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The above individuals were classed as vagrants and were recovered at various sites in eastern North America and in western Europe south to the Azores. Regular transatlantic migrants include Manx Shearwater Puffinus puffinus, Great Shearwater Puffinus gravis, Black-legged Kittiwake Rissa tridactyla, Arctic Tern Sterna paradisaea, Sooty Tern Sterna fuscata, Brent Goose Branta bernicla, Ruddy Turnstone Arenaria interpres, Red Knot Calidris canutus, Purple Sandpiper Calidris maritima, Common Ringed Plover Charadrius hiaticula, Northern Wheatear Oenanthe oenanthe, and several other species that move between Greenland and Europe.

Mainly from Dennis (1981, 1987, 1990).

The above individuals were classed as vagrants and were recovered at various sites in eastern North America and in western Europe south to the Azores. Regular transatlantic migrants include Manx Shearwater Puffinus puffinus, Great Shearwater Puffinus gravis, Black-legged Kittiwake Rissa tridactyla, Arctic Tern Sterna paradisaea, Sooty Tern Sterna fuscata, Brent Goose Branta bernicla, Ruddy Turnstone Arenaria interpres, Red Knot Calidris canutus, Purple Sandpiper Calidris maritima, Common Ringed Plover Charadrius hiaticula, Northern Wheatear Oenanthe oenanthe, and several other species that move between Greenland and Europe.

Mainly from Dennis (1981, 1987, 1990).

America, among Eurasian Wigeon Anas penelope and others on the west coast of North America, and among Ring-billed Gulls Larus delawarensis now wintering annually in small numbers in western Europe (with at least five ring recoveries, Table 10.5). However, with small or inconspicuous species in little known areas, one can seldom be certain that they have not always been there, although they may have increased in recent years. The presence of an unknown population of Swinhoe's Petrel Oceanodroma monorhis in western Europe may account for the appearance of individuals in northeast England. Several have now been caught and identified from their DNA, including one individual in four successive years, but the nearest known nesting colonies occur on the other side of the Eurasian landmass, off Korea (Pitches & Cleeves 2005).

Not all migration-related range expansions result from genetically influenced directional changes. While most birds drifted off course may either die or re-orientate and get back on course, drift may occasionally lead to the colonisation of new areas, and so have lasting biogeographical consequences. Many of the species now found on oceanic islands are likely to have descended from ancestors that were long ago blown off course by winds. Such a process led to the colonisation of the New World by Old World Cattle Egrets Bubulcus ibis (Maddock & Geering 1994), and to the establishment of many species introduced to New Zealand on various oceanic islands to the south, involving water crossings of up to 1200 km (Williams 1953). Many other birds probably reach remote areas and breed there for a time, but without establishing a lasting population, such as the Fieldfare Turdus pilaris in Greenland (Salomonsen 1951). Imagine the odds against two Spotted Sandpipers Actitis macularia from North America reaching the same Scottish locality and nesting thousands of kilometres from their normal range. Yet it happened on at least one occasion (Wilson 1976).

An increase in vagrancy is sometimes followed by colonisation. In several bird species that started to breed in Britain during the twentieth century, breeding was usually preceded by increasing populations in continental Europe and increasing numbers of vagrants to Britain (O'Connor 1986). The Little Egret Egretta garzetta provides a striking example.

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