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Transportation noise affects urbanized, rural, and otherwise unaltered habitats. Given expanding transportation networks, alterations in the acoustic landscapes experienced by animals are likely to be pervasive and persistent (i.e. chronic). It is important to understand if chronic noise exposure alters behavior and physiology in free-living animals, as it may result in long-lasting impacts, such as reduced reproductive success. Here, we experimentally tested the effects of chronic traffic noise on baseline and stress-induced corticosterone (the primary avian glucocorticoid), parental feeding behavior, and fitness proxies in breeding tree swallows (Tachycineta bicolor). Our results show that chronic traffic noise is related to altered corticosterone in both adult female and nestling tree swallows, suggesting that noise may be a stressor in both groups. In adult females, our results suggest that traffic noise is related to a limited ability to respond to subsequent acute stressors (i.e. reduced stress-induced corticosterone levels after handling). Further, our results show no evidence of habituation to noise during the breeding season, as the negative relationship between traffic noise and adult female stress-induced corticosterone became stronger over time. In nestlings, we found a positive relationship between traffic noise exposure and baseline corticosterone. Finally, we found a negative relationship between traffic noise and nestling body condition, despite no detectable effects of noise on nestling provisioning (e.g. parental feeding rate, or insect bolus size/composition). These results highlight the potential long-term consequences of chronic noise exposure, as increased baseline corticosterone and reduced nestling body condition in noise-exposed areas may have negative, population-level consequences., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Migration is an energy-demanding life-history period and also a significant population-limiting factor of long-distance migratory birds. It is important to understand how corticosterone, the main energy regulating hormone in birds, is associated with behavioural and physiological changes during migration. According to the migration modulation hypothesis (MMH), individual birds may express elevated levels of baseline corticosterone to facilitate fuelling, but down-regulate the adrenocortical response in order to protect skeletal muscles from the catabolic effects of the hormone. We measured the baseline and stress-induced levels of corticosterone in barn swallows (Hirundo rustica L.) during early stages of autumn migration. Here, we show that, while barn swallows clearly responded to the capture and handling stress by increasing the corticosterone level, the strength of this acute response was related to their energetic condition: birds with high body mass responded more rapidly and had lower peak values of corticosterone than lighter birds. Further, the baseline levels of corticosterone correlated negatively with the magnitude of the adrenocortical response. Barn swallows did not show elevated baseline levels of corticosterone in the course of autumn, which suggests that, instead of fuelling, the birds were actively migrating. Our results indicate that MMH also applies to aerial feeders, whose foraging habits differ from model birds of previous studies.

We determined mercury concentrations in tree swallows, Tachycineta bicolor, from Massachusetts and Maine with different levels of contamination. Baseline and stress-induced plasma corticosterone concentrations from adults and nestlings (Massachusetts only) were compared with mercury concentrations. In Massachusetts, adult baseline corticosterone was negatively correlated with blood mercury, but showed a nearly-significant positive correlation with feather mercury. There was a negative relationship between baseline corticosterone and blood mercury in nestlings and between baseline corticosterone and egg mercury. There was no relationship between mercury and stress-induced corticosterone in any of the groups, or with baseline corticosterone in Maine sites where mercury levels were lower. The findings suggest blood and egg mercury may be a better indicator of current condition than feather mercury. Further, mercury contamination may not alter stress-induced corticosterone concentrations in tree swallows but appears to have a significant impact on baseline circulating corticosterone.