Divergence in foraging behavior of foliage-gleaning birds of Canadian and Russian boreal forests

We compared foraging behavior of foliage-gleaning birds of the boreal fores t of two Palaearctic (central Siberia and European Russia) and two Nearctic (Mackenzie and Ontario, Canada) sites. Using discriminant function analysi s on paired sites we were able to distinguish foliage-gleaning species from the Nearctic and Palaearctic with few misclassifications. The two variable s that most consistently distinguished species of the two avifaunas were th e percentage use of conifer foliage and the percentage use of all foliage. Nearctic foliage-gleaner assemblages had more species that foraged predomin antly from coniferous foliage and displayed a greater tendency to forage fr om foliage, both coniferous and broad-leafed, rather than twigs, branches, or other substrates. The greater specialization on foliage and, in particul ar, conifer foliage by New World canopy foliage insectivores is consistent with previously proposed hypotheses regarding the role of Pleistocene veget ation history on ecological generalization of Eurasian species. Boreal fore st, composed primarily of spruce and pine, was widespread in eastern North America, whereas pockets of forest were scattered in Eurasia (mostly the mo untains of southern Europe and Asia). This may have affected the population s of birds directly or indirectly through reduction in the diversity and ab undance of defoliating outbreak insects. Loss of habitat and resources may have selected against ecological specialization on these habitats and resou rces.