Using habitat-specific population trends to evaluate the consistency of the effect of species traits on bird population change

• We assess how population trends of UK birds vary among habitats.
• Population trends were especially negative in woodlands and urban settlements.
• Trends were largely driven by large-scale drivers acting across habitats.
• The magnitude of declines of humid zone migrants varied among habitats.

Many species are undergoing rapid population declines, while other species have increased. Previous work has related population change to species traits to elucidate the drivers of population change. However, this assumes that these drivers operate consistently across habitats. We use national-scale monitoring data on UK bird abundance from 1994–2012 to calculate habitat-specific population trends, allowing us to evaluate whether the effect of species traits was consistent between habitats. Although we found significant interactions with habitat for traits relating to migratory behaviour, diet, nest site and habitat specialisation, the direction of these trait effects was generally consistent between habitats. This suggests that large-scale processes operating across habitats are responsible for many changes in bird populations, although processes operating within habitats can modulate the effect of these drivers. Despite this, differences in population trends between habitats remain when variation in population trends due to species identity is accounted for, indicating that some habitat effects do occur. By identifying the scale at which drivers of population change operate, it is possible to target conservation actions more directly. Population declines were most evident in woodland and urban habitats, and we suggest that these habitats should be the focus of increased research and conservation effort if declines evident in many bird species are to be reversed.