Anthropogenic noise alters the perception of a predator in a local community of great tits

Abstract

Anthropogenic noise is increasing at an alarming rate in urban as well as rural ecosystems and detrimental effects have been reported on many animals relying on acoustic communication. Little is known regarding the impact of different types of noise on community level predator perception and breeding behaviour. Here, we presented a predator model alone or a predator combined with a specific noise type, such as traffic, a lawnmower or a chainsaw, to breeding pairs of great tits, Parus major , giving them the opportunity to perform mobbing behaviour that could provide public information to their neighbours. We then measured the provisioning behaviour of adjacent tit pairs, which were 50–150 m away from the focal pairs' nests. The adjacent breeding pairs decreased nest visits when focal birds were exposed to the sparrowhawk model or to the sparrowhawk model combined with the lawnmower noise. Neighbouring pairs did not reduce the rate of nest visits when focal birds were exposed to the hawk model combined with the traffic or the chainsaw noise. The distance from focal nests did not alter the noise effect on neighbouring pairs. We suggest that auditory masking is the most likely mechanism to explain why noise compromises public information. The chainsaw and traffic noise overlap with the frequency of mobbing calls and disrupt the transmission of auditory signals in the community. Further, when the hawk presentation was combined with the chainsaw noise, which was the type of noise that had the highest frequencies, the latency of mobbing by the focal birds was strongly increased, and the number of species involved in mobbing was reduced. This study demonstrates that the signalling function of mobbing is ineffective in noisy environments which ultimately impacts fitness via increased predation to adults or their offspring. • Focal great tits give mobbing calls in response to a sparrowhawk presentation. • Neighbouring pairs reduce nest visit rate when focal birds mob the hawk. • Neighbours do not respond to mobbing calls along with a chainsaw or traffic noise. • Acoustic masking by high-frequency noise disrupts the transmission of mobbing calls. • Low-frequency noise does not disrupt the transmission of public information.