Plumages, Molts, and Structure

Red-tailed Hawks have 10 functional primaries (p7-p10 notched and p6-p9 emarginated), 14-16 secondaries (including three tertials), and 12 rectrices. Wings are moderately rounded and tail is moderately squared. No geographic variation in molt strategies has been published but it is possible that populations wintering in colder climates (e.g., eastern and northern resident subspecies) may undergo less-protracted molts and replace fewer flight feathers per year, on average, than those wintering in temperate and subtropical climates (e.g., western, southern, and highly migratory subspecies); see Definitive Prebasic Molt (below). Polymorphism occurs to various degrees geographically, with a light morph occurring in all subspecies, a dark morph occurring in most (especially western) subspecies, and a white morph ("Krider's Red-tailed Hawk") occurring in one or two subspecies. Morphs by age described here; geographic variation in plumage aspect and (to a lesser extent) size is also marked. See Systematics for descriptions of plumage aspect in 12 recognized subspecies.

Following general description based primarily on detailed descriptions of eastern subspecies B. j. borealis (for light and white morphs) and western subspecies B. j. calurus (for dark morph) in Friedmann (Friedmann 1950a Friedmann, H. (1950). Birds of North and Middle America, Part 11. U.S. National Museum Bulletin no. 50. Close ), Roberts (Roberts 1932 Roberts, T. S. (1932). A manual for the identification of the birds of Minnesota and neighboring states. University of Minnesota Press, Minneapolis, MN, USA. Close ), Oberholser (Oberholser 1974 Oberholser, H. C. (1974). The Bird Life of Texas. University of Texas Press, Austin, TX, USA. Close ), Palmer (Palmer 1988f Palmer, R. S. (1988f). "Red-tailed Hawk." In Handbook of North American birds, Vol. 5, Part 2, 96-134. New Haven, CT: Yale Univ. Press. Close ), Wheeler (Wheeler 2003b Wheeler, B. K. (2003). Raptors of Western North America. Princeton University Press, Princeton, NJ, USA. Close , Wheeler 2003b Wheeler, B. K. (2003). Raptors of Western North America. Princeton University Press, Princeton, NJ, USA. Close ), and examination of museum specimens by authors; see Pyle (Pyle 2008 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, CA, USA. Close ) for age-related criteria. See Systematics for comparative descriptions of other subspecies. Sexes similar in all plumage aspects.

Natal Down

(May-Jun). Protoptile down short, white; bare skin on femur. Nestlings downy until about 18 d post-hatching; down is whitish or pale neutral gray (Smithe 1975 Smithe, F. B. (1975). Naturalist's Color Guide. American Museum of Natural History, New York, NY, USA. Close : 86) on days 5–7, becoming much longer and glaucous (80) (lighter on head) by day 9. A white occipital spot is visible in most hatchlings.

Juvenile Plumage

(Aug-Jul) characterized by uniform wear to all feathers including primaries, secondaries, and rectrices (Pyle 2005c Pyle, P. (2005). Remigial molt patterns in North American Falconiformes as related to age, sex, breeding status, and life-history strategies. Condor 107(4):823–834. Close ,Pyle 2006 Pyle, P. (2006). Staffelmauser and other adaptive strategies for wing molt in larger birds. Western Birds 37:179–185. Close , Pyle 2008 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, CA, USA. Close ).

Light morph with head, cheeks, scapulars, nape, upperwing coverts, inner secondaries, and tertials dark fuscous (21), with little or no cinnamon-brown or russet margins on the feathers and white bases resulting in somewhat ragged and patchy white appearance; rump and upper tail coverts pale neutral gray barred with fuscous. Tail with thin and tapered rectrices, hair brown (119A) crossed by 8-12 fuscous bands of approximately equal width, and narrowly tipped with whitish. Primaries and secondaries variably light neutral gray (85), the primaries paler along inner webs (contrasting with darker secondaries) and with indistinct sepia bars and tips, and the secondaries with narrow and distinct dusky band. Chin, throat, breast, thighs, flanks, and under tail coverts white, usually unmarked (throat and thighs sometimes spotted with fuscous), with an abdominal band of elongated sepia (119) markings. Underwing coverts white with dark markings to lesser coverts and tips of primary coverts; markings otherwise scattered, not as concentrated as in Definitive Basic Plumage. Photographs available in Moritsch (Moritsch 1983a Moritsch, M. Q. (1983a). Photographic guide for aging nesting Red-tailed Hawks. Boise Dist., Idaho: USDI Bur. Land Manage., Snake River Birds of Prey Project. Close ), and illustrations available in Palmer (Palmer 1988f Palmer, R. S. (1988f). "Red-tailed Hawk." In Handbook of North American birds, Vol. 5, Part 2, 96-134. New Haven, CT: Yale Univ. Press. Close ).

Dark morph has entire head, body, wings, except the remiges and thighs fuscous; upper tail coverts cinnamon-rufous (40) basally; under tail coverts pale cinnamon (39) subterminally very broadly marked with fuscous and edged with cinnamon-rufous; primaries, secondaries, and rectrices as in light morph (above).

White morph ("Krider's Red-tailed Hawk") generally similar to light morph (above; and see also Definitive Basic Plumage, below) but upperparts more heavily mottled white; underparts whiter with thinner and paler brownish streaking; tail white with more diffuse and curved dark bands of paler brown (illustration inPyle 2008 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, CA, USA. Close ).

Formative Plumage

(Sep-Jul) shown by some but not all individuals. Aspects of each morph similar to those of Juvenile Plumage (above) but some body feathers fresher and intermediate in appearance between those of Juvenile and Definitive Basic (below) plumages, the upperpart feathers darker and without extensive white basally. Uniformly juvenile wing and tail feathers retained.

Second Basic Plumage

(Aug-Jul). Aspects of each morph similar to those of Definitive Basic Plumage (below) but some juvenile body (especially rump) feathers and/or wing coverts, 1-4 juvenile outer primaries (among p7-p10), 1-6 juvenile secondaries (among s3-s4 and s6-s9), and/or 1-4 juvenile rectrices (usually among r2 and r5) retained, contrastingly worn, and showing aspect of Juvenile Plumage (above). Replaced second basic rectrices sometimes with distinct narrow bars near shaft or (rarely) extending across both webs (illustration in Pyle 2008 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, CA, USA. Close ). Small proportion (~5-10%) of individuals can undergo a complete molt and can be indistinguishable from birds in Definitive Basic Plumage.

Definitive Basic Plumage

(Sep-following Feb) characterized by mixed generations of basic body (especially rump) feathers, and 2-5 sets of basic feathers among primaries and secondaries, in Staffelmauser patterns; replacement sets in primaries defined by a worn feather immediately distal to a fresh proximal feather, and those of secondaries showing mixed generations in various sequences (Clark et al. 2004 Clark, W. S., R. D. Chancellor, and B. U. Meyburg (2004). Wave moult of the primaries in accipitrid raptors, and its use in ageing immatures. In Raptors Worldwide: Proceedings of the VI World Conference on Birds of Prey and Owls (R. D. Chancellor and B. U. Meyersburg, Editors). World Working Group on Birds of Prey, Budapest, Hungary. pp. 795–804. Close ; Pyle Pyle 2005c Pyle, P. (2005). Remigial molt patterns in North American Falconiformes as related to age, sex, breeding status, and life-history strategies. Condor 107(4):823–834. Close , 2006, Pyle 2008 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, CA, USA. Close ). Number of sets equates to minimum ages of 2-5 years; individuals wintering to north and east may average more sets in older birds than those wintering to south and west.

Light morph with upperparts, including the head, auriculars, occiput, nape, scapulars and interscapulars margined with cinnamon-brown (33) to russet (34), these edges broadest and most conspicuous on the nape and anterior interscapulars, which are more uniformly fuscous than in Juvenile Plumage (above); forehead generally whitish; upperwing coverts hair brown to dusky brown (19); lower back and rump somewhat paler, rarely hair brown washed with rufescent; uppertail coverts variable, whitish washed with cream (54) and buff (24) to nearly solid robin rufous (340) and more or less barred with cinnamon-brown. Retrices hazel (35) to cinnamon-rufous narrowly tipped with whitish and crossed by a subterminal band of sepia; the subterminal band variable from nearly absent or incomplete to complete and as much as 13 mm in width. Primaries and secondaries hair brown to grayish, the outermost two primaries (p9-p10) broadly tipped with sepia and remaining primaries barred fuscous along inner webs (not contrasting substantially with pattern of secondaries), the secondaries with indistinct and wider dusky band and narrowly tipped with pale hair brown and sometimes some whitish, and the tertials generally washed with cinnamon-brown and with much white. Lores whitish with black shafts to the feathers; malar stripe dark fuscous; chin and middle of throat usually plain whitish, sometimes streaked with dark olive-brown (28); sides of throat and breast dark olive-brown, the feathers fuscous centrally, bordered with ferruginous (41), and edged with whitish; remaining underparts whitish with the upper abdomen and sides barred and streaked with olive-brown, dusky brown, or warm sepia (pale brown shafts sometimes occur on the feathers of the lower breast) and thighs often washed pale buff and sometimes indistinctly barred with pale hazel; undertail coverts whitish. Underwing coverts whitish with lesser coverts and tips to primary coverts VanDyke brown (121); rest of coverts occasionally marked with sepia.

Dark morph uniformly fuscous to tawny (38) including the entire head, body, upperwing and underwing coverts, and thighs. Rectrices, primaries, and secondaries similar to light morph but dark areas on the tips of the remiges more extensive.

White morph ("Krider's Red-tailed Hawk") paler overall, with aspect generally similar to light morph (above) but upperparts, especially head, nape, back, upperwing coverts, and upper tail coverts noticeably streaked or spotted with white, and white on interscapulars washed pale tawny; underparts much whiter with less brownish; tail variable from pure white subterminally barred with fuscous and with several small incomplete bars along the shaft, with a single subterminal band, or uniformly sayal brown (223C), tipped with white and subterminally banded with fuscous. See also Systematics.

Molt and plumage terminology follows Humphrey and Parkes (Humphrey and Parkes 1959 Humphrey, P. S., and K. C. Parkes (1959). An approach to the study of molts and plumages. Auk 76(1):1–31. Close ) as modified by Howell et al. (Howell et al. 2003 Howell, S. N. G., C. Corben, P. Pyle, and D. I. Rogers (2003). The first basic problem: a review of molt and plumage homologies. Condor 105:635–653. Close , Howell et al. 2004 Howell, S. N. G., C. Corben, P. Pyle, and D. I. Rogers (2004). The first basic problem revisited: reply to commentaries on Howell et al. (2003). Condor 106:206–210. Close ). Red-tailed Hawk exhibits a Modified Basic Strategy (Howell et al. 2003), including complete prebasic molts and a limited preformative molt in some individuals (Pyle 2005a Pyle, P. (2005). First-cycle molts in North American Falconiformes. Journal of Raptor Research 39(4):378–385. Close ), but no prealternate molts (Palmer 1988f Palmer, R. S. (1988f). "Red-tailed Hawk." In Handbook of North American birds, Vol. 5, Part 2, 96-134. New Haven, CT: Yale Univ. Press. Close , Johnsgard 1990b Johnsgard, P. A. (1990). Hawks, Eagles and Falcons of North America: Biology and Natural History. Smithsonian Institution Press, Washington, DC, USA. Close , Wheeler 2003b Wheeler, B. K. (2003). Raptors of Western North America. Princeton University Press, Princeton, NJ, USA. Close ,Wheeler 2003b Wheeler, B. K. (2003). Raptors of Western North America. Princeton University Press, Princeton, NJ, USA. Close ;Pyle 2008 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, CA, USA. Close ; Figure 6). The third prebasic molt typically results in definitive plumage aspect, with juvenile and/or formative feathers usually retained through the second cycle.

Prejuvenile (First Prebasic) Molt

complete, May-Aug, in the nest. Primary sheaths begin erupting at 13–15 d and primaries and secondaries apparent at 17–19 d. Juvenile tail feathers visible at 21–23 d. At 29–31 d, head is 90% downy (white occipital spot evident), dorsal wing is 90% feathered, and breast is 50% feathered; legs beginning to feather, upper tail coverts are well-developed, and ear openings are completely covered. By 33–35 d, head is 50% feathered, dorsal body feathering is 95% complete, and breast is 90% feathered (Moritsch 1983a Moritsch, M. Q. (1983a). Photographic guide for aging nesting Red-tailed Hawks. Boise Dist., Idaho: USDI Bur. Land Manage., Snake River Birds of Prey Project. Close ). Juvenile plumage well developed at time of first flight.

Preformative Molt absent to limited, Sep-Mar, primarily on non-breeding grounds; often begins in fall, suspends over winter, and resumes in spring (Pyle 2005a Pyle, P. (2005). First-cycle molts in North American Falconiformes. Journal of Raptor Research 39(4):378–385. Close ). Can include up to 20% of body feathers but appears to be absent in many individuals (Pyle 2005a Pyle, P. (2005). First-cycle molts in North American Falconiformes. Journal of Raptor Research 39(4):378–385. Close , Pyle 2008 Pyle, P. (2008). Identification Guide to North American Birds, Part II: Anatidae to Alcidae. Slate Creek Press, Point Reyes Station, CA, USA. Close ). No wing coverts or flight feathers replaced.

Second Prebasic Molt

(formerly considered "First Prebasic Molt") incomplete-complete, Feb-Oct, primarily on breeding grounds (although individuals not breeding during this cycle); can occasionally commence or complete on non-breeding grounds. Wing molt often begins in late Apr or in early May; tail molt begins after the wings, is conspicuous in Jun, and continues through Aug. Molt typically without suspensions during breeding season (see Definitive Prebasic Molt, below) but occasionally suspends for northbound or southbound migrations. Replacement of juvenile body feathers sometimes complete but some rump and scattered other body feathers and/or wing coverts often retained. Sequence of flight-feather replacement as in Definitive Prebasic Molt but outer 1-4 juvenile primaries (among p7-p10) and corresponding primary coverts, 1-6 juvenile secondaries (among s3-s4 and s6-s9), and/or 1-4 juvenile rectrices (usually among r2 and r5) typically retained, to commence Staffelmauser (stepwise) replacement patterns (Pyle 2005c Pyle, P. (2005). Remigial molt patterns in North American Falconiformes as related to age, sex, breeding status, and life-history strategies. Condor 107(4):823–834. Close , 2006); molt can be complete in 5-10% of individuals.

Definitive Prebasic Molt

incomplete, Apr-Nov; commences on breeding grounds but sometimes can complete on non-breeding grounds. Often suspended during the breeding season: breeding females typically begin replacing primaries during egg laying, and males a bit later, while mates are incubating. Nonbreeders and failed-breeders probably begin molting earlier. Primaries replaced distally (p1 to p10), secondaries replaced proximally from s1 and s5 and distally from the tertials, and rectrices replaced in sequence r1-r6-r3-r4-r2-r5 on each side of tail. Molt pattern among primaries and secondaries exhibits Staffelmauser (Bierregaard 1974 Bierregaard, Jr., R. O. (1974). Incomplete wing molt and erythrism in Red-tailed Hawks. Auk 91 (3):618-619. Close ; Clark et al. 2004 Clark, W. S., R. D. Chancellor, and B. U. Meyburg (2004). Wave moult of the primaries in accipitrid raptors, and its use in ageing immatures. In Raptors Worldwide: Proceedings of the VI World Conference on Birds of Prey and Owls (R. D. Chancellor and B. U. Meyersburg, Editors). World Working Group on Birds of Prey, Budapest, Hungary. pp. 795–804. Close ; Pyle 2005c Pyle, P. (2005). Remigial molt patterns in North American Falconiformes as related to age, sex, breeding status, and life-history strategies. Condor 107(4):823–834. Close , 2006) whereby incomplete molts result is a series of commencement points, beginning with termination points of previous prebasic molt and also initiating new series commencing at p1, s1, s5, and/or the tertials. Replacement thus typically proceeds in 2-4 (rarely 1 or 5) waves through the wing. Staffelmauser appears to be a product of insufficient time to undergo a complete wing-feather molt but has adaptive benefits in producing multiple small gaps in the wing during molt, which retains wing integrity and ability to fly and forage (Tucker 1991 Tucker, V. A. (1991). The effect of molting on the gliding performance of a Harris' Hawk (Parabuteo unicinctus). Auk 108:108–113. Close , Shugart and Rohwer 1996 Shugart, G. W., and S. Rohwer (1996). Serial descendant primary molt or Staffelmauser in Black-crowned Night-Herons. Condor 98:222–233. Close ,Pyle 2005c Pyle, P. (2005). Remigial molt patterns in North American Falconiformes as related to age, sex, breeding status, and life-history strategies. Condor 107(4):823–834. Close ).

Bill

Black in newly hatched birds, becoming dark (dusky brown to sepia), becoming lighter basally; gape cream to buff (124).

Iris

Dark in newly-hatched birds, becoming grayish then buff yellow (53) in juveniles, spectrum yellow (55) during first winter, and slowly grading to hair brown in older hawks.

Legs And Feet

Buff-yellow to sulfur yellow (57) with dark talons. Tarsus unfeathered.

Linear Measurements

No overall geographic trends in size evident (Appendix 3). Wing chord, culmen, and toe of females average consistently longer than in males across range, but tail length in males and females is nearly the same along the west coast of Canada (alascensis), and males average same or slightly longer tarsus in 6 of 14 populations measured (CRP). Largest birds from Florida (umbrinus), and sw. Texas (fuertesi), smallest from nw. coast (alascensis) and Jamaica and Puerto Rico (jamaicensis) (Brown and Amadon 1968 Brown, L. H., and D. Amadon (1968). Eagles, Hawks, and Falcons of the World. McGraw-Hill, New York, NY, USA. Close ). Within calurus, wing chord, tarsus depth, tail length, hallux claw and culmen vary concordantly across geographic range, but tail length varies independently of these, and tarsus length shows an opposite pattern of variation (Fitzpatrick and Dunk 1999 Fitzpatrick, B. M. and J. R. Dunk. (1999). Ecogeographic variation in morphology of Red-tailed Hawks in western North America. Journal of Raptor Research 33 (4):305-312. Close ). In general, largest calurus individuals occur in arid southwestern deserts and California grasslands, smallest in Pacific Northwest, although birds from the Pacific Northwest have the longest tarsi.

This pattern of variation does not follow the traditional Bergmann/Allen ecogeographic rules, and may reflect adaptations to prey size and water conservation (James 1970a James, F. C. (1970a). Geographic size variation in birds and its relationship to climate. Ecology 51: 365–390. Close , Fitzpatrick and Dunk 1999 Fitzpatrick, B. M. and J. R. Dunk. (1999). Ecogeographic variation in morphology of Red-tailed Hawks in western North America. Journal of Raptor Research 33 (4):305-312. Close ). Birds captured and measured during fall migration from three different flyways indicate that eastern birds (n = 12, measured at Cape May, NJ) have significantly shorter tail, wider tarsus, longer hallux, and longer culmen (p ≤ 0.001) than birds in the Goshute Mountains, NV (n = 152) and Manzano Mountains, NM (n = 62) (Pearlstine and Thompson 2004 Pearlstine, E. V. and D. B. Thompson. (2004). Geographic variation in morphology of four species of migratory raptors. Journal of Raptor Research 38 (4):334-342. Close . Birds flying through Manzano Mountains have significantly longer wings than birds passing through Goshute Mountains or Cape May.

Mass

Individuals during the breeding season (presumably mostly juvenile and adult borealis and calurus) averaged 1,224 g for females (n = 100) and 1,028 g for males (n = 108; Craighead and Craighead 1956). Juvenile males trapped during migration in Wisconsin averaged 945.3 g (698–1,296; n = 32), and juvenile females averaged 1,222 g (904–1,455; n = 24) (H. Mueller in Palmer 1988f Palmer, R. S. (1988f). "Red-tailed Hawk." In Handbook of North American birds, Vol. 5, Part 2, 96-134. New Haven, CT: Yale Univ. Press. Close ).

Mean body mass of birds captured at Cape May, NJ during fall migration was 1,134.4 g (sd = 143.6, n = 12), significantly heavier (p ≤ 0.001) than birds from Manzanos, NM (950.2 g; sd = 124.3, n = 62) or Goshutes, NV (933.4 g; sd = 150.5, n = 152). Mean body masses of two adult males and two adult females trapped in the rain and cloud forests of Puerto Rico were 795 g and 1023 g, respectively. Sexual dimorphism in body weight is most pronounced in the Puerto Rican population (Snyder and Wiley 1976 Snyder, N. F. R. and J. W. Wiley. (1976). Sexual size dimorphism in hawks and owls of North America. Ornithological Monographs 20. Close ). No seasonal variation noted.