Bird Utilisation of Vertical Space in Urban Environments

In an increasingly urbanised world, it is important to understand how species interact with human-modified landscapes across all spatial dimensions. Urban areas, modified for higher density living, are characterised by buildings, airborne vehicles, and other uses of the airspace. These obstructions can alter the available vertical habitat space and hence impact species that rely on the vertical partitioning of resources. Nonetheless, studies in urban areas typically use 2D variables, which are unsuitable as proxies for 3D processes. To address this gap, bird surveys were conducted across three different types of urban environments that reflect a gradient of extensive to intensive within Brisbane, Australia. Bird activity was recorded across a range of heights. While exceptions occurred, we found that urban birds generally interacted with their environment at heights that reflected the taller structures along the urban gradient. Grouping species by urban tolerance (i.e., whether an urban avoider, adapter, or exploiter) and foraging level helped explain why some species could utilise certain height profiles across the urban structural gradient where others could not. A better understanding of how birds use urban vertical spaces can help identify habitat features that facilitate urban biodiversity and support conservation management in urban environments.