ARCTK VOL. 37, NO. 3 (SEPTEMBER 1984) P. 204-287

Phenotypic Variation ,among Thick-billedMurres from Colonies in Hudson Strait. A.J. GASTON,’ G. CHAPDELAINE,* and D.G. NOBLE’

ABSTRACT. Thick-billed Murres (Uria.hvio) breeding in the Canadian Arctic are restricted to a small number of colonies, all comprising more than 10 OOO pairs. Five of these colonies are scattered through HudsonStrait. We collected adultbreeders at three of the colonies - Digges Island, Hantzsch Island, and Akpatok Island- and compared wing and bill measurements and body weights to lookfor intercolonydifferences. Significant intercdony differences were present forall measurements and a discriminant functionanalysis showed that sane individuals fall compleley outside the rangeof variation for the other colonies..Because of the presence of the Laurentide ice-sheet over Hudson Strait, the present colony sites could not have been occupied for more than 10 OOO years. If the observed differences reflect differences in genotype then their evolutionmust have occurred over this perid. Key words: Thick-billed Murre, Uria lomvia, phenotypic variation, Hudson Strait, evolution

R&SUMfi. Les Marmettes de Brunnich (Vria lomvia) nichent dans I’arctique canadien et sontr6parties dans un petit nombre de colonies de 10 OOO couples et plus. Cinq de ces colonies se retrouvent dam le dhroit d’Hudson. Nous avons collectionnedes adultes dans trois de ces colonies: lles Dig- ges, Hantzsch et Akpatok. Nous avons cornpar6 les mesures de la longueur de l’aile et du bec ainsi que les poids pour verifier s’il y avait des differences entre les colonies. Nous avons observe des differences significatives.entre.lesmesurations et les poids des trois colonies et I’analyse discriminante.nous indique que quciques specimens se situent en dehors des limites de variation des autres colonies.A cause de la prhnce du glacier Laurentien sur le dbitd’Hudson durant la dernibre glaciation, I’occupationdes sites actuelspar la Marmette de Brunnich daterait d’environ 10 OOO am. Si.les.diff6rencesobserveeS traduisent des genotypes differem, leur evolution se serait produite B I’interieur de cette p&iode. Mots clb: Ma- de Brunnkh, Uria lomvia, variation des phenotypes, detroit d’Hudson, evolution

Traduit par les auteurs.

INTRODUCTION variation in measurements withinthis area and also differences between birds from these. colonies and those from colonies on The Thick-billed Murre (Uria lomvia L.) has a circumpolar Lancaster Sound. distribution in arctic and subarctic waters (Voous, 1961). The species is divided into three, perhaps four races, exhibiting clinal variation with increasingwing.and bill length eastwards acrossthe Atlantic and northern Eurasia (Vaurie, 1965). Populations. nesting in eastern Canada are the smallest and belong to the race U. lomviu lomviu (A.O.U., 1957). Some variation within the Canadian populationwas detected by Storer (1952) who showed that birds from Baffin Bay were generally smaller than those from the small, peripheral col- onies in the Gulf of St. Lawrence. Healso showed that sexual dimorphism in the Thick-billed Murre was very slight, par- ticularly in Atlantic populations, being most marked in bill depth. Populations of Thick-billedMurres in arcticCanada are concentrated in a few very large colonies, allexceeding I f 10 OOO pairs and ranging up to OOO pairs (Gaston, 1980). 300 FIG. I. Map of Hudson Strait showing the position of Thick-billed Murre col- They are distributed in the Lancaster Sound-Jones Sound area onies from which birds were collected. (four colonies), east Baffin Island (one colony) and Hudson Strait(five colonies) (Brown et ul., 1975;Gaston, 1980). Measurements of samples from three Lancaster Sound col- METHODS onies are similar, suggesting that the populationis phenotypi- cally fairly uniform within thisarea (Birkhead and Nettleship, Samples at Digges Sound were takenby AJG and DGN dur- 1981.; Gaston and Nettleship, 1981). Recent field workby the ing June-August 1980-1982; those at Akpatok and Hantzsch Canadian Wildlife Service at three of the colonies in Hudson islands were taken in August 1982 by GC and AJG, respec- Strait - Digges Sound, Akpatok Island (south), and Hantzsch tively. The majority of birds collected at Digges Sound were Island (Fig. 1) - hasenabled us toexamine inter-colony shot on the water 5-25 km from the colony, while those taken

‘Canadian Wildlife Service, Migratory Birds Branch, Ottawa, Ontario, Canade K1A OE7 %anadh Wildlife Service, QuCbec Region, Ste-Foy, Quebec, Canada G1V 4H5 HUDSONSTRAXTMURRES 285 at the othertwo colonies were capturedon thebreeding cliffs. RESULTS Only birds from Digges Sound with fully developed brood Sexual Dimorphism patches were included in these comparisons.A sample of birds taken on the cliffs at this colony did notdiffer significantly in The large sample of birds collected at Digges Sound showed any measurement from those obtained atsea, and both samples significant .differences between the sexes in all-measurements have therefore been combined for analysis. Because all the except wing length. Females had slightly longer wings than birds used in our analysis were breeding adults, they were malesbut males exceeded females in all other dimensions likely to havebeen more than three years old [by analogy with (Table 1). These results are in agreement with Storer (1952) CommonMurres (Uria aalge L.) (Birkheadand Hudson, who also found that males werelarger than females in bill and 1977)l. Hence, our comparisons are unlikely to be affectedby tarsus measurements, but found no significant difference in age-related differences. wing length. Results for Akpatok Island were similar to those All birds at Digges Sound were weighed within12 h of col- at Digges Sound, with all trends inthe same direction, but dif- lection with a 3-beam balance reading to within 0.1 g; at the ferences were significant only .for the white line.At Hantzsch other two colonies weused “Pesola” spring balances cali- Island females exceeded malesin all measurements except bill brated to 20 g but estimated to within 10 g. One wing was depth, but none of these differences were significant. Sample measured to the nearest1 mm from the carpus to thetip of the sizes vary somewhat for different measurements because some longestprimary by flatteningit along a ruler. Fourbill birds were damaged in collection and because a proportion of measurements (“white line”, “culmen”, “nostril”, and birds collected at Digges ‘Sound could not be weighed. “depth”) were taken using vernier calipers reading to0.1 mm (Fig. 2). At Digges Sound and Akpatok Island all birds were kiiled and sexed by dissection, but at Hantzsch Island only .12 Inter-colony Comparisons birds were sexed, the remainder being measured and released Comparing samples of knownsex, we .found significant dif- alive. ferences among the three colonies in all measurements except the culmen (Table1). Birds from Akpatok Island were smaller than those from the other two colonies in weight, wing length andbill depth, whilefemales from Hantzsch Island were larger in white line .and nostril measurements (Duncan mul- tiple range test, Pc0.05). Because the sample of birds of known sex from Hantzsch Island was rather small, we also combined our data for .both Sexes for all three colonies to examineintercolony variation. When this was done all measurements considered showed sig- nificant intercolony variation (Table 2). Birds from Akpatok Island were lighter and had shorter wings than those from .the other two colonies. Those from Hantzsch Island had signifi- cantly longer bills, the difference being most striking .for the

TOP VIEW lineand nostril measurements. The only measurementfor which all paired comparisons were significant.was‘bill depth, with birds from Digges Sound having the deepest and those from Akpatok Island the shallowest bills.

TABLE 1. Sexual dimorphism among Thick-billed Murres at three colonies in Hudson Strait

Male Female - - P X S.D. N X S.D. N Digges Sound Weight '(g) . 972.53 91.89 94 939.04 98..99 53 0.046 Wing length (mm) 217.24 5.72 122 216.60 6.04 83 N.S. Bill; line (mm) 55.98 2.11 127 54.42 2.20 84

Akpatok Island Weight (g) 842.w 56.54 10 821.70* 56.87 12 N.S. Wing length (mm) 207.30* 6.95 10 208.80* 5.00 13 N.S. Bill; line (mm) 56.26 2.62 10 53.85 2.36 11 co.01 depth (m) 14.02* 0.9 IO 13.59* 0.72 11 N.S. culmen (mm) 35.19 1.72 IO 34.63 2.01 11 N.S. nostril (mm) 28.03 2.27 IO 27.90 . 1.49 11 N.S.

Hantzsch Island Weight (g) 93400 38.47 5 968.57 100.40 7 N.S. Wing length (mm) 218.80 7.33 5 220.00 6.19 . 7 N.S. Bill; line -(mm) 55.w 1.45 5 57.63* 2.83 7 N.S. depth (mm) 14.56 0.36. 5 14.37 0.60 7 N.S. culmen (mm) 35.48 1.31 5 35.71 2.94 7 N.S.

nostril Imm).I 28.86 0.97 5 29.53* 2.'28 7 N.S. * Differs significantly from.the other two colonies (PcO.05, Duncan multiple range test) TABLE 2. Measurements of adult Thick-billed Murres at three colonies in Hudson Strait (sexes combined)

Measurement. IslandDigges HantzschSound Island Akpatok F P - - - X S.D. N X S.D. N X S.D. N *eight (9) %1.67 %.36 148 831.09* 56.36 22 958.05 62.34 95 24.59 <0.001 Winglength (mm) 216.96 5.75 215 208.17* 217.045.83 23 5.58 69 25.23 cO.001 Bill; line (mm) 55.37 2.28 211 55.00 2.72 21 56.89* 2.15 95 16.07 <0.001 depth (mm) 14.67* 0.85 211 13.80* 0;85 21 14.40*' 0.55 95 14.22 ~0.001~ culmen (mm) 34.44 ,199 220 34.76 1.88 21 35~77 1.89 95 15.35 co.001 nostril (mm) 28.04 1.54 219 27.% 1.85 21 29.43*26.71 1.59- 95 <0.001 * Population differs significantly from both the other colonies in this measurement (Duncan multiple range test, Pc0.01) DISCUSSION

The principal components analysis demonstrates clearly that measurements' recorddd-for some birds at both Hantzsch and Akpatok. islandsfall completely outside the rangeof variation for the large-sample from. Digges Sound. This seems to ex- clude the possibility thatobserved,differences are the result of biased sex ratios or age composition among thethree samples. In comparison with the. differences recorded in the present study, those between colonies in the Lancaster Sound/Jones Sound area seem to. be smaller. Birkheadand Nettleship (198 l), comparing measurements for breeding birds 'at Cape Hay, Bylot Island, andCoburg Island, found. a small dif- ference in culmen length, butno significant .difference in culmen depth or body weight. There was no significant dif- ference in culmen. length between these. colonies and birds fromPrince Leopold Island (Gaston and Nettleship, 1981). FIG. J. Scattergram of first and second canonical discriminant.functionsshow-. ingthe position of group-centroidsfor the threepopulations compared: A - Body weights. and culmen measurements at the Laneaster Akpatok Island: D - Digges Sound: H - HantzschIsland. Sound/Jones Sound colonies wereclosest to thoserecorded at HUDSON STRAIT MURRES 287

TABLE 3. Formulae used in calculating unstandardized canonical sent separate demes. This has implications for conservationin discriminant functions (CDF) suggesting that a severe population decline at one colony is unlikely to be compensated by appreciable immigration from CDF 1 = 0.0930 Wing + 1.0147 Depth - 0.1177 Culmen - 0.3630 Nostril elsewhere. It also supports the contention by Gaston and Net- CDF 2 = 0.1076 Wing - 0.1716 Depth - 0.3545 Culmen + 0.5027 Nostril tleship (1981) that arctic Thick-billed Murre colonies probably have been endogamous for a long time.

Akpatok Island, although weights were slightly heavier, but ACKNOWLEDGEMENTS the possibility of systematic differences in measuring techni- ques usedby different peoplemake such comparisons We would like to thank all those who worked uswith in the field; R. unreliable. Anderson, P. Brousseau, R.D. Elliott, J. Geale, M. Guillemette, 1.L. Jones, B. Lyon, M.A. Purdy, S. Smith, and B.J. Spears. Thanks also Assuming that the observed differences in phenotype repre- to Polar Continental Shelf Project and the crew of Canadian Coast- sentcolony-specific characteristics, thequestion arises of guard Icebreaker Pierre Radisson for logistic support, and to Andy whether they are theresult of environmentaldifferences Thtriault of the Departmentof Indian Affairs andNorthern Develop- operating during the period of growth, or of differences in ment for varied kinds of assistance. The workwas partially funded by genotype resulting from selection or random gene fixation. Petro-Canada and the baseline studies programmeof Department of Environment as part of the Offshore Labrador Environmental Pro- The first alternative seems unlikely because, although chicks gramme. Figures were drawnby the Drafting Department of Environ- do grow at colony-specific rates (Gastonet af., in prep.), they ment Canada. leave the colony at only about 20% of adult weight (Gaston and Nettleship, 1981). In addition, the lightest chicks atdepar- REFERENCES turefrom the colony are thosefrom Digges Sound, where AMERICAN ORNITHOLOGISTS UNION.1957. The A.O.U. Check-list of adultweights are heaviest. Chicksundergo most of their NorthAmerican Birds, 5th Edition.American Ornithologists Union. development at sea and during this period chicks from three all 691 p. colonies are probably intermingled as theymake their way ANDREWS, J.T. and FALCONER, G. 1%9. 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Population parameters for the Without evidence on actual gene frequencies, the presence Common Guillemot Uriu ualge. Ornis Scandinavica 8(2):145-154. BIRKHEAD, T.R. and NETTLESHIP, D.N. 1981. Reproductive biology of of genotypic differences between birds fromthe three colonies Thick-billed Murres (Uria lomviu): an inter-colony comparison. Auk remains hypothetical. However, if there are significant differ- 98(2):258-269. ences in genotype, this would indicate that the three popula- BROWN, R.G.B., NETTLESHIP, D.N., GERMAIN, P., TULL, C.E., and tions have probably been separated for a considerable period DAVIS, T. 1975. Atlas of Eastern Canadian Seabirds. Ottawa: Canadian Wildlife Service. 220 p. of time. The presenceof the Laurentide ice-sheet over Hudson FLINT, R.F. 1971. Glacial andQuaternary Geology. New York: John Wiley. Bay and Hudson Strait during the last glacial period excludes 829 p. the possibility that the HudsonStrait colonies could have been GASTON, A.J. 1980. 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Cambridge, MA: Harvard Uni- measurements to calculate approximaterates of evolution versity Press. 797 p. among the colonies. However, we have no way to judge the NIE, N.H., HULL, C.H., JENKINS, J.G., STEINBRENNER, K., and importance of the “founder principle” (Mayr, 1948, 1963) in BENT, D.H. 1975. Statistical Package for the Social Sciences. 2nd Ed. determininginitial differences amongfounder populations. New York: McGraw-Hill. 675 p. ORR, C.D. and WARD, R.M.P. 1982. The fall migration of Thick-billed These may have consisted of very few individuals and hence Murres near Southern Baffn Islandand Northern Labrador. Arctic contained only a small portion of the genetic variation within 35(4):531-536. the populationsfrom whichthey originated. Random dif- STORER, R.W. 1952. Acomparison of variation, behaviour and evolution in ferences among these founder gene poolsmay have established the seabird genera Uriu and Cepphus. 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