eWestern Birds
The Quarterly Journal of Western Field Ornithologists
Populations of Waxwings in Idaho
Daniel M. Taylor
ABSTRACT: I explored the winter distributions of the Cedar Waxwing (Bombycilla cedrorum) and Bohemian Waxwing (B. garrulus) in Idaho by means of the results of Christmas Bird Counts from 1980 to 2016. In northern Idaho the Bohemian was significantly more abundant, but in southern Idaho its numbers declined significantly, as the frequency of large-scale irruptions dropped. Annual variability in the Bohemian Waxwing was significantly greater than that of the Cedar in both regions of Idaho. In neither species was variation in the two regions correlated. In southern Idaho numbers of the Cedar Waxwing decreased with elevation while that of the Bohemian increased. Both species were more numerous in count circles that include mountain slopes than in those consisting of valley floors only, a preference stronger in the Cedar Waxwing than in the Bohemian. A positive correlation between the Cedar Waxwing’s abundance and the size of the human population in southern Idaho suggests an effect of ornamental plants. In neither species in neither region did I find a correlation between the birds’ abundance and mean temperature in November or December. Limited data on the annual variability in the production of wild fruit in northern Idaho showed no significant correlations with waxwing numbers in that region.