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Recognizable Forms

Subspecies of the Great Horned Owlby

Ron Pittaway

IntroductionThe Great Horned Owl (Bubovirginianus) is found throughout mostof Ontario, north almost to HudsonBay IJames 1991). Its deep basshooting, Whoo, hoo-hoo, whooo,whooo is a familiar night sound.

During the day, it often roosts ina secluded, thick evergreen and mostof the time would go undetected butfor the keen eyesight of its tormentor,the American Crow (Corvusbrachyrhynchos). A flock of crows,cawing loudly, often betrays thepresence of a roosting Great HornedOwl.

Getting a good look at residentbirds in southern Ontario is generallydifficult because they are usuallywary of humans. However, thenorthern forms of the Great HornedOwl which wander to southernOntario in winter, are often less waryand more easily observed. Speirs(1985) noted that the periodicmovements of northern Great HornedOwls into southern Ontario areassociated with populationfluctuations in the Snowsboe Hare(Lepus americanus). However, some(particularly young) may move southevery winter (Houston 1978).

In this note, I discuss theoccurrence and identification of therecognizable forms of the GreatHorned Owl in Ontario. In addition,this is the first time that a descriptionand photograph appear in the birding

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literature of the distinctive northernOntario subspecies B. v. scalariventris(Snyder 1961). See Figure 1.

TaxonomyGeographical variation is

pronounced in the Great HornedOwl. Here I follow the treatment ofJames (1991) who lists foursubspecies (races) in Ontario: therufous nominate race B. v. virginianusof southern Ontario; the grayish raceB. v. scalariventris of most of northernOntario; the whitish race B. v.subarcticus of extreme WesternOntario; and the blackish Labradorrace B. v. heterocnemis which wandersto Ontario in winter.

James (1991) follows Snyder(1961) in treating B. v. scalariventris asa valid subspecies, distinct from B. v.subarcticus. In April 1993, I examinedthe large series of scalariventris in theRoyal Ontario Museum. I believe thatscalariventris would be widelyaccepted as a valid subspecies todayif Snyder (1961) had published hisdescription in the more widelyavailable Auk, and perhaps if theAmerican Ornithologists' Union hadupdated the 1957 list of subspecies(now urgently in need of revision).

In the Fifth Edition of theAmerican Ornithologists' UnionCheck-list (1957), B. v. subarcticus islisted as B. v. wapacuthu. However,the original description of wapacuthuis confusing and cannot with

certainty be associated with either theGreat Horned Owl or the Snowy Owl(Nyctea scandiaca) so the namewapacuthu is invalid and should bediscarded "into the waste bin ofsynonyms" (Manning 1952, Todd1963, Browning and Banks 1990,Dickerman (1991a). Most authorsnow use subarcticus instead ofwapacuthu.

In addition, Godfrey (1966, 1986)noted that the large series of paleGreat Horned Owls in the CanadianMuseum of Nature from the southernparts of the prairie provinces referredto B. v. occidentalis in the A.O.D.Check-list (1957) "is not separablefrom subarcticus from farther north".Dickerman (1991b) also concludedthat occidentalis was not a validsubspecies and that it should becomesynonymous with subarcticus.

See the comments on subspecieson page 310 in Godfrey (1986) andpages 48,91 and 92 in James (1991).

PlumagesThe sexes of the Great Horned

Owl are similar in appearance, exceptthat females on the average are largerthan males. First year birds andadults are also similar in colouration."The downy young moult directlyinto the colors of the adults"(Taverner 1942).

"Nominate" Great Horned Owl(B. v. virginianus)

The widespread nominatesubspecies is the breeding form insouthern Ontario (James 1991). It isusually a permanent resident beingless prone to wandering than thenorthern forms.

It is distinguished from the otherOntario subspecies by its "medium

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dark coloration with distinctiveamount of redness in the plumage"(Godfrey 1986). As well, the black­rimmed facial discs are usually aclear rusty colour (Taverner 1942).For a typical example of this southernrace, see John Crosby's illustration onPlate 42 in The Birds of Canada(Godfrey 1986).

"Snyder's"Great Horned Owl(B. v. scalariventris)

L.L. Snyder (1961) of the RoyalOntario Museum described thepopulation of pale Great HornedOwls breeding in most of northernOntario (except the extreme westernparts) as distinct from B. v.subarcticus, and named it B. v.scalariventris. See Figure 1. Taverner(1942) was aware of this form, statingthat it was "too dark for subarcticus,too white for any other race ... withlittle or no red of virginianus' '. Heregarded it as an intergradepopulation of subarcticus xheterocnemis. However, the large anduniform series of scalariventris in theRoyal Ontario Museum from across800 kilometres of northern Ontariostrongly supports its recognition as avalid subspecies (Snyder 1961).Consequently, James (1991) alsoaccepted scalariventris as a valid race.

Snyder's race breeds in northernOntario from near the Manitobaborder eastward to the Quebecborder (and probably beyond), southto approximately Thunder Bay, SaultSte. Marie and North Bay, where itintergrades with nominate virginianus(Snyrer 1961, James 1991). In winterit wanders to southern Ontario. Mostreports of pale (gray) Great HornedOwls in southern Ontario arereferable to scalariventris.

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Classic individuals of scalariventrisare easily distinguished fromnominate virginianus by theirdistinctive gray colouration andgeneral absence of rufous in theplumage. The facial discs are usuallya pale gray, sometimes with a tinge ofrufous. From the much more whitishsubarcticus, Snyder's race isdistinguished by its darkercolouration and "broader, moreregular and darker bars ventrally". Inbroad terms, scalariventris is "morecoldly grey with bolder bars below"(Snyder 1961). See Figure 1.

"Arctic" Great Horned Owl(E. v. subarcticus)

The Arctic race breeds east of theRocky Mountains, across the borealforest and prairies to northernOntario (Godfrey 1986). However,Snyder (1961) considered most of thenorthern Ontario population to bedistinct from subarcticus anddesignated it as a separate subspecies,scalariventris. (See Figure 1 andprevious account of this race.) James(1991) stated that subarcticus breedsalong the western fringe of theprovince where it intergrades withscalariventris. The Arctic race wanderselsewhere in the province, especiallyin winter; for example, Taverner(1942) listed specimens fromAlgonquin Park and Toronto, but it ismuch rarer in southern Ontario thanSnyder's race.

Classic examples of subarcticusare much more extensively whitethan scalariventris, "with more vagueand sparse dark markings below"(Snyder 1961). The facial discs are"white to light ashy, rarely with atinge of rufous" (Taverner 1942).Illustrations of the Arctic race appear

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on page 239 of the NationalGeographic Guide (Scott 1987), onPlate 32 in Birds of Canada (Taverner1937), and on page 173 of A FieldGuide to the Birds (Peterson 1980).Also see Figure 1.

Occasionally a very whitish GreatHorned Owl (almost as white as adark Snowy Owl) is sighted. Thesetypical birds are probably safelycalled subarcticus. However, keep inmind that most pale (gray) birds seenin southern Ontario are referable toSnyder's race, scalariventris.

"Labrador" Great Horned Owl(B. v. heterocnemis)

The dark Labrador race breeds inNewfoundland and Labrador south tocentral Quebec (Godfrey 1986). Inwinter heterocnemis wanders tosouthern Ontario (James 1991).Taverner (1942) listed specimensfrom Ottawa, Peterborough County,Peel Region, Toronto and St. Thomas.

I saw a "Labrador" Great HornedOwl at Aylmer, Quebec, near Ottawaone winter when I was a teenager. Itwas tame (unlike most of the localbirds) and allowed me to observe itclosely. I identified it from thedescription in the subspecies sectionof the old Peterson's Field Guide(Peterson 1947) which is still a usefulreference on subspecies!

The Labrador race differs fromthe nominate race by its much darker(sootier) colouration and heavierbarring below. On classic individuals,"the barring often obliterates thewhite markings, giving a black­breasted appearance" (Peterson1947). In addition, the facial discs areusually a dark brownish-gray insteadof a clear rusty as in the nominaterace.

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An illustration by Roger ToryPeterson of a "Labrador" GreatHorned Owl can be found on Plate 18in The Birds of Newfoundland (Petersand Burleigh 1951). The sameillustration, but not labelled as theLabrador race, is found on Plate 21 ofthe more widely available Birds ofNova Scotia (Tufts 1986).

SummaryFour well-marked forms of the

Great Horned Owl are found inOntario. Although intergrades occur,typical individuals of these forms aredistinctive and recognizable in thefield. One form, the "Snyder's" raceB. v. scalariventris, is described herein the birding literature for the firsttime. This gray race accounts formost of the reports of " Arctic" GreatHorned Owls in southern Ontario.

AcknowledgementsI thank Bill Crins, Earl Godfrey,Michel Gosselin, Phill Holder, RossJames, Mike King, Ron Tozer, andMike Turner for much valuableadvice in the preparation of this note.Ross James and Jim Dick kindlyallowed me to examine skins in theRoyal Ontario Museum. I would liketo thank Ross James of the RoyalOntario Museum for permission touse the photograph illustrated inFigure 1.

Literature citedAmerican Ornithologists' Union. 1957. Check­

list of North American Birds, 5th edition.American Ornithologists' Union,Washington, D.C.

Bent, A. C. 1938. Life Histories of NorthAmerican Birds of Prey. Part 2. United StatesNational Museum Bulletin 170. Washington,D.C.

ONTARIO BIRDS AUGUST 1993

Browning, M.R. and R.C. Banks. 1990. Theidentification of Pennant's "Wapacuthu Owl"and the subspecies name for the populationof Bubo virginianus from the western HudsonBay. journal of Raptor Research 24: 80-83.

Dickerman, R. W. 1991a. Specimens of thesubarctic nesting populations of Great HornedOwls from New York, New jersey andConnecticut. Kingbird 41: 154-157.

Dickerman, R. W. 1991b. On the validity ofBubo virginianus occidentalis Stone.Auk 108: 964-965.

Godfrey, W.E. 1966. The Birds of Canada.National Museum of Canada Bulletin 203.

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

Houston, C.S. 1978. Recoveries ofSaskatchewan-banded Great Horned Owls.Canadian Field-Naturalist 92: 61-62.

James, R.D. 1991. Annotated Checklist of theBirds of Ontario. Second Edition. LifeSciences Miscellaneous Publications, RoyalOntario Museum, Toronto.

Manning, T.H. 1952. Birds of the west jamesBay and southern Hudson Bay coasts.National Museum of Canada Bulletin 125:1-114.

Peters, H.S. and T.D. Burleigh. 1951. The Birdsof Newfoundland. Department of NaturalResources, St. John's.

Peterson, R. T. 1947. A Field Guide to theBirds. Houghton Mifflin Company, Boston.

Peterson, R. T. 1980. A Field Guide to theBirds. Houghton Mifflin Company, Boston.

Scott, S.L. fed.} 1987. Field Guide to theBirds of North America. National GeographicSociety, Washington, D.C.

Snyder, L.L. 1961. On an unnamed populationof the Great Horned Owl. Life SciencesDivision, Royal Ontario Museum,Contribution No. 54: 1-7.

Speirs, J.M. 1985. Birds of Ontario. Volume 2.Natural Heritage/Natural History Press,Toronto.

Taverner, P.A. 1937. Birds of Canada. TheNational Museum of Canada, Ottawa.

Taverner, P.A. 1942. Canadian races of theGreat Horned Owls. Auk 59: 234-245.

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

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Tufts, R. W. 1986. Birds of Nova Scotia. ThirdEdition. Nova Scotia Museum, Halifax.

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

Notes

Double-brooding in OntarioLoggerhead Shrikes

byRon Pittaway

IntroductionThe Loggerhead Shrike (Laniusludovicianus) is well-known to bedouble-brooded, and even triple­brooded in the southern part of itsrange (Bent 1950). Double-broodingis defined as the laying of a secondclutch of eggs after the fledging of thefirst brood (Campbell and Lack 1985).Peck and James (1987) reported thatin Ontario "the protracted breedingseason indicated the probability ofdouble broods, although none werereported". In this note, I report thefirst evidence of double-brooding bythe Loggerhead Shrike for theprovince.

ObservationsOn 8 May 1992, I observed a

Loggerhead Shrike on a nest in ahawthorn (Crataegus sp.) in CardenTownship, Victoria County. Whenchecked the next day, the nest wasfound to hold six eggs (IsabelleBisson, pers. comm.). The young leftthe nest sometime before 11 June1992, and at least three fledged young

were observed being fed by theadults near the nest site for severalweeks afterwards.

On 24 June 1992, Stan Flemmingand I found a newly built nest nearthe location of the first nest. Nearbywe observed three juveniles from thefirst nest following and noisilybegging for food from the adults. Thisobservation followed three days ofunusually cold, wet weather whichhad greatly reduced insect numbers.

On 2 July 1992, a female shrikeflushed from the second nest. Thenest contained three eggs. Nearby themale and three almost independentjuveniles were obse:ved ~unting forinsects. One of the Juvemles waspecked hard several times by theadult male when it attempted to begfor food. This was an indication thatthe young from the first nest werenearly fully weaned.

On 8 July 1992, I noted that thefemale was incubating four eggs inthe second-clutch nest while nearbythe male still attended three young

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