Effects of anthropogenic disturbances on bird functional diversity: A global meta-analysis

•We provide the first global meta-analysis of bird functional diversity and human disturbances.•Bird functional diversity responded negatively to disturbances.•Isolation, logging and urbanization had negative effects on functional diversity.•Disturbances could jeopardize birds’ functions, possibly threatening ecosystem resilience. Anthropogenic disturbances represent the main threat to biodiversity around the globe, yet effects are not restricted to species loss. Assessing the functional diversity, which measures the range and value of ecological traits of organisms, can provide a more direct link between biodiversity and ecosystem functioning. Therefore, as species’ responses to disturbances depend on their ecological traits, ecosystem functions are likely to be also imperiled by human perturbations. Although the literature on the effects of disturbances on functional diversity has been increasing, results are highly varied. Here, we provided the first comprehensive global meta-analysis on the effects of human disturbances on functional diversity of birds. We also performed subgroup analyses by region, habitat specialization, functional trait, functional diversity index and disturbance type. Our results indicate a consistent negative effect of disturbances on bird functional diversity, regardless of the variability caused by the different predictor variables considered. Specifically, we revealed that studies that were conducted in the tropics, focused on feeding traits and calculated functional diversity and richness indices presented negative responses to disturbances. Additionally, the functional diversity of birds, regardless of habitat specialization, was also negatively affected by anthropogenic disturbances. Lastly, habitat isolation, logging and urbanization exhibited a consistent negative effect on the functional diversity of birds, whereas agriculture, habitat loss and multiple disturbances had no detectable influence. These results indicate that anthropogenic disturbances can be detrimental to birds, possibly jeopardizing their ecological functions and threatening ecosystem resilience. We therefore suggest that conservation efforts should particularly focus on reducing or mitigating the effects of these three disturbances to at least diminish their effects on avian functional diversity. Additionally, we highlight the need for novel studies to simultaneously investigate the direct relationship between disturbance, functional diversity and especia