Pesticide doses, landscape structure and their relative effects on farmland birds

Agricultural changes related to the intensification of farming practices and the simplification of landscape elements often occur simultaneously. Their respective effects on biodiversity are thus difficult to disentangle and are poorly understood. This study assessed the relative contribution of each component of agricultural intensification on taxonomic and functional bird communities. The bird communities studied were composed of 70 species, both farmland and non-farmland birds, found in 66 fields covering three main cereal departments of France. Herbicide dose was related to measurable negative effects on the Community Specialization Index (CSI). Overall, the proportion of habitat specialists, particularly of herbivorous species, decreased, and the proportion of generalists increased as pesticide doses increased. Pesticides also had a positive effect on total abundance and richness, whereas no influence of insecticide or fungicide doses could be detected. Landscape simplification was associated with a loss of bird species diversity and an increase in the CSI. Our findings suggest that the intensification of agriculture in this area, as reflected by increasing pesticide doses, modified communities by homogenizing species assemblages, whereas landscape element simplification led to the selection of only a few typical farmland birds enabled to persist in a simplified arable landscape. These results highlight the importance of combining taxonomic with functional diversity indices to fully understand changes in communities that occur in response to agricultural intensification.