Nocturnal resting behaviour in urban great tits and its relation to anthropogenic disturbance and microclimate

The ecological novelty of urbanisation poses many challenges to animals. We investigated whether anthropogenic disturbance (artificial light at night and noise) and abiotic factors in cities (temperature and humidity) predict nocturnal activity and rest in free-living urban great tits (Parus major). Our study is the first to relate nocturnal rest in wild birds to levels of noise pollution during the night, an issue that has been shown to be particularly damaging to human health. Unlike previous work on nocturnal behaviour of urban birds, we considered the combined effect of anthropogenic disturbance and urban microclimate to acknowledge that the umwelt of an animal is composed of multiple environmental variables. Using infrared cameras, we observed the nocturnal resting behaviour as a proxy for sleep in 17 birds in nest boxes deployed across the city of Munich, Germany. Although we found marked differences in resting behaviour between individuals, this variation was not related to the measured environmental factors. This finding contrasts earlier studies that reported nocturnal resting behaviour of birds to vary with temperature and light exposure. Although we did not find evidence that urban environmental factors disrupt resting behaviour in great tits, their sleep might still be impaired by the anthropogenic disturbances. To elucidate this issue, further studies are necessary that, for instance, measure brain activity. SIGNIFICANCE STATEMENT: Urbanisation is a subject of growing concern among scientists, conservationists and policy makers alike. Yet surprisingly, little is known about the impact of urbanisation on wildlife. We investigated whether anthropogenic disturbance (artificial light at night and noise) and microclimate (temperature and humidity) predict patterns of nocturnal activity and resting behaviour in urban great tits (Parus major). Although patterns of resting behaviour differed markedly between individuals, this variation was not related to the measured environmental factors. Our findings are in contrast to previous studies on the effects of urban microclimate and light pollution. At the same time, they suggest that opposing effects of different urban ecological factors may level each other out and thus should be considered in combination.