Trait-mediated effects of anthropogenic noise on bird behaviour and fitness

Birds are considered especially vulnerable to anthropogenic noise because of their reliance on acoustic information. Single-species research shows that noise can impact different aspects of bird behaviour and consequently reduce their fitness. However, we have a limited understanding of how ecological and life-history traits mediate responses to anthropogenic noise across species. We performed a meta-analysis to quantify noise impacts on bird behaviours (communication, cognition, aggression, risk, foraging and habitat use) and fitness-related responses (growth, physiology and reproduction), and how bird traits, such as nesting and habitat type, mediated those responses. Using 944 effect sizes from 160 bird species across six continents, we found that anthropogenic noise significantly affected various behaviours as well as physiology and had strong negative effects on reproductive responses. We also found that anthropogenic noise had stronger negative effects on bird reproduction for species that nest nearer to the ground, while growth and physiological responses were stronger for species that nested in open rather than cavity nests and those living in deciduous forests, respectively. Our results highlight the characteristics of those birds most vulnerable to noise pollution and inform how conservation actions can best reduce the impacts of human-made noise in those species' habitats.