RELATIONS BETWEEN BODY-SIZE, ABUNDANCE AND TAXONOMY OF BIRDS WINTERING IN BRITAIN AND IRELAND

We examine the relation between body size, abundance, and taxonomy in the wintering bird assemblages in Britain and Ireland. The regression slope of abundance on body size across species in both assemblages is not significantly different from that predicted by an 'energetic equiv alence rule', but the proportion of the variance in abundance explaine d by body size is very low. Previous work on breeding bird assemblages has found the novel relation that the correlation between size and ab undance across species within a tribe is itself positively correlated with the degree of taxonomic isolation of the tribe from other tribes in the bird fauna. We show that the same relation holds within bird tr ibes in the two wintering assemblages. Furthermore, evidence for this relation is found by using two different measures of bird abundance, d espite these two abundance measures showing very different correlation s with body size across species. Although these patterns in the data a re consistent, some are not formally statistically significant (p = 0. 089 or greater). Excluding coastal, stocked, feral and recently coloni zing species increased the significance of time since origin of a trib e on species abundances. We conclude that the relation between size an d abundance in bird tribes is somehow related to bird taxonomy. While acknowledging the unlikely nature of such an effect, we tentatively pr opose hypotheses for two mechanisms that could produce the observed pa tterns.