Vagrancy or migration: why do American teals cross the Atlantic?

Authors: Eduardo DE JUANA and Ernest F. J. GARCIA

E-mail: edejuana@bio.ucm.es

Published: Volume 57(2), December 2010. Pages 417-430.

Language: English

Keywords: Anas carolinensis, Anas discors, blue-winged teal, green-winged teal, transatlantic migration, vagrancy and wintering

Summary:

An analysis of published transatlantic records of the blue-winged teal Anas discors and the greenwinged teal Anas carolinensis provides evidence that both species are regular migrants in small numbers to Europe and Africa and that they are not merely vagrants, as hitherto believed. Their occurrence is independent of the prevalence of westerly winds arising from variation in the North Atlantic Oscillation. Unlike transatlantic vagrants, annual record totals of both teals in Europe do not vary greatly between years. There is a high percentage of spring teal records, whereas most transatlantic vagrant species appear mainly in autumn. Each year the Nearctic teal records in Europe show a slow and predictable spread from north to south reflecting their migratory calendar in the Americas, with distinct spring and autumn peaks in northern areas and more winter records further south. As in the Americas, a higher proportion of green-winged teals occur further north and blue-winged teals are relatively more numerous in the south. The apparent lengths of stay of green-winged teals are longer in more southern areas, where the birds apparently winter, than further north, where they mainly occur on passage. This study suggests that the systematic recording and analysis of observations of rarities is worthwhile in order to reveal new migration patterns.

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