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Recognizable Forms

Subspecies and Morphs of theRed -tailed Hawk

byRon Pittaway

IntroductionHawkwatching has been growing inpopularity by leaps and bounds inrecent years. Increasingly,hawkwatchers are recording the ageclasses (adult and immature).subspecies [races] and morphs (colourphases] of the hawks passing theirlookouts.

The Red-tailed Hawk (Buteojamaicensisl is a highly variablespecies, having a number ofrecognizable forms. In this note Idiscuss the status and identificationof the Red-tailed Hawk subspeciesand morphs in Ontario. I also willreview the question of whether"Krider's" Red-tailed Hawk(B. j. hrideriii and "Harlan's"Red-tailed Hawk (B. j. harlanii arevalid subspecies, or morphs.

TaxonomyFor subspecies in this account, I

follow the treatment used by Godfrey(19861.See Pittaway (19911for a listof the subspecies and morphs foundin Ontario.

The "Eastern" Red-tailed Hawk(B. j. borealisl "breeds over most ofthe province" (James 19911.Observant watchers will occasionallysee the other following forms in theprovince: "Western" Red-tailedHawk (B. j. calurusl and its colour

morphs; "Krider's" Red-tailed Hawk;and "Harlan's" Red-tailed Hawk.

Since I will be discussing whetherKrider's and Harlan's hawks are validsubspecies or just colour morphs, areview of the differences between asubspecies and a morph is in order.Under the rules of taxonomy, asubspecies is considered to be adistinct subdivision of a speciesoccupying a separate geographicalbreeding range exclusive of othersubspecies. Subspecies intergrade[interbreed] freely with relatedsubspecies where their ranges meet.Subspecies are recognizedtaxonomically by a formal scientificname; for example, the "Eastern"Red-tailed Hawk is Buteo jamaicensisborealis. The third part of thescientific name, borealis, is the nameof the subspecies. On the other hand,morphs are not formally recognizedtaxonomically by a scientific name.The key difference between a morphand a subspecies is that morphsconstitute two or more distinct formswhich coexist over a wide area in aninterbreeding population, often evenin the same brood.

Plumages, Molts and AgeingThe sexes in the Red-tailed Hawk

are similar, except that females onaverage are somewhat larger. Likemost hawks, there are two distinct

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age classes and plumages: immature(juvenile) and adult. In hawks, mostbirders prefer to use the termimmature for birds which are injuvenile plumage. "The juvenileplumage is assumed in the nest and isretained until the next midsummermoult, when the adult plumage isassumed at approximately fifteenmonths of age" (Taverner 1927).Adults undergo a prolonged moltannually during the summer months.For additional details of plumagesand molts see Palmer (1988).

AlbinosAlbinistic Red-tailed Hawks are

regularly encountered. They rangefrom partial albinos, having variousmixtures of white and normalfeathers, to completely white birds.Partial albinos usually show a patchypattern quite unlike "Krider's" Red-tailed Hawk. See the illustration onPlate 11 in the Peterson hawk guide(Clark and Wheeler 1987). Totalalbinos could be confused with whitemorph Gyrfalcon (Fa/co rusticoluss,but differ in "behaviour, generalshape and flight style" (Lish andVoelker 1986).

"Eastern" Red-tailed Hawk(B. j. borealis)

This subspecies of the Red-tailedHawk is the common large hawk inmost of Ontario. The distinctiverufous tail of a soaring adult is visibleat a great distance. Immature birdshave barred, brownish -grey tails andlike adults usually have a distinctlystreaked band across the belly.Overhead, the dark patagial marks atthe leading edge of the inner wing arediagnostic of both adults andimmatures. See Plate 11 in Clark andWheeler (1987).

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The plain red tail, usually with anarrow black subterminal band, is atrait of the Eastern subspecies(Taverner 1936, Godfrey 1986). SeeFigure 1. It is almost invariably alight morph bird. I could find noreports in the literature of rufous ordark morph birds breeding in easternCanada.

Interestingly, Todd (1950, 1963)named the northern population of the"Eastern" Red-tailed Hawk breedingin the spruce-fir forests from NovaScotia to Alberta as Buteo jamaicensisabieticola. This subspecies was notrecognized by the AmericanOrnithologists' Union (A.O.U.)Check-list (1957) or by Palmer(1988). Godfrey (1986) stated that hehad not "seen adequate material toappraise it". However, Godfrey (pers.comm. 1993) has said that Todd(1950) was probably correct innaming this northern subspecies.Dickerman and Parkes (1987)supported the recognition ofabieticola, and reported a breedingrecord south to Frontenac County,Ontario. If this subspecies were to beformally recognized, then trueEastern borealis would be restricted tothe deciduous forests of extremesouthern Ontario and the easternUnited States except Florida.

Typical adults of this proposed"Spruce-Fir" subspecies, abieticola,differ from more southern birds "inhaving bold, heavy, dusky to blackstreaking on the feathers of the bellyband. The throat is never pure whiteas in many borealis, and may be soheavily streaked as to appear almostblack ... The ground color of theunderparts of abieticola averages morerichly colored (buffy) than in borealis,overlapping somewhat with the palest

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borealis

kriderii

calurus

harlani

Figure 1: Adult tail patterns of four Red-tailed Hawk subspecies.Drawings by Peter Burke.

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individuals of calurus," Immatures"often may be identified as such bythe greatly increased area of blackishventral streaking, in some instancesforming almost a solid band"(Dickerman and Parkes 1987).

During the peak flight of 371Red-tailed Hawks at CranberryMarsh, Durham Region, 25 October1992 (Barker 1993), and being awareof the description of B. j. abieticola, Inoted that most of the birds weretypical of this proposed race.Whether or not this is a validsubspecies, it is certain that northernRedtails are much more heavilymarked than their extreme southernOntario counterparts.

"Western" Red-tailed Hawk(B. j. calurus)

The highly polymorphic Westernsubspecies, calurus, breeds east tocentral Manitoba, where itintergrades with the Eastern Red-tailed Hawk (Godfrey 1986). "As amigrant and wintering bird, itregularly occurs along the Atlanticseaboard" [Dunne et al. 1988). It is a"rare wanderer" throughout Ontariofrom autumn to spring (James 1991).

Western Redtails are usuallydivided into three morph categories:light (most common morph), rufous,and dark, with various intermediates.Clark and Wheeler (1987) provideillustrations and a thoroughdiscussion of these morphs.

Adult light morph WesternRedtails are like Eastern Redtails buthave distinctly rufous-washedunderparts and rufous-barred legfeathers. A characteristic of allmorphs of the Western subspecies isthat the red tail is often crossed byseveral sharply defined black bars[Taverner 1936). The black on the tailvaries from flecking to complete

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cross-barring. Note to, that thesubterminal band is usually wider.See Figure 1. The Western adult onPlate 11 in Clark and Wheeler (1987)is somewhat intermediate between atypical light morph and the rufousmorph on Plate 14. Note the blackbarring on the red tails. Immaturelight morph Western Redtails areoften difficult to separate fromEastern immatures.

Rufous and dark morph WesternRedtails are less frequent in thepopulation than are the light morphbirds, but they are reported moreoften than the latter. A rufous morphadult was seen by Alan Wormingtonat Point Pelee on 24 October 1992(Henshawand Kerr 1992). Rufousmorph immatures are oftendistinctive; see Plate 14 in Clark andWheeler (1987). I saw a dark morphadult on 20 October 1990 nearSaintfield, Durham Region [Bain andHenshaw 1991). At first I thought itwas a dark morph Rough-leggedHawk (Buteo lagopus) and would haveoverlooked it had I not stopped mycar to view it with binoculars. To myamazement, it was a beautiful all-black Redtail except for silveryunderwing flight feathers and abarred red tail. Immature dark morphWestern Redtails are usually difficultto separate from immature Harlan's.

It is generally assumed thatrufous and dark morph Redtails withred tails seen in Ontario are of theWestern subspecies since suchmorphs are virtually unknown in theEastern race. When it can be seen,the black-barred red tail of the adultWestern should further support theidentification of this subspecies. If indoubt about the subspecies, just callthem rufous and dark morph Red-tailed Hawks.

"Kriders" Red-tailed Hawk(B. j. kriderii)

This is a very pale form whichbreeds on the southern prairies eastto extreme western Ontario (Godfrey1986, James 1991). Krider's is a raremigrant in southern Ontario(Taverner 1927, James 1991). Typicaladults are like bleached EasternRedtails, being much whiter overallwith a whitish or pinkish tail. SeeFigure 1. Immatures are similar toadults, but have a whitish cross-barred tail. In flight, Krider's has adistinctive white-headed appearance.Both adult and immature Krider'scommonly show large whitishrectangular patches on the upperwings, leading to confusion with theimmature light morph FerruginousHawk (Buteo rega/is). See theexcellent illustrations of Krider's onpage 195 of the National GeographicGuide [Scott 1987) and the perchedadult and flying immature on Plate 11in the Peterson hawk guide (Clarkand Wheeler 1987).

Currently most authorities followthe A.O.U. Check-list (1957) intreating Krider's as a subspecies ofthe Red-tailed Hawk. However,Taverner (1936) and Palmer (1988) donot recognize Krider's as a validsubspecies but consider it to be acolour morph. Dr. W. Earl Godfrey[pers. comm. 1993) now also believesthat Krider's may be a morphbecause "it occurs side by side withother Red-tailed Hawks in the samebreeding population". The A.O.U.(1957) stated that "there areextensive areas of intergradation withB. j. borealis on the east and B. j.calurus on the west". Since Krider'scoexists (and interbreeds) over a largebreeding range "where it is

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outnumbered by the Eastern form"[Clark and Wheeler 1987); therefore,Krider's is by definition a morph andnot a valid subspecies. In any case,typical Krider's are distinctlyrecognizable in the field.

"Harlan's" Red-tailed Hawk(B. j. harlani)

Harlan's Hawk is "a variablepopulation in Alaska and westernCanada formerly regarded as adistinct species" (Sibley and Monroe1990). It migrates through the prairieprovinces and winters mainly in thesouth-central United States. There isa specimen record from Pennsylvania(Dickerman and Parkes 1987). andGerry Smith (pers. comm. 1993) hasseen Harlan's twice in springmigration at Derby Hill, New York,at the southeast corner of LakeOntario. There are a few sightrecords for southern Ontario.

Classic adult Harlan's Hawks arequite recognizable if the distinctivetail is seen well. They are similar tothe other dark morph Redtails butlack the diagnostic red tail, andusually they have "much whitespeckling on breast and underwingcoverts" [Clark and Wheeler 1987).The tail is "mottled and freckled withblack, grey, white and red in variousproportions and with longitudinalstreaks instead of transverse bars"(Godfrey 1986). See Figure 1.Immatures have barred tails and aredifficult to separate from other darkmorph Redtails [Clark and Wheeler1987). Harlan's interbreeds withother subspecies; for example, thereare recognizable intergrades betweenHarlan's and Western Redtailsshowing characteristics of bothsubspecies. Harlan's Hawk isnormally a dark morph bird;

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however, it is reported that Harlan'shas both a light morph and a rarebarred-tailed morph (Clark andWheeler 1987, Mindell 19851.It isquestionable whether these morphsare pure Harlan's or birds showingintergrade traits with othersubspecies.

The taxonomic status of Harlan'sHawk has changed several timesbetween species and subspecies sinceits discovery by Audubon in 1829(Julian 19711.The A.O.D. Chec~-list(19571listed it as a distinct species.Since Harlan's Hawks interbreedfreely with other Red-tailed Hawks, itcannot be a separate species underthe biological species concept. TheA.O.D. (19731reassigned Harlan's tosubspecies status. However, thedebate continued whether Harlan'swas a valid subspecies or a colourmorph having no taxonomic status.Mindell (19831appears to havesettled the matter. He presented veryconvincing evidence that Harlan's hasan extensive core breeding rangeexclusive of other Red-tailed Hawksubspecies, although a small numberof intergrades occur throughout itsrange. Harlan's is therefore a validsubspecies (Mindell 19831.Nevertheless, Palmer (19881stillpreferred to consider Harlan's amorph.

In summary, Cade (19901believesthat the Harlan's Hawk represents Habreeding population that becameisolated in a Pleistocene refugium,where these hawks achieveddistinctive morphologicaldifferentiation from other Red-tailedHawk populations but failed toachieve reproductive isolation, so thaton recontact of formerly separatedpopulations, there has been exchangeof genes".

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ConclusionFor those hawkwatchers wanting

more information, there are two fieldguides to the hawks that I highlyrecommend: The Peterson Guide tothe Hawks (Clark and Wheeler 19871and Hawks in Flight (Dunne et al.19881.Both books cover Red-tailedHawk subspecies and morphs inconsiderable detail.

AcknowledgementsI thank Dan Brunton, Peter Burke,Bill Crins, Bob Curry, Rim Eckert,Earl Godfrey, Michel Gosselin, RonTozer and Mike Turner for muchvaluable help in the preparation ofthis note. Peter Burke kindlyprovided the illustrations whichgreatly enhance this note.

Literature citedAmerican Ornithologists' Union. 1957.

Check-list of North American Birds. 5thedition. American Ornithologists' Union,Washington, D.C.

American Ornithologists' Union. 1973.Thirty-second Supplement to the AmericanOrnitholigists' Union Check-list of NorthAmerican Birds. Auk 93: 875-879.

Bain, M. and B. Henshaw {editors}. 1991.Annual Bird Report, Durham Region,Ontario, 1990. Published by the editors.

Barker,J. 1993. Cranberry Marsh Raptor Watch,Year End Report - 1992. Unpublished.

Code, T.J. 1990. Review of Palmer, R.S. [Editor}.1988. Handbook of North American Birds,Diurnal Birds of Prey, Volume 4 and 5.Auk: 213-216.

Clark, W.S_ and B.K. Wheeler. 1987. A FieldGuide to Hawks. Houghton Mifflin Company,Boston.

Dickerman, R. W. and K.C. Parhes, 1987.Subspecies of the Red-tailed Hawk in theNortheast. Kingbird 37: 57·64.

Dunne, P., D. Sibley and C. Sutton. 1988.Hawks in Flight. Houghton Mifflin Company,Boston.

Godfrey, W.E. 1986. The Birds of Canada.Second Edition. National Museum of Canada,Ottawa.

Henshaw, B. and H. Kerr. 1992. Ontarioround-up, October and November 1992.Birders Journal I: 358-366.

[ames, R.D. 1991. Annotated Checklist of theBirds of Ontario. Second Edition. LifeSciences Miscellaneous Publications,Royal Ontario Museum, Toronto.

[ulian, P.R. 1971. Harlan's Hawk, a challengingtaxonomic and field problem. Birding 3:67-71.

Lish, J. W. and W.G. Voelker. 1986. Fieldidentification aspects of some Red-tailedHawk subspecies. American Birds 40:197-202.

Mindell, D.P. 1983. Harlan's Hawk IButeojamaicensis harlanil: a valid subspecies.Auk 100: 161-169.

Mindell. D.P. 1985. Plumage variation andwinter range of Harlan's Hawk IButeojamaicensis harlanil. American Birds 39:127-133.

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Palmer, R.S. 1988. Handbook of North AmericanBirds, Volume 5, Diurnal Raptors [Part 21.Yale University Press, New Haven andLondon.

Pittaway, R. 1991. Checklist of recognizableOntario bird forms. Ontario Birds 9: 49-55.

Scott, S.L. [ed.]. 1987. Field Guide to theBirds of North America. National GeographicSociety, Washington, D.C.

Sibley, e.G. and B.L. Monroe jr .. 1990.Distribution and Taxonomy of Birds of theWorld. Yale University Press, New Havenand London.

Taverner, P.A. 1927. A study of Buteo borealis,the Red-tailed Hawk, and its varieties inCanada. Victoria Memorial Museum,Bulletin 48: 21 pages including colour plates.Canada Department of Mines, Ottawa.

Taverner, P.A. 1936. Taxonomic comments onRed-tailed Hawks. Condor 38: 66-71.

Todd, W.E.e. 1950. A northern race ofRed-tailed Hawk. Annals. Carnegie Museum,Pittsburgh.

Todd, W.E. C. 1963. Birds of the LabradorPeninsula and Adjacent Areas. CarnegieMuseum and University of Toronto Press.

Ron Pittaway, Box 619, Minden, Ontario KOM 2KO