Table 104 The main seasons and proposed means of occurrence of some vagrants in western North America

Spring overshoots from Eurasia to the North Pacific islands (Aleutians, Pribilofs and St Lawrence Islan)

Spring overshoots to Point Barrow (northern Alaskan coast)

Possible autumn mirror-image migrants from Eurasia to western North America

Possible autumn mirror-image migrants from eastern to western North America

Possible autumn long-distance reverse migrants from Eurasia to North Pacific Islands

Garganey Anas querquedula, Common Pochard Aythya ferina, Common Scops Owl Otus scops, Oriental Cuckoo Cuculus saturatus, Common Cuckoo Cuculus canorus, Fork-tailed Swift Apus pacificus, Brown Shrike Lanius cristatus, Eurasian Bullfinch Pyrrhula pyrrhula, Arctic Warbler Phylloscopus borealis

From Eurasia: Wood Sandpiper Tringa glareola, Grey-tailed Tattler Tringa brevipes, Little Stint Calidris minuta, Curlew Sandpiper Calidris ferruginea, Fieldfare Turdus pilaris, Dusky Thrush Turdus naumanni, Eyebrowed Thrush Turdus obscurus, Arctic Warbler Phylloscopus borealis, White Wagtail Motacilla alba, Pallas's Reed Bunting Emberiza pallasi;

From North America: Wilson's Phalarope Phalaropus tricolor, Scarlet Tanager Piranga olivacea, Eastern Kingbird Tyrannus tyrannus, Bobolink Dolichonyx oryzivorus

Tufted Duck Aythya fuligula, Eurasian Wigeon Anas penelope, Baikal Teal A. formosa, Slaty-backed Gull Larus schistosagus, Dotterel Charadrius morinellus, Spotted Redshank Tringa erythropus, Eurasian Jacksnipe Lymnocryptes minimus, Curlew Sandpiper Calidris ferruginea, Ruff Philomachus pugnax, Northern Wheatear Oenanthe oenanthe, Red-throated Pipit Anthus cervinus, Dusky Warbler Phyllscopus fuscatus, White Wagtail Motacilla alba lugens (breeds Japan-Kamchatka), Olive-backed Pipit Anthus hodgsoni, Brambling Fringilla montifringilla, Rustic Bunting Emberiza rustica

Brown Thrasher Toxostoma rufum, Dickcissel Spiza americana, Blackpoll Warbler Dendroica striata and 28 other species of eastern warblers

Wood Warbler Phylloscopus sibilatrix to Shemya (Aleutian Islands)

Mainly from Robertson (1980).

much further south, including Alpine Swift Apus melba, Woodchat Shrike Lanius senator, Eurasian Hoopoe Upupa epops, Rock Thrush Monticola saxatilis and others (Table 10.2).

Much longer overshoots occasionally occur, as shown by the appearance in spring of Cave Swallows Hirundo fulva from normal Caribbean breeding areas north as far as Nova Scotia (McLaren 1981), and the appearance of various Eurasian and North American species at Point Barrow on the northern coast of Alaska, hundreds of kilometres beyond their normal breeding range (Table 10.4). Such occurrences in birds migrating mainly overland have usually been dismissed as 'judgement errors' induced by unusually strong winds. Alternatively, while migrating in the proper direction, they may simply fail to 'switch off' their migration drive at the appropriate time, and continue travelling.

Whenever overshoot birds are closely examined, they are almost always found to be in their first year of life, and are usually males. Spring overshoots also often occur relatively early in the year, arriving in their overshoot areas at about the time they would have been expected in their normal breeding areas, another indication that they were normal spring migrants that travelled too far.

The appearance of occasional individuals well beyond their usual winter range is also frequent, as may been seen from the records of normally more northerly wintering birds in southern Europe or the southern States of America. Northern rarities in California include Snowy Owl Nyctea scandiaca, Common Redpoll Carduelis flammea and Snow Bunting Plectrophenax nivalis among landbirds, and Ivory Gull Pagophila eburnea, Ross Gull Rhodostethia rosea and Thick-billed Murre (Brunnich's Guillemot) Uria lomvia among seabirds.

The likelihood of a species occurring in a particular area as an overshoot depends primarily on the orientation of its migration route. For example, if a Woodchat Shrike Lanius senator heading from West Africa to Spain overshoots its breeding area, and continues on its normal heading, it is likely to end up in the British Isles. On the other hand, a Masked Shrike Lanius nubicus heading from East Africa towards eastern Europe is more likely to end up in Scandinavia, where indeed there have been several spring records.

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