, DISTRIBUTION, AND EVOLUTION OF GOLDEN (PLUVIALIS DOMINICA AND PLUVIALIS FULVA)

PETER G. CONNORS BodegaMarine Laboratoryand Museumof VertebrateZoology, University of California, BodegaBay, California 94923 USA

ABSTRACT.--Adiscriminant function analysisof specimenmeasurements separates 96% of two formsof LesserGolden in breedingplumage, previously described as subspecies. The formsbreed sympatricallyin northwestAlaska and are not isolatedby habitat,but the incidence of specimensphenotypically intermediate between the two forms is no higher there than in areasof allopatry. The absenceof a cline of intergradesor of a hybrid zone indicatesthat the forms are reproductivelyisolated through assortativemating and are sep- arate species.To explain the processof speciationin thesevery similar forms, I proposethat the evolutionof geneticallycontrolled and markedlydifferent migrationroutes (Pluvialis dominicato South America and Pluvialisfulva to the central and western Pacific and Indian oceans)during Pleistoceneglacial isolation may have selectedagainst hybrids during sub- sequentsecondary contact of populations.This would lead to adaptationsin behavior and plumage,such as the differencein male undertail covertsreported here, that would produce assortativemating and reproductiveisolation in sympatry.Thus, the requirementsof migra- tion and winter range drive the processof speciation.Received 2 August1982, accepted 28 January1983.

Two forms of Lesser (or American) Golden 1957). Both forms have been collected at sev- Plover have been treated by almost all authors eral localities in Alaska from Barrow to the coast as subspecies,Pluvialis dominica dominica and P. of the Bering Sea. Fulva is more common south d. fulva(for example,Peters 1934, American Or- of Bering Strait and dominicapredominates nithologists'Union 1957, Bock 1958, Johansen nearer Barrow (Conover 1945). The problem in 1958, Bannerman 1961, Vaurie 1964, Mayr and determining ranges, and the primary reason Short 1970,Johnsgard 1981). The elucidationof these forms have been considered subspecies, their statushinges on their distribution and in- is their close similarity in appearance, espe- teractions on breeding grounds in northwest cially in breeding plumage. Publisheddescrip- Alaska, which, in spite of several published tions of this plumage rely on characterssuch discussions(Conover 1945, Bailey 1948, Ga- as "brighter gold spotting"on the backof fulva brielson and Lincoln 1959), remain obscure. I and a tendency for dominicato "show more have applied a multivariate statisticalapproach white, especially on forehead and sides of to a study of museum specimens,with the sur- breast" (Prater et al. 1977). In juvenal and adult prising result that I find no evidence of inter- winter plumages the forms are more easily gradation or of interbreeding in regions of separated,primarily on the basisof the yellow- sympatry. I therefore suggest that separate buff (fulva) comparedwith brownish-grey(do- speciesstatus for the two forms is appropriate. minica)coloration on much of the body feath- The form dominica breeds on arctic and sub- ering, but even thesequalities will not separate arctic tundra from Baffin Island in Canada west all individuals. to northwest Alaska. Fulva breeds from north- Differences in size have long been noted, west Alaska west to the Yamal Peninsula in Si- however, with wing length serving to separate beria, where its range overlapsthat of the Eur- a large proportion,but not all, of the Alaskan asian (or Greater) Golden Plover (Pluvialis (Conover 1945). Bailey (1948) noted that apricaria).Wintering rangesof the two Ameri- "where the two breeding areas come together can forms are distinct: dominica winters in South in Northern Alaska, there are many specimens America,and fulvawinters in southernAsia and which can not be satisfactorily identified sub- on many Pacificislands south to Australia and specifically,"and someauthors have concluded New Zealand (American Ornithologists' Union that the two forms interbreed in this region, 607 The Auk 100: 607-620. July 1983 608 PETERG. CONNORS [Auk,Vol. 100 resulting in intergradeswhere the rangesover- lap (Gabrielsonand Lincoln 1959, Vaurie 1964). A more thorough analysis of this problem has been stalled by the lack of clear intermediate charactersto indicate hybridization, becausethe parent forms differ only in degree rather than presenceor absenceof characters. A few authors have considered the forms as distinct species.Portenko (1939) suggestedthis, but subsequently(Portenko 1981) listed them as subspeciesand even suggestedthat P. apri- cariaand P. dominicamay not be specificallydis- tinct. [This latter view has no apparent support among taxonomists. Mayr and Short (1970) Fig. 1. Specimen collection regions in northwest considered apricariaand dominicato comprisea Alaska(Regions 1-4) and boundariesof assumedpar- speciesgroup, or, at the closest,a superspecies.] ent populations (D and F). Stresemannand Stresemann(1966) and Kinsky and Yaldwyn (1981) assignedfull speciesstatus to fulva primarily becauseof apparent differ- grounds, Siberia and St. Lawrence Island, 11 speci- ences in the molt and maturation schedules of mens, late May-July; migration, Japan,Korea, north I- and 2-yr-old birds of the two forms. Because China, 34 specimens,6 April-2 June; migration or of these differences and the distinct migra- winter grounds, south China and Pacific islands, 15 tions, the Ornithological Society of New Zea- specimens,6 April-30 May. The assumedparent do- land (1980) now lists Pluvialisfulva instead of minica population was derived from: breeding P. d. fulva. grounds,northeast Alaska (eastof 156øW;Fig. 1), 41 The central questions remain, however. Do specimens,northern Canada, 29 specimens, all late dominicaand fulva interbreed freely? Are the May-July; migration,Alberta, 8 specimens,late May. parent forms sympatric, or does a zone of in- Five additional specimenscollected in eastern Si- tergradation connect their ranges in northwest beria (KoliutschinBay) on one date (18 July 1909) were excluded from the fulva parent group in the Alaska?If they do not interbreed, what are the analysis,because they appear to representa popula- selective forces and isolating mechanismsthat tion of dominica.Four of the birdsare classedby the have separatedthese very similar forms? discriminant function analysis as dominica,and the fifth as intermediate between the two forms. The five

METHODS birds are statisticallyseparable from the 60 birds in the parent fulva group (P < 0.0001). The step of ex- I measured369 specimensobtained from 13 North cluding thesespecimens is risky in view of my prin- American museums (listed in the Acknowledg- cipal assumption that location is indicative of form ments).Because I wished to establishbreeding ranges in RegionsD and F. It is taken only becausethe en- in northwest Alaska from museum specimens, for tire local sampleof five specimensis internally con- which nesting information is seldom available, I con- sistentand clearly distinguishablefrom the remain- sideredonly adult birds taken on breeding grounds der of the Region F sample.An explanationbased on in late May, June,and July. Goldenplover eggsusu- distribution of forms rather than on individual vari- ally hatch during early and mid-July (Conover 1945, ation within a form thereforeseems appropriate. The Gabrielson and Lincoln 1959), and successfulbreed- Koliutschin Bay sample may represent a local breed- ers tend chicks for a period of days or weeks after ing group of dominicaor a wanderingflock from out- hatching. Some movements of failed or successful side the area; in either case,it would be misleading breedersdo occurduring this time, especiallyin late to include them with the fulva parent group. July (Myers and Pitelka 1980); among the specimens I made the following measurementson all 369 studied, however, only 8% were collected after 20 specimens:(1) wing chord length--average of both July, with an additional 12%taken 15-20 July. Thus, wings, adjusted for wear when appreciable; (2) ex- the assumptionof local breeding is reasonablefor posedculmen length; and (3) tarsuslength--average most of the 226 northwest Alaska specimens. of both tarsi. Tarsi were measuredfrom the posterior To determine characteristicsof parent forms where depressionof the tibio-metatarsusjoint to the distal the number of specimensfrom breedinggrounds was end of the central processof the metatarsus(Hub- limited, as in the caseof fulva in Siberia, I included bard 1970). some late-spring migrants as follows: breeding On all specimens not in molt (254 specimens), I July 1983] GoldenPlover Taxonomy 6O9

T^BLE1. Golden plover specimen measurements(mean ñ standard deviation).

n Wing Tarsus Culmen W/T x C Region D (dominica) Males 42 177.6 ñ 4.3 43.9 + 1.2 22.7 ñ 1.1 0.178 + 0.011 Females 35 176.8 + 3.9 43.6 ñ 1.8 22.6 ñ 1.1 0.180 ñ 0.012 Region F (fulva) Males 44 165.1 ñ 4.2 44.3 + 1.5 23.6 + 1.0 0.158 + 0.010 Females 16 165.5 ñ 5.5 44.5 ñ 1.5 23.5 ñ 1.5 0.159 ñ 0.014 D vs. F, sexes combined P < 0.0001 P < 0.03 P < 0.0001 P < 0.0001

recorded the following measurementsand categori- indicates the relative contribution of each variable to zations:(4) height, along foreheadcenter line, of the the separation (Nie et at. 1975). band of black feathering from culmen to white band; Analysis variables were derived from the list of (5) height of double band of black plus white feath- measured variables. For all birds these were lengths ering;(6) percentageof breastfeathering that is black of wing (W), tarsus(T), cutmen (C), and ratios W/T, rather than white on a scale of less than 50% black, W/C, and W/T X C. Although the ratiosof normally through 50-75%, 76-90%, and 91-97%, to 98-100%; distributed variates are not normally distributed, ! (7) percentageof undertail covertsthat is black rather judged the deviation to be slight in thesecases, be- than white on a scaleof lessthan 10%black, through causea comparisonof ratios of population means of 10-35%, 36-65%, and 66-90%, to 91-100%; and (8) measuredvariables with population means of indi- boldness of tail barring, an estimate of the contrast vidually computedratios gives an estimateof the non- between light and dark bands, on a scale of faint (1) normality of ratios,and the differencesbetween these through moderate(2) to bold (3). Measurements(4) meansfor three ratios and two groups(fulva and do- and (5) are susceptibleto variationdue to differences minica) were less than 0.4% in all cases. in specimen preparation techniques. No correction A discriminant function analysiswas repeated for was made for this potential variation, but the large birds not in molt. I used the same six mensural vari- number of collectorsresponsible for these specimens ables plus six plumage variables--height of black makessystematic, biasing variation unlikely. forehead band (BBAND), height of white forehead ! also recordedthe degree of wear of primariesfor band (WBAND), difference in the percentageof black all birds, in four categories(none, light, moderate, feathering between breast and undertail coverts heavy; Prater et at. 1977).Only 13%of the specimens (BUDIF)--and three variables derived from the three had primaries worn sufficiently to require a correc- catagoriesof tail barring--each variable (T•, T2, T3) tion (1-8 mm) added to the measured length to in- had the value 1 or 0 depending on whether the tail dicate original length. The correction was an esti- barring was (1) or was not (0) faint (T•), moderate(T2) mate based on the relative width of the rachis at the or bold (T3). This last conversion is necessary to sat- feather's tip in comparisonswith the unworn pri- isfy statisticalassumptions of discriminant function maries of other birds. For wing and tarsuslength, a analysis.The difference in breast and undertail co- single measurementwas used when right or left vert blackness, rather than the original measure- member was not measurable. For four specimens no ments, is used to avoid potential confusion arising tarsusmeasurement was possible,and two specimens from birds beginning to molt but not recognizedas lacked cutmen measurements; mean values were sub- such, or from individual differences in overall black- stituted in the analysis. nessarising from age or other factors.The transfor- I applied step-wisediscriminant function analysis mation emphasizesthe relative colorationof the two (DFA) to the parent groups, region F vs. region D plumage areas. (Fig. 1), maximizing Rao's V (Nie et al. 1975). This After deriving the discriminantfunction that max- procedurecombines the measuredvariables, weight- imally separatedthe parent groups, I classifiedall ed with computedcoefficients, to form a new linear individuals collectedin northwest Alaska as fulva or function that maximally separatesthe two popula- dominicaon the basis of their discriminant scores, and tions statistically.The advantageof the procedureis ! computedthe probabilitiesof these classifications. that it considersdifferences between populations in all variables simultaneouslyrather than addressing RESULTS AND DISCUSSION measurementsindependently. The resultant separa- tion is thereforestatistically greater than that provid- Sexualdifferences.--There are no significant ed by any single measurement.Rao's V is a gener- differencesbetween sexesin any of the length alized statistical measure of the distance between measurements (Table 1). Size dimorphism is populations on the discriminant function axis and common in Scolopacidae(sandpipers), females 610 PETERG. CONNORS [Auk, Vol. 100

s0 average difference of 13% in the ratios of wing to tarsus times culmen. The two forms differ in E 6O proportion even more than in wing length. The plumage difference most widely pre- • 4c sentedin the ornithologicalliterature to distin- guish fulva from dominicain breeding dressis • •o the brightnessof gold spotting on the back. I found this qualitative character to be highly oi 0 50% 51 75% 76 90% 91 97% 98-[c0% variable and broadly overlapping between Breast blackness forms. Both forms have yellow spotsand white spots, with intensity, size, and relative num- Fig. 2. Sexualdimorphism in blacknessof breast bersof spotsvariable among individuals. Many in breeding plumage,fulva and dominicacombined. June specimensonly. Females,n = 43. Males, n = 89. fulva do appear brighter than many dominica, but the difference is not easily quantifiable and seems too inconsistent to be useful. None of the measuredplumage charactersis being larger in most species,but in the Family significantly different between femalesof fulva (plovers) most speciesshow little and dominica, but males differ in several re- or no dimorphism (Prater et al. 1977). Weights spects(Table 2). The difference in the percent- of female dominicaat Barrow exceed weights of age of black feathering between breastand un- malesthroughout the summer,however, by 14% dertail coverts is sharp. Males of both forms in May and June, decreasingto 6% in July and have almost completely black breastsand faces, August, as weights of both sexesincrease (t- but undertail coverts of dominica are black, test:May-June, n = 26, P < 0.001;July-August, lightly spotted or banded with white, whereas n = 35, P = 0.17; unpublished data of F. A. Pi- those of fulva are predominantly white with telka). In view of this, the close agreement in variable black markings (Fig. 3). The height of size within both groups shown in Table I is the blackforehead band is alsosignificantly dif- surprising. Breeding plumages, of course,are ferent between forms, but the white-band quite different, most males having essentially height, frequently mentioned in published de- uniform black breastsand females typically in- scriptions, is less different in these samples. cluding scatteredlight featherson the breast Male fulva frequently have more boldly barred and face (Fig. 2). tails than do dominica, but this difference is also Differencesbetween fulva anddominica.--The quite variable. Additionally, Portenko (1981) close similarity of size between sexespermits pointedout that fulvain breedingplumage have combining sexes for comparisonsbetween a narrow white band interrupted by black forms. Populationmeans of wing, tarsus,and patchesalong the flanks, whereas dominicahave culmen lengthsall differ significantlybetween completely black flanks. I did not quantify this fulvaand dominica,with meansof wing length characteristicon all specimens,but among male showing the greatestdifference (dominica7% specimensin breeding plumageat the Museum greater).Note, however,that tarsusand cul- of Vertebrate Zoology it is highly correlated men lengthsare greaterin fulva, producingan with colorationof undertail coverts:male fulva

TABLE2. Differencesin male breeding plumagesof dominicaand fulva.

n BUDIF a BBAND b WBAND c TAIL a

Region D (dominica) 36 16.1 + 17.0 2.41 +_0.78 8.07 + 1.62 2.36 + 0.68 Region F (fulva) 25 69.4+_ 19.9 1.42+ 0.82 7.28+ 1.55 2.68+ 0.56 P < 0.0001 P < 0.0001 n.s. n.s.

' Percentageblackness of breastminus percentage blackness of undertailcoverts. bHeight of blackforehead band (mm). ßHeight of white forehead band (ram). a Mean of categoryvalues for boldnessof tail barring:1 faint, 2 = moderate,3 - bold. July 1983] GoldenPlover Taxonomy 611

Fig. 3. Typical male breeding plumagesshowing similar dorsal spottingand differencesin amount of white on flanks and undertail coverts.Fulva, 3 birds on left; dominica,3 birds on right. have white undertail coverts and white along 61) and repeating the DFA brings the total cor- flanks;dominica are predominantly black in both rectly classifiedto 96.4%. This is a very good these areas. separation,but it remainsslightly overlapping, Discriminantfunction analysis.--Wing length, indicating that almost 4% of individuals from the first variable selected by the DFA, pro- our assumedparent populations would still be duced the greatest contribution to separation identified as the other form. These birds are of region F and region D samples,as indicated representedby the overlapping tails in the dis- by Rao's V (Table 3). The three variables sub- tributions of discriminant scores based on men- sequentlyselected improved the separation.The sural charactersfor regions D and F (Fig. 4). quality of separationcan be tested by reclassi- The distributions are normal, and they define fying all region F and region D individualswith the individual variation expected in popula- the discriminant function already derived. This tions of fulva or dominica. procedure correctly classified94.2% of the 138 The bottom plot in Fig. 4 presentsthe distri- individuals as belonging to their region of or- bution of discriminant scores for all 226 indi- igin, that is, as fulva or dominica.Adding plum- viduals from northwestAlaska, regions 1-4 (see age variables for males not in molt (a subsetof Fig. 1). This distribution is bimodal and can be

TABLE3. Discriminant function analysisof dominica(Region D) vs. fulva (Region F).

Step Significance of Function entered Variable Rao's V added variable coefficients

1 Wing 266 P < 0.0001 -0.2058 2 Wing/(tarsus X culmen) 358 P < 0.0001 229.3 3 Culmen 362 P < 0.05 2.137 4 Wing/tarsus 387 P < 0.0001 -11.38 Constant -8.405 612 PETERG. CONNORS [Auk, Vol. I00

12 REGION D TABLE4. Relativeabundance of golden plover forms n= 78 in northwest Alaska (see Fig. 1).

Region Species 1 2 3 4 fulva 8.0% 19.2% 83.9% 73.5% dominica 92.0% 80.8% 16.1% 26.5% • 8 n 100 26 62 38 REGION n = 60

distribution accordingly at -0.104, the P value of significanceof the shift improvesby an or- der of magnitude. n: 226 The combination of variables used in the dis- criminant function makes interpretation of the measured shift difficult, but it seems to indicate that birds of both forms are longer-winged in REGIONSI-4 northwest Alaska. Reasons for such a pattern are not apparent. If both forms shifted closer together on the discriminant function axis, -4 -2 0 2 4 character convergence, clinal variation, or in- Discrimmont score tergradation between interbreeding popula- Fig. 4. Distributions of discriminant function tions would be suggested;if, on the other hand, scoresof golden plover specimens.Region D, domin- the distributions shifted apart in opposite di- ica;Region F, fulva;Regions 1-4, northwestAlaska. rections on the axis, the likely interpretation See Fig. 1. would be character displacement arising from competition between noninterbreeding popu- lations. Instead, the parallel shift in both forms generated from the two parent distributions, may suggestecotypic variation, with both fulva slightly shifted toward negative discriminant and dorninicaresponding similarly to require- scores.I have tested for this shift by splitting ments of breeding in northwest Alaska (cli- the region 1-4 distribution into two unimodal mate, habitats, migration distances,etc.). portions, separated at the discriminant value Distributionof fulva anddominica.--Applying (0.221) indicating equal probabilities of be- the observed shift to the discriminant classifi- longing to distribution D or distribution F. cation procedure based on mensurat characters These half-distributions then test as signifi- and supplementingthese resultswith the clas- cantly different from the comparableD and F sification based on plumage characters,I iden- distributions (Mann-Whitney and t-tests: P < tified 93% of all 369 specimensas fulva or do- 0.04). The amount of shift along the discrimi- minica (probability of at least 0.90, and nant function axis is approximately -0.325, 9% agreement between mensural and plumage of the separation between fulva and dorninica classification).An additional 5% of specimens means. This value was calculated by compar- can be classedas "probably" one form or the ing corresponding distribution means and is other, and 2% of specimens are impossible to the average of fulva (=-0.312) and dorninica assignto either form. I divided northwest Alas- (=-0.338). A graphic method gives similar ka specimensinto four groupsbased on regions values. This test for a shift is conservative, be- shown in Fig. 1. The groups were arbitrarily causethe dividing value chosen was based on chosen but were based on the availability of the absence of a shift; this has the effect of in- collectedspecimens. Proportions of fulva and cluding intermediatescores in the dorninicahalf dominicain different regionsvaried widely, but and excludingintermediate scores from the ful- both forms occurred throughout northwest va half. To the extent that a shift is real, this Alaska (Table 4). Both sexes of both forms have arbitrary division will tend to obscurethe shift. been collectedin eachregion during early June, If we accept the shift and divide the bimodat the period when local breeding is most prob- July 1983] GoldenPlover Taxonomy 613 able. The general pattern showsan increasein erholser (1938) described golden plovers in the proportionof fulva toward the Bering Strait, Louisiana as rare transient visitors. Bent (1929) with dominica more common in the northern- estimated that the speciespopulation reached most regions. There is a slightly higher inci- a low point about 1900, when "it had become dence of dominicain region 4, the southern- scarcewhere it once abounded; no more big most, than in region 3, but this may partly flights occurred; and in many places it was reflect a larger component of possibly migrat- rarely seen." Changes in game laws occurred ing birds from late July in the region 4 sample. in time, however, and the speciesproved ca- No region contained equal numbers of fulva pable of a strong increasein population after a and dominica, but there were no available col- reductionof the artificially high mortality rate. lectionsfrom the most likely area, between the Today the speciesis widespread and common Bering Strait and Kotzebue,a distanceof about in suitablehabitat throughout the North Amer- 260 kin. Four birds identified as dominica were ican arctic. also collectedon a single date at a site in east- Becauseof differences in migration routes, ern Siberia, but whether these represent breed- the heavy shooting in eastern North America ing or migrating birds is unknown (see Meth- devastatedonly dominica(probably including ods). Portenko (1981) reported a nesting Alaskan birds), while Alaskan fulva migrating identified as dominicafrom Wrangel Island and to Pacific islands were less drastically affected. statesthat dominicawas an uncommon nesting Fulva have probably been taken for food for bird in northeast Siberia at the end of the last centuriesby Pacific island natives, and heavy century and beginning of the present century. sport gunning occurred in Hawaii consider- The region of sympatry, from Barrow to Nu- ably later than in easternNorth America (Mun- nivak Island at least, covers a distance of over ro 1945), but the overall impact on fulva pop- 1,300 kin, but the specimen collection dates ulationsis unlikely to comparewith the impact ranged over a century (1877-1980). It is quite of market gunning of dominicain the late 19th possiblethat the ranges of one or both forms century. We might have learned a great deal have varied over time, in unison or indepen- about population interactions of the two forms dently. At an extreme, an apparent pattern of if we had density estimatesbefore and after sympatry in museum specimensmight result this period. Museum specimensindicate that from allopatric populationswhose rangeshave the proportion of dominicacompared to fulva in shifted over the entire region of collection.We regions 1 and 2 combinedand in regions3 and know this is not the case, because both forms 4 combined has been higher, but not signifi- have been collected at several sites within sin- cantly so, since 1930 than it was in the preced- gle years,and my own collectionsinclude fulva ing half century (P < 0.06, two-tailed X2 test). and dominicadefending adjacent territories at Such a change would be expectedfor dominica CapeKrusenstern in region 2. Rangeshifts may, recovering from a depressedpopulation level. however, explain some of the apparent sym- Of course, the museum collections do not sam- patry. ple all times and places equally; some collect- The relative population densities of the two ing bias may affect this comparison.No marked forms have probably changed independently range changesare indicated: both forms were during the past century as a result of heavy collectedover the samerange of sympatry dur- sport and market gunning of dominicaduring ing both periods, and comparisonof discrimi- migration, which occurredin easternand cen- nant scoredistributions between early and late tral North America in the late 19th century periods for all four regions does not indicate (Bent 1929). Numerous published reports in- any range shifts. Thus, the conclusionof wide- dicate that American Golden Plovers were spreadsympatry seemsinescapable. among the most abundant of all North Amer- Lackof evidenceof fulva-dominica hybrids.- ican migrants before that period, and by the Becausethe two forms lack distinctive plumage early 1900's most authors were lamenting the characters,hybrids cannot be identified by the disappearanceor drasticdecline in numbersof presenceof clear hybrid characters.Unless the this speciesat all localities. Audubon (1840) de- differencesin size, proportion,and plumageare scribeda spring hunt near New Orleans in 1821 controlledby an extremely simple gene system in which 200 gunners shot an estimated48,000 [such as a single switching gene as proposed golden plovers in one day. A century later, Ob- by Smith (1969) to explain the lack of inter- 614 PETERG. CONNORS [Auk,Vol. 100

TABLE5. Incidenceof phenotypicallyintermediate golden plovers in northwestAlaska, Regions 1-4.

Percentageof sample within interval

n A B Expected,if no hybridization 10.0% 20.0% Expected,if free hybridization 27-39% 45-64% Observed, Regions 1-4 226 9.7% 20.8%

mediates between the small ringed plovers breeding,the incidenceof intermediatesshould Charadriussemipalmatus and C. hiaticulaon Baf- be the same as that calculated for the parent fin Island], we can expact hybrids to exhibit populations (10%). intermediatecharacteristics within the range of I repeated this test for a wider interval con- continuous phenotypic variation in the two taining 20% of the parent populations.Table 5 parent populations. On the discriminant func- presentsexpected percentages of sample distri- tion axis, the most probable distribution for hy- butions included in each of these intervals for brids would be unimodal and intermediate be- assumptionsof (1) no hybridization or (2) free tween the peaks of fulva and dominica hybridization forming a hybrid zone encom- distributions (Schueler and Rising 1976, Neff passingthe samplearea (Short 1969). Two sets and Smith 1978). Becauseof the similarity of of valuesfor free hybridization reflectdifferent parent forms, however, some presumed pure assumptionsof heterogeneityand are meant to parent types occur in this intermediate range. provide a range of expectedvalues: the larger Thus, individual hybrids cannot be distin- number in each interval assumesthe same hy- guished phenotypically. To circumvent this brid or intergrade distribution width as ob- limitation, I measured the incidence of these served for parent distributions; the smaller phenotypically intermediate plovers in sam- number indicates a distribution with standard ples from different regions in the following deviation 50% greater than parent populations, manner. The parent distributions,regions D and indicating increased heterogeneity due to F, can be fit with normal curves. From these backcrossingof hybrids (Schuelerand Rising theoretical curves, I calculated the interval on 1976). The actual incidence of intermediates in the discriminant function axis that contains 10% the combined regions 1-4 is almost precisely of each distribution. There existsone, but only that expected on the assumption of no hybrid- one, interval that satisfiesthis requirement, and ization and differs significantlyfrom either as- it containsthe overlapping tails of both distri- sumption of free hybridization (P < 0.001, x 2 butions. test). With this result, the shift of -0.325 ap- This approach carries a significant benefit: plied to the interval used to test specimensfrom any mixture of samplestaken from pure parent regions 1-4 is seen to be conservative, because populations should include the same 10% of an unwarranted shift would place the interval individuals within the specified interval, closer to a peak of the bimodal distribution, whether the mixture containsall fulva, all do- incorrectly increasingthe number of interme- minica, or any proportion between these ex- diates within the interval. Because the number tremes. Thus, we need not identify birds before recorded equals the minimum expectation, we we look for intermediates. After shifting the can be confident that the shift does not intro- interval by -0.325 on the discriminant func- duce such an error. tion axis (to account for the distributional shift If, however, a very narrow hybrid zone were describedabove), we can identify intermediate to exist,the effectof combininglarge samples phenotypes in samplesfrom northwest Alaska. of pure parent phenotypestaken from outside If the population in regions 1-4 is a mixture of the area of contact would be to mask the exis- interbreedingfulva and dominica,the resultant tence of the expected hybrid intermediates. genetic intermediates should contribute to a Distributionsof discriminant scoresfor regions greater than 10% portion of phenotypes in the 1-4 are shown by region in Fig. 5, with interval intermediate zone. In the absence of inter- A (the 10% interval) indicated. These depict a July1983] GoldenPlover Taxonomy 615

t2 TABLE6. Incidence of phenotypically intermediate REGION golden plovers in each region (see Fig. 1). n = •00

Percentage of sample within interval

Region n A B D 78 7.7% 17.9% n.s. REGION F 60 10.0 18.3 n.s. 1 100 7.0 20.0 n.s. 4[n=26 2 26 11.5 19.2 n.s. 3 62 11.3 17.7 n.s. -- , : • 4 38 13.2 28.9 n.s. Expected, if no n:62 hybridization 10.0 20.0

portant. Both forms nest on well-drained tun-

REGION: dra on slopes and uplands or on ridges and / REGION4 high polygonsin lowland tundra (Drury 1961, Sauer1962, Johnsgard 1981, Portenko 1981). At Cape Krusenstern,I found both formsnesting 4 -2 0 2 4 in an areaof parallelformer beach ridges. Both E)lsGrlrT/InOF/•, score fulvaand dominicaterritories included sections Fig. 5. Distributions of discriminant function of the samefew adjacentridges. No habitat dis- scoresof golden plover specimensfrom northwest tinctionswere apparent to me,and birdsof both Alaska.See Fig. 1. Interval A, containing 10%of par- forms must have been in contact repeatedly ent phenotypes,is indicated. during the season.More extensive observa-, tions or collections are needed, especially if thesecan include a large samplesize at a single rather broad zone of sympatry, as described locality during a single season.Nevertheless, above.None of thesesmaller regionsis sugges- with present information, the conclusionof tive of a hybrid zone. In Table 6, the actual substantialreproductive isolation through as- incidenceof intermediatesin each region shows sortativemating seemsunavoidable. no significant difference from that expectedin Taxonomicstatus.--Because of the large re- the absenceof any hybridization between par- gion of sympatryand the strongindication of ent forms. Only in Region 4, with a small sam- assortativemating, the prevailing treatmentof ple size,is the incidenceof intermediateshigher theseforms as subspecies is inappropriate.They than expectedin both intervals (5 vs. 3.8, 11 vs. satisfythe acceptedcentral requirement for bi- 7.6); this difference remains nonsignificant and ologically distinct species,the occurrenceof doesnot approachexpected results for a hybrid sympatry without interbreeding (Mayr 1969). zone (Table 5). I conclude that these data show Short (1969) presenteda hierarchical classifi- no pattern of elevated incidenceof phenotypic cation of avian subspeciesgroups, superspe- intermediatesin regions of sympatry, indicat- cies,and related specieson the basisof hybrid- ing strongly assortativemating. If hybrids oc- ization interactions. The apparent interaction cur at all, they are much less common than of fulva and dominicaplaces them well beyond would be expected if fulva and dominicawere Short's"taxonomic species border," to be clas- freely interbreeding. Field data sufficient to sified as allospeciesof a superspecies(Amadon deny or support assortative mating in these 1966) or as related, but not allospecific,species. forms are lacking, but I have collected three Initially, this conclusion may seem surpris- pairsof ploverson their breedingterritories in ing, primarily becauseof the extremelysimilar region 2: two dominica-dominicapairs at Cape appearanceof the two forms.Short (1969), in Krusenstern,and one fulva-fulva pair at Kot- fact,alludes to the expecteddistinctness of even zebue, 60 km distant. subspeciesas being sufficientto permit recog- Habitat isolation does not appear to be im- nition of hybrids;yet theseforms fail that test. 616 PETERG. CONNORS [Auk, Vol. 100

He arguesrightly that "the often considerable loo morphological differences between forms in- terbreedingin a hybrid zone is no reasonfor reluctance to merge them," because the two • 8o forms apparently "accept each other as conspe- cific." Conversely, the absenceof prominent morphological differences between sympatric forms assortativelymating is no reasonto merge them, when the two forms themselves show such a reluctance to merge. We must not con- fuse our own ability to distinguish forms with •_ 2o the ability of the birds themselves.At present, analyses of behavioral repertoires of the two ¸ speciesare unavailable; in future these may Fresh Light Moderate Heavy show important differences. Two other distinctionsbetween fulva and do- Primary wear minicahave occasionallybeen proposedas evi- Fig. 6. Difference in frequency of primary wear dence of sufficient distinctnessto convey sep- classesin specimensof P. dominica(shaded portion, arate speciesstatus. The forms differ markedly n = 220) and P. fulva (striped portion, n = 148). in migration routes and wintering areas, and they may differ in schedulesof molt and mat- uration amongyoung birds on winter grounds. correspondto 1-yr-old birds (as suggestedby Kinsky and Yaldwyn (1981)interpret plumages Johnson and Johnson unpubl.), the data indi- of birds found on South Pacific wintering cate that many more fulva than dominicareturn groundsduring the boreal summeras indicat- to breeding grounds during their first spring. ing that young fulva remain in winter quarters This is the opposite of the situation described longer (1.5 or 2.5 yr) than young dominica(0.5 by Kinsky and Yaldwyn and Stresemannand yr, Stresemannand Stresemann1966). Their re- Stresemann,although it, too, suggestsa dis- suits differ in several respects from those of tinction between the forms. Johnson and Johnson (unpubl.) on molt and Nomenclature.--Theappropriate speciesdes- migration of fulva in Hawaiian winter quarters, ignations Pluvialisdominica (Muller) and Pluvi- however, and the situation with wintering do- alisfulva (Gmelin) are obvious,but severalcom- minicaremains poorly defined. My own exam- mon names are possible. The dichotomy of ination of breeding specimens does not sup- Greater (P. apricaria)and Lesser(P. dominica,in- port their contention. Some almost 1-yr-old cluding P. fulva) Golden Plovers (Palmer 1967, fulva can be identified amongAlaskan speci- Johnsgard1981) becomesinappropriate when mens in breeding plumage by their distinctive we must treat three species. Other common juvenile rectrices (see Kinsky and Yaldwyn name adjectivesfor apricariain Englishinclude 1981), but I could not confidently distinguish Golden (Bannerman 1961), European Golden all young birds of both forms in breeding dress. (Bent 1929), and Eurasian Golden (A.O.U. 1957). The condition of primaries provides a useful Names used recently for dominica(excluding indicator,however: first-year birds in Junehave fulva) include American Golden (Bent 1929,. primaries acquired as juveniles 10 months ear- Bailey 1948)and EasternAmerican Golden (Ga- lier, and theseusually show considerablewear brielson and Lincoln 1959). For fulva, at least comparedto those of older birds, whose pri- seven names exist: Pacific Golden (Bent 1929, maries are nearer 5 months old (Prater et al. Bailey 1948), Western American Golden (Ga- 1977) or 7 months old (Johnson and Johnson brielson and Lincoln 1959), Asiatic Golden unpubl.). Figure 6 comparesprimary wear be- (Bannerman 1961, Vaurie 1964), Eastern Gold- tween fulvaand dominicaamong birds collected en (Royal AustralasianOrnithologist's Union in spring migration (57 specimens) and on 1968), Least Golden (Ornithological Society of breeding grounds (311 specimens).The same New Zealand 1980), Siberian (Portenko 1981), criteria were applied to all specimens.The dis- and Asian Lesser Golden (Johnsgard 1981). I tributions differ (P < 0.001, X2 test) primarily suggestthat all three speciesbe given names in moderate and heavy wear classes.If these consistingof a single adjectivepreceding gold- July1983] GoldenPlover Taxonomy 617

en plover and that this adjectivereflect their and C. pusilla)suggests that dominicamight have obvious differencesin range rather than the been isolated during the last glaciation in a more subtle differences of size. This eliminates tundra refuge in the northwest Canadian ar- some names but still leaves choices. Eurasian chipelago (Banks Island), while fulva bred in best describesthe breeding range of apricaria, refuges around the Bering Sea and in eastern and Americanis clearly the choicefor dominica. Siberia. Precise locations and sequencesof iso- Three regional possibilitiesfor fulva, Asiatic, lation periodsare disputable,but a general pat- Asian, and Siberian, are somewhat ambiguous tern of glacial isolation into three regions as- in view of the occurrenceof apricariain those sociated with present breeding ranges is regions.Western American ignores the major probable. portion of the species'range, and Easternis I proposethat, during these periods of iso- ambiguousor misleadingover a large portion lation, separatewintering areasand migratory of the globe.The remaining name,Pacific, fails pathwaysevolved in each of the three groups. to accountfor that portionof the wintering area For arctic, tundra-breeding precursorsof fulva in the Indian Ocean, but it is unambiguous and and dominica,these involved long-distance mi- informative. I suggest the names Eurasian grations to areas south of their breeding Golden Plover (P. apricaria),Pacific Golden ranges--southeastAsian and western Pacific Plover (P. fulva),and AmericanGolden Plover areas for fulva, South American for dominica. (P. dominica). These developmentsentailed a significant en- Speciationof fulva and dominica:a hypothe coding of different genetic information in the sis.--Theseresults present us with a puzzle: two forms. Evidence for genetic control of mi- what factors in the evolution of these two tun- gration comesfrom studies of orientation be- dra-breedingbirds, so similar in appearanceand havior in many avian species,including Pluvi- ecology,have producedthe presentreproduc- alisfulva (Sauer 1963), and from the widespread tive isolation?I suggestan explanationthat de- observationthat juvenilesof golden ploversand pendsnot on the conditionson the breeding many other shorebirds migrate southward to grounds but rather on the migratory require- their first wintering grounds severalweeks af- ments of the two forms. This is a purely spec- ter adults have left the breeding grounds. A ulative suggestionthat I offer becauseit is plau- detailed map of wintering areasmay not be the sible and because it focuses attention on the inheritance of young plovers, but at least a di- importanceof migrationin the evolutionof rection, and probably a distance, must be in- theseand many other taxa of migrant birds. cluded, as in the vector navigation hypothesis Speciationof the three speciesrepresenting of Schmidt-Koenig(1973) and as shown for the almostcircumpolar golden plover complex Sylviid warblers (Berthold 1978). probablyoccurred during glacial periods of the During the period of geographicisolation, Pleistocene. Larson (1957) proposed that the only small changes in breeding behavior, forms were isolated during the warmest inter- plumage,size, or breeding habitat may have glacialperiod in cold tundra refugia in north- evolved. As the rangesof both forms expanded ern Greenland(apricaria) and the highlandseast post-glacially,bringing fulva and dominicapop- and west of the Bering Strait (dominica-fulva) ulationsinto secondarycontact, these may have and were also isolated during the last glacial allowed some recognition of forms but would periodin tundra refugia in Europeand western not, in themselves,have provided the selective Siberia (apricaria),the Bering Sea area (fulva), force for isolation of the forms. For example, and eastern North America (dominica).Johan- differencesin size may provide a basisfor some sen (1958) postulateda similar history, with mateselection. Other speciesof shorebirdshave apricariamoving westwardfrom an ancestral been shown to choose mates according to size Siberian form and dominicamoving eastward at (Jehl 1970), and, if the present differencesin a later date. Fulva would have remained in the size and proportionexisted at initial secondary easternSiberian and BeringSea area during the contact and individuals of the two forms chose last glaciation.A comparisonwith the evolu- mates on a basisof matching winglength (the tionary historiesgiven by Ploeger(1968) for single measurementthat differsmost between pairssuch as White-frontedGeese (Anser albi- forms), then 15-20% of the populationswould fronsfrontalis and A. a. gambelli)and Western have chosenmates of the oppositeform (Table and Semipalmatedsandpipers (Calidris mauri 1). If individuals could integrate the differ- 618 PETERG. CONNORS [Auk,Vol. 100 ences in size and proportion of several mea- sources,nor is timing a very flexible factor in surements as well as our discriminant function view of the short summer period in high lati- and choseon a strict size-matchingbasis with- tudes);(2) differencesin vocalizations,a possi- out errors, then 6% of the populations would bility that has not yet been fully analyzed; or still be mismatched(Fig. 3 and Discussion).This (3) differencesin pairing displays or in plum- may be a small enough proportion to maintain age featuresused in pairing displays.My spec- breeding stocksas distinct as the museum data imen studies do indicate a few plumage differ- indicate (J. R. Jehl, Jr. pers. comm.). Size-based ences in these otherwise very similar species. mating, however, provides no selective disad- As noted earlier, the least ambiguous differ- vantage to these hybrids; in fact, at the edges ence is color of undertail coverts in males. These of the zone of sympatry there would be a se- feathersin dominicamales are usuallyblack with lective advantageto individuals of the rare form somewhite markings;in fulva males,undertail that either were of a size similar to the common coverts are mainly white with some black form or would be willing to mate with little markings. In view of my conclusionthat assor- regard for size matching. Both these advan- tative mating occursin these two specieswhere tages would operate to produce more hybrids they are sympatric, we might expect that the and more intermediate-sized birds in the zone undertail covertsof males figure prominently of sympatry. Thus, size differences that may in a breeding ground display of at least one of have evolved during geographic isolation can the speciesand that this display should occur provide an important basis for mate selection, early in the season,for example in early pair- but they must be coupled with selective forces bond formation or preceding copulation. Such to maintain reproductive isolation in sympatry. a display has been observed by F. A. Pitelka The differences in migration and winter (pers. comm.) at Barrow, Alaska. The difference ranges between the two forms may have pro- in color of the flanks of males (mostly white in vided such a selective force. Requirements of fulva; black in dominica)would be apparent in juvenile migration might exert severe selection raised wing displays (Drury 1961, Sauer 1962). pressuresagainst hybrid offspring. I do not in- Less emphatic plumage differences (boldness sist that the result of hybridizing an Argentine of tail barring, width of forehead bands, migrant with a Samoan migrant would neces- brightness of gold spotting) may also play a sarily be a bird that migratesmidway between role, but published descriptions of breeding these two locations and expires at sea, but the displays have not been exhaustive, and no such result of this cross might function poorly in explanation has yet emerged. some respect.There may be no way to combine I considered and rejected an alternative the information for two very different migra- method of assortativemating that depends on tory routes into a single plan that is also suc- pair formation occurring in winter or during cessful.Not only might the direction be inap- spring migration. In this case hybrid pairs propriate (western Pacific Ocean), but distance, would be effectively excluded, as both species timing, or even motivation to migrate might migrate in allopatry. Sauer (1962) reported that be altered. Shorebirds of many species are fulva arrived on breeding grounds on St. Law- known to wander widely from their normal rence Island, Alaska, in 1960 already paired, migratory ranges, but we do not know whether but this is a difficult observation to make with or not they return to nest successfully on certainty. F. A. Pitelka and J.P. Myers (pers. breeding grounds in subsequentyears. comm.) interpret their early-season observa- If the result of unsuccessfulmigration is loss tions of golden plovers (mainly dominica)at of reproductionfor any reason,selection against Barrow over many yearsas indicating that birds hybrids would be extremely powerful. In this arrive unpaired, and Jehl (1968) presented sev- situation, behavioral isolating mechanisms eral arguments against the assumptionof early would be likely to evolve in regions of sym- pairing in shorebirds. parry, building on initial differences in size, This proposal for the speciation process in plumage, or behavior that permit at least par- dominicaand fulva remainsentirely speculative. tial recognition of forms. These behavioral iso- Its interest lies in its recognition of the poten- lating mechanisms might include (1) differ- tial importance of migration and winter fea- ences in timing of nesting (but this is not tures in the life cycle of migratory birds, such suggestedby published nest dates from many asrecently discussed by Myers(1981i concern- July1983] GoldenPlover Taxonomy 619 ing the evolution of sandpiperbreeding social LITERATURE CITED systems.Whereas most discussionsof bird spe- AMADON,D. 1966. The superspeciesconcept. Syst. clarion revolve around diverging adaptations Zool. 15: 245-249. to breedingconditions, my proposalaccepts that AMERICAN ORNITHOLOGISTS' UNION. 1957. Check-list breeding-ground adaptations may have re- of North American birds. Baltimore, Amer. Or- mained similar for both forms. The range ex- nithol. Union. pansion on breeding grounds following geo- AUDUBON, J. J. 1840. The birds of America, 1840- graphic isolation during the glacial period 1844. Quoted in Bent (1929). would have been a continuousprocess of small BAILEY,A. F. 1948. Birds of arctic Alaska. Colorado stepsas the range of suitable breeding tundra Mus. Nat. Hist. Popular Ser. No. 8. changed.No correspondingcontinuous change BANNERMAN, D. A. 1961. The birds of the British of winter range toward fulva is possiblefor do- Isles, vol. I0. Edinburgh, Oliver and Boyd. BENT, A. C. 1929. Life histories of North American minica,however. The winter ranges cannot be- shore birds: golden plovers. U.S. Natl. Mus. Bull. come sympatric without enormous discrete 146: 175-202. changesin wintering areas.Thus, geographic BERTHOLD,P. 1978. Concept of endogenouscontrol isolation of breeding populations permits spe- of migration in warblers. Pp. 275-282 in clarion,but geographicisolation of winter pop- migration, navigation and homing (K. Schmidt- ulations drives speciation.This approachmay Koenig and W. T. Keeton, Eds.). Berlin, Spring- also be pertinent to analysesof speciationin er-Verlag. other migrant charadrii, for example Ringed BOCK,W. J. 1958. A generic review of the plovers Plover (Charadriushiaticula) and Semipalmated (Charadriinae, Aves). Bull. Mus. Comp. Zool. Plover (C. semipalmatus)(Wynne-Edwards 1952, 118(2): 25-97. CONOVER,B. 1945. The breeding golden plover of Smith 1969) and several pairs of other closely Alaska. Auk 62: 568-574. related shorebirdtaxa separated or overlapping DRURY,W. H., JR. 1961. The breeding biology of in the Bering Strait region (Jehl 1973). I rec- shorebirds on Bylot Island, Northwest Territo- ognize that support for this theory will be dif- ries, Canada. Auk 78: 176-219. ficult to gather; I offer it for its heuristic value. GABRIELSON,I. N., & F. C. LINCOLN. 1959. Birds of Alaska. Washington, Wildl. Mgmt. Inst. and ACKNOWLEDGMENTS Stackpole Co. HUBBARD,J.P. 1970. Geographic variation in the This researchwas supportedby the Bureauof Land Dendroicacoronata complex. Wilson Bull. 82: 355- Managementand the National Oceanicand Atmo- 369. sphericAdministration as part of the Alaska Outer JEHL,J. R., JR. 1968. Review: The shorebirds of North Continental Shelf Environmental Assessment Pro- America. Auk 85: 515-520. gram (OCSEAP),Contract No. 03-5-022-84.I thank 1970. Sexual selection for size differences Frank A. Pitelka for his constant encouragement, in- in two speciesof sandpipers. Evolution 24: 311- terest,and suggestions;Ned K. Johnsonfor advice 319. and assistancewith museum specimen work; and 1973. Breeding biology and systematicre- GeorgeF. Barrowclough,Carolyn S. Connors,Joseph lationships of the Stilt Sandpiper. Wilson Bull. R. Jehl, Jr., OscarW. Johnson,J.P. Myers, David W. 85: 115-147. Norton, Kimberly G. Smith, JosephG. Strauch, Jr., JOHANSEN,H. 1958. Revision und Entstehung der and DeclanTroy for many helpful suggestions,which Arktischen Vogelfauna. 2. Tell: Revision der contributed to the final version of this manuscript. Grues-Passeresund Entstehung der Arktischen Finally, I gratefully acknowledgethe loan of speci- Vogelfauna.Acta Arctica 9: 1-131. mens from these museums: American Museum of JOHNSGARD,P.A. 1981. The plovers, sandpipers,and Natural History; California Academy of Sciences; snipes of the world. Lincoln, Nebraska, Univ. Carnegie Museum; Chicago Academy of Sciences; Nebraska Press. Denver Museum of Natural History; Field Museum KINSKY,F. C., & J. C. YALDWYN. 1981. The bird fauna of Natural History; Los Angeles County Museum; of Niue Island, Southwest Pacific, with special Museum of ComparativeZoology, Harvard Univer- notes on the White-tailed Tropic Bird and Gold- sity; Museum of Zoology, University of Michigan; en Plover. Natl. Mus. New Zealand Misc. Ser. Museum of Vertebrate Zoology, University of Cali- ' No. 2. fornia,Berkeley; National Museumof Canada;United LARSON, S. 1957. The suborder Charadrii in arctic StatesNational Museum of Natural History; and Uni- and boreal areas during the Tertiary and Pleis- versity of Alaska Museum. tocene. Acta Vertebratica 1: 1-84. 620 PETERG. CONNORS [Auk,Vol. 100

MAYR, E. 1969. Principles of systematiczoology. Khoz." Leningrad, Glavsevmorput, vol. 5. Quot- New York, McGraw-Hill. ed in Vaurie (1964). --, & L. L. S•ORT. 1970. Speciestaxa of North 1981. Birds of the Chukchi Peninsula and American birds. Nuttall Ornithol. Club Publ. Wrangel Island. Translated from Russian and No. 9. published for Smithsonian Inst. and Natl. Sci. MUNRO, G.C. 1945. Protection for Hawaiian shore- Found. New Delhi, Amerind Publishing Co. birds. Elepaio 5: 63-65, 72-75. PRATER,A. J., MARCHANT,J. I-•., •r J. VUORINEN. 1977. MYERS,J.P. 1981. Cross-seasonal interactions in the Guide to the identification and aging of Holarc- evolution of sandpiper social systems.Behav. tic . Tring, Hefts., British Trust Ornithol. Ecol. Sociobiol. 8: 195-202. ROYAL AUSTRALASIAN ORNITHOLOGIST'S UNION. 1968. , & F. g. PITELKA. 1980. Effect of habitat con- The official checklist of the birds of Australia, ditions on spatial parameters of shorebird pop- with supplements 1 to 9. Adelaide, Libraries ulations. Report to U.S. Dept. Energy. Board South Australia. NEFF, N. g., & G. R. SMITH. 1978. The multivariate SAUER,E. G.F. 1962. Ethologyand ecologyof gold- analysisof hybrid fishes.Syst. Zool. 28: 176-196. en plovers on St. Lawrence Island, Bering Sea. NIE, N. I-•., C. I-•. HULL, J. G. JENKINS, K. STEIN- Psychol.Forsch. 26: 399-470. BRENNER,•r D. I-•. BENT. 1975. SPSS, statistical 1963. Migration habits of Golden Plovers. package for the social sciences.New York, Proc. 13th Intern. Ornithol. Congr.:454-467. McGraw-Hill. SCHMIDT-KOENIG,K. 1973. Ober die Navigation der OBER•IOLSER,•-•. C. 1938. The bird life of Louisiana. Vogel. Naturwissenschaften60: 88-94. Dept. Conservation, State of Louisiana, Bull. 28. SCHUELER,F. W., •r J. D. RISING. 1976. Phenetic evi- ORNIT•IOLOGICAL SOCIETY OF NEW ZEALAND. 1980. dence of natural hybridization. Syst. Zool. 25: Amendments and additions to the 1970 annotat- 283-289. ed checklist of the birds of New Zealand. No- S•ORT,L.L. 1969. Taxonomicaspects of hybridiza- tornis (Supplement) 27: 1-23. tion. Auk 86: 84-105. PALMER,R. S. 1967. Species accounts. Pp. 143-267 SMIT•, N. G. 1969. Polymorphism in ringed plo- in The shorebirds of North America (G. D. Stout, vers. Ibis 111: 177-188. Ed.). New York, Viking Press. STRESEMANN, E., & V. STRESEMANN. 1966. Die Mau- PETERS,J. L. 1934. Check-list of birds of the world, set der Vogel. J. Ornithol. 107: 1-448. vol. 2. Cambridge, Harvard Univ. Press. VAURIE,C. 1964. Systematicnotes on Palearcticbirds. PLOEGER,P.L. 1968. Geographicaldifferentiation in No. 53. Charadriidae:the genera Charadriusand arctic Anatidae as a result of isolation during the Pluvialis. Amer. Mus. Novitates 2177. Last Glacial. Ardea 56: 1-159. WYNNE-EDWARDS,V.C. 1952. Zoologyof the Baird PORTENKO,L.A. 1939. Fauna Anadyrskogo Kraya, expedition (1950). 1. The birds observed in cen- Ptitsy, pt. 1. Trudy Nauchno-Issled. Inst. Poliar. tral and southeast Baffin Island. Auk 69: 353-392. Zemled. Zhivotn. i Promys. Khoz., set. "Promys