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The Journal of the Ontario Field OrnithologistsVolume 10 Number 2 August 1992

72

Recognizable Forms

Subspecies and Morphs of the Snow Gooseby

Ron Pittaway

IntroductionThe Snow Goose (Chen caerulescenslhas two distinct subspecies: thenominate Lesser Snow Goose (c.c.caerulescensl and the Greater SnowGoose (C.c. atlanticusl. The twosubspecies differ in their distribution,size, structure and weight, and eachoccurs in two distinct colour morphs[phases}, The blue morph is commonin the Lesser subspecies, but rare inthe Greater subspecies [Godfrey19861.The two morphs were onceconsidered separate species - - theSnow Goose and the Blue Goose(A.O.U. 19571.

The Greater and Lesser SnowGoose subspecies can often beidentified in the field if one knows allthe differences in their distribution,morphs, size and structure.

This note first outlines importantinformation about the distribution,populations, and identification of thetwo subspecies in Ontario. Secondly,it describes the historical changes inthe distribution and populations ofthe two morphs. Thirdly, it explainsthe fascinating genetic and behavioraldifferences between the two morphs.

Lesser Snow GooseThe Lesser Snow Goose

subspecies is the normallyencountered race in most of Ontario.except in eastern Ontario east ofOttawa where increasing numbers of

Ol\'TARIO BIRDS ACGL'ST 1992

Greater Snow Geese have occurred inrecent years. The Lesser Snow Goosebreeds in the low Arctic (south andwest of the Greater Snow Goose]south along the Ontario coasts ofHudson Bay and lames Bay [Godfrey19861.In Ontario populations, theblue morph is more common than thewhite morph. For example, the bluemorph constitutes 70 to 75% of thebreeders at Cape Henrietta Maria[Lumsden in Cadman et al 19871.Large numbers of Lesser Snow Geesestage in southern lames Bay. Most ofthe lames Bay populations migratewest of southern Ontario, but smallnumbers are seen in the south.Usually the blue morph predominatesamong migrant Lesser Snow Geeseseen in southern Ontario. Since theblue morph is rare in the Greatersubspecies, a mixed flock having ahigh percentage of blue morph birdscan be identified confidently asLesser Snow Geese. In addition,Lesser Snow Geese are noticeablysmaller in comparison with the twolarge races of the Canada Goose(Branta canadensis interior and B.c.maximal found in southern Ontario,whereas Greater Snow Geese appearalmost as big.

Greater Snow GooseThis larger eastern subspecies

breeds in the Canadian eastern highArctic and northern Greenland. and

winters along the Atlantic coast of theUnited States. Historically, the entirepopulation staged in spring and fallalong the St. Lawrence River nearQuebec City (Godfrey 1986). In 1900,the population of Greater SnowGeese staging along the St. Lawrencewas estimated to be 2-3,000 [Bellrose1976). Greater Snow Geese have beenincreasing rapidly in recent years,with an estimated population of356,000 along the St. Lawrence Riverin the spring of 1991 including137,000 at Lac St. Pierre,approximately 100 kilometres down-river from Montreal where they wereuncommon a decade ago (Yank et al,1991). The population staging alongthe St. Lawrence River in the fall of1991 was estimated at 500,OOO![YvesAubry, pers. comm.]. Henri OueUet[pers, comm.] of the CanadianMuseum of Nature reports thatGreater Snow Geese are now beingseen in numbers near Montreal. Thisrecent spread of Greater Snow Geesemay be due to an increase in theirfood resources. They are usingcroplands more now which meansthat the population can increase andexpand in distribution.

The Greater Snow Goose was notlisted for Ontario by James (1991).However, the rapidly expandingnumbers of Greater Snow Geese closeto the provincial border suggestedthat they should be occurring ineastern Ontario. The first reportedevidence of the Greater subspecies inOntario was documented in thespring of 1986 when birdsphotographed by Bruce Di Labio[pers. comm.] east of Ottawa atRiceville, Prescott County, wereidentified as Greater Snow Geese byGraharn Cooch of the CanadianWildlife Service. Bruce DiLabio [pers,

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comm.] reports that Greater SnowGeese now occur annually in easternOntario. He observed over 2,000Greater Snow Geese at Riceville on31 March 1991 and over 2,400Greater Snow Geese at Bourget,Russell County, on 3 April 1991. Theabove flocks were more than 99%white morph birds. Some of the bluemorph birds observed with the aboveflocks were the same size as thewhite morph Greater Snow Geeseindicating the occurrence of bluemorph Greater Snow Geese inOntario [Bruce DiLabio, pers.comm.],

Smaller numbers of Greater SnowGeese also occur in fall. For example,Bruce DiLabio [pers, comm.]observed 11 Greater Snow Geesewith a flock of Canada Geese on 3November 1991 near Cornwall. Oneof the above Greater Snow Geese hadbeen neck banded in Delaware on 8November 1990.

Greater Snow Geese may beoccurring occasionally farther west inOntario. A flock of 40 white morphbirds observed on 29 March 1991near Lake Scugog in Durham Regioncould have been Greater Snow Geese[Bain and Henshaw 1992).Commenting on the aboveobservation, Paul Prevett [pers.comm.] of the Ministry of NaturalResources stated that "there was ahigh probability that a flock of 40white morph birds at this locationwas Greater Snow Geese" .

Since the blue morph is rare inthe Greater subspecies and commonin the Ontario population of theLesser Snow Goose, any large flock ofall white morph birds seen in easternOntario almost certainly involvesGreater Snow Geese. In addition,

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Snow Geese often can be identified tosubspecies in direct comparison withthe large races of the Canada Goose.Greater Snow Geese are chunkier andthicker necked than Lesser SnowGeese and appear almost as big aslarge Canada Geese. Lesser SnowGeese are always somewhat smallerthan large Canada Geese. Insummary, as noted by J.R. Forster (inBent 19251. "the measurements of thegreater snow goose do not wellillustrate its real superiority in size; itis a much heavier bird than itswestern relative, with a much morestocky build, thicker neck, and largerhead. It is generally recognizable at aglance in the flesh." In the past, theGreater Snow Goose and the LesserSnow Goose were largely isolatedfrom one another. Recently, theirranges have begun to overlap. Thetwo subspecies may become blurredby more intermediate-sized birds[intergrades] in the future.

Morph TaxonomyThe Snow Goose and Blue Goose

were originally believed to be distinctspecies. This view lasted for a longtime because of the very differentappearance of the two forms. Also,no mixed pairs were reported whenBlue Geese were first discoveredbreeding in the Arctic in 1929 (Soper19301· At that time, the Snow Gooseand Blue Goose had allopatric(separate I breeding and winteringranges, and they appeared to bedistinct species. In fact, Cooke (19881reported that the Snow Goose andBlue Goose may have been separatesince the last ice age and began tointerbreed 40 to 80 years ago,probably because of humanalterations in their winter habitat thatbrought the two forms together.

o TARIO BIRDS AUGUST 1992

The taxonomic status of the SnowGoose and Blue Goose remainedconfused for some time. Manning etal (19561 preferred to consider threesubspecies: Greater Snow Goose,Lesser Snow Goose and Blue Goose.Following studies of breedingcolonies with mixed pairs, Cooch(19611 proposed that the Blue Goosewas a colour morph of the LesserSnow Goose. The AmericanOrnithologists' Union (19731subsequently lumped the two formsas colour morphs.

There continues to be a gradualmixing of the two morphs on thebreeding and wintering grounds. Thefirst blue morph Greater Snow Geesewere reported in 1973 (Palmer 19761.suggesting interbreeding (gene flow]between blue morph Lesser SnowGeese and Greater Snow Geese.Except for the size difference, theblue morph is identical in bothsubspecies. The blue morph appearsto be increasing in the Greater SnowGoose. Nevertheless, it currentlyconstitutes less than one percent ofthe populations moulting on BylotIsland, NWT or staging along the St.Lawrence in Quebec (Yves Aubry,pers. comm.],

Morph GeneticsThe plumage colour of the Snow

Goose is controlled by a single gene.This gene has two forms calledalleles. A blue morph has twodominant blue alleles, one from eachparent. Similarly, a white morph birdhas two recessive white alleles. Apair of white morphs will produceonly white offspring, and a pair ofblue morphs only blue offspring.However, when a white morphcrosses with a blue morph, theoffspring inherit both a white allele

and a blue allele for plumage colour.Since the blue allele is incompletelydominant over the recessive whiteallele, the offspring of a cross aremore like a blue morph but withvarying amounts of white on thebelly. Excellent illustrations of theintermediate or white- bellied morphare found on plate 10 in The Birds ofCanada (Godfrey 19861 and on page65 in the National Geographic FieldGuide to the Birds of North America(Scott 19871.

Interestingly, the offspringproduced by a pair of white-belliedmorphs (intermediate morphs] willoccur in the ratio of twointermediates to one white to oneblue morph. The reason that purewhite or pure blue morphs can resultfrom a pair of intermediates isbecause each intermediate carriesalleles for both white and blueplumage. Each intermediate passes ononly one allele (white or blue] forplumage colour to each offspring.Therefore, if the offspring inherits awhite allele from each parent then itwill be a white morph, and so on.The above situation is similar to ablue-eyed child being born to brown-eyed parents where the child inheritstwo recessive alleles for blue eyes,one from each parent. The offspringof an intermediate morph and a whitemorph will occur in a ratio of oneintermediate to one white. Similarly,the offspring of an intermediate and ablue will also occur in a one-to-oneratio.

In the Checklist of RecognizableOntario Bird Forms (Pittaway 1991l.the intermediate morphs were listedas the "white x blue morph" whichimplied that this form was the resultonly of a mixed white and blue pair.

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Since intermediates can result fromother combinations of morphs aswell, I now prefer to call this formthe "white-bellied morph".

Morph BehaviourIn mixed colonies, both morphs

usually pair selectively with geese ofthe same plumage colour asthemselves. The principal forcecontrolling mate selection appears tobe family colour, with most younggeese later choosing mates of thesame colour as their parents andsiblings (Cooke 19881. Enough mixedpairs occur to prevent the twomorphs from becoming separatespecies. The frequency of mixed pairsis around 15% (Cooke 19881. Theoffspring of a mixed pair may choosea mate of either colour. One of thereasons that mixed pairs occur is thehabit Snow Geese have of laying theireggs in other Snow Goose nests. Forexample, if the female of a blue pairlays an egg in a white pair's nest, theyoung blue morph will be imprintedon a white family. As an adult, it willmost likely choose a white mate.Neither morph appears to have asurvival advantage over the other.Mixed pairs and their intermediateoffspring also show no reduction inreproductive success.

ConclusionThe next time that you observe

Snow Geese, it is my hope that aknowledge of their subspecies,morphs, genetics, ecology andbehaviour will make your birdingthat much more enjoyable.

AcknowledgementsIt would be impossible to write aboutSnow Geese or other recognizable

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forms without consulting with manyknowledgeable individuals. I wish tothank Yves Aubry, Fred Cooke, BillCrins, Bruce DiLabio, CendrineHuemer, Chris Lemieux, RoryMacKay Henri Ouellet, RichardPoulin, Paul Prevett, Ken Ross, RonTozer and Mike Turner for theirvaluable help.

Literature citedAmerican Ornithologists' Union. 1957.

Check- List of North American Birds.5th edition. American Ornithologists' Union,Washington, D.C.

American Ornithologists' Union. 1973.Thirty-Second Supplement to the AmericanOrnithologists' Union Check-List of NorthAmerican Birds. Auk 90: 411-419.

Bain, M. and B. Henshaw {editors}. 1992.Annual Bird Report, Durham Region,Ontario, 1991. Published by the editors.

Bellrose, F. G. 1976. Ducks, Geese and Swans ofNorth America. Stackpole Books, Harrisburg,Pennsylvania.

Bent, A.G. 1925. Life Histories of NorthAmerican Wild Fowl. United States NationalMuseum Bulletin 130, Part 1I, Washington,D.C.

Cadman, M.D., P.F.J. Eagles andF.M. Helleiner {compilers}. 1987.Atlas of the Breeding Birds of Ontario.University of Waterloo Press, Waterloo,Ontario.

Cooch, F. G. 1961. Ecological aspects of theBlue-Snow Goose complex. Auk 78: 72-89.

Cooke, F. 1988. Genetic Studies of Birds - TheGoose with Blue Genes. Plenary Lecture 3.XIX Congressus InternationalisOrnithologicus, Ottawa. Volume I [HenriOuellet, editor]. National Museum of NaturalSciences, Ottawa.

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

[ames, R.D. 1991. Annotated Checklist of theBirds of Ontario. Second Edition. RoyalOntario Museum, University of TorontoPress.

Manning, T.H., E.O. Hohn andA.H. MacPherson. 1956. The Birds ofBanks Island. National Museum of CanadaBulletin 143: 1·144.

Palmer, R.S. {editor} 1976. Handbook ofNorth American Birds. Volume 2: Waterfowl(Part 11. Yale University Press, New Haven,Connecticut.

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

Scott, S.L. {editor}. 1987. National GeographicSociety Field Guide to the Birds of NorthAmerica. Second Edition. NationalGeographic Society, Washington, D.C.

Soper, J.D. 1930. The Blue Goose. Departmentof the Interior, Ottawa.

Yank, R., Y. Aubry and M. Gosselin. 1991.The Spring Season, Quebec Region. AmericanBirds 45: 412-414.

Ron Pittaway, Box 619, Minden, Ontario KOM2KO