where appropriate (e.g. extent of occurrence, population size).

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