Noise affects nest-box choice of 2 competing songbird species, but not their reproduction

Anthropogenic noise levels are steadily increasing worldwide and may potentially affect many species. Short-term experimental noise exposure under field and lab conditions has revealed that noise can affect the behavior and physiology of birds. However, few studies have been able to link these short-term effects to longer-term consequences. Here, we report on 2 long-term noise exposure field experiments to assess the direct and indirect effects of noise on avian reproductive success. In one experiment, we provided 2 types of nesting sites in our study area, a nest-box with traffic noise broadcast inside, as well as a control nest-box. We found great tits (Parus major) to avoid breeding in noisy nest-boxes, in particular when they had both nest-box types available in their territory. Interestingly, we found blue tits (Cyanistes caeruleus) to breed more often in the noisy nest-boxes compared with the control nest-boxes. In another experiment, we randomly assigned nest-box treatments to breeding great tits after settlement and started noise exposure prior to egg laying or hatching. We found no significant effect of noise treatment on clutch size, number of fledglings, or any other life-history trait we measured. Our results show that great tits avoid breeding in noisy locations. Birds that are however forced to breed in noise, either through experimental manipulation or potentially through competitive exclusion, do not suffer from reduced reproductive success. Thus, anthropogenic noise can affect settlement behavior, but breeding inside a noisy nest-box has no reproductive consequences, at least not for great tits.