The drivers of avian abundance: patterns in the relative importance of climate and land use

Aim Climate and land use can have important effects on the local abundances of species, but few studies have investigated the relative impacts of these factors. Here, we quantify the relative importance of climate, land use and surrounding population size in determining the abundances of birds across a continent. Location Europe. Methods We used species abundance models to identify the relative importance of different environmental predictors for estimating the local abundances of 342 species of European breeding birds. Models controlling for phylogeny were used to relate species life history and ecological traits to the climate:land use importance ratio. The mean of this ratio, across all species occurring in a given area, was mapped to explore spatial variation in the major drivers of abundance. Results At the scale examined, climate is generally more important than land use in determining species abundances. However, the abundance of species in neighbouring areas is also a major correlate. Among climate variables, temperature is of greater importance than moisture availability in determining abundances. The relative importance of these variables varies with latitude, with temperature being most important in the north, and moisture availability in the south. Differences in the importance of specific drivers are related to species ecological traits: climate is more important for determining the abundance of species that have larger global ranges or a smaller body mass. Main conclusions Abundances of species occurring in northern Europe, an area predicted to experience climatic changes of high magnitude, are most sensitive to climate, particularly temperature. Given the greater confidence in future projections of temperature than precipitation, this increases confidence in projections of the impacts of climate change on species in the north, whilst attempts to predict future populations in central and southern Europe may be dependent on less predictable changes in land use and precipitation.