Morphometric features of Pacific and American Golden- with comments on field identification

OSCAR W. JOHNSON & PATRICIA M. JOHNSON

Departmentof Ecology,Montana State University,Bozeman, MT59717 USA. OWJohnson2105@aoLcom

Johnson,O.W. & Johnson,P.M. 2004. Morphometricfeatures of Pacific and American Golden-Ploverswith commentson field identification. Study Group Bull. 103: 42-49.

We measured linear dimensions and evaluated identification criteria in Pacific and American Golden-Plovers (Pluvialisfidvaand P. dominica)captured for banding.Most of thefidva sampledwere winteringbirds in Hawaii,representative of themid-Pacific flyway; additionalfidva and all dominicawere from breeding grounds on the SewardPeninsula, Alaska. The sexeswere monomorphicin dominica,and for all practicalpurposes infidva as well. On average,fulvafemales had shorterhead, bill, andtarsus lengths than males, but at a scale of <1.0 mm for eachdimension. Interspecific comparisons showed longest wings in dominica,longest bills andtarsi infidva, andno differencein headlengths. Unpublished data provided by colleaguesstudying plovers in Siberiaand Canadaenabled us to compareour Alaska findingswith breedinggrounds elsewhere. There appearsto be little, if any, variationinfidva wing lengthsfrom the easternend (SewardPeninsula) to near the westernend of the breedingrange (Taimyr Peninsula);however, other linear dimensions decreased from eastto west.American Golden-Plovers breeding on the SewardPeninsula (western end of their range)had shorterwings and tarsi, but longerbills than nestingat the oppositeend of the rangenear Churchill, Manitoba.We foundmost field identificationcriteria described in the literatureto be lessthan satisfactory becauseof variabilityand overlap between the two .The onlyreliable characteristics were breeding plumage,number of primariesexposed beyond the longest tertials (2-3 infidva,4-5 in dominica),and primary projectionpast the end of the tail (estimatedat 0-9 mm infidva, 12-22 mm in dominica).In field situations involvingmoulting birds and birds in non-breedingplumage, unequivocal species identification may be impossiblein somecases.

INTRODUCTION Memorial Cemetery of the Pacific (for descriptionsand locationsof theseareas, see Johnson et al. 2001a,c). Add/- The purposesof this paper are to report measurements tionalfidva (n = 14, caughtin 2000) werefroin a wintering obtainedduring bandingof Pacific and American Golden- populationabout 1,300 km southwestof Oahu at Johnston Plovers(./hlva and P. dominica),and to shedlight Atoll (16ø44'N, 169ø32'W), and others(n -- 44, trapped on criteria useful in identifying these somewhat similar 1988-2002) from breedinggrounds on the SewardPenin- species.Our long-termstudies of ecologyin Hawaii sula,Alaska (64ø5 I'N, 166ø05'W;see Johnson et al. 200lb). andAlaska together with morerecent radiotelemetry inves- All of thedominica (n -- 46, trapped1988-2003) were nest- tigations(Johnson et al. 1993; 1997a,b;2001a,b,c) have in- ing birdscaptured on the SewardPeninsula at the samesites volvednumerous marked birds, with an especiallylarge set asfulva(the two speciesbreed sympatrically in thatregion). of dimensionsforJ'tdva. The two taxa are relativelyeasy to The ploverscaptured in Hawaii were caughtl-2 hours distinguishwhen birds are in breedingplumage during spring beforesunrise in mistnets (Johnson et al. 1997b,2001c). At andsummer, but at othertimes identification can be problem- JohnstonAtoll, somebirds were caughtin mist nets,others atic. Becausespecies identity was certain for all ploverswe in a self-triggering60 cm diameterclap-net (patterned after sampled(every individual in breedingplumage), this wasan the "luchock"design, Priklonsky 1960) baited with boiled idealopportunity to evaluatevarious interspecific character- egg. In Alaska,bothfidva and dominicawere capturedon isticsaside from breedingcoloration. Examination of these theirnests with eitherthe clap-netor a droptrap. featureswas prompted partly by inquiriesfrom birders seek- All of the birds were bandedin the springor summer ing advice about ways to separatethe two species.These when they were either nearing departurefrom wintering observershad seenwhat appearedto be./tdva(migrants in grounds(late March-April, Oahu and JohnstonAtoll) or non-breedingplumage) in regionswhere one would expect nesting(late May-June, Alaska). Each individual was in only dominica.We hopethe comparisonsand tests of field sexuallydimorphic breeding plumage when examined, and criteriapresented here will provehelpful in suchsituations. primaryfeathers of adultsthat had been replaced during the winter were completelygrown (Johnson& Johnson1983, STUDY AREAS AND METHODS Johnson& Connors1996). First-yearfidva were readily identifiedfroin their worn, retainedjuvenile primaries; no Most ofthefidva (n = 544, captured1979-2002) camefrom similarage-criterion is apparentin dominica(Connors 1983, threewintering ground study sites on Oahu,Hawaii: Bellows Johnson& Johnson1983, Johnson& Connors1996, Byrk- Air Force Station, Hickam Air Force Base, and National jedal & Thompson1998).

Bulletin 103 April 2004 42 Johnson & Johnson: Features of Pacific and American Golden-Plovers 43

We recordedthe usualmorphometric dimensions: wing RESULTS length (flattened, straightenedprimaries) to the nearest 1.0 mm; total headlength (posterior occipital to tip of bill), Standard linear dimensions bill length(along culmen to junction with featheringon fore- head), and tarsuslength (tibio-tarsaljoint to distal end of Wing, head, bill, and tarsusmeasurements are shown in tarsus)to 0.1 mm.Each measurement followed the technique Table 1, and summarizedhere for eachspecies. illustratedby Howes& Bakewell (1989). Sometimes,espe- ciallywhen we hadlarger catches, not all measurementswere Pacific Golden-Plover madeon everyindividual. Our wing, head,bill, andtarsus meansincorporate smaller Oahu and Seward Peninsula sam- We pooledthe wing lengthsof adult malesand femalesas plesreported earlier by Johnson& Connors(1996). Several therewas no significantdifference between them (t = 0.77, colleaguesprovided us with unpublishedmeasurements from P = 0.44, df = 409). Variable wear of juvenile primaries fulva captured(in somecases freshly collected) at various made a similar test infeasiblefor first-yearplovers, and we breedingground sites in Siberia;and from dominicanesting pooledwing lengthsfor the entirefirst-year group. The dif- nearChurchill, Manitoba. These data sets, compiled with the ference in wing length between adults and first-year birds samemeasurement techniques as we used,allowed statisti- (172 mm vs. 168 mm) was highly significant(t = 12.04, cal comparisonsbetween our findingsand dimensionsof P < 0.0001, df = 600). Other linear comparisonsbetween ploversfrom otherregions. adult and first-yearmales, and between adult and first-year Supplementingthe standardmeasurements, we madea femalesshowed no differencesin total head length (males, systematiceffort (mostly in 2002 and2003) to evaluatead- ! = 0.80, P -- 0.43, df = 246; females, t = 1.88, P = 0.06, ditional dimensions and characteristics that various sources df = 183); bill length (males,t = 0.04, P = 0.96, df-- 252; (seeJohnson & Connors1996, and Byrkjedal & Thompson females, t = 1.27, P = 0.20, df = 185); or tarsus length 1998) haveconsidered useful as interspecificcriteria. From (males, t = 1.03, P = 0.30, df = 239; females, t = 0.25, capturedbirds, we recordedtwo featuresof thefolded wing: P = 0.80, df-- 176). Thus, for head, bill, and tarsus we the numberof primary tips exposedbeyond the longest pooledadult and first-year samples for eachsex. Analysis of tertials,and the distance(to 0.1 mm) betweenthe tips of pri- the pooledsamples revealed slight, but nonethelesssignifi- maries9 and 10. We alsomeasured (to 0.1 mm) the length cant,differences with femalesaveraging smaller than males of the unfeatheredtibia (from the tibio-tarsaljoint to the tips for all dimensions:total headlength (58.0 mm vs. 58.9 mm, of feathersencircling the proximaltibia), bill lengthin rela- t = 7.16, P = <0.0001, df = 431); bill length (24.2 mm vs. tionto the eye,and distance from the base of thebill to the 24.5 mm, t -- 2.93, P = 0.003, df = 439); and tarsuslength rearedge of theeye. The two eye-relatedmeasurements were (45.6 mm vs. 46.1 mm, t = 2.88, P = 0.004, df= 417). madealong a straightline extendingfrom the tip of thebill Dimorphismat this scale(

Table 1. Length measurements (in mm) of Pacific and American American Golden-Plover Golden-Ploversa. Data shown as means+SD (range, n). We pooledwing lengthssince there was no significantdif- Pacific Golden-Plover b American Golden-Plover c ference between males and females (t = 1.50, P •- 0.14, df = 44). The samewas true of total headlength (t = 0.31, Wing 172ñ4.1 (158-184, 411) 184ñ3.9 (176-192, 46) P = 0.76, df = 40), bill length(t = 1.32, P = 0.19, df: 43), 168ñ4.2 (148-178, 191) and tarsuslength (t = 0.25, P = 0.80, df = 41). There was Total head 58.5ñ1.3 (54.1-62.1,433) 58.2ñ1.0 (55.6-60.1, 42) essentiallyno correlationbetween wing length and tarsus Bill 24.3ñ1.1 (20.2-27.6,441) 22.8ñ0.8 (21.0-24.7, 45) length(r 2 = <0.01,P = 0.72,df = 41); negligiblecorrelation betweenwing lengthand total headlength (r 2 -- 0.02, Tarsus 45.9ñ1.6 (41.7-49.9,419) 44.1ñ1.2 (41.9-46.6, 43) P = 0.41, df = 40), and tarsus length and bill length For bothspecies, sexes are pooledthroughout the table (seeResults). (r2 = 0.04,P = 0.19,df = 41);and wea k positivecorrelation The sampleconsists of birdsfrom Oahu, Joh•ston Atoll, andthe Seward betweentotal headlength and tarsus length (r 2 = 0.17, Peninsula,Alaska (see Methods). First line of wing length = pooled P -- 0.007, df = 40). adults;second line = pooledfirst-year birds. The two groupswere sepa- ratedbecause first-yearfidva have wings shortened by wear of juvenile Interspecificcomparison primaries.All othernumbers for PacificGolden-Plovers in thetable rep- resentpooled adult and first-yearbirds. Wing lengthswere muchdifferent in the two specieswith Measurementsare from nestingbirds on the SewardPeninsula. Criteria dominicaaveraging 12 mm longerthanfulva. We foundno for identifyingfirst-year American Golden-Plovers are uncertain,thus significantdifference between total headlengths (58.5 mm eachvalue = pooledsample of all birdsexamined.

Bufferin 103 April 2004 44 Wader Study Group Bulletin in.fulva vs. 58.2 mm in dominica; t = 1.52, P = 0.13, tips, only two individualsshowed two tips; among23 cap- df = 473). However,bill andtarsus lengths were significantly tureddominica, 22 had four exposedprimaries and onebird different: 24.3 mm inj•hlva vs. 22.8 in dominica(t: 9.43, five. Similarly,the projection of primarytips past the tail was P = <0.0001, df = 484); and45.9 infulva vs. 44.1 in domi- obviouslydifferent in thetwo species.Amongfu/va (n = 50), nica (! = 7.20, P = <0.0001, df = 460). estimatesranged from 0 mm (primary tips aligned with rectrixtips, in a few casesthe primaries actually fell slightly Variation across breeding ranges short of the end of the tail) to an estimated maximum of 9 mm beyondthe tail. In dominica(n = 34), estimatedpro- In eachspecies, we foundstatistically significant differences jection pastthe tail rangedfrom 12-22 min. Relativeto the betweenour samplepopulations and comparableunpub- bill, thesedimensions approximate primary projection of<« lishedmeasurements from othergeographic areas (Table 2). bill lengthinfu/va and_>« bill lengthin dominica. P. fu/va fromthe Alaskaend of the species'range showed a Other identificationclues (bill length,tarsus length, dis- cleartendency for largersize in all dimensionsexcept wing tancebetween the tips of primaries9 and 10, length of the lengthas comparedto birdsnear the oppositeend of the unfeatheredtibia, bill/eye relationships,and tips of tertialsin range on the Taimyr Peninsula;and domin/cafrom the relationto the tail) were lessuseful field characteristicsas we SewardPeninsula had shorterwings and tarsi than birds at foundconsiderable interspecific overlap for all of thesefea- Churchill,but averagedlonger bills thanthe latter(Table 2). tures(Tables 1 & 3). The separationbetween primary tips 9 and 10 rangedfrom 0 mm (feathersthe samelength) to 6 mm Features and measurements relating to amongfulva,and from 2-9 mm in all dominicabut one (the field identification latterindividual scaled 0.5 ram). Of44fu/va, 9 birds(20%) showed primary tip separation of 1 mm or less; most Disregardingbreeding plumage, the number of primarytips dominica(17 of 23, 74%) exceeded4 min. Mean length of exposedbeyond the longesttertials and the projectionof the unfeatheredtibia differedsignificantly between the two primarytips relative to thedistal end of thetail werethe most plovers(t = 7.82, P = <0.0001, df = 58) withfulva averag- satisfactoryinterspecific criteria (Table 3). All birdscaptured ing nearly4 mm longerthan dominica. When projected rear- for banding and numerousfree-ranging individuals were ward, the bill extendedbeyond the eye in nearly all fu/va clearlyseparable (though see Fig. 2) to speciesfrom primary (91%) andmost domin/ca (62%) with meandistance past the tipsvisible past the tertials(2-3 infulva, 4-5 in dominica). rear edge of the eye 2.6 mm and 1.6 ram, respectively. Of 44fidva in the hand,almost all (42) had threeexposed Althoughmean distance from the baseof the bill to the rear

Table 2. Comparable mean linear measurements (in mm) of Pacific and American Golden-Plovers from different parts of their breeding ranges a.

Regionb & source Wing Total head Bill Tarsus

P. fulva c 1. Thisstudy, 170(158-178, 44) d 57.2 (54.1-59.3,44) 23.2 (20.2-25.5,44) 44.8 (42.0-48.2,44) Seward Peninsulasample only 2. Anadyrregion, P. Tomkovich(in litt.) 172 (166-177, 11) 56.9 (55.2-59.0, 10) 23.5 (21.9-26.6, ll) 43.9 (42.5-46.6, 10) 3. northeasternYakutia, 170 (59) - 26.2 (59) 43.3 (59) Gavrilov(1998) P -- <0.0001 P-- 0.003 4. easternTaimyr Peninsula, 167(158-174, 75) 56.4 (53.3-58.6, 79) 22.9 (20.2-25.6, 79) 43.5 (40.5-47.4, 79) M. Soloviev & T. Sviridova (in litt.) ? = <0.0001 P = 0.002 P = <0.000l 5. northernTaimyr Peninsula, 170 (162-178, 23) 56.2 (54.5-57.9, 9) 22.6 (20.8-23.9, 23) 44.3 (41.8-50.4, 23) P. Tomkovich (in litt.) P = 0.049 P = 0.047 6. westernTaimyr Peninsula, 169 (158-177, 56) 56.4 (51.4-59.3, 56) 22.1 (19.9-24.8, 57) 42.9 (39.3-47.9, 56) H. Schekkerman& I. Tulp (in litt.) P = 0.009 P = <0.0001 ? - <0.0001

P. dominica

7. This study,Seward Peninsula 184 (176-192, 46) 58.2 (55.6-60.1,42) 22.8 (21.0-24.7, 45) 44.1 (41.9-46.6, 43) 8. Churchill,Manitoba 190 (183-198, 31) 58.7 (56.2-60.4, 3)e 22.3 (20.8-24.2, 30) 44.9 (41.7-47.6, 38) J. Klima (in litt.) P = <0.0001 P = 0.014 P = 0.007

Bold indicatesthose dimensions that diflkr significantly(by t-testsat 0.05 level of significance)from our SewardPeninsula samples (no. l,fulva; or no. 7, dominica). Geographiccoordinates: I & 7 ScwardPeninsula this study - 64ø5I'N, 166ø05'W;2. Anadyrregion - two sitesat 64ø22'N,177ø25'E and 64ø55'N, 168ø35'E;3. northeasternYakutia - approx.68øN, 160øE;4. easternTaimyr- 72ø5I'N, 106ø02'E;5. northernTaimyr -three sitesbetween 76ø04'N, 98ø32'Eand 73ø37'N,82ø20'E; 6. westernTaimyr- 73ø20'N,80ø32'E; 8. Churchill- 58ø44'N,93ø49'W. All of our dimensionsfbr SewardPeninsula/idva represent pooled adult (n = 35) andfirst-year birds (n = 9). In Table 1, we calculatedwing lengths separatelyfor the two agegroups, but herewe havemerged them for consistencywith otherwing lengthmeans in the tablewhich presumably in- clude at least some first-year individuals. Rangesand/or sample sizes in parentheses. Insufficient data for t-test.

Bulletin 103 April 2004 Johnson & Johnson: Features of Pacific and American Golden-Plovers 45 marginof the eye showedonly slightinterspecific variation Pearce-Higgins2002). Table4 summarizespublished dimen- (22.0 mm in dominica vs. 21.4 mm infulva, Table 3), the sionsforfuh,a anddominica. We referto this compilation differencewas statisticallysignificant (t -- 3.02, P = 0.003, mostlyin passingsince comparing these reports with present df: 71). Almostallfulva hadtertials extending close to the findingsis complicatedby severalfactors including: differ- end of the tail. This feature varied amongdominica with encesin methodology[particularly when measuringwing tertial tips rangingfrom aboutmid-tail to near its terminus lengthsas the sourcesin Table4 variouslyused chord dimen- like fulva. sions(Johnston & McFarlane1967, Connors 1983), flattened primaries,possibly not straightened(Parmelee et al. 1967), DISCUSSION flattenedand straightenedprimaries (Vaurie 1964, Prateret al. 1977, Cramp& Simmons1983, Barter 1988, Johnsonet Recentradio-tagging studies of PacificGolden-Plovers have al. 1989), or unspecifiedmethods (Dementicy et al. 1951, showna major mid-Pacificmigratory link betweenwinter- Kozlova 1961, Portenko 1972, Byrkjedal & Thompson ing groundson Oahuand breeding grounds in Alaska(John- 1998)];shrinkage of museumspecimens which tends espe- sonet al. 1997b,2001a; O.W. Johnsonet al. unpubl.data). cially to reducewing lengths(Prater et al. 1977); and un- From thesefindings and otherrecords (Johnson & Connors knownfractions of first-yearfulvain mostsamples (i.e., birds 1996), it is reasonableto assumethatfulva winteringin the with wornjuvenile primaries,see Methods) which would north-central Pacific are from the eastern end of the breed- biaswing lengthmeans. Determining maximum wing length ing range - especially Alaska and perhapsalso adjacent by flatteningand straightening primaries, thus eliminating all Siberia.Notably, Barter's (1988) measurementsoffulva in curvatures,is muchthe preferredmethod (see Evans 1986) Victoria, Australia (total head length of 57.2 mm, n =30; asit rulesout variation in measuringtechnique. In living and/ wing andbill lengthsin Table4), suggestsimilar provenance or freshly collectedfulva,the differencebetween this and for birds in that part of the winter range. Alaska nesting othermethods (chord, or flattenedprimaries not straight- groundsare at the extremeeastern end of the PacificGolden- ened)has been found to vary for individualbirds by 4-12 Plover breedingrange, most of which extendswestward mm (O.W. Johnsonunpubl., M. Soloviev& T. Sviridovain acrossSiberia to the Yamal Peninsula.Conversely, our sam- litt., P. Tomkovichin litt.); presumably,dominica vary simi- ple of American Golden-Ploversis from the westernend of larly. We discountthe shorttarsus lengths (Table 4) reported their North Americanbreeding range, and in a regionwhere in eachspecies by Vaurie (1964) andPrater e! al. (1977) as fulva anddominica nest sympatrically. Details of breeding they deviatefrom the restof the table andprobably indicate andwintering distribution for bothplovers are describedby a differencein measurementtechniques. Johnson& Connors(1996), Byrkjedal& Thompson(1998), In Table2 we compareour findingson the SewardPenin- and Johnsonet al. (2001a). sulawith unpublisheddimensions from breedinggrounds Our findingsof significantinterspecific differences (i.e., elsewhere.Because all thesedata were obtainedusing the fulva averagingshorter wings, but longertarsus and bill than samemeasurement procedures, problems like those men- dominica),and essentiallyno intraspecificvariation in meas- tioned aboveare of little concern.Reading downward, the urementsbetween the sexesin either speciesagree with recordsforfulva are arrangedfrom eastto west.In a system- earlier studies(Connors 1983, Cramp & Simmons 1983, aticreview of the genusPluvialis from museumspecimens, Paulson 1993, Johnson & Connors 1996, Byrkjedal & Vaurie (1964) reportedmeanfulva wing lengthsof 171 mm Thompson1998). Sexualmonomorphism also is character- in Alaska (almostthe entire samplewas "collectedon the istic of the other two Pluvialis species(Eurasian Golden- Seward Peninsula") vs. 166 mm in "northeasternSiberia" PloverP. apricaria andGrey PloverP. squatarola;Jukema (exactlocations not indicated).Vaurie's findings, along with andPiersma 1992, Byrkjedal & Thompson1998, Yalden & other measurementsfrom Siberia (Table 4), implied that

Table 3. Featuresassociated with field identification of Pacificand AmericanGolden-Plovers a,b. Mean in mm+SD(range, n) givenwhere possible.

Pacific Golden-Plover American Golden-Plover

Primarytips exposedbeyond longest tertials 2-3 in all birds (n = 44) 4-5 in all birds (n: 23) Primaryprojection past end of the tailc 0-9 mm (n = 50) 12-22 mm (n = 34)

Distancebetween the tips of primaries9 & 10 2.7ñ1.7 (0-6.0, 44) 5.0ñ1.7 (0.5-9.0, 23) Lengthof unfeatheredtibia 20.4ñ1.8 (17.6-24.1, 37) 16.7ñl.7 (14.8-21.2, 23) Percentwith bill projectingbeyond rear edge of eyed 91% (40 of 44) 62% (18 of 29) Bill projectionbeyond eye d 2.6ñ1.2 (0.2-5.2, 40) 1.6ñ0.9 (0.3-3.7, 18) Baseof bill to rearedge of eyed 21.4ñ0.9 (19.0-23.l, 44) 22.0ñ0.9 (20.0-24.0, 29) Tertial lengthrelative to tail lengthc tertials extend to distal third of tail, variable from half to distal third end at or neartail tip in mostbirds of tail

Featuresconsidered here are basedon descriptivesummaries of the two speciesby Johnson& Connors(1996) and Byrkjedal& Thompson(1998). Wheren -- 40 or 44fulva,the sample consists of 12from the Seward Peninsula, Alaska, remainder captured on Oahu, Hawaii; where n =37,28 were caughton Oahu and 9 on the SewardPeninsula. All dominicawere trappedon the SewardPeninsula. Estimatesbased on observationsof free-rangingbirds (see Methods). SeeMethods for proceduresrelating to bill/eyemeasurements.

Bulletin 103 April 2004 46 Wader Study Group Bulletin

Alaskanfulvatended to be longer-wingedthan Siberianfulva studyskins collected at oppositeends of thebreeding range (Johnson& Connors1996, Byrkjedal& Thompson1998). ("SW" and "NW Alaska" comparedto "W. Hudson B.") However, the wing lengthsreported here from living and showedonly slightly shorterwings in the west (approxi- freshlycollected birds do not substantiatethis as we found mately 180 mm vs. 182 mm), nearlyequivalent bill lengths, with onlyone exception (eastern Taimyr) no significantvari- and longertarsi in the west (about44 mm vs. 42 mm). ation from the SewardPeninsula westward (Table 2). With The remainingdiscussion concerns field identificationof regardto otherlinear dimensions,there were no apparent the two species,and includescertain features of plumages, differencesbetween our Alaska sampleandfulva measured moulting,and migration(for detailedtreatments of the lat- in theAnadyr region of easternSiberia. This changedfurther ter topics, see Johnson& Connors 1996, Byrkjedal & westwardin Siberia where birds had significantlyshorter Thompson1998). Becausedominica begin departing their (thoughactual values are relatively small)heads, bills, and SouthAmerican wintering grounds as early as January, most tarsi(Table 2). A similareast to westpattern is evidentin bill pre-breedingmoulting takes place while birdsare en route andtarsus measurements compiled from museumspecimens north.A similarpattern occurs withfulva winteringin the far by Byrkjedal& Thompson(1998). Becausethe head,bill, SouthernHemisphere, whereas birds in Hawaii typically and tarsussamples in Table 2 overlappedbroadly between completetheir pre-breeding moult before departure. Thus in regions,none of thesedimensions offers much promise as a both species,the plumagesof springtransients may vary criterion for identifyingfulva from specific areas of the from partial breeding (with attendantproblems of iden- breedingrange. Notably, Gavrilov' s (1998) meanbill meas- tification)to full breedingdepending on whereand when the urementfrom Yakutia is approximately3-4 mm longerthan ploversare observed.From roughlyApril to July,breeding any otherfidva samplein Table 2. Whetherthis has to do plumageis fully developedand identificationproblems are with measurementtechnique or reflectsa regionaldifference minimalas birds (especially males) show well definedinter- (we suspectthe former) is uncertain. specificdifferences in breedingcoloration that are clearly Our sample of American Golden-Plovers in western depictedin most field guides. Adults begin their post- Alaska had significantlyshorter wings andtarsi, and longer breedingbody moult on the nestinggrounds, and by fall bills than their counterpartsacross the continentat Church- migrationthe mix of old and new feathersmay blur the ill, but measurementsin the two groupsoverlapped substan- distinctionbetween species. Various sources (e.g., Golley & tially (Table 2). Contrary to our findings from live birds, Stoddart1991, Johnson& Connors1996, Mullarney et al. Byrkjedal & Thompson's(1998) examinationof dominica 1999, Sibley 2000) have pointed out that in all plumages

Table 4. Mean linear measurements(in mm) of Pacificand AmericanGolden-Plovers from other investigationsa,b.

Region & Source(s) Wing Bill Tarsus

P. fulva

Siberia(mostly museum specimens: Dementiev et al. 1951, 160-166 (26-121) 23.4 (51) c 43.5 (51) c Kozlova 1961. Vaurie 1964, Portenko1972, Cramp & Simmons1983)

Alaska, Siberia, St. Lawrence Is., Japan,Korea, China, Pacific Islands 165 (60) 23.5 (60) 44.4 (60) (museumspecimens: Connors 1983) SewardPeninsula (museum specimens: Vaurie 1964) 171(46) 29.3 (46)0 40.9(46) Wake Island(freshly collectedspecimens: Johnston & McFarlane 1967) 163 (43) -- --

EnewetakAtoll (freshly collectedspecimens: Johnson et al. 1989) 172 (31) -- --

Australia (capturedspecimens: Barter 1988) 174 (35) 23.7 (31) --

Not indicated(museum specimens: Prater el al. 1977) 163 (60) 22.5 (70) 41.6 (68) Not indicated(museum specimens: Byrkjcdal & Thompson1998) 164 (193) 22.9 (189) 43.8 (192)

P. dominica

northernCanada (freshly collected& museumspecimens: Vaurie 1964, 18l- 185 (8-148) 21.7-23.3 (8-147) ½ 42.zk43.3 (8-147) e Parmeleeet al. 1967, Cramp & Simmons 1983)

Alaska, Canada(museum specimens: Connors 1983) 177 (77) 22.6 (77) 43.7 (77) Pt. Barrow (museumspecimens: Vaurie 1964) 184(32) 30.7(32) d 40.0(32) Not indicated(museum specimens: Prater el al. 1977) 183 (40) 23.1 (54) 41.4 (56) Not indicated(museum specimens: Byrkjedal & Thompson1998) 179 (282) 22.5 (279) 43.4 (273)

Portionsof the tableare from a compilationby Johnson& Connors(1996). Somesources give measurements tbreach sex. Based on ample evidence of nolinear variation between the sexes (see text), we simplified the table by averagingthese measurements. Where a rangeis shown,the data represent different parts of a particularregion. Sample sizes listed in parenthe- ses. Bill andtarsus measurements from Cramp& Simmons(1983). Measured from skulls. Bill and tarsusmeasurements from Parmeleeet al. (1967), Cramp& Simmons(1983). • Bulletin103April2004 Johnson & Johnson: Features of Pacific and American Golden-Plovers 47 fulva typically have more brightly colouredyellowish the field asbill lengthrelative to the eye wasfrequently im- upperpartsthan dominica, the lattertending to be greyish. possibleto assesswithout the in hand. While this differenceis often a usefulfield distinction,par- The tertial/tail relationshipas a field mark was described ticularlywith birdsin eitherjuvenile or non-breedingplum- by both Golley & Stoddart(1991) and Byrkjedal & Thomp- age,it is by nomeans infallible. We haveobserved individual son (1998). Accordingto the latter source,"the tip of the fulva with dominica-likegreyish leathering (similar to Plate longesttertial endsjust beyondthe tail basisin the Ameri- 13 in Golley & Stoddart 1991) during fall and winter in can, but over the outer third of the tail in the Pacific". Most Hawaii; andother workers have noted deceptive interspecific ofthejhlva we observedconformed to the statedpattern, but overlapin juvenile and non-breedingplumages such that dominicawere more variable with tertialsranging from about colorationcould not be usedto identify the speciesof some the half-way point on the tail to the distal third. In a few individuals (Connors 1983, Dunn et al. 1987, Marchant & instances, we noted individuals with tertials somewhat Higgins 1993,Paulson 1993, Beaman& Madge 1998). shorter(•hlva) or longer(dominica) than more typical birds Most identificationproblems will occurfrom Augustto (Figs2 & 3). All suchvariants retained species-specific wing March whenbirds are not in breedingplumage, and during andtail features(i.e., visibleprimary tips andprimary pro- that period structuralfeatures (Table 3) becomeespecially jection beyondthe tail), thoughthe wings of the dominica importantas interspecific criteria. Of the featureslisted, the shown in Fig. 2 required close viewing to confirm four first two (exposedprimary tips and primary projection exposedprimary tips. Conceivably,someone observing the beyondthe tail) were by far the most useful and accurate. sameplover at much greaterdistance might be able to see Presumably,the numberof primariesvisible beyondthe onlythree exposed primaries (suggestingfulva) on a birdthat tertials (2-3 infulva, 4-5 in dominica)remains a reliable couldbe in partialbreeding or nonbreedingplumage. How- indicatorthroughout fall migrationas tertialsprobably are ever, there shouldbe no confusionas to speciessince the not sheduntil birds reach winter quarters.However, the long primary projectionof this individual (aboutthe same moult and wear of tertials need further evaluation. It is im- lengthas the bill) would clearly indicatedominica. portantto notethat very closespacing of primarytips 9 and Basedon our findingsof extensivemorphometric over- 10 (relativelycommon infulva, muchless frequent in our lap betweenfulvaand dominica along with scantstatistical sampleof dominica)may give the visual impressionof a correlationbetween linear measurements,we concludethat singlefeather when viewed in the field, andthus lead to an thereare only three reliable visual criteria for distinguishing incorrectcount. This is unlikelyto resultin misidentification thesetwo ploversin the field: primaryexposure beyond the offulva, but it couldbe misleadingfor somedominica (i.e., tertials,primary projection past the endof the tail (bothfea- countingthree tips pastthe tertialswhen there are actually tures less accuratewhen birds are moulting on wintering four). Projectionof the outermostprimaries past the tail grounds),and breeding plumage during spring and part of the (0-9 mm infulva, 12-22 mm in dominica)is likely a solid summer.Other features(bill and leg lengths,distance be- criterionduring most of theyear in bothspecies, except when tweentips of primaries9 and 10 on the foldedwing, etc.) are thesefeathers are being replaced during the annualmoult on oftenhelpful in anyseason, but they can also be misleading. winteringgrounds (Johnson & Connors1996, Byrkjedal& The two speciesare illustratedand describedrelatively Thompson1998). well in major field guides(Mullarney et al. 1999, Kaufman Although our measurementsfurther substantiatedthat 2000, Sibley2000, Alsop 2001, National GeographicSoci- fulva haveon averagea longerbill andleg (bothtarsus and ety 2002). However, there are problemsin someof these unfeatheredtibia) and lessdistance between the tips of pri- guidesthat might cause confusion: Kaufman gives no details maries 9 and 10 than dominica, there was considerable on primary/tertial/tailcharacteristics saying only that "fall interspecificoverlap (Tables 1 & 3). Thus,these features and winter"fulva "have shorterwingtips" than dominica; haveonly limited application in thefield. Other investigators Mullarney et al., Kaufman, and Alsop all lack sufficient reachedsimilar conclusions about leg andbill lengthspoint- information on females and sexual dimorphism;neither ing outthe subjectivenature of estimatingsuch dimensions Kaufman nor Alsop treat juvenile plumagesadequately; in field situations(see caveatsin Dunn et al. 1987, Golley Sibleygives confusing plumage time framesfor bothtaxa as & Stoddart 1991, Paulson 1993, Mullarney et al. 1998). adultswith "nonbreeding"feathering in "Apr" and full Somehave suggested bill shapeas a helpfulidentification "breeding"plumage in "Sep"do not fit knownmoult sched- feature.However, descriptions are confusing and somewhat ules (Johnson& Connors1996, Byrkjedal & Thompson contradictory:e.g.,fulva have the "slimmestbill" anddomi- 1998); the breeding range map forfulva in Alaska (see nica have "a broaderbase to the bill" (Golley & Stoddart Johnsonet al. 2001a) needsrevision in each of the field 1991),fulva havea "thick"bill ascompared to a "shortthin guideslisted (except Mullarney et al. whichdoes not include bill" in dominica(Alsop 2001), "bill appearsthicker" infulva a map); Sibleydescribes a "flight song"only for dominica (NationalGeographic Society 2002). Our photos(Fig. 1) as "wit wit weeewit wit weee",but a very similarcall also showthat these subtleties are inconsistentand certainly too is characteristicoffulva andin bothspecies this vocalization subjectiveto be reliablefield criteria. is often given on the ground(see "complex whistle" in We wereespecially curious as to theusefulness of bill/eye Johnson& Connors1996, "trilling song"in Byrkjedal & relationshipsput forth by Byrkjedal & Thompson(1998) Thompson1998), neither the foregoingcall nor any of sev- who statethat when the bill is projectedrearward it "reaches eral otherbreeding ground vocalizations (all fundamentalto well beyondthe eye in Pacific,but barelyacross the eye in separatingthe two formson the tundra,see Connors et al. AmericanGolden-Plovers". Although we oftenfound this to 1993, Johnson& Connors 1996, Byrkjedal & Thompson be correct,there alsowere individualsin each specieswith 1998) arementioned in any of the othertreatments. Of the the oppositepattern such that their identities (if basedonly field guideslisted, Mullarney et al. and Sibleyprovide the on this characteristic)could easily be misinterpreted(Table most useful comparisonsof the two species.For anyone 3, Fig. 1). Moreover,this criterionwas difficult to applyin seekinga photographicarray of theseplovers, we recom-

Bulletin 103 April 2004 48 Wader Study Group Bulletin

mend:Dunnet al. (1987), Golley& Stoddart(1991), Paulson Hayman, P., J. Marchant & T. Prater. 1986. Shorebirds:An identifi- (1993), Rosair& Cottridge(1995) thoughone of thefulva cation guide to the of the worM. HoughtonMifflin, Boston. theylabel as "breedingmale" is actuallya moultingbird of Howes, J. & D. Bakewell. 1989. Shorebird studies manual. Asian Wetland Bureau Publ. 55. Koala Lumpur, Malaysia. uncertainsex, and Byrkjedal & Thompson(1998). Johnson, O.W. & P.G. Connors. 1996. American Golden-Plover Finally, our best adviceto birderstrying to interpreta (Pluvialis dominica), Pacific Golden-Plover(Pluvialis fulva). In The questionableplover in non-breedingplumage is to concen- Birds of North America,No. 201-202 (A. Pooleand F. Gill, eds.).The tratemostly on itsprimary tip exposureand primary projec- Academy of Natural Sciences,Philadelphia, and The American Orni- tion characteristics.Recognize also (we concurwith Hayman thologists'Union, Washington,D.C. et al. 1986, Dunnet al. 1987, Paulson1993, Kaufman2000) Johnson,O.W. & P.M. Johnson.1983. Plumage-molt-age relationships in "over-summering"and migratory LesserGolden-Plovers. Condor thatdespite the best efforts of dedicatedobservers to confirm 85: 406-419. extralimitalrecords of theseplovers, some of the latterwill Johnson, O.W., A.J. Bennett, L. A!sworth Ill, L.A. Bennett, P.M. be impossibleto identifywith certainty. Johnson, J.R. Motgatt & R.J. Kienholz. 2001a. Radio-tagged Pacific Golden-Plovers:The Hawaii-Alaska link, springdestinations, ACKNOWLEDGEMENTS and breedingseason survival. •. Field Ornithol. 72: 537-546. Johnson, O.W., P.L. Brunet, A.E. Brunet, P.M. Johnson, R.J. Our studieswere variously funded over the years by the Kienholz & P.A. Brusseau. 200lb. Featuresof breedingbiology in Pacific and American Golden-Ploversnesting on the SewardPenin- NationalGeographic Society, U.S. Fish and Wildlife Serv- sula, Alaska. Wader Study Group Bull. 95: 59-65. ice, Hawaii AudubonSociety, and Moorhead State Univer- Johnson, O.W., P.L. Brunet, J.J. Rotel!a, P.M. Johnson & A.E. sity (Minnesota).We thankofficials of the U.S. Air Force, Brunet. 200lc. Long-term study of apparent survival in Pacific U.S. Veterans Administration, and the Hawaii Division of Golden-Ploversat a winteringground on Oahu,Hawaiian lslands. Forestryand Wildlife for permitsand access to studysites in 118: 342-351. Hawaii. The U.S. NationalPark Servicein Nome kindly pro- Johnson, O.W., P.G. Connors, P.L. Brunet & J.L. Maron. 1993. Breeding ground fidelity and mate retention in the Pacific Golden- videdlodging and logistical support for portionsof ourwork Plover. Wilson Bull. 105: 60-67. in Alaska. We are indebted to Joanna Klima, Hans Schek- Johnson,O.W., P.M. Johnson,P.L. Brunet, A.E. Brunet, R.J. Kienholz kerman, Mikhail Solovies, Tanya Sviridova, Pavel Tom- & P.A. Brusseau. 1997a. Male-biasedbreeding ground fidelity and kovich,and Ingrid Tulp who graciouslyshared with us their longevityin AmericanGolden-Plovers. Wilson Bull. 109:348-351. unpublishedmeasurements of plovers;and to RichardLund Johnson, O.W., M.L. Morton, P.L. Brunet & P.M. Johnson. 1989. Fat for statisticaladvice. Over the years,many peoplehelped us cyclicity,predicted migratory flight ranges,and featuresof wintering behavior in Pacific Golden-Plovers. Condor 91: 156-177. captureand band plovers - we are especially grateful to Johnson,O.W., N. Warnock, M.A. Bishop, A.J. Bennett, P.M. Johnson Phillip Bruner, Andrea Bruner, Paul Brusseau, Shirley & R.J. Kienholz. 1997b. Migration by radio-taggedPacific Golden- Gaisford, Kelly Gaisford, Mark Johnson,Lee Johnson, Plovers from Hawaii to Alaska, and their subsequentsurvival. Auk RonaldKienholz, Aleen Kienholz,Robert Pyle, Leilani Pyle, 114: 521-524. andSigrid Southworth for theirinvaluable assistance. Joanna Johnston,D.W. & R.W. McFarlane. 1967. Migrationand bioenergetics Klima readan earlydraft of themanuscript and sent construc- of flight in the . Condor69: 156-168. tive comments.Reviewer John Marchant made helpful sug- Jukema, J. & T. Pierstoa. 1992, Golden PloversPluvialis apricaria do not show sexual dimorphy in external and internal linear dimensions. gestionsthat muchimproved the final version. Limosa65: 147-152. [in Dutch with Englishsummary]. Kaufinan, K. 2000. Birdsof NorthAmerica. Houghton Mifflin, New York. REFERENCES Kozlova, E.V. 1961. Fauna USSR,Bit&, Vol. 2, No. 1, Pt. 2. USSR Acad. Sci., Moscow-Leningrad. [In Russian]. A!sop, F.J. I!1. 2001. Smithsonianhandbooks birds of North America, Marchant, S. & P.J. Higgins. 1993. Handbookof Australian, New Zea- westernregion. DK PublishingInc., New York. land and Antarctic birds, Vol. 2. Oxford Univ. Press, Melbourne. Barter, M.A. 1988. Biometrics and moult of Lesser Golden Plovers Mullarney, K., L. Svensson,D. Zetterstrihn & P.J. Grant. 1999. Birds' Pluvialis dominica fulva in Victoria. Stilt 13:15-19. of . PrincetonUniv. Prcss,Princeton. Beaman, M. & S. Madge. 1998. Thehandbook o['bird identificationJbr National Geographic Society. 2002. Field guide to the birds, 4th ed. Europeand the westernPalearctic. Princeton Univ. Press,Princeton, NJ. National GeographicSociety, Washington,D.C. Byrkjedal, I. & D. Thompson. 1998. Tundra plovers.' The Eurasian, Parmelee, D.F., It.A. Stephens & R.H. Schmidt. 1967. The birds of Pacific and American Golden P/overs and . T & AD southeastern Victoria Island and adjacent small islands. Nat. Mus. Poyser Ltd., London. Canada Bull. 222, Ottawa. Connors, P.G. 1983. , distribution,and evolution of golden Paulson,D.R. 1993. Shorebirds'of the Pacific Northwest.Univ. Wash- plovers (Pluvialis dominica and Pluvialis [idva). Auk 100: 607-620. ingtonPress, Seattle. Connors, P.G., B.J. McCafiery & J.L. Maron. 1993. Speciation in Portenko, L.A. 1972. Birds of the Chukchi Peninsula and Wrangel golden-plovcrs,P/uvia[is domin/caand P../•tlva: Evidencefrom the Island, •ol. I. Translatedfrom Russianand publishedin 1981 for the breeding grounds.Auk 110:9 20. SmithsonianInst. andNatl. Sci. Found.Amerind Publishing Co., New Cramp, S. & K.E.L. Simmons, Eds. 1983. The birds of the western Delhi. Palearctic, Vol. 111.Oxtbrd Univ. Press, Oxtbrd. Prater, A.J., J.It. Marchant & J. Vuorinen. 1977. Guide to the identi- Dementiev, G.P., N.A. G!adkov & E.P. Spangenberg,Eds. 1951. Birds fication and ageingof holarcticwaders. British Trust for Ornithology, of the Soviet Union, Vol. I1[. Translatedfrom Russianand published Field Guide 17. in 1969 by Israel Programfor Scientific Translations,Jerusalem. Priklonsky, S.G. 1960. Use of automatic"luchock" traps for bird catch- Dunn, J.L., J. Morlan & C.P. Wilds. 1987. Field identification of forms ing. Zool. Zh. 39: 623-624. [in Russian]. of LesserGolden-Plover, pp. 28-33 in Proc.4th Internatl. Identifica- Rosair, D. & D. Cottridge. 1995. Photographicguide to the shorebirds tion Meeting (1986). InternationalBirdwatching Center, Eilat, Israel. of the worM. Factson File Inc., New York. Evans, P.R. 1986. Correct measurementof the wing-length of waders. Sibley, D.A. 2000. National AudubonSociety.' The Sibleyguide to birds. •2•der Study Group Bull. 48: I l. Knopf, New York. Gavrilov, V.V. 1998. Morphometricparameters of wadersbreeding at Vaurie, C. 1964.Systematic notes on Palearcticbirds. No. 53. : north-eastYakutia. Ornitologia 28: 200-207. [in Russianwith Eng- The generaCharadrius and Pluvialis.Am. Mus. Novit. 2177. lish summary]. Yalden, D.W. & J.W. Pearce-Higgins. 2002. Biometricsand moult of Go!ley, M. & A. Stoddart. 199 l. Identification of American and Pacific breedingEurasian Golden PloversPluvialis apricaria. Wader Study GoldenPlovers. Birding I/Vorld4: 195-204. Group Bull. 98: 50. • Bulletin103April2004 Johnson & Johnson: Features of Pacific and American Golden-Plovers 49

Fig. 1. Bill/eyerelationships in ploversnesting on the SewardPeninsula, Alaska. By scalingalong a straightline pass- ingfrom the tip of the bill acrossthe nasalopening to the eye (see Methods),the readercan easilyverify the following dimensions:upper left - male fulva, backwardprojection of bill extends beyondthe eye; upper right- female fulva, bill projectsto rearedge of eye;lower left - male dominica,bill falls at rear of eye; lowerright- femaledominica, bill extends beyond the eye. Left hand photos are consistentwith Byrkjedal& Thompson's(1998) rearwardprojection of the bill as an interspecificcriterion (see Discussion); righthand photosare not. Also, note variabilityin the shapes of bills (see Discussion).

Fig. 2. Breeding male dominica photographedon the Seward Peninsula, Alaska. This individual shows the lengthyprojection of primariespast the tail characteristic of the species. However, the tertials are unusual as they extend fulva-like to near the distal end of the tail. As the birdmoved about while being photographed,it was evident that the tip of the 7th primarywas visible (but just barely) beyond the longest tertial.

Fig. 3. Two malefulva in breedingplumage just beforespring migration from Oahu. Like many fulva, both birds have primary tips moreor lessaligned with the end of the tail, buttheir tertials resemble those of somedominica in thatthey extend only to about half the length of the tail.