An analysis of character variation in red-eyed and Philadelphia vireos (Aves: Vireonidae) in Canada

Abstract

Red-eyed and Philadelphia vireos are broadly sympatric and occasionally syntopic across Canada. Collections were made at seven localities in a transect from central Alberta to central Quebec and measurements taken on six morphological characters. Analysis of variance located significant differences among locality samples for bill length, bill depth, and tarsus length in the red-eyed vireo, and for bill depth, wing length, tail length, and tarsus length in the Philadelphia vireo. A posteriori analysis of variance determined subsets of localities that did not differ significantly, and demonstrated discordant variation in most characters. In red-eyed vireos a positive regression of bill length and width on mean and minimum temperatures of collecting localities suggested variation in accordance with Allen's rule. In the Philadelphia vireo regression analyses showed an increase in tarsus length with a decrease in temperature and precipitation, the temperature effect being the opposite of variation predicted by Allen's rule. Multivariate analysis of variance further demonstrated significant phenetic differences among samples of both species. Projection of locality means and confidence regions onto first and second canonical axes showed that for the red-eyed vireo, with the exception of one sample, localities in proximity geographically tend to be in proximity in the character space. This was not true for the Philadelphia vireo in which selection for variation in the characters may be predominantly off the breeding grounds.