Conclusions
Our data suggest that nestling white-crowned sparrows experience
phenotypic effects in response to elevated levels of traffic noise.
However, contrary to our predictions, nestlings exposed to traffic noise
responded with decreased CORT responses and increased condition
compared with control nestlings. These results indicate that
anthropogenic noise may affect nestling development, but noise alone
does not explain the previously observed negative impact of roads
on nestling development (Crino et al., 2011). This suggests that factors
other than noise, such as chemical pollution, mechanical vibration,
dust, increased predation and edge effects, may be more important
in causing road impacts in this species. Research addressing noise
impacts on adult birds has found wide variation among species in the
response to noise, with some species showing increased abundance
and others showing decreased abundance in noisy areas (e.g. Francis
et al., 2009) as well as wide variation in the degree of behavioral
plasticity in response to noise (Francis et al., 2011; Hu and Cardoso,
2010). Therefore, further studies are needed to determine whether the
observed lack of (or positive) impact of noise on nestling development
is generalizable to other species of birds.