Population Ecology of Snowy Owls during Winter on the Great Plains of North America

Abstract

We used data from Christmas Bird Counts (1961-1984) and road counts (1983-1985) to study the winter population ecology of Snowy Owls (Nyctea scandiaca) on the Great Plains of North America. Numbers of owls wintering between 45°N and 53°N increased with latitude. Owl abundance fluctuated from year to year, but fluctuations were not synchronous among count localities across the Great Plains. Owls first appeared on our study sites in southwestern Alberta in early November and individuals continued to arrive until late December or early January. Spring departure occurred during late February and early March, with a few owls remaining until late March. During midwinter, the mean number of owls censused on four study sites ranged from 1.3 to 5.8 owls/100 km in 1983-1984 and from 1.7 to 10.2 owls/100 km in 1984-1985. Although all age-sex classes were represented on the Alberta study areas in both winters, adult birds predominated. Both the Christmas Bird Count data and our fieldwork indicate that owl dispersion is patchy, and that the abundance of owls within patches may vary markedly from year to year. We recommend that future studies of winter raptor populations select multiple study sites to permit detection of patterns that occur over areas larger than a single study site.