Foraging niches of foliage-gleaning birds in the northernmost taiga in Finland

Abstract

The study area was located near the northern coniferous forest margin . Seven niche dimensions (habitat, tree species, tree size, feeding height in tree, tree part, foliage substrate, feeding technique) were recorded and these were combined in four multidimensional axes . The foliage-gleaning guild consisted of four species, whichcomprised 52-76% of the total bird community, depending on forest type. The Siberian Tit Paruscinctus and the Siberian Jay Perisoreus infaustus are specialists of virgin coniferous forests, whereas the Brambling Fringilla montifńngilla and the Willow Warbler Phylloscopus trochilus are forest habitat generalists . The multidimensional (seven-dimensional) foraging niches of the Siberian Tit and Siberian Jay were broader than those of the Brambling and Willow Warbler. Tree species, tree part andfoliage substrate were the mostimportant dimensions segregating the foliagegleaning species from each other . The foraging niche of the Siberian Jay deviated most from those of the other species . Body size was connected with segregation ofspecies onthe microhabitat dimensions, especially on tree part and foliage substrate, but not on macrohabitat (habitat, tree species, tree size) and foraging height dimensions. Body size differences can be considered effective with respect to the foraging of the species The broad niches of the two sedentary species, the Siberian Tit and Siberian Jay, are suggested to be adaptations to the harsh physical conditions in these northern latitudes. The migratory species, the Brambling and Willow Warbler, preferred seasonally abundant foraging resources in deciduous trees and on leaves and needles. Due to forest management, the Willow Warbler has increased in northern Finland during recent decades, whereas the Siberian Tit and Siberian Jay have decreased. These population trends are discussed in relation to the foraging niches of the species .