Olive grove intensification negatively affects wintering bird communities in central Spain

Agricultural intensification is a persistent and growing threat to biodiversity worldwide. Olive groves cover extensive areas in the Mediterranean basin and play a fundamental role as refuge and wintering quarters for many bird species, but the effects of their current intensification on bird communities remain unclear. This study aims to evaluate the response of wintering birds to the management of olive groves with different degrees of intensification (traditional, intensive and super-intensive management) in central Spain. Based on two bird censuses conducted in 25 groves in early and late winter, we examined the influence of habitat structure and composition at different spatial scales on species richness and abundance of the entire farmland bird community, and of the diet-based functional groups. Total species richness tended to decrease with intensive olive grove management, probably due to reduced habitat heterogeneity, whereas total abundance did not, indicating the capacity of intensive and super-intensive olive groves to sustain large numbers of wintering birds. The negative effect of intensification was particularly evident in frugivore species richness, while frugivore abundance was positively (but marginally) associated with olive fruit availability. Granivorous species were positively associated with lower vegetation cover, but insectivorous species did not respond to intensification gradients. Species richness and abundance (total and by diet-based functional groups) also decreased from early to late winter, which may be due to the effect of olive harvest, but also to an extreme cold event. Overall, our findings show how olive grove intensification and the associated management practices result in significant changes in habitat structure and composition at different spatial scales, thus affecting wintering bird communities.