Spatial niche segregation between bird species in the Białowieża primeval forest (NE Poland)

Abstract

Drivers of bird niche separation in temperate primeval forests have not yet been determined, due to the low number of intact forest sites. Here, we analyzed the general patterns of niche usage on trees by birds’ assemblages. We tested how tree species affect the sharing of space in an assemblage of birds and their level of specialization. We conducted our study in the Białowieża primeval forest (NE Poland). During two breeding seasons, we observed bird positions on trees, divided into three vertical and six horizontal zones in 768 observation points. Based on the interaction networks framework we calculated the Kullback-Leibler distance d′ as a metric of species specialization and the resource range RR index, which estimates the species’ specificity based on the fraction of space utilized with a non-zero performance. The d′ index was the highest in the lower understory for all parts of the tree on the basis of the position from the trunk. The RR index was the highest in the lower understory for all parts based on the position from the trunk. Regarding the tree species, the lowest d′ index was observed in all tree species together, and hornbeam, whereas the highest in oak. At the tree species level, the RR index was the lowest for hornbeam. We show tree species importance in forest space sharing in the case of bird assemblages. Hornbeam, alder, and spruce are universal species that were used by birds almost entirely. In contrast, oak, lime, and maple were only partially used. Tree species with less complex structures could shape bird assemblages, as they could offer birds much fewer niches to realize. Therefore, we showed that high specialization and niche separation are drivers of high bird diversity. Consequently maintaining a diverse stand structure is crucial for biodiversity conservation.

Keywords

• Tree use
• Niche partitioning
• Foraging guild
• Specialization
• Habitat filtering
• Foundation species