During the spring seasons of 1977-1985, birders in the western Aleutians observed large numbers of Asiatic migrants whose occurrence was relatively predictable. These birds regularly arrived during fair weather, sometimes in large mixed flocks, came from the southeast, and were exhausted upon arrival. This set of observations is consistent with an expected pattern of normal transoceanic migration. Because non-passerines seemed to arrive in the early morning and passerines in the afternoon and evening, a localized departure point is suggested. A simple model of migration mechanics suggests that departure was from the south-central Kurile Islands.

303 Dunhagen Place Cary, North Carolina 27511 USA 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 patr6n de movimiento es predecible; llegan las aves de forma regular cuando las condiciones climato16gicas son buenas. Estas vienen del suroeste y como consecuencia del viaje transų ocefinico 11egan exhaustas. Dado el caso de que las aves que no son canoras parecen llegar temprano en la mafiana, mientras que los Passeriformes durante la tarde y la noche, se sugiere en el trabajo un punto particular de partida localizado en las Islas Kurile del sur. Since 1977, birders have visited the western Aleutians, principally Attu Island, in search of Asiatic species that occur during spring migration. Compared to North America and western Europe, relatively little is known about east Asian migration routes, largely because of political difficulties facing researchers (McClure 1974). Thus, the body of ob- servers on Attu has provided an opportunistic data base by which some aspects of east Asian migration may be understood provided that two assumptions are true: (1) the Asiatic species recorded are representative of the regular east Asian migration rather than "hapless" storm-blown vagrants; (2) the migratory route taken is representative of that used by birds which more closely track the Asian coast. 102] ,. H. Tore J. Field Ornithol. Spring 1988 q- Vol. 59, No. 2 Asiatic Migrants.' Western Aleutians [ 103 AREA AND METHODS From mid-May through early June, 1977-1985, observations of Asiatic species were made on Attu Island, Alaska in the western Aleutians. Observations were limited almost exclusively to the southeastern coast of the island. Although the number of observers on the island varied con- siderably among years, all the data reported (e.g., to American Birds) were compiled by Larry Balch, Dan Gibson, Ben King, or Thede Tobish, all experienced observers and trip leaders. The data presented are those reported by these individuals in American Birds and made directly avail- able to me. In addition, I visited Attu during the 1978 and 1980 seasons and have included data from my daily field notes. Also, I have gleaned reports from American Birds for sightings from other islands in the western Aleutians during the study period. RESULTS AND DISCUSSION From mid-May through early June, 1977-1985, at least 66 Asiatic species were recorded in the western Aleutians, mostly Attu. Of these, 42 occurred regularly, some in moderate numbers (Table 1) and 24 were rare to accidental in occurence (Table 2). Most of these species arrived during fair weather and occasionally in waves. For example, from 18 to 22 May 1980, I observed several large flocks of Bramblings with an assortment of other species (e.g., Rustic Bunting, Hawfinch, Oriental Greenfinch, Red-throated and Olive tree-pipits) arriving daily. The flocks included approximately 20-80 or more birds. The maximum daily count of 156+ Bramblings (Table 1) was based on the estimates of a single observer and was probably conservative. Other examples of sizable flocks include 22 Terek Sandpipers that I saw in 1980 and at least 25 Lanceo- lated Warblers reported in 1984 (Larry Balch, pers. comm.). Over the years, migrants have arrived in distinct temporal patterns. On Attu, migrant Asiatic shorebirds and some passerine groups (e.g., finches and Turdus thrushes) peak during the third week of May whereas small Muscicapid thrushes, flycatchers and warblers peak during the first week of June (2 wks later). These data are generally comparable with those of mainland populations (Dement'ev et al. 1966). Typically, birds arrived on the coast in exhausted condition. Over the next few days, many of them drifted "inland" and then disappeared (presumably due to de- parture). Some species evidently bred. For example, Eurasian Wigeon and Tufted Ducks were common and usually occurred in pairs and in 1980, a pair of Bramblings were behaving as if on territory. During the 1980 season, I found that most passerines seemed to arrive on Attu in the afternoon and evening (Table 3). For example, about 2000 on 26 May along the coast at Murder Point, Dan Gibson found an Eye- browed Thrush that had recently arrived. In the late evening (ca. 2100) of 29 May also at Murder Point, Ben King found a Gray Bunting that was exhausted and behaved as if it had just arrived. On 31 May about 1700, I observed an Olive Tree-Pipit fly in from the SSE and land TABLE 2. Occurrence of Asiatic species recorded in only one spring season from 1977 to 1985 in the western Aleutian Islands (including Attu Island). Number of Species Year individuals Spot-billed Duck (Anas poecilorhyncha) Steller's Sea-Eagle (Haliaeetus pelagicus) Eurasian Kestrel (Falco tinnunculus) Northern Hobby (Falco subbuteo) Oriental Pratincole ( Glareola maldivarus) Common Ringed Plover (Charadrius hiaticula) Black-winged Stilt (Himantopus himantopus) Little Stint (Calidris minuta) Sharp-tailed Sandpiper ( Calidris acuminata) Curlew Sandpiper (Calidrisferruginea) Jack Snipe (Lymnocryptes minimus) Pin-tailed Snipe (Gallinago stenura) Black-tailed Gull (Larus crassirostris) Common Cuckoo (Cuculus canorus) Lanceolated Warbler (Locustella lanceolata) Mugimaki Flycatcher (Ficedula mugimaki) Brown Flycatcher (Muscicapa latirostris) Red-flanked Bluetail ( Tarsiger cyanurus) Siberian Blue Robin (Luscinia cyane) Brown Shrike (Lanius cristatus) Gray Bunting (Emberiza variabilis) Pallas' Reed-Bunting (Emberiza pallad) Common Reed-Bunting (Emberiza schoeniclus) Eurasian Bullfinch (Pyrrhula pyrrhula) 1985 1 1980 1 1984 1 1983 1 1985 1 1982 1 1983 1 1983 1 1980 1982 2 1981 1 1984 1 1980 1 1982 1 1984 25+ 1985 1 1985 1 1982 1-2 1985 1 1984 1 1980 1 1980 1 1977 a 1 1978 1 a Six observers compared to approximately 50 in all other years. exhausted on the rocky shore. About two hours later, a Eurasian Skylark arrived. Conversely, non-passerines appeared to arrive late at night or early in the morning because they were not often seen arriving but were typically found during the first "sortie" of searches in the morning (ca. 0800-000). I developed a simple model to predict potential departure points as- suming an average departure time of one hour after dark (Gauthreaux 1971), and range of flight speeds of 62-66 km/h for non-passerines and 40-44 km/h for passetines (Lee 1963, Pettingill 1970, Williams et al. 1978). Great circle distances for each of nine possible departure points were calculated (Fig. 1, Table 4). For each of these points, arrival times on Attu were calculated assuming that the migrants flew the shortest possible route (Table 4). Clearly, variables such as wind velocity and direction, and deviations from the "ideal" route would affect actual arrival times. Based on the assumption of morning arrival (e.g., 0100-0900) of non-passerines and afternoon-evening arrival (e.g., 1400-2200) of pas- setines, the model predicts that migrants reaching Attu embarked on their trans-Pacific flight from the southern Kurile Islands (Fig. 1, Locations C-E). 106] M.H. Tm,e J. Field Ornithol. Spring 1988 T^BLE 4. Predicted schedules for Asiatic migrants arriving on Attu Island, Alaska from nine possible departure points (see Fig. 1). Non-passerines Passerines Flight Average Average Location distance to flight Estimated time flight Estimated time 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 departure points predicted by the model are supported by a variety of empirical evidence. First, the predicted overseas flight distance of less than 2000 km is energetically feasible. Williams et al. (1978) have shown that western Atlantic fall migrants can successfully complete a 3500 km journey. Second, of the 42 species that occurred two or more spring 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 observation is more consistent with an hypothesis of regular migration rather than extreme vagrancy. Alerstam and Pettersson (1977) have noted that as a migrant nears its breeding grounds, its tolerance for course deflections and diversions decreases. The geography of eastern Asia (Fig. 1) is such that the further north a migrant departs from land, the greater the angle of deflection (away from the "ideal" flight path) to reach Attu. Conversely, the greater the distance to the breeding grounds, the less the angle of deflection to reach Attu and the more tolerant a bird would be of such deviations. Although significant east-west deflections in migration routes do occur (Gauthreaux, pets. comm.), this is an unlikely explanation for the majority of migrants seen on Attu. Aside from the large number and predictability of migrants, birds reaching Attu from Kamchatka would landfall on the west side of a mountainous island 67 km long. With observations concentrated in the southeast corner, this hypothesis would not explain exhausted birds ar- riving from the southeast. In summary, the Asiatic species that occur on the western Aleutians represent a portion of the regular spring migration along the eastern coast of Asia. Many of the birds observed arrive after an overseas flight of 1600-2000 km from the south-central Kurile Islands. Presumably, after an appropriate rest, some of these birds complete the migration to their 60 ų N BERING SEA ATTU SEA OF 'd"' ß , ? OKHOTSK STUDY SITE 50 ų N PACIFIC OCEAN 150 ų E 160 ų E 170 ų E FIGURE 1. Northwestern Pacific Ocean indicating locations of the study site on Attu Island, Alaska and nine possible departure points for migrants reaching Attu: A--Shiriya Point, Honshu, Japan; B--Nemuro, Hokkaido, Japan; C--Iturup Island, USSR; D-- Urup Island, USSR; E--Simushir Island, USSR; F--Rasshua Island, USSR; G-- Kharimkoton Island, USSR; H--Baykovo Island, USSR; I--Kronotskiy Peninsula, Kamchatka, USSR. breeding grounds in Asia. Others apparently find the Aleutians suitable for breeding and conclude their migration there. ACKNOWLEDGMENTS I extend my appreciation to the United States Coast Guard which maintains Attu Island and generously allows birders to venture there annually. I also thank Larry Balch for making Attu accessible to the general birding populace, without whom these data would not exist. I also thank Dr. James A. Gessaman for his assistance in preparation of the manuscript. LITERATURE CITED ALERSTAM, T., AND S.-G. PETTERSSON. 1977. 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