Exhibits variation in plumage coloration and morphometrics (see Appearance, below; Appendix 2); somewhat clinal on continent with Aleutian Is. Peregrines most distinctive and morphometrically uniform. Resident populations generally conform to Gloger's rule (darker in areas of higher relative humidity) and Bergmann's rule (larger size at higher latitudes); migratory northern breeders smaller, however (CMW in Porter et al. 1987). Birds breeding in cold, dry climates (F. p. tundrius) are palest; in hot, dry climates (F. p. anatum) have tints of browns and reds; in humid climates (F. p. pealei and some F. p. anatum) usually saturated with tints of darker grays and grizzle. During nonbreeding season, those resident farthest north (F. p. pealei) are largest, and smallest birds resident (F. p. anatum) in southern portions of breeding range or migratory (F. p. tundrius and F. p. anatum). Great individual variation can occur locally (e.g., n. Hudson Bay; Court et al. 1988a), Gulf of Alaska (R. J. Ritchie pers. comm., CMW). Interpretation of this variation, while perhaps only a result of intergradation, is confounded by variation introduced by expanding gene pools of an earlier reduced population and biased contribution of particular genotypes; in 1990 on Tanana River, AK, young banded from a banded female were members of 6 pairs in a recovering population with 15 pairs (White et al. 1995b). In recovering populations some variation will be short term until stabilizing selection occurs. Morphologically recognizable local populations still occur, or did (e.g., Four Corners Area, U.S., Okanagan Valley, British Columbia), suggesting genetically differentiated local populations and high philopatry. Each named subspecies has ≥2 subgroups, in some cases quite distinctive; e.g., Aleu-tian subgroup of F. p. pealei heavily marked on crop and throat of adult male and immature uniformly dark in pigmentation, while in Queen Charlotte Is. subgroup, crop of adult male is usually white and little marked and immatures from pale (tundra-like) to dark similar to those of Aleutians; F. p. tundrius from Greenland has longer wing and a statistically significantly wider malar stripe than F. p. tundrius from remainder of range. Eastern F. p. anatum larger and darker than western F. p. anatum. In e. U.S., re-introduction of exotic subspecies and progeny from a small gene pool have produced patterns different from those of extirpated populations. It is not clear how rapidly morphometric characteristics can or will become fixed; also close inbreeding not infrequent (Tordoff and Redig 1999a). DNA microsatellite analysis of population genetic structure showed that samples of 3 North American subspecies were no more genetically distinct from each other than populations of nominate F. p. peregrinus from n. and s. Sweden (Nesje et al. 2000).
Nineteen subspecies recognized here, following White et al. (White et al. 1994b); 3 within North America: F. p. anatum, F. p. pealei, and F. p. tundrius (see C. M. White in Palmer 1988c for descriptions and distribution; see Appendix 2). So-called Pallid Falcon (F. kreyenborgi) of South America, apparently a color morph of subspecies F. p. cassini (Ellis and G 1983, Mcnutt 1984). Barbary Falcon, subspecies F. p. pelegrinoides (including F. p. babylonicus) found across n. Africa to central Asia (Mongolia), sometimes treated as separate species.
F. p. anatum Bonaparte, 1838. North America south of tundra to n. Mexico, except Pacific Northwest. See discussion under F. p. tundrius .
F. p. tundrius White, 1968. Arctic tundra of North America and Greenland. Museum specimens of predecline birds clearly demonstrate that a larger percentage occurred on pale end of variation, most noticeable in immatures, than following recovery, where now there is more overlap with pale variants of F. p. anatum, which also seem to have increased with recovery. May simply be stochastic as function of gene pool makeup prior to or during recovery. Immature, compared to F. p. anatum, more muted overall, upperparts more brown or umber than fuscous, with margins ochre to pinkish buff. Head much paler, often giving impression of totally whitish buff with pale-umber shaft lines; pale buffy-white ocelli more extensive. Malar-stripe thinner, often with horizontal break about 5 mm below eye and pale auricular frequently twice width of dark malar stripe (see Plate 17b in Cade 1960, for example, from Yukon River, AK). Underparts background more buff than tawny, streaked with umber, frequently only as shaft lines on thighs in palest birds. Tail-bars similar to color of feather edgings of upperparts. Soft parts vary from blue-gray to greenish to pale yellow (e.g., legs and feet in 1 brood of 4 varied from pale blue to greenish to yellow, each different). Adult F. p. tundrius upperparts not as contrasting as anatum, head and upper back more similar to lower back and rump; less slaty, paler blue. Pale nuchal-collar or ocelli may be well developed. White forehead-band often as much as 10 mm. White auricular more extensive, frequently less than 10 mm from eye, although Greenland birds with wider malar stripe, less extensive white auricular. Underparts less patterned, especially in center of belly, and frequently background wash appears slightly yellowish.
F. p. pealei Ridgway, 1873. Coastal Pacific Northwest from Washington north to w. Alaska, Aleutian and Commander Is., and possibly Kamchatka and Kuril Is. In immature, wide variation in southern portion of range (3 more or less distinct variants), but generally darker overall than F. p. anatum . Upperparts typically more slate (chaetura black, with nuchal-collar) ocelli poorly defined, usually lacking edgings; where edgings occur, more whitish with subtle olive-grayish to olive-yellowish tint. Underneath usually lacking definite tawny background wash (more olive) except in palest individuals (which resemble F. p. tundrius). Underparts typically very much darker because streaking much wider, with streak sometimes covering entire feather, except for pale whitish-buff margin. Central rectrices most frequently without bars; occasionally pale spots in place of bars. Tail-tip whitish with greenish-yellow tint. Only dark variants known in Aleutians. Soft parts at fledging in Aleutian F. p. pealei pale yellowish. Adult F. p. pealei hard to characterize because of difference between birds in south part of range and Aleutians (darker, more heavily spotted, and lacking tints of yellow or buff), but upperparts more slaty, fuscous-black with lower back and rump less blue, so less contrasting with mantle and head than in F. p. anatum or F. p. tundrius . Usu-ally no or only hint of forehead-band except those in southern part of range, where forehead-band may exceed 10 mm. Background of underparts more whitish with tint of yellowish or olive. Markings color of back, but bold, broad, with spots and teardrops extending into crop (crop usually without spots, whiter, especially in southern portion of range). Soft parts in Aleutian F. p. pealei, at least, pale lemon yellow in contrast to deeper yellow orangish in F. p. anatum and F. p. tundrius .
Peregrine Falcon formerly placed in separate genus Rhynchodon, now merged with Falco . Prairie Falcon clusters in same clade with Peregrine Falcon based on some courtship behavior, vocalizations, karyotype (macrochromosome pairs 48 in both species, fewer than other large falcons), and molecular data (based mainly on cytochrome b; Wrege and Cade 1977, Schmutz and Oliphant 1987, Helbig et al. 1994). Prairie Falcon thought closer to Peregrine Falcon than to Gyrfalcon (Steenhof 1998). Taita Falcon (Falco fasciinucha) is probably allied with Peregrine Falcon in same subgenus based on courtship, vocalization, and behavior (contra Cade 1982b). Genus Falco placed in subfamily Falconinae (Tribe Falconini) according to phylogenetic analysis based on molecular (cytochrome- b gene of mitochondrial DNA) and morphological (syringeal supporting elements) characters (Griffiths 1999).