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Anthropogenic noise affects humans and wildlife globally. Birds, in particular are susceptible to its effects, because of their reliance on acoustic communication for survival and reproduction. Decades of research show that singers adapt their songs to noisy conditions, but much less is known about how impaired communication affects receivers, and how it affects sexual selection and fitness. Anthropogenic noise has been shown to reduce breeding success. However, not many studies have simultaneously investigated the effects of noise on settlement, population structure and breeding success at different stages of the breeding cycle. We know even less about the effects of noise on large geographical scales that transcend the population level. This thesis aims to understand the effects of noise on the breeding success and communication of European birds. Specifically, in order to investigate the effects of noise on nest site selection together with its effects on breeding success, I studied a population of blue tits exposed to a gradient of road traffic noise. To understand the scale of the problem, I developed a methodology to combine citizen-science breeding data with government noise maps, and I tested this approach across two countries and eleven bird species. At the population level, I found that noise affected reproductive success, with negative impacts on nestling body condition and survival. Despite these effects, blue tits were more likely to breed in noisier nest sites, although these were also more likely to be occupied by first year breeders. I found that negative effects were not restricted to one population, but they were also evident at a countrywide level and on multiple species, with the most significant impact at the nestling stage. In order to investigate a factor that might play a role in affecting breeding success, I used a playback experiments to test the assessment of performance of a territorial song under different ambient noise conditions. I found behavioural evidence that noise may affect the assessment of structural differences in signal quality of conspecifics, thus altering territory defence and, by inference, leading to suboptimal mate choice. This thesis concludes that the effects of noise on birds are significant even in species common in noisy areas, and that presence of a species should not be interpreted as a lack of effects. |
