Agricultural intensification affects birds' trait diversity across Europe

Agricultural intensification reduces the taxonomic diversity of bird communities, but its influence on functional diversity has been less studied. Here, we analyze the response of functional diversity of different cereal farmland bird communities across Europe to a gradient of agricultural intensification. We collected bibliographical information on life history traits (i.e. body mass, brain size, age of sexual maturity, clutch size, number of clutches, lifespan) of 30 species of birds recorded during field surveys in eight European countries. The index "brood value" was calculated to know each species' level of reproductive investment per clutch. Intensification gradients at two spatial scales were obtained from field data through PCA, related to management practices at the field scale and the variation in structure and composition of farmland at the landscape scale respectively. We calculated the functional diversity index (FD) and the community-weighted mean (CWM) for each trait and sampling area, and linear mixed models in relation to the two intensification gradients were performed. Results showed that stronger intensification at the field level favors the assembly of shorter-lived communities and bird species with smaller relative brain sizes, also decreasing overall trait diversity. It also restricts the range of strategies for parental investment, reducing the functional diversity of the brood value index. More intensive field management would favor bird communities dominated by generalist and even introduced and/or managed hunting species, while putting at risk those farmland- and grassland-adapted species, typically more associated with the provision of ecosystem services. This highlights the relevance of field management (agrochemicals use, ploughing frequency) for the functional composition of bird communities and the conservation of farmland biodiversity. These findings add to existing knowledge on how species' pace of life and cognitive capacity interact with drivers of global change, such as agricultural intensification.