Noise as a global change driver: a meta-analysis of its fitness consequences for birds

Anthropogenic noise is a widespread yet underappreciated global pollutant. Despite mounting evidence that noise may affect the physiology and behaviour of birds, its consequences for fitness, and thus its capacity to impact population and evolutionary processes, remain unclear. Here, we conduct a pre-registered systematic review and meta-analysis of the causal effects of anthropogenic noise on avian fitness, both at the mean and variance levels. We synthesised 535 effect sizes from 53 experimental studies (45 species) published between 1990 and 2024. Our results demonstrate that overall, avian fitness is reduced by noise exposure, with a consistent negative impact observed across various direct and indirect fitness measures. This suggests that the consequences of noise exposure are not limited to a single behavioural or physiological pathway. Effects were stronger when exposure occurred before fledging, suggesting that the early juvenile life stage is a particularly sensitive window. Notably, the magnitude of the effects depended on the ecological realism of the experimental exposure: realistic anthropogenic noise led to stronger negative effects than synthetic or acoustically unrealistic stimuli. This finding highlights the importance of reproducing the acoustic conditions that animals encounter in their natural environments when assessing the consequences of sensory pollution. In contrast, fitness effects were not consistently related to noise level or exposure duration, suggesting that the biological consequences of noise cannot be understood from noise dosage alone. By demonstrating that anthropogenic noise can reduce avian fitness independently of other environmental stressors, and suggesting that anthropogenic noise may also lead to an increase in variance in direct fitness (i.e., the opportunity for selection), our synthesis establishes noise pollution as a crucial aspect of ecological change. Consequently, anthropogenic noise should be considered alongside more conspicuous drivers of global change as a potentially important force affecting the performance, persistence, and dynamics of wildlife populations.