Distribution-Abundance Relationships of Some Arizona Landbirds: A Matter of Scale?

Distribution and local abundance of 62 landbird species were measured in winter across an elevational gradient in the Huachuca Mountains of southeastern Arizona. The number of 35—m radius plots and the number of habitats occupied by the species were positively correlated with their average abundances within occupied plots and habitats. Common species were no more conspicuous than rare ones, as measured by detectability on variable distance point counts. The same species that were most abundant locally also were most abundant on Christmas bird counts across Arizona and throughout the western United States. The positive correlation between distribution and abundance of winter landbirds appear to be neither an artifact of conspicuousness, nor a consequence of the geographic scale of comparison. Rather, it seems to be an intrinsic property of the species themselves, and one that has important ecological and evolutionary implications. An individualistic approach to avian ecology is indicated, emphasizing comparisons of rare and common species.