Tree species preferences for foraging site and ways in which the preferences affect the distribution, abundance and species composition of arboreal woodland avifauna

The tree species preferences by six arboreal bird species and their role in structuring the bird communities in woodland were investigated in two sites in County Durham. Each bird species showed a preference or avoidance for most of the tree species in both study sites. The patterns of tree preference were different for each bird species, and were the basis for efficient partitioning of the foraging niches in woodland. Bird species showed significantly less overlap in tree species choice than in any of the other four niche dimensions examined, making it the most important dimension of the foraging niche. The tree species preferences of the bird species were reflected in the distribution of the birds within the woods. For each pair of bird species the degree of similarity in tree species choice and birds' distribution in the wood were identical. Bird species richness was predictable from tree species richness. There were significant positive correlations between all pairs of the following factors: bird species diversity, tree species diversity, bird species richness, tree species richness, bird density, and the percentage of broadleaved trees. Bird density was negatively correlated with the size of the wood (or compartment), apparently due to an edge effect. Seasonal and year to year changes in the tree preference by birds were explicable in terms of changes in the relative abundance of arthropod prey and other foods available in the trees.