Seven species of Phylloscopus warblers breed in the middle taiga subzone of Central Siberia. We studied their territorial distribution over 18 breeding seasons between 1978 and 1996. 
Phylloscopus inornatus, the most abundant breeding bird species in the study area, breeds in dense clusters of territories. In some habitats, these clusters are very unstable from year to year, providing an excellent opportunity to study the influence of P. inornatus on the territorial distribution of other species. We present a method for quantifying decreases in a species’ breeding density caused by the presence of a competing congener. Analysing all possible combinations of species, we found reciprocal territorial avoidance between P. inornatus and P. proregulus as well as between P. inornatus and P. collybita. This is consistent with the hypothesis that territorial avoidance occurs between the species of greatest morphological similarity. The occurrence of territorial avoidance is not explained by habitat characteristics such as vegetation cover and productivity. However low productivity may be necessary for territorial avoidance to occur. 
An alternative explanation for the observed territorial separation of some species, derived from the Fretwell‐Lucas model of habitat occupancy, is examined and rejected. Causes and implications of clustering behaviour of P. inornatus are also discussed.

We studied ecological and evolutionary aspects of habitat choice in a group of closely related bird species to gain insight into factors influencing bird community structure. Seven species of Phylloscopus warblers breed sympatrically in the middle taiga subzone of Central Siberia. We examine how the distribution of species among habitats is related to morphology, phylogeny and competition, and we compare our results with an earlier study on the ecomorphology of Phylloscopus warblers in Kashmir. We found that in Siberia, large warbler species prefer productive habitats with mostly deciduous vegetation, whereas small species occupy poor coniferous forests. Possible explanations for this finding remain to be tested in the future. Moreover, we found a tendency for species with large feet, small bills and short wings to occupy habitats with an abundance of bush thickets near the ground. In the Kashmir study, competition was considered a major factor in structuring the Phylloscopus community, and patterns of habitat choice were not influenced by phylogenetic relationships. In strong contrast, we found that in the Siberian community, closely related species occupy similar habitats. We discuss whether this conservative evolution of habitat preferences in Siberia may be due to low intensity of interspecific competition or to other ecological factors.

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