Multi-scale settlement patterns of a migratory songbird in a European primeval forest

The drivers of animal settlement are core topics in ecology. Studies from primaeval habitats provide valuable but rare insights into natural settlement behaviour, where species are unconstrained by habitat fragmentation and modification. We examined whether territorial male songbirds (wood warblers Phylloscopus sibilatrix) exhibited clustered distributions when settling in extensive primaeval forest. We tested whether settlement patterns were consistent between years, the influence of habitat preference and the spatial extent of these processes. Remote sensing (airborne LiDAR and satellite multi-spectral) and field survey data were combined to investigate settlement at the landscape (tens of km2), plot (46–200 ha) and microhabitat (20 m diameter) scales, by sampling across 5.9 × 4.5 km of the Białowieża National Park (Poland) during 2018–2019. We assessed bird distribution patterns using nearest neighbour analyses, and habitat preference with generalized linear mixed models. Variation in bird density between plots and years was suggestive of large-scale clustering at the landscape scale. At the local plot scale, any clustering was masked by territoriality, with birds appearing dispersed or randomly distributed. At the microhabitat scale within territories, birds preferred a tall, closed canopy forest structure and avoided a dense herb layer of wild garlic patches. Settlement appeared unconstrained by the availability of preferred habitat at the plot scale, which remained unsaturated. Wood warbler settlement apparently involved hierarchical decisions at multiple spatial scales, compatible with potential social attraction, territoriality, habitat preference or predator avoidance. Selecting an appropriate scale of analysis is an important consideration when assessing the clustering of territorial species.