SHORT COMMUNICATIONS

Hybridization of Glaucousand Herring Gulls at the MackenzieDelta, Canada

LARRY B. SPEAR PointReyes Bird Observatory,4990 ShorelineHighway, Stinson Beach, California 94970 USA

Interbreedingbetween two holarcticspecies, the 7-10; I usually could not see primary 6 adequately. GlaucousGull and Herring Gull (Larushyperboreus Each gull was missing one or two of primaries 5-8 and L. argentatus)has been documented only at Bear becauseof molt. This exposedany pigmentation on Island (Barents Sea) and Iceland (reviewed by In- the inner vane of at least one primary, but necessi- golfsson1970). Ingolfsson (1970) classifiedparental tated that HI's be based on 2-4 feathers instead of 5. and hybrid phenotypesrelative to pigmentationpat- This did not decreasemy ability to observeprimary terns of distal primaries,where a hybrid index (HI) characteristicsbecause the outer two primaries, es- of 0 = pure hyperboreusand HI 5 = pure argentatus, pecially primary 10, are most likely to show inter- although "an occasionalpure bird (argentatus)may mediate characterstates (Ingolfsson 1970). scoreas low as 4.2." Basedon this system,interbreed- Only 5.1%of the individualshad HI's of argentatus ing in North Americahas been suspected.In 595 mu- or intermediates(Table 1). Although at leastone col- seum specimens(most taken during the breeding ony of argentatuswas located at the delta(Sitidgi Lake) season)of the two speciesfrom Canada and Alaska, approximately 75 km from the coast(see Campbell Ingolfsson(1970) found 7 with HI's of 4.0-4.6, and 1973), no primary breeding sitesof this specieswere 26 with HI's of 0.2-1.8. However, with the possible visited. The ratios of hyperboreus,argentatus, and hy- exceptionof two birds with HI's of 1.8 and 4.0, only brids did not vary significantlybetween locations (G two obvioushybrids are known from North America: test, P > 0.05). Pigmentation patterns of the distal a bird (HI = 3.6) collected at San Diego, California, primaries of intermediates were similar to those ob- and a bird (HI = 3.0-3.5) collected at Pt. Barrow, servedby Ingolfsson(1970) in Iceland (see examples Alaska(Ingolfsson 1970; Jehl 1971,MS). While work- of Canadian hybrids in Fig. 1A, B). HI values of in- ing nearthe MackenzieDelta, Canada,in August1984, termediatesaveraged 3.1 + 0.9 (n = 51), tending to- I observedhybrid hyperboreusx argentatusregularly, ward argentatus(Fig. 2). I doubt if intermediateswith and documented the first instance of interbreeding of the two speciesin North America. TABLE1. Censusesof adult GlaucousGulls, Herring During 9-31 August 1984, I used 8x binoculars Gulls,and their hybridsin the vicinity of the Mac- and a 20-45 x spotting scopeto study the frequency kenzie Delta, Canada, 1984. of variousphenotypes among adults at two breeding sites[Kay Point, Yukon (69ø13'N,138ø17'W), and Es- Number seen capeReef, Yukon (68ø59'N,137ø11'W)], at three loaf- Location Her- Inter- ing sites[Tuktoyaktuk dump and harbor,Northwest and date Glaucous ring mediate TotaP Territories (69ø27'N, 133ø05'W), and Pauline Cove, Herschel Island, Yukon (69ø34'N, 138ø55'W)],and once Tuktoyaktuk dump at sea(69ø37'N, 133ø07'W) when gulls were attracted 10 August 395 2 14 411 to our drifting boat. Most adults were probably res- 31 August 598 4 22 624 identsbecause young were being fed at colonies,and Tuktoyaktuk harbor the postbreedingdispersal does not begin until late 9 August 139 0 5 144 Augustor early September(Barry and Barry 1982). 30 August 262 3 12 277 I distinguishedgulls of the hyperboreus-argentatus BeaufortSea, 15 km N of Tuktoyaktuk type from Thayer's Gulls (L. thayeri,of which only 14 August 51 0 5 56 two were seen) by their larger size, lighter mantle color,yellow to orangeeye rings, pale yellow irises, Kay Point and, in the caseof pure argentatus,their wing-tip pat- 17 August 18 0 2 20 tern (see MacPherson 1961, Smith 1966). I observed EscapeReef and classifiedeach intermediate according to Ingolfs- 20 August 49 0 3 52 son's(1970) system.Unlike Ingolfsson(1970), I did Pauline Cove not collect specimens,and therefore used a larger scaleinterval (0.5) than his (0.2). This produced less 21 August 120 1 7 128 precise classifications.To reduce the chance of in- Total 1,098 8 51 1,157 cluding the same individual more than once, data Percentage 94.9 0.7 4.4 100.0 from only one sessionof observationsat eachof the aAt sites where two counts were made, only the six locations were used in the analyses. data collectedwhen the largest count was made were My HI estimatesare basedon scrutinyof primaries included in the total.

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1.0 1.5 2D 2.5 50 3.5 4.0 4.5 Hybrid Index Fig. 1. Gullsseen in the vicinityof the Mackenzie Delta. (A) Tuktoyaktukdump, bLW.T.,HI = 2.0. (B Fig. 2. Distribution of hybrid indicesof 51 Her- ring Gull x GlaucousGull intermediates(HI = 0.5- and C) Mated pair near Kay Point,Yukon coast. HI of bird on left = 3.5-4.0;bird on right was a pure 4.5) encounteredat randomin the vicinity of the GlaucousGull. (D) Tuktoyaktukdump, bLW.T.,31 MackenzieDelta during August1984. (No gullswith HI's of 0.5 were seen.) August1984. Characteristics of this fledglingnearly identicalto that of one of two fledglingsassociated with pair shown in B and C. The pigmentationpattern of both young resembled heavilymarked hyperboreus. One had distalprimaries that correspondedto N4 of the Munsell Neutral Chart HI's -> 1.5 were overlooked, but some birds with (MunsellColor Co.,Baltimore, Maryland), i.e. darker HI's -< 1.0 may have been. than expectedof first-yearhyperboreus; its bill, al- Eye rings of hyperboreusand intermediatesvaried thoughlighter toward the base,was not distinctly fromyellow to orange,with a few appearingscarlet- bicoloredas typical of first-yearhyperboreus (see Fig. orange(see VillalobosColor Chart in Palmer 1962). 1D for photo of young with similar characteristics). In ? argentatus,eye ringswere yellow (4), orange- The primariesand bill of the secondwere character- yellow(2), or orange(1). Thesefindings are similar istic of hyperboreus(see Grant 1982:photos 324, 326 to thoseof Ingolfsson(1970). Smith (1966),however, for similar types). notedonly yellowand orangeeye rings, respective- At the EscapeReef colony,where I found 90 active ly, in hyperboreusand argentatusbreeding in the east- nest sites, 3 of 52 adults had intermediate HI's: 1.5, ern Canadian Arctic. At the Mackenzie Delta, iris col- 2.0, and 3.0 (Table 1); all other adultsappeared to be or was uniform pale yellow in all adults.The mantle pure hyperboreus.Of 119 fledglings,? had sooty-col- colorin 3 of 8 argentatuswas darker than that of the oredprimaries, and at least15 did not havedistinctly hyperboreus,however, and each of these 3 birds had bicoloredbills. One deadfledgling had primarypig- yellow eye rings. menration correspondingto a Munsell value of N3, I foundonly onemixed pair nestingsolitarily (i.e. i.e. more like argentatusthan hyperboreus. no other gulls nestingwithin ! kin) on a mainland The evidencesuggests that interbreedingbetween beachabout 2 km southeastof Kay Point.When first hyperboreusand argentatusoccurs regularly but at a seen from the boat 100 m from shore, the adults were low frequencyin the vicinityof the MackenzieDelta. attendingtwo large fledglingsthat beggedat least Hybridizationin this region may not be surprising. twice from the argentatus-likeadult. I estimatedthis Although hyperboreusare primarily coastalbreeders bird'sHI at 3.5, althoughit tendedtoward 4.0 (Fig. and argentatusbreed mainly in the interior, the Mac- lB, C). Fromits size(marginally larger than its mate) kenzie Delta offers both habitats. Furthermore, the and dominant,more aggressive behavior, I judgedit Mackenzie human population has increasedseveral- to be the male;the smallerbird appearedto be pure fold during the past 15 years becauseof extensive hyperboreus.When a small boat was landed on the BeaufortSea oil exploration,and this has probably beach,the two adultstook flight and landed30 m increasedthe availabilityof refuseto gulls. A resul- offshore,and the young swam out to them. Their tant increasein the gull population and colonization presumednest was located among driftwood near to of new locations,or attractionof argentatusto favor- wherethe familywas first seen.After our party re- able feeding areasnear the coast,or both, would in- treated,the four birdsflew backto their territory. creasethe latter'scontact with hyperboreus.Although January1987] ShortCommunications 125

evidence suggeststhat interbreeding was occurring for Can. Wildl. Serv., Edmonton, and Dome Pe- at least occasionallybefore the recent change in the troleum Ltd. and Esso Res. Can. Ltd., Calgary, human population (see Ingolfsson 1970, Jehl MS), Alberta. there is increasingevidence that human activityis an CAMPBELL,R.W. 1973. Baseline study of selected important factor facilitating breakdown in mecha- nestingwaterbirds on the northwestMackenzie nismsthat prevent interbreeding (seeSmith 1966 for Delta, Northwest Territories and Yukon, 1972. review of isolating mechanisms).For example, hu- Section 3. In Towards an environmental impact man activity is thought to be primarily responsible assessmentof the Mackenzie gaspipeline from for the mass immigration of argentatusto Iceland, Alaska to Alberta. Winnipeg, Manitoba, Envi- which resulted in extensive hybridization with hy- ronmental Protection Board. perboreus(Ingolfsson 1970). Similarly, hybridization GRANT,P. J. 1982. Gulls: a guide to identification. between argentatusand Glaucous-winged Gulls (L. Berkhamsted,England, T. & A.D. PoyserLtd. glaucescens),another coastalbreeder, is mostcommon INGOLF$$ON,A. 1970. Hybridization of Glaucous near human settlements associated with Alaskan Gulls (Larushyperboreus) and Herring Gulls (L. fisheries (Williamson and Peyton 1963, Patten 1980). argentatus)in Iceland.Ibis 112:340-362. Further study of isolating mechanismsand contin- JEHL,J. R., JR. 1971. A hybrid Glaucousx Herring ued monitoring of phenotype frequenciesare need- Gull from SanDiego. California Birds 2: 27-32. ed, however, to identify and assessall factorsrespon- MAcPI-mRSON,A. H. 1961. Observationsof Canadian sible for interbreeding between these species. Arcticgulls, and on taxonomyof L. thayeriBrooks. I thank L. Pearson,who skippered the boat, and Arctic Inst. North Amer., Tech. Pap. No. 7: 1-40. G. Alliston for providing backgroundliterature. I am PALMER,R. $. 1962. Handbook of North American very grateful to G. W. Miller, W. J. Richardson,and birds, vol. I. New Haven, Connecticut, Yale Univ. B. Wursig for encouragingthis study and reviewing Press. an earlier draft. D.G. Ainley, J. R. Jehl, Jr., and E. C. PATTEN,$. M., JR. 1980. Interbreeding and evolu- Murphy also provided helpful comments on the tion in the Larusglaucescens-Larus argentatus com- manuscript,K. Hill developedthe photographs,and plex of the southcoast of Alaska.Unpublished E. Tuomi typed the final draft. I thank them all for Ph.D. dissertation,Baltimore, Maryland, Johns their help. This study was funded by the U.S. Min- Hopkins Univ. erals ManagementService, Alaska OCS Region,un- SMIT•I, N. G. 1966. Evolution of some arctic gulls der a contract to LGL Ltd., and is PRBO contribution (Larus):an experimentalstudy of isolatingmech- No. 342. anisms. Ornithol. Monogr. 4. WILLIAMSON,F. S. L., & L. J. PEYTON. 1963. Inter- LITERATURE CITED breedingof Glaucous-wingedand Herring gulls BARRY,$. J., & T. W. BARRY.1982. Seabird surveys in the CookInlet region,Alaska. Condor 65: 24- in the Beaufort Sea, Amundsen Gulf, and Prince 28. of Wales Strait, 1981 season.Unpublished Rept. Received21 January1986, accepted 11 July 1986.

HistologicalEvidence for the SystematicPosition of Hesperornis (Odontornithes: Hesperornithiformes)

PETER HOUDE Divisionof Birds,National Museum of NaturalHistory, Smithsonian Institution, Washington,D.C. 20560USA

In his original description of Hesperornis,0. C. 1978, Cracraft 1980, Balouet 1983). Cracraft's treat- Marsh (1880) noted similarities between this Creta- ment of Hesperornisis exemplaryof the uncertainty ceous toothed "diver" and modern ratites (Struthion- that still existsabout its systematicposition. Cracraft iformes). Subsequently,Hellmann (1927) correctly (1982)concluded that Hesperorniswas a memberof a demonstrated the ecomorphological similarity of monophyleticclade that includesthe neognathous Hesperornisto loons (Gaviiformes),but, in so doing, loonsand grebes(Podicipediformes), but, more re- he incorrectlyrenounced the similaritiesof Hesperor- cently, he (in press)considered it as the sistergroup nis and ratites. Eventually, Gingerich (1973) de- of Ichthyornisplus Neornithes. scribed Hesperornisas possessinga paleognathous I examinedthe histologicalstructure of Hesperornis palate,but, from Gingerich'sown reconstruction,the bone as part of an effort to determine the correct palate of Hesperornisdid not satisfythe criteria that polarity of histologicalcharacters in the bonesof pa- collectivelydiagnose the paleognathouspalate as de- leognathousand neognathousbirds, which I treated scribed by Bock (1963) (Brodkorb 1976, McDowell elsewhere(Houde in pressa). I was surprisedto find