Distribution and population fluctuations of wintering Snowy Owls (Nyctea scandiaca) in North America

Abstract

Christmas Bird Count data from 1952 to 1981 were used to examine the geographic distribution and population fluctuations of wintering Snowy Owls (Nyctea scandiaca) in North America south of the breeding range. Wintering owls were most abundant and regular in occurrence in the northern Great Plains and Midwest regions of North America. To the south of these locales, and on both east and west coasts, owl abundance averaged 10–100 times lower and varied dramatically from year to year. Numbers of Snowy Owls fluctuated synchronously within the east coast area, the west coast area, and possibly the Great Plains, but fluctuations were not synchronous among these three areas. Time-series analyses did not support the hypothesis of cyclic winter invasions. Earlier studies from eastern North America included only a small portion of the continental population of Snowy Owls and, consequently, their conclusions may have been biased. Our findings strongly suggest that Snowy Owls may not be cyclic invaders, but rather are regular migrants over much of their winter range.