Observations of Asiatic Migrants in the Western Aleutians
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JOURNAL OF FIELD ORNITHOLOGY Publishedby Association of Field Ornithologists VOL. 59, NO. 2 SPRING1988 P^GES101-208 j. Field Ornithol., 59(2):101-109 OBSERVATIONS OF ASIATIC MIGRANTS IN THE WESTERN ALEUTIANS MICHAEL H. TOVE 303 DunhagenPlace Cary, North Carolina27511 USA Abstract.--During the spring seasonsof 1977-1985, birders in the westernAleutians ob- servedlarge numbers of Asiaticmigrants whose occurrence was relatively predictable. These birdsregularly arrived during fair weather,sometimes in largemixed flocks, came from the southeast,and were exhaustedupon arrival. This set of observationsis consistentwith an expectedpattern of normaltransoceanic migration. Because non-passerines seemed to arrive in the early morningand passetinesin the afternoonand evening,a localizeddeparture pointis suggested.A simplemodel of migrationmechanics suggests that departurewas from the south-central Kurile Islands. OBSERVACIONES DE EMIGRANTES ASIATICOS EN LAS ALEUTIANAS DEL OESTE Resumen.--Desde el 1977-1985 observadores de aves localizados en las Aleutianas del oeste han notado durante la primavera la migraci6n de un gran ndmero de aves asifiticas.E1 patr6nde movimientoes predecible; llegan las avesde formaregular cuando las condiciones climato16gicasson buenas.Estas vienen del suroestey comoconsecuencia del viaje transø ocefinico11egan exhaustas. Dado el casode que las avesque no soncanoras parecen llegar temprano en la mafiana, mientras que los Passeriformesdurante la tarde y la noche,se sugiereen el trabajo un punto particular de partida localizadoen las Islas Kurile del sur. Since1977, birdershave visited the westernAleutians, principally Attu Island, in searchof Asiatic speciesthat occurduring springmigration. Compared to North America and western Europe, relatively little is known about east Asian migration routes, largely becauseof political difficultiesfacing researchers(McClure 1974). Thus, the body of ob- serverson Attu has providedan opportunisticdata baseby which some aspectsof east Asian migration may be understoodprovided that two assumptionsare true: (1) the Asiatic speciesrecorded are representative of the regular east Asian migration rather than "hapless"storm-blown vagrants;(2) the migratory route taken is representativeof that usedby birds which more closelytrack the Asian coast. 101 102] ,•. H. Tore J.Field Ornithol. Spring 1988 q- Vol.59, •o. 2 AsiaticMigrants.' Western Aleutians [ 103 104] M.H. Tore J.Field Ornithol. Spring 1988 AREA AND METHODS From mid-May through early June, 1977-1985, observationsof Asiatic specieswere made on Attu Island, Alaska in the western Aleutians. Observationswere limited almostexclusively to the southeasterncoast of the island. Although the number of observerson the island varied con- siderablyamong years, all the data reported (e.g., to American Birds) were compiledby Larry Balch,Dan Gibson,Ben King, or Thede Tobish, all experiencedobservers and trip leaders.The data presentedare those reportedby theseindividuals in AmericanBirds and madedirectly avail- able to me. In addition, I visitedAttu during the 1978 and 1980 seasons and have includeddata from my daily field notes.Also, I have gleaned reports from American Birds for sightingsfrom other islands in the westernAleutians during the study period. RESULTS AND DISCUSSION From mid-May through early June, 1977-1985, at least 66 Asiatic specieswere recordedin the western Aleutians, mostly Attu. Of these, 42 occurredregularly, somein moderatenumbers (Table 1) and 24 were rare to accidentalin occurence(Table 2). Most of thesespecies arrived during fair weather and occasionallyin waves. For example, from 18 to 22 May 1980, I observedseveral large flocks of Bramblings with an assortmentof other species(e.g., Rustic Bunting, Hawfinch, Oriental Greenfinch,Red-throated and Olive tree-pipits)arriving daily. The flocks includedapproximately 20-80 or more birds. The maximum daily count of 156+ Bramblings (Table 1) was based on the estimatesof a single observerand was probablyconservative. Other examplesof sizableflocks include22 Terek Sandpipersthat I saw in 1980 and at least25 Lanceo- lated Warblers reportedin 1984 (Larry Balch, pers. comm.). Over the years, migrants have arrived in distinct temporal patterns. On Attu, migrant Asiatic shorebirdsand some passerinegroups (e.g., finchesand Turdusthrushes) peak duringthe third week of May whereas small Muscicapidthrushes, flycatchers and warblerspeak duringthe first week of June (2 wks later). These data are generally comparablewith thoseof mainland populations(Dement'ev et al. 1966). Typically, birds arrived on the coastin exhaustedcondition. Over the next few days,many of them drifted "inland" and then disappeared(presumably due to de- parture). Somespecies evidently bred. For example,Eurasian Wigeon and Tufted Ducks were commonand usually occurredin pairs and in 1980, a pair of Bramblingswere behavingas if on territory. During the 1980 season,I foundthat mostpasserines seemed to arrive on Attu in the afternoonand evening(Table 3). For example,about 2000 on 26 May alongthe coastat Murder Point, Dan Gibson found an Eye- browed Thrush that had recentlyarrived. In the late evening(ca. 2100) of 29 May also at Murder Point, Ben King found a Gray Bunting that was exhaustedand behavedas if it had just arrived. On 31 May about 1700, I observedan Olive Tree-Pipit fly in from the SSE and land Vol.59, No. 2 AsiaticMigrants.' Western Aleutians [ 105 TABLE2. Occurrenceof Asiatic speciesrecorded in only one spring seasonfrom 1977 to 1985 in the western Aleutian Islands (including Attu Island). Number of Species Year individuals Spot-billedDuck (Anaspoecilorhyncha) 1985 1 Steller's Sea-Eagle (Haliaeetuspelagicus) 1980 1 Eurasian Kestrel (Falco tinnunculus) 1984 1 Northern Hobby (Falcosubbuteo) 1983 1 Oriental Pratincole ( Glareolamaldivarus) 1985 1 Common Ringed Plover (Charadriushiaticula) 1982 1 Black-winged Stilt (Himantopushimantopus) 1983 1 Little Stint (Calidris minuta) 1983 1 Sharp-tailed Sandpiper ( Calidrisacuminata) 1980 Curlew Sandpiper(Calidrisferruginea) 1982 2 Jack Snipe (Lymnocryptesminimus) 1981 1 Pin-tailed Snipe (Gallinagostenura) 1984 1 Black-tailed Gull (Larus crassirostris) 1980 1 Common Cuckoo (Cuculuscanorus) 1982 1 Lanceolated Warbler (Locustellalanceolata) 1984 25+ Mugimaki Flycatcher(Ficedula mugimaki) 1985 1 Brown Flycatcher(Muscicapa latirostris) 1985 1 Red-flanked Bluetail ( Tarsigercyanurus) 1982 1-2 Siberian Blue Robin (Lusciniacyane) 1985 1 Brown Shrike (Lanius cristatus) 1984 1 Gray Bunting (Emberizavariabilis) 1980 1 Pallas' Reed-Bunting (Emberizapallad) 1980 1 Common Reed-Bunting(Emberiza schoeniclus) 1977 a 1 Eurasian Bullfinch (Pyrrhulapyrrhula) 1978 1 a Six observerscompared to approximately50 in all other years. exhaustedon the rockyshore. About two hourslater, a EurasianSkylark arrived. Conversely,non-passerines appeared to arrive late at night or early in the morningbecause they were not oftenseen arriving but were typicallyfound during the first "sortie" of searchesin the morning (ca. 0800-000). I developeda simple model to predict potential departure points as- sumingan averagedeparture time of one hour after dark (Gauthreaux 1971), and rangeof flight speedsof 62-66 km/h for non-passerinesand 40-44 km/h for passetines(Lee 1963, Pettingill 1970, Williams et al. 1978). Great circle distancesfor each of nine possibledeparture points were calculated(Fig. 1, Table 4). For eachof thesepoints, arrival times on Attu were calculated assumingthat the migrants flew the shortest possibleroute (Table 4). Clearly, variablessuch as wind velocityand direction, and deviationsfrom the "ideal" route would affect actual arrival times. Basedon the assumptionof morning arrival (e.g., 0100-0900) of non-passerinesand afternoon-eveningarrival (e.g., 1400-2200) of pas- setines,the modelpredicts that migrantsreaching Attu embarkedon their trans-Pacificflight from the southernKurile Islands (Fig. 1, Locations C-E). 106] M.H. Tm,e J.Field Ornithol. Spring 1988 Vol.59, No. 2 AsiaticMigrants: Western Aleutians [ 107 T^BLE4. Predictedschedules for Asiaticmigrants arriving on Attu Island, Alaska from nine possibledeparture points (see Fig. 1). Non-passerines Passerines Flight Average Average Location distanceto flight Estimatedtime flight Estimatedtime on Fig. 1 Attu (km) time (h) of arrival (h) time (h) of arrival (h) A 2618 41 1527-1757 62 1115-1715 B 2279 37 1030-1348 54 0348-0900 C 1988 31 0606-0806 47 2112-0142 D 1811 28 0339-0527 43 1727-2133 E 1651 26 0115-0251 39 1345-1733 F 1514 24 2324-0054 36 1054-1424 G 1458 23 2236-2400 35 0936-1300 H 1203 19 1857-1909 29 0403-0654 I 747 12 1233-1355 18 1815-1957 The departurepoints predicted by the modelare supportedby a variety of empirical evidence.First, the predictedoverseas flight distanceof less than 2000 km is energeticallyfeasible. Williams et al. (1978) have shown that westernAtlantic fall migrantscan successfullycomplete a 3500 km journey. Second,of the 42 speciesthat occurredtwo or morespring seasons (Table 1), only three (Garganey,Common Pochard and White-throated Needletail) apparently do not breed at or north of the latitude of the Aleutians (Flint et al. 1984). This observationis more consistentwith an hypothesisof regular migrationrather than extremevagrancy. Alerstam and Pettersson(1977) have noted that as a migrant nears its breeding grounds,its tolerancefor coursedeflections and diversionsdecreases. The geographyof easternAsia (Fig. 1) is suchthat the further north a migrant departs from land, the greater the angle of deflection(away