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Articles

Bicknell's Thrush in Ontarioby

Henri Ouellet

IntroductionThe Gray-cheeked Thrush (Catharusminimus), a typical bird of thenorthern boreal forest, occurs duringthe breeding season fromNewfoundland to Alaska but smallpopulations have been recorded alsoin the northern New England statesand in northeastern Siberia (A.O.U.1983, Bent 1949, Stepanyan 1990,Godfrey 1986). Geographic variationwas noticed and described by a fewauthors (Bicknell 1882, Ridgway1882) mainly during the last centurywhich led to the recognition of threesubspecies (Wallace 1939, A.O.U.1957). Of these, Bicknell's Thrush(Catharus minimus bicknelli) wasdescribed by Robert Ridgway (1882)from specimens taken in themountains of New England. Hereported that the specimens hestudied had a smaller size and thattheir plumage was more brownish onthe back when compared withspecimens taken farther north, inCanada and in Alaska (Ridgway 1882,1907). Several years later, in animportant work that was to become aclassic biosystematic study, GeorgeWallace (1939) published the resultsof his studies of the distribution, lifehistory, and taxonomy of the NewEngland states population withcomparisons based primarily onmorphological aspects with breedingbirds taken in other parts of therange. He established that birds from

Newfoundland belong to a differentpopulation from those of themainland and that they should berecognized as a distinct subspeciesand that mainland birds in the rest ofthe range belonged to anotherpopulation.

Bicknell's Thrush has beenrecognized since by most authors as asubspecies of the Gray-cheekedThrush. In addition to the markedmorphological differences found inspecimens from New England, NovaScotia, and the Gaspe Peninsula(Quebec), the song of these birds wasbelieved to be unlike that of otherpopulations (Gillet 1935). Wallace(1939) confirmed the song differencesbut these were ignored by Stein(1956) and everybody else.

The winter distribution ofBicknell's Thrush remained relativelyunknown and much confusionpersisted about the wintering rangesof the three subspecies until Wallace(1939) reidentified the type andascertained its origin. Followingseveral periods of field observation,the examination of specimens inmuseum collections, and thecomparison of song recordings fromvarious parts of the range of theGray-cheeked Thrush, in easternCanada and the United States, Ibecame aware of strong differenceswhen birds of southern Quebec (c.m. bicknelli) were compared to birds

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from Newfoundland, Labrador, andnorthern Quebec (c. m. aliciae andminimus). These peculiaritiesconvinced me to undertake a detailedstudy of the southeastern population.I have examined breeding specimensof known sex in fresh or relativelyfresh plumage from Labrador,Massachusetts, New Brunswick,Newfoundland, New Hampshire,New York, Nova Scotia, Quebec,Saint- Pierre and Miquelon, andVermont. I have studied alsomigratory and wintering specimensfrom Ontario, Quebec, the MaritimeProvinces, Manitoba, Saskatchewan,Illinois, Iowa, Maryland,Massachusetts, Minnesota, Montana,Nebraska, New Jersey, New York,North Dakota, South Carolina,Virginia, Wisconsin, Belize, Bermuda,Colombia, Costa Rica, DominicanRepublic, Ecuador, Guatemala,Guyana, Honduras, Panama, SwanIslands (U.S.A.), and Venezuela todetermine the migration patterns andwinter range of the southeasternpopulations.

Results

Several color classes weredetermined using the dominantcoloration of the specimens. Eachspecimen was then assigned to one ofthe color classes. I found thatspecimens of bicknelli usually havethe dorsal regions "olive brown", andthat "olive" is dominant in theminimus group, whereas "olive gray"does not occur in breeding bicknelli.Strong differences were found in thecoloration of the tail of bicknelliwhere it is consistently "chestnut",in contrast with the "olive" or "olivebrown" tail of minimus and aliciaespecimens. My data also indicate thatmales of bicknelli have more buffy

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throats than those of the other twogroups and that the white of theunder parts is duller in bicknelli thanin the other samples, having a grayishtint or wash.

The color of the soft parts inbicknelli is different from that of theother two subspecies in being "brightpale yellow" at the base of themandible, varying from "blackishbrown" to "black" on the maxilla,and ranging from "light purpishflesh" to "purplish flesh" on the legs.The soles of the feet are pale andvary from " flesh " to "dull paleyellow" in bicknelli whereas they arebrighter "yellow" in the otherpopulations.

Series of measurements analyzedstatistically show that bicknelli hasthe smallest measurements, and thatspecimens from northern Quebec,including northern Labrador, havethe largest body dimensions, with theNewfoundland population beingintermediate in size for mostdimensions. Wing length is shortestin bicknelli (male: mean = 92.9mm;female: mean = 87.7mm) as well astail length (male: mean = 68.7mm;female: mean = 65.6mm), tarsuslength (male: mean = 29.2mm;female: mean = 28.9mm) andexposed culmen length (male: mean= 12.7mm; female: mean =

12.6mm).Field recordings of songs by

myself or provided by a colleague1J. T. Marshall) or obtained from theCornell University Library of NaturalSounds were used in the analyses,comparisons of songs from differentpopulations, and field experiments.The frequency of the bicknelli songs isconsistently higher and does not falltowards the end of the song as in

minimus but remains constant orincreases. This difference can bedetected in the field by a carefullistener and provides an accuratemeans of separating this populationfrom the others. The high frequenciesof the call notes are higher in bicknellithan in minimus but the lowfrequency is not different. Similarly, Ifound no difference in the durationof the call notes.

In a series of playbackexperiments, songs previouslyrecorded in central and southernQuebec, including the EasternTownships and the Gaspe Peninsula,were played back in various habitatsand in areas where Gray-cheekedThrushes had been recorded or whichseemed suitable for this species. Myresults show that no reaction wasobtained from the playbacks of aliciaeor minimus songs in the range ofbicknelli. However, songs of bicknellidrew reactions in over 45 per cent ofthe playbacks.

A biochemical analysis ofmitochondrial DNA (mtDNA)revealed a strong differentiationbetween Catharus minimus and C. m.bicknelli and an important divergencebetween the two taxa. These resultsindicate that this divergence tookplace approximately 1 million yearsago.

The Gray-cheeked Thrush occursin the Boreal Forest Region (Rowe1972) and is found primarily inmature coniferous stands and morerarely in tall shrubby growths in thetaiga or above tree line (A.O.V. 1983;Godfrey 1986) in Labrador andnorthern Quebec. On the other hand,southern populations from southernQuebec, the Maritime Provinces, andthe New England States have been

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reported in scrubby coniferousstands, mostly spruce, up to tree line(Palmer 1949; Wallace 1939), andmore rarely in deciduous habitats.My observations in the GaspePeninsula and elsewhere in southernQuebec show that the birds of thesouthern population are not restrictedto thick stands of stunted conifers onsteep mountain slopes or near tree­line but that they were morenumerous in second growth standscharacterized by relatively youngconifers of small size, such as BalsamFir and White Spruce mixed withearly second growth deciduousspecies. It appears that it is now morenumerous in this habitat than in thehabitat that had been considered untilnow to be the typical habitat of thetaxon.

The known distribution ofBicknell's Thrush (Map I) has l:1eenestablished on specimens incollections, on published datarecorded south of the St. LawrenceRiver, and on fully documentedobservations obtained during severalbreeding seasons. The breeding rangeof Bicknell's Thrush may have beenbroader in the past, particularly alongthe north shore of the Gulf of St.Lawrence, but there is little evidenceto substantiate this hypothesis. It canbe found in the highlands of NewBrunswick (Squires 1976, fide AJ.Erskine), in Vermont (Laughlin andKibbe 1985, Spear 1976, Perkins andHowe 1901), and in New York State(Bull 1974, Merriam 1884) and innorthwestern Maine, northern NewHampshire, Massachusetts, andnort~1ern Vermont.

The migration pattern ofBicknell's Thrush is not well knownbut specimens in various collections

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Catharus bicknelli

Cathorus m. minimus

minimus aliciae

MAP500 kmo

Map 1: Breeding distribution of Bicknell's Thrush in Eastern North America.

establish its presence in migration inConnecticut, New Jersey, New York,South Carolina, Virginia, NewBrunswick, Nova Scotia, Quebec,Ontario, Bermuda, and the BahamaIslands. Bicknell's Thrush probablyoccurs more frequently in migrationalong the Atlantic coast from Quebecto Florida than what is revealed bythe reports. In spite of the difficultyof identifying it in the field and theunpredictability of occurence in theinterior, it probably occurs in theinterior of the continent as well butin smaller numbers. For this reason,

it is to be expected in Ontario,particularly during the fall migration,from mid-August to late September.A "rare migrant in the south" ofOntario (James 1991:62), I haveidentifed only one fall bicknellispecimen originating in the province.

In winter, the range of Bicknell'sThrush appears to be restricted toislands in the Caribbean region butmore information is needed to mapits winter distribution and estimateits population on the islands·.---A.ll thecollections that I have studied'

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revealed no specimen of Bicknell'sThrush taken anywhere in Central orSouth America.

The partial results presented hereand in a forthcoming more elaboratereport (Ouellet 1993) show clearlythat the bicknelli population of theGray-cheeked Thrush (Catharusminimus) is different from it and thatit satisfies all the requirementsnecessary to consider it as a fullspecies. I have therefore proposedthat it be considered as a full species:Bicknell's Thrush (Catharus bicknelliJ.Careful observations of migratingthrushes, particularly in the fall, andsome luck, may reveal that this birdis a regular migrant in parts ofOntario, probably in the St. LawrenceRiver region.

Literature citedAmerican Ornithologists' Union. 1957. Check­

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

American Ornithologists' Union. 1983. Check­list of North American Birds. 6th edition.American Ornithologists' Union,Washington, D.C.

Bent, A.C. 1949. Life Histories of NorthAmerican Thrushes, Kinglets, and their Allies.United States National Museum Bulletin 196.

Bicknell, E.P. 1882. A sketch of the home ofHylocichla aliciae bicknelli, Ridgway, withsome critical remarks on the allies of the newrace. Bulleting of the Nuttall OrnithologicalClub 7: 152-159.

Bull,]. 1974. Birds of New York State.Doubleday/Natural History Press, New York.

Gillet, L. 1935. The thrushes of our woods.Yale Review 24: 743-759.

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

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

Laughlin, S.B. and D.P. Kibbe reds). 1985.The Atlas of Breeding Birds of Vermont.University Press of New England, Hanoverand London.

Merriam, C.H. 1884. Third addendum to thepreliminary list of birds ascertained to occurin the Adirondack Region, NortheasternNew York. Auk 1: 58-59.

Ouellet, H. 1993 (in pressl. Bicknell's Thrush:taxonomic status and distribution. WilsonBulletin 105.

Palmer, R.S. 1949. Maine Birds. Bulletin of theMuseum of Comparative Zoology 102: 1-656.

Perkins, G.H. and C.D. Howe. 1901.A preliminary list of the birds found inVermont. Twenty-first Vermont AgriculturalReport 1901: 85-118.

Ridgway, R. 1882. Descriptions of two newthrushes from the United States. Proceedingsof the United States National Museum 4:374-379.

Ridgway, R. 1907. The birds of North andMiddle America. Part IV. United StatesNational Museum Bulletin 50: 1-973.

Rowe, ].S. 1972. Forest Regions of Canada.Canadian Forestry Service Publication 1300:1-172.

Spear, R.N., Jr. 1976. Birds of Vermont. GreenMountain Audubon Society.

Squires, W.A. 1976. The Birds of NewBrunswick. Second Edition. MonographSeries, New Brunswick Museum 7: 1-22!.

Stein, R. C. 1956. A comparative study of"advertising song" in the Hylocichla thrushes.Auk 73: 503-512.

Stepanyan, L.S. 1990. Conspectus of theornithological fauna of the USSR. Nauka,Moscow.

Wallace, G.J. 1939. Bicknell's Thrush, itstaxonomy, distribution, and life history.Proceedings of the Boston Society ofNatural History 41: 211-402.

Henri Ouellet, Canadian Museum of Nature, Box 3443, Station "D",Ottawa, Ontario KIP 6P4.

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