Trans-Hemispheric Movements of Holarctic Anatidae: The Eurasian Wigeon (Anas penelope L.) in North America

There are many records of Palearctic breeding waterfowl wintering in the Nearctic, and vice-versa. This trans-hemispheric exchange has apparently increased in the past two or three decades. The most frequent Palearctic water- fowl species visiting the Nearctic is the Eurasian wigeon (Anas penelope L.). Records of this species in North America are examined for the period 1947-81. There has been a spectacular increase in wigeon records since 1966 in western North America. The Pacific flyway, used as a wintering area by Siberian breeding birds, now accounts for 90% of Christmas Bird Count records in American Birds. Atlantic flyway records, provided mainly by Icelandic breeding birds, have re- mained static or marginally declined. Analysis suggests that these changes are largely independent of variations in observer effort and recording locations. Other waterfowl show similar patterns. The evidence is strong that wigeon, along with other members of the Anatidae, are exhibiting a recent upward trend in the long-established interchange between the Nearctic and Palearctic. The causes of this trend are uncertain.