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Home , Chusovaya, Falconidae, Gyrfalcon, Ufa (river)

j. RaptorRes. 26(2):81-88 ¸ 1992 The Raptor ResearchFoundation, Inc.

DISTRIBUTION AND COLOR VARIATION OF IN

DAVID H. ELLIS, CATHERINE H. ELLIS, GREY W. PENDLETON U.S. Fish and WildlifeService, Patuxent Wildlife ResearchCenter, Laurel, MD 20708

ANDREI V. PANTELEYEV ZoologicalInstitute, Academy of Sciences,19903d St. Petersburg,Russia

IRENA V. REBROVA ZoologicalMuseum, Moscow Lomonosov State University,103009 Moscow K-9, Russia

YURI M. MARKIN CentralOrnithological Station, Oka StateReserve, 391072 Po Lakash,Spassk Region, Ryazan District, Russia

ABSTRACT.--(Falco rusticolus) museum specimens in Moscow (73) and St. Petersburg(132) were dividedinto four colorclasses (gray, light gray, white gray, and white) and four longitudinalbelts representingmajor physiographicregions of northern Russia. Gray variants predominatedin the west and central regions.White were most commonin extremeeastern , but were occasionally found even west of the Mountains. Frequencieswere as follows: European Russia 4% white, 50% gray (the remainderwere intermediates);western Siberia 0% white, 58% gray; central Siberia 15% white, 42% gray; and easternSiberia 47% white, 33% gray. Remarkably, in the easternmostsubregion, white birds predominatedeven near the southernmostextension. Becausethe northernmostportions of the 'range in continentalRussia are in central Siberia where white variants were rare, we proposethat a better predictorof the white variant is longitude,not latitude. White birds were most frequent at the easternreaches of both the Palearcticand Nearctic. The bestenvironmental correlates of this distribution pattern may be the southwardbending thermal isoclines proceedingeastward toward Greenlandor Kamchatka,where bothland massesare bathedby coldoceanic currentsof origin. By contrast,the western reachesof both land massesare bathed by warm currents. In these western reaches,Gyrfalcon summer distribution is displacednorthward and dark variants predominate. The breedingrange of the Gyrfalcon, determinedby mapping the locationsof the specimenswe examined,differs little from the range proposedin 1951.

Distribuci6ny variaci6ndel coloren el Gerifalte en Rusia EXTRACTO.--Esp•cimensde Gerifalte (Falcorusticolus), existentes en museosde Moscfi (73) y San Petesburgo(132), fueron separadosen cuatroclases de colores(gris, gris claro, blancogrisiceo y blanco) dentrode cadauna de las cuatroregiones longitudinales que representanlas mayoresregiones fisiogrificas del norte de Rusia. Las variantesgrises predominan en las regionesdel oestey del centro.Las aves blancasson mils comunesen el extremoeste de Siberia, y hastason ocasionalmente encontradas al oeste de los Montes Urales. Las frecuenciasson las siguientes:Rusia europea4% blanco,50% gris (el resto estabaen el intermedio);Siberia occidental 0% blanco,58% gris; Siberia central 15% blanco,42% gris; y Siberia oriental 47% blanco, 33% gris. Es de notar que aves blancaspredominan aun cerca de la extensi6nsur de la subregi6nextremo-oriental. Las porcionesdel extremonorte de la regi6n de Rusia continental,donde se halla esta especie,estiin en Siberia central dondelas variantesblancas son raras. Por estoproponemos que un mejor pronosticador de la variante blancaes la longitudy no la latitud. Las avesblancas son mils frecuentesen los extremos orientalestanto del Paleirtico comodel Neirtico. E1 mils importantefactor de esteambiente, que corre- lacionacon estatendencia de distribuci6n,es el isoclinotermal que se curva hacia el sur y que continfia hacia el este,en direcci6nde las regionesde Groelandiao Kamchatkaque sonbafiadas por corrientes ocelnicasfrlas de origen irtico. En contraste,el oestede estasdos regioneses bariadopor corrientes cilidas. En estaszonas occidentales, la distribuci6nde verano del F. rusticolesse desplazahacia el norte; y predominanlas variantesoscuras.

81 82 DAVID H. ELLIS ET AL. VOL. 26, NO. 2

E1 fireade reproducci6nde estehalc6n, basada en lossitios donde fueron colectados los esp6cimens de museo,no es muy diferentede la propuestaen 1951. [Traducci6nde Eudoxio Paredes-Ruiz]

In the four decadessince publication of Demen- for dates (from the Julian to Gregorian calendars)and tiev's (1951) monograph on the Gyrfalcon (Falco locations(from pre- to post-revolutionaryregions). Spec- imens that lacked sufficient data were excluded from our rusticolus),little new informationhas been published analysisas were the few birds with spuriousdata. For in English on this speciesfor the former SovietUnion example,we excludedZIAS No. 75403 (which by color (comprisingnearly 50% of the species'breeding and sizeis a large second-yearfemale Gyrfalcon)because range). Dementiev's(1951) southernlimit of breed- its original label identifiedit as a male PeregrineFalcon ing is well substantiatedby museumspecimens, but (F. peregrinus);its collectiondate and localeare alsobetter matchesfor a breedingperegrine. did not loop southto includethe middleUral Moun- This study required that we deal with the difficulties tains where he (Dementiev 1960) reportedthat Gyr- presentedby the possibletaxonomic affinities of the Gyr- falconsbred a century earlier as far south as the ,Saker (F. chefrug),and Altay (or Altai) Falcon (F. , and Byelaya Rivers (seeFig. 1). rusticolus/cherrugaltaicus). Our responsewas to include Recent decadeshave seena trend in the published only birds that were clearly Gyrfalconsof the non-Altay Falcon ,judging either by collectionlocation and date, literature toward simplifying(i.e., eliminating un- or by .This separationwas difficult for only a dulations) and compressingDementiev's (1951) few immatures,those which had the spottedtail pattern breedingrange without offeringsupporting data (e.g., thoughttypical of Sakers.As Cade (1982) indicated,some Cade 1982, Flint et al. 1984). These changes,if Sakersalso have Gyrfalcon-likebarred tails. We includedonly one specimen(ZIAS No. 75497) that correct, would signal population declinesand/or had previouslybeen treated as an Altay Falcon (cotypeof abandonment of formerly occupied range. The Gennaialorenzi: considered synonymous with F. r./c. al- boundarywe report is little changedfrom Demen- taicus,Sushkin 1938, Vaurie 1961). This specimenwas a tiev's 1951 map, thereforewe affirm the accuracyof large,gray femaleGyrfalcon and lackedthe brown dorsal backgroundcolor that characterizeseven the most Gyr- his map and recommendits continueduse until more falcon-likeof the supposedAltay types.Its location,near information is obtained. the southern end of the and over 1000 Dementiev (1951, 1960) noted the general trend km from the mountainsof Central where the Altay for Gyrfalconsto be lighter in colorand larger pro- Falcon reportedlyoccurs (Dementiev and Gladkov 1951), ceedingeastward acrossEurasia. Portenko (1972) and collection date (October or November 1900) are a goodmatch for a migrating Gyrfalcon. also noted that the white variant predominateson Recognizingthat colorvaries along a continuum(Vau- the Chukchi Peninsula.We provide frequenciesof tie 1961), we nonetheless,for comparisonpurposes, grouped color variants for the breadth of Russia based on all the specimensinto eight age/color classesas follows: examination of 205 specimens(91 adult and 114 white variants (adult and juvenile) were birds with white as a dorsalbackground color; white gray birdswere adults juveniles)in the two primary collectionsin Rus- with dorsaldark barring approachingthat of gray adults sia, the University of Moscow ZoologicalMuseum but with very little gray in an otherwisewhite dorsal (UMZM) and the ZoologicalInstitute of the Aca- background;white brownbirds, the correspondingjuvenile demic Sciences(ZIAS) in St. Petersburg. In dis- variant,were palebrown dorsally with light tips and edges cussingcolor variation, we amplify Vaurie's (1961), and were lightly streakedwith brown ventrallyon a pale creambackground color; light gray birds(and light brown Cade's(1982), and Palmer's(1988) observationsthat juveniles)had the heavilybarred dorsal pattern of normal Gyrfalconplumage is infinitelyvariable along a con- gray adults(or brown mantle if juveniles)but their dorsal tinuum from the whitest individualsto dark gray or backgroundcolor, and oftenthe hue of their light and dark "black" birds. To recognizecolor phasesor, more bars, was much lighter than the gray variant (or brown variant if juvenile); gray (or brown if juvenile) variants precisely,color morphs (e.g., white, gray, brown, differed from light gray (or light brown) birds in having black) is misleading. It is instructive, however, to darkergray (or brown) pigmentationdorsally. Gray adults report regional trends in the occurrenceof light, often had a light gray wash ventrally, especiallyon tibias dark, and intermediate birds. and lowerbelly, while juveniles had darkerventral streak- ing and a darker buff wash than other variants.Birds in mixed plumage(molting) providedevidence that the four METHODS juvenileclasses molt into correspondingadult classes(e.g., This study is based primarily on examination of the white brown juveniles becomewhite gray adults). Ex- Gyrfalcon skins, specimen tags and cataloguesat the amplesof adults (and two juveniles) representingmost of UMZM (73 specimens)and the ZIAS (132 specimens). our light and dark variantsare illustratedin Weick's(1980) Great effort was expendedto translateold Russianscript Plate 39. Juveniles,although often showing a grayishbloom JUNE 1992 COLORVARIATION IN RUSSIANGYRFALCONS 83 or even indistinctgrayish bars on brown plumage, were 127705 and 127706) collectedin July 1918 along nevergenerally gray as Palmer ( 1988:383,387) repeatedly the Lower Tunguska River. The summer limit we states. present(Fig. 1) followsDementiev's (1951) bound- BecauseGyrfalcons from narrow longitudinal zones probably mix somewhaton the wintering grounds and ary line and shows the historic southern limit of couldthereby confuse our interpretationof regionaltrends, montane breeding in the central Ural Mountains we analyzeda data subsetconsisting entirely of (Dementiev 1960). Our map also adds one minor collectedMay through August. Becausethe number of southward extension in central Siberia to include a summerspecimens in eachlongitudinal belt was too small to make all of the comparisonswe sought,we increased juvenile (ZIAS No. 168211) collectedon 16 July our samplesize by: 1) translatingall juvenile plumaged 1956 in the upper drainage of the Yana River. birds into their correspondingadult category,2) pooling In Figure 1, we also plot a juvenile (ZIAS No. summer and non-summercollections, and 3) pooling 15 75428) collected9 August 1937 in western Siberia longitudinalzones (of 10 degreeseach) into four major near the town of Surgut (on the Ob River) about longitudinalregions that reflect important physiographic regionsof Russia (seeFig. 1). These manipulationspro- 450 km south of Dementiev's (1951) line. An adult vided for 70, 60, 33, and 42 birds respectivelyin the west female collectedin June 1904 in Irkutsk Province to east longitudinal regions. (central Siberia), most of which is well south of To further minimize the problem of having birds from Dementiev's(1951) line, could not be mappedbe- one longitudinal region in summer collectedin a neigh- boring region in winter, we chosenatural physiographic causeits collectionlocation information was toogen- boundariesbetween regions.The Ural Mountains divide eral. One or both of thesespecimens would extend the first two regions, European Russia (30ø-60øE) and the summerrange. Juveniles,however, begin wan- westernSiberia (60ø-90øE),and probably serveas an ef- dering even in July (Cramp et al. 1980) and De- fectivebarrier to prevent mixing of wintering birds. The mentiev (1951) included neither record, so we omit latter region, western Siberia, constitutesthe lowlands be- tween the Ob and Yenisey Rivers which are unlike the them also. We suspect,however, that a thorough third region,the topographicallycomplex Central Siberian searchof the areasimmediately south of our bound- Uplands (90ø-150øE).The easternSiberian region (150øE - ary line would, especiallyin favorableprey years, 169øW) is not well demarcatedfrom the neighboringre- yield many summerand breedingrecords. gion to the west. There is, however, a somewhat artificial Our work did not concentrate on winter records. separationoccasioned by the completelack of specimens for a 10 degreewide boundary(140ø-150øE) between the We note, however, that Dementiev's (1951) demar- two regions. cation of the southern limit of winter distribution of We usedtwo methodsof contingencytable analysisto Gyrfalconsextends much further south than illus- comparethe proportionsof each color variant amongthe four regions.Specimens were assumedto be independent. trated by either Cade (1982) or Cramp et al. (1980) We know of only oneexception to this rule (i.e., two birds Perhapsthe best explanationof this discrepancyis were presumedsiblings). Because few summerspecimens that Cade describeshis line as representingthe were available, we used Fisher's exact test (Agresti 1990: southernlimit of the "usualwinter migration" range 59-64) to testthe hypothesisthat colorvariants were equally without offering evidence, whereas Dementiev's distributedamong the regionsin summer. For the entire data set, we used log-linear models (Agresti 1990:130- (1951) line includesall records.Cramp et al. (1980) 134) to test these same hypotheses.We also used 1 df may have been influencedby authors who reported contrastsfor specifictests associated with departuresfrom marked Gyrfalcon declinesin western dur- the hypothesisof equalproportions of colorvariants among ing this century. The only author they cite for Rus- the four regions. sia,however, presented no informationon Gyrfalcon populations(Galushin 1977). There is a sizablecorps RESULTS AND DISCUSSION of field ornithologistsand many active field stations Recent works (e.g., Cade 1982) show summer in Russia. Until the observational records from these distribution significantly restricted from that pre- sourcesare collated,we must rely on the specimen sentedby Dementiev(1951). Even publicationsby records presented in Dementiev's (1951) mono- Russianauthors (Flint and Potapov1984, Flint et graph. al. 1984), with accessto a dozen or so post-1951 The distribution of color variants in Russia was Russianlanguage publications on the Gyrfalcon,have discussed briefly by Vaurie (1961). H e reportedthat also eliminated the irregularities in Dementiev's white birds constitute50% of the populationeast of (1951) line, eventhough Dementiev's major south- the Lena River (Fig. 1), with white birds found as ward extension in central Siberia was made to ac- far west as the PechoraRiver (just west of the Ural commodatetwo recentlyfledged young (ZIAS Nos. Mountains) and composing4% of the population 84 DAVID H. ELLIS ET AL. VOL. 26, NO. 2

• KURILiSLANi)8

ol I JuNw 1992 COLORVARIATION IN RUSSIANGYRFALCONS 85

Table 1. Number of Gyrfalconspecimens of four color Table 2. Number (and proportion)of Gyrfalconspeci- classescollected in four regionsof Russianduring summer mensof four colorclasses collected in fourregions of Rus- (May-August). sia.

REGION REGION

EURO- EURO- COLOR PEAN WESTERN CENTRAL EASTERN COLOR PEAN WESTERN CENTRAL EASTERN VARIANT RUSSIA SIBERIA SIBERIA SIBERIA VARIANT RUSSIA SIBERIA SIBERIA SIBERIA

Gray 5 4 6 2 Gray 35 (0.50) 35 (0.58) 14 (0.42) 14 (0.33) Light gray 2 1 4 1 Light gray 18 (0.26) 15 (0.25) 10 (0.30) 5 (0.12) White gray 0 1 0 1 White gray 14 (0.20) 10 (0.17) 4 (0.12) 3 (0.07) White 1 0 0 4 White 3 (0.04) 0 (0.00) 5 (0.15) 20 (0.47) Total 8 6 10 8 Total 70 60 33 42

between the Lena and Pechora Rivers. We examined of white birds and a lower proportionof gray birds two white adults and one white juvenile from Eu- than the other regionscombined (Table 1). ropeanRussia: the furthestwest was an adult (ZIAS When we pooleddata for the entireyear, the most 75352) collectedin November in the Archangel re- apparent regional trend (Table 2) was the preva- gion. White birds found in winter in European Rus- lenceof white birds in easternSiberia (47%). Only sia may not representthe continentalbreeding pop- 55% of the birds in this region were of the gray ulation, but may be from Spitzbergen or other variant and 67% were lighter than the normal gray northern islands. Vaurie (1961) noted that the type. Proceedingwest, the proportionof light gray "black" Gyrfalcon, numerically important only in to white types dropsto 57% in central Siberia, then Labrador in eastern North America, is absent from 42% for western Siberia, but rises again to 50% for Eurasia. However, he reportedthat one bird he ex- European Russiaeven though fully white birds make aminedfrom Europewas virtually asdark as "black" up only 4% of the latter population.The absenceof Gyrfalconsfrom easternNorth America. Further, white specimensfor western Siberia is surprising Dementiev(1960) reported3 blackGyrfalcons among becausePleske (1928) reported white birds for the 99 birds held by a Russian Czar. We did not en- region, and white nestlingstaken from the Yamal counterany dark specimensfrom EuropeanRussia. Peninsula are now in the propagationproject at the It bears mention that Vaurie's (1961) comments Oka State Nature Reservein Ryazan Province. and the distributional patterns we report, do not The differencesin colorcomposition among regions includerecords for the Altay Falcon (Central Asia) were statisticallysignificant (X•'= 54.91, df = 9, P for which many individuals,both juvenile and adult, < 0.001). Based on this test, 1 df contrastsyielded closelyresemble juvenile "black" Gyrfalcons from the followingresults. As with the summerspecimens, Labrador. Dementiev (1951:26) had earlier com- the easternSiberia region had the highestproportion mentedon the remarkable "parallel coloration"of of white falconsand, conversely,the lowest propor- the darkestAltay Falconsand the "melanisticvari- tion of the other three variants (X•'= 41.51, P < ant of the North American Gyrfalcon." 0.001). The samplefrom central Siberia alsohad a Using the summerspecimens alone (Table 1), no higher proportionof white birds and a lower pro- significantdifference was found (FI = 11.76, P = portionof the othervariants than either of the two 0.119) in the proportionsof color classeswhen all regionsto the west(X 2 = 7.21, P = 0.007), but not four regionswere compared.However, when the aslarge a proportionof whitebirds as eastern Siberia specimensfrom the three westernmost regions, which (X2 = 9.28, P = 0.002; Table 2). had no indicationof differentpatterns of colorvari- The data for Russia as a whole seem to contradict ation (FI = 5.078, P = 0.635), were combinedand Brown and Amadon's (1968:844) generalizationthat comparedwith thosefrom eastern Siberia, there was the proportionof white Gyrfalconsincreases with a statisticallysignificant difference (FI = 9.507, P increasinglatitude. In continentalRussia, the north- = 0.011). EasternSiberia had a higher proportion ernmostregions occupied by the Gyrfalconare not 86 DAVID H. ELLIS ET AL. VOL. 26, NO. 2 in easternSiberia where white forms predominate, We proposethat the primary trend in colorvari- but around the Taymyr Peninsulain westernand ation for Eurasia and probably for the Nearctic central Siberia where white forms are rare. Rather, (Neoarctic) is for the white variant to become in- the strong trend for Russia is for white forms to creasinglyprevalent proceeding eastward across the predominatein the easternmostand perhaps the two land masses. Prevalence of the white form cor- southernmostextensions of the species'range, the relatesbetter with longitudethan latitude. A similar Chukchi and Kamchatka Peninsulas. From Kam- trendis alsoreported for Rough-leggedHawks (Bu- chatka,5 of 17 specimens(29%) were white and 9 teolagopus) in the Palearctic(Dementiev and Glad- of 17 (53%) were of the three lighter variants;for kov 1951:307). the nearby CommanderIslands, 6 of 8 specimens We accountfor this light in the east and dark in were white. Unfortunately few summer specimens the west phenomenonby examiningthermal iso- are available from these areas, so little can be said clines and oceanic currents for both land masses. about frequenciesof the four variants as breeders, Cleveland (1986) showsthat the eastern areas of but Stejneger(1885) reportsthat the white, not the both regionsare colderat comparablelatitudes than gray, variant is the only knownbreeding Gyrfalcon the centralor westernregions. This coldereast and on Bering Island, largestof the CommanderIslands. warmer west pattern is probablybest explained by Both of the summer adults from Bering Island col- the presenceof northflowing, warm oceaniccurrents lected by Stejneger,and now housedat the U.S. along the westernreaches of these primary land- National Museum, are white. masses(the Alaska and Bering Currents for North Kamchatka and the Commander Islands are also America, and the Norway Current, the northeast of interestbecause they extendto and beyond55øN, extensionof the Gulf Stream, for ), and the latitude Cade (1982) proposesas the general southflowing cold currentsbathing the easternex- southernlimit of Gyrfalconbreeding. The basisfor tensions(the east and Labrador currents includingall of Kamchatkais perhapsthe statement for the Nearctic and the Anadyr and Oya currents by Dementievand Gladkov(1951) that the species for Siberia). summersnear Petropavlovsk,near the southerntip. Anotherway to look at the influenceof temper- Dementiev and Gladkov (1951), however, dispute ature is to compare mean annual temperatures Yamashina's(1931) claim that the speciesoccasion- (Cleveland 1986) at the southernmostextensions of ally breedsfurther souththan Kamchatka,on the Gyrfalcon distribution.Although Labrador and middle Kuril Islands. Kamchatka (at the easternreaches) are far southof Kamchatkais mappedwithin the breedingrange Norway and the AlaskanPeninsula (the western by all authors,even Flint et al. (1984), who state, reaches),all four areaslie in the samethermal zone however,that no eyrie has yet been found there. (-1 ø to +4 ø C mean annual temperature). More recently,Lobkov (1986) reportedthat Gyr- If, assuggested by a grossinspection of Gyrfalcon falconsbreed regularly on northernKamchatka. Ob- distribution worldwide, ocean current temperatures servationsof pairsin summerfurther southindicate areof primaryimportance in determiningGyrfalcon that Gyrfalconsmay breedon the eastcoast as far breedingand prevalenceof the white variant, then, southas 100-200 km north of Petropavlovsk.Lob- within broad limits, nestingpopulations on small kov(1986), however,provides no records for summer islands should reflect this influence even more than pairson the westernslope of Kamchatka,so perhaps populationson largeland masses.This meansthat the summerrange shouldbe adjustedeastward. island-nestingGyrfalcons should be found further The occurrenceand evenbreeding of white birds southoff the easternreaches of the two primary land on the Commander Islands at or beyond Cade's masses and further north off the western reaches. (1982) proposedsouthern breeding limit is remark- The white form should also be more common on able. Even in North America,white Gyrfalcons,al- islands than on the mainland at comparablelati- thoughmuch more prevalent in northernGreenland tudes.The presenceof only white breederson the and adjacentislands (Salomonsen 1950), are found CommanderIslands supportsthis hypothesisand with fair regularityin Ungava near the southern givescredence to Y amashina's(1931) statementthat extremity of the species'North American range Gyrfalconsoccasionally breed in the middleKuril (Palmer 1988). Islands (ca. 47øN). JUNE 1992 COLORVARIATION IN RUSSIANGYRFALCIONS 87

Further, if the oceantemperature theory as stated evolution of North American races of the , aboveis generally correct,local exceptionsto this F. colurnbarius).In recent times, these demes met rule shouldbe explicable on the basisof local ocean and to somedegree mixed. Today white and black temperatures. For example, complete absenceof birds occur in both Labrador and Greenland. We white breederson , at 65øN and only 300 km proposethat the modern day persistenceof strong from Greenland,seems to violatethe generalocean- regional trends in color prevalencein the eastern thermoclinerule. On closerinspection, however, we Nearctic is due in part to two factorsthat impede note that Iceland is bathedon all sidesby a north- panmixia.First, the LabradorSea probably acts as ward extendingtongue of the warm North Atlantic a barrierto geneflow, andsecond, the light anddark Current (Cleveland 1986) and as a result is better variantsprobably have a selectiveadvantage where suited for gray birds. Salomonsen(1950:447) re- they are mostcommon and are thereforefavored. ported that for the eastern Nearctic the prevalence In summary, extant specimensin the two muse- of white birds increaseswith decreasingtempera- ums, ZIAS and UMZM, substantiate Dementiev's ture. A detailedisland-by-island comparison of color (1951) summerdistribution map. The data for Rus- variant ratios with isotherms for air and water is sia also prompted us to re-evaluate interpretations needed,and may be possibleusing existingcollec- of environmentalcorrelates of Gyrfalcondistribution tions worldwide, but is beyond the scopeof this and color variation worldwide. It appearsthat lat- paper. We believe that such a treatment will show itude is not the bestpredictor of Gyrfalconpresence that midsummerwater and/or air temperaturesare or color. Rather, climate, as reflectedby isotherms the bestpredictors of Gyrfalcon presenceand color and as relatedto the temperatureof oceaniccurrents, prevalenceworldwide. better correlateswith Gyrfalcon breeding distribu- To betterunderstand the importanceof colorpoly- tion and the prevalenceof each color variant. Our morphism in the Gyrfalcon, data on summer and conclusion,that climate is more important than lat- winter food habits are needed. These data will be itude, is supportednot only by the presenceof a most convincingif dissimilar diets can be demon- higher proportionof white birds at the easternreach- strated for white and dark variants in their zones of es of both the Nearctic and Palearctic,but alsoby sympatry. the extreme southward extensions(south of 55øN) The ecologicalsignificance of variouscolor morphs of Gyrfalcon breeding distribution at the eastern within a populationhas been demonstratedfor per- reachesin Labrador and Kamchatka and, converse- haps only one raptor. In the Red-tailed Hawk (B. ly, northward contractionsat the westernreaches of jarnaicensis)different color morphs perch, and pre- both the Palearctic and Nearctic. sumablyforage, differently (Preston1980). Rohwer ACKNOWLEDGMENTS and Paulson(1987) alsodiscuss the advantagesof a predatorspecies having more than onemorph within We thank Dr. Vladimir V. Loskot, Curator of Orni- thology at the ZIAS, St. Petersburg, and Dr. Pavel the samepopulation. In addition,the ParasiticJae- Tomkovich, Curator of Birds at the UMZM for accessto ger (Stercorariusparasiticus) exhibits a light morph collections.Dr. Yevgeni Sokolov facilitated our work in more commonlyin the northern parts of its range St. Petersburg.Lynda Garrett and Wanda Manning, L•- and a dark morph comprising70-80% of birds in brarians at the Patuxent Wildlife Research Center, were most helpful in procuring old or obscurepublications. We the southernlimits of the species'breeding range in are grateful to the following personsfor reviewing th•s Great Britain (Berry and Davis 1970). These au- manuscript:M.R. Fuller, J. Hatfield, C.J. Henny, C S thors report somestrong color morph correlatesin Houston, D.P. Mindell, S. Wiemeyer and C.M. White timing of breedingand prey selection. Travel was funded by the U.S. Fish and Wildlife Service, The presenceof very dark birds in Labrador can the National Aeronauticsand Space Administration, and a private philanthropist. perhaps be best explained on the basis that these dark birds are descendantsof a populationadapted LITERATURE CITED to a warmer or more humid southernclimate during AGRESTI,A. 1990. Categoricaldata analysis.John Wiley a time when a deme of dark falconswas separated and Sons, New York. by Pleistoceneice from morenortherly refugia where BERRY,R.J. ANDP.E. DAVIS. 1970. Polymorphismand white and gray populationspersisted (Palmer 1988; behavior in the Arctic Skua (Stercorariusparasiticus) see Temple 1972 for a similar explanation of the Proc. Royal Soc.London B 175:255-267. 88 DAVID H. ELLIS ET AL. VOL. 26, No. 2

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