Functional traits explain responses of Appalachian birds to vertical and horizontal forest structure.

Species interact with habitat based on their functional traits, but it is unclear how specific traits interact with the multiple components of habitat structure. To address this knowledge gap for forest-dwelling bird communities, we leveraged forest structure information from NASA's Global Ecosystems Dynamics Investigation (GEDI) spaceborne light detection and ranging (LiDAR) mission alongside broad-scale observations of bird occurrence from eBird. Using a custom implementation of the hierarchical modelling of species community (HMSC) approach, we estimated relationships between functional traits and the responses of bird populations to vertical and horizontal forest structure. Although variable importance indicated that climate and elevation explained the most variation in bird occurrence, we discovered two strong signals of trait interactions with species' responses to forest structure: specialized foraging strategies explained birds' responses to vertical structure, while larger bodied birds with high flight efficiency showed weaker responses to both vertical and horizontal structure. Other functional traits such as diet and nest height were also associated with responses to vertical and horizontal structure, but with greater uncertainty. Our results demonstrate the explanatory power of functional traits in describing birds' interactions with habitat and suggest that functional traits may play a role in structuring species' responses to forest structure. The use of broad-scale forest structure and bird occurrence data clarifies the impact of behaviour and morphology on habitat use, better quantifying the relationships between birds and their environment.