High levels of anthropogenic noise produced in urban areas are known to negatively affect wildlife. Although most research has been focused on the disturbances of communication systems, chronic noise exposure can also lead to physiological and behavioural changes that have strong consequences for fitness. For instance, behavioural changes mediated by anthropogenic noise (e.g. quality of parental care) may alter development and could influence nestling phenotype. We tested if nestling metabolism

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... was influence by traffic noise in an urban exploiter, the house sparrow Passer domesticus. We experimentally exposed breeding house sparrows from a rural area to a playback of traffic noise and we examined the impacts of this experimental procedure on metabolic rates and morphology of nestlings. We did not find an effect of traffic noise on the morphology of nestlings. Surprisingly, we found that disturbed nestlings had overall lower metabolic rates and mass-adjusted metabolic rates than undisturbed birds. Our results suggest a specific effect of noise exposure per se, rather than an indirect effect of anthropogenic noise through the quality of parental care. Both the proximate mechanisms and the ultimate consequences of such metabolic changes on nestlings remain unknown and deserve future experimental studies. Compared to natural environments, urban areas are characterized by structural simplification (McKinney 2002), increased pollution (Roux and Marra 2007), obtrusive nocturnal light levels (Kempenaers et al. 2010), and disturbing anthropogenic noise (Barber et al. 2010); all of which are known to negatively affect wildlife (Grimm et al. 2008). Accordingly, species richness and diversity are overall reduced in urban environments (Marzluff and Ewing 2001, McKinney 2008). High levels of anthropogenic noise have recently been highlighted as an 'urgent conservation priority' (Francis and Barber 2013). This is especially true, and well-studied, in avian species for which life-history traits strongly relies on acoustic communication (Catchpole and Slater 2008, Slabbekoorn 2013). Indeed, disturbances and interferences in avian communication systems have strong impacts on territorial establishment and defence (Mockford and Marshall 2009), mate choice and pair bonds (Swaddle and Page 2007), and parent-offspring communication (McIntyre et al. 2014) leading to overall reduced avian reproductive performances in noisy environments (Halfwerk et al. 2011). Noise pollution may also affect an organism through processes that are not directly connected to the disruption of communication channels. For instance, chronic noise exposure can produce specific physiological and behavioural effects that can have direct and indirect consequences for fitness (Kight and Swaddle 2011, Francis and Barber 2013).