SUMMARY
Roads have been associated with behavioral and physiological changes in wildlife. In birds, roads decrease reproductive success
and biodiversity and increase physiological stress. Although the consequences of roads on individuals and communities have
been well described, the mechanisms through which roads affect birds remain largely unexplored. Here, we examine one
mechanism through which roads could affect birds: traffic noise. We exposed nestling mountain white-crowned sparrows
(Zonotrichia leucophrys oriantha) to experimentally elevated traffic noise for 5days during the nestling period. Following
exposure to traffic noise we measured nestling stress physiology, immune function, body size, condition and survival. Based on
prior studies, we expected the traffic noise treatment to result in elevated stress hormones (glucocorticoids), and declines in
immune function, body size, condition and survival. Surprisingly, nestlings exposed to traffic noise had lower glucocorticoid
levels and improved condition relative to control nests. These results indicate that traffic noise does affect physiology and
development in white-crowned sparrows, but not at all as predicted. Therefore, when evaluating the mechanisms through which
roads affect avian populations, other factors (e.g. edge effects, pollution and mechanical vibration) may be more important than
traffic noise in explaining elevated nestling stress responses in this species
SUMMARYRoads have been associated with behavioral and physiological changes in wildlife. In birds, roads decrease reproductive successand biodiversity and increase physiological stress. Although the consequences of roads on individuals and communities havebeen well described, the mechanisms through which roads affect birds remain largely unexplored. Here, we examine onemechanism through which roads could affect birds: traffic noise. We exposed nestling mountain white-crowned sparrows(Zonotrichia leucophrys oriantha) to experimentally elevated traffic noise for 5days during the nestling period. Followingexposure to traffic noise we measured nestling stress physiology, immune function, body size, condition and survival. Based onprior studies, we expected the traffic noise treatment to result in elevated stress hormones (glucocorticoids), and declines inimmune function, body size, condition and survival. Surprisingly, nestlings exposed to traffic noise had lower glucocorticoidlevels and improved condition relative to control nests. These results indicate that traffic noise does affect physiology anddevelopment in white-crowned sparrows, but not at all as predicted. Therefore, when evaluating the mechanisms through whichroads affect avian populations, other factors (e.g. edge effects, pollution and mechanical vibration) may be more important thantraffic noise in explaining elevated nestling stress responses in this species
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