The Snowy Owl winters in open fields throughout Canada and the northern United States, where it is monitored by the Christmas Bird Count (CBC). The majority of the population breeds in Canada, so the North American results from the CBC likely represent the Canadian population. The species' reproductive success is linked to the abundance of small mammals on the breeding grounds, and winter distributions are also affected by regional variation in the abundance of their small mammal prey (Parmelee 1992, Cheveau et al. 2004). As a result, CBC counts of Snowy Owls in winter fluctuate, with irruptive years spaced at 3 to 5 year intervals. Still, CBC results for North America suggest a 60% decrease in abundance of wintering Snowy Owls since about 1970, though the reliability of this assessment is considered medium due to the CBC's semi-standardized methods and incomplete coverage of the species' wintering population. The Snowy Owl is below the lowest acceptable level relative to its national population goal (see North America graph below).
Additional information on: Christmas Bird Count (CBC)
