Evidence that multiple anthropogenic stressors cumulatively affect foraging and vigilance in an urban-living bird

Climate change and anthropogenic noise are two of the most widespread human-induced stressors affecting wildlife populations globally. However, the effects of these stressors are rarely investigated together, despite the fact that they often co-occur, particularly in urbanized areas and can have a multitude of adverse effects on species. Here, we compared the effects of heat stress and anthropogenic noise, both when presented alone and together, on the behaviour of wild Western Australian magpies, Gymnorhina tibicen dorsalis. Birds were presented with a playback of background noise and a playback of anthropogenic (plane) noise under both heat stress and nonheat stress conditions. Consistent with previous studies, we found both heat stress and anthropogenic noise reduced foraging and increased vigilance behaviours of magpies. Importantly, exposure to these two stressors simultaneously led to a greater change in behaviour, revealing that the simultaneous occurrence of two anthropogenic stressors had a more marked effect on behaviour compared to either stressor alone. This study provides some of the first evidence of the additive impact of heat stress and anthropogenic noise on the behaviour of a wild urban-dwelling bird species. Such findings highlight the importance of considering multiple stressors when looking at the effects of human-induced rapid environmental change on animals, since anthropogenic stressors rarely occur in isolation.