Road traffic noise modifies behaviour of a keystone species

• Isolating the specific impacts of road noise on animals has proved challenging.
• We use playbacks to explore behaviour of prairie dogs exposed to road noise.
• Noise lowered aboveground activity, increased vigilance and reduced foraging.
• First experimental evidence that key behaviours are altered in a free-ranging mammal.
• Mitigation of road impacts requires understanding different disturbance factors.

Prey species have to balance their foraging and vigilance behaviour in order to maximize nutritional and energetic intake while avoiding predation. Anthropogenic noise, a ubiquitous form of human disturbance, has the potential to influence antipredator behaviour through its effects on predator detection and perceived risk. Noise might increase perceived risk as predicted by the risk disturbance hypothesis, reduce risk by providing protection from disturbance-sensitive predators, or have no effect on antipredator behaviour if animals are tolerant of nonlethal forms of human disturbance. Road traffic is a pervasive source of anthropogenic noise, but few studies have experimentally isolated the effects of road noise on behaviour. Using systematic playback experiments, we investigated the influence of traffic noise on foraging and vigilance in a keystone species in North American prairie systems, the prairie dog, Cynomys ludovicianus. Exposure to road traffic noise significantly lowered aboveground activity, reduced foraging and increased vigilance, as predicted by the risk disturbance hypothesis. These effects were prevalent irrespective of temperature, a strong influence on such behaviours, and they were consistent across the 3-month study period, providing no evidence of habituation. Our results provide the first experimental investigation of the potential costs of this ubiquitous disturbance in a free-ranging mammal, demonstrating that road noise can alter key survival behaviours of this ecologically pivotal species. These findings highlight that the presence of animals in a location is no guarantee of population and ecological integrity, while also underlining the potential synergistic impacts of noise on a species that has already experienced severe declines across its historic range due to human disturbance. Globally, roadways have profound impacts on biodiversity, and quantifying the behavioural and fitness costs associated with different forms of disturbance such as noise is crucial for mitigation.