Artificial nest boxes are critical nesting sites for secondary cavity-nesting birds; however, they are often placed near roadways and in urban areas that experience noise pollution and other human-caused stressors. Recent correlative studies document both negative and positive influences of noise pollution on reproductive success. Additionally, observational studies have not determined which stage of the breeding process is most vulnerable to noise pollution-settlement, incubation, and/or provisioning. Here, we controlled for possible effects from non-random settlement and eliminated potential effects of roadways, such as collisions and chemical and light pollution, by experimentally introducing traffic noise into nest boxes after clutch initiation in two secondary-cavity nesting bird species. We found no evidence for an influence of noise on clutch size, brood size, number of fledglings, or overall nest success in western bluebirds (Sialia mexicana). In contrast, we found that ash-throated flycatcher (Myiarchus cinerascens) nests exposed to noise had lower reproductive success than quiet nests due to higher rates of abandonment at the incubation stage. Our results match recent research demonstrating that ash-throated flycatchers avoid energy-sector noise in their nest placement and, when they do nest in noise, experience stress hormone dysregulation and fitness costs. The lack of a response among western bluebirds differs from reported declines in reproductive success due to exposure to energy-sector noise; however, the absence of a response matches the response seen in other species using an in-box noise playback experiment. These results suggest that in-box noise exposure experiments may be appropriate for assessing noise impacts at the nest, and through some pathways (e.g., direct effects of noise on nestlings), but do not capture other ways in which noise can negatively affect birds during the breeding season that may ultimately cause declines in fitness. Additionally, although manipulative experiments that examine the influence of a single anthropogenic stressor on a single life stage can help reveal causal pathways, urban and other human-dominated environments are characterized by many stressors and future studies should seek to understand how noise interacts with other stressors to impact birds and other wildlife. Finally, in light of mounting evidence demonstrating declines in reproductive success due to noise, our results suggest that nest box placement near roads may be counterproductive to efforts to bolster population densities of some species.
Effects of Experimental Noise Exposure on Songbird Nesting Behaviors and Nest Success Tracy Irene MulhollandAnthropogenic noise is an increasingly prevalent global disturbance. Animals that rely on the acoustical environment, such as songbirds, are especially vulnerable to these sounds. Traffic noise, in particular, overlaps with the frequency range of songbirds, creating masking effects. We investigated the effects of chronic traffic noise on provisioning behaviors and breeding success of nesting western bluebirds (Sialia mexicana) and ash-throated flycatchers (Myiarchus cinerascens). Because anthropogenic noise exposure has the potential to interrupt parent-offspring communication and alter vigilance behaviors, we predicted that traffic noise would lead to changes in provisioning behaviors, such as fewer visits to the nest box, for each species. We also predicted the noise to negatively influence one or more metrics reflective of reproductive success, such as nest success, clutch size, number of nestlings or number of fledglings. Importantly, we were able to eliminate self-sorting among individuals with respect to noise and other possible effects of traffic, such as collisions and pollution, by experimentally introducing traffic noise into nest boxes after clutch initiation using playback systems. Our results indicate no effect of traffic noise on S. mexicana reproductive measures, despite seeing changes in provisioning behaviors suggestive of an increased stress response. However, M. cinerascens experienced fitness consequences from chronic anthropogenic noise exposure when combined with the effect of year. Despite equal clutch sizes to flycatchers in boxes with no noise exposure, noise-treated flycatcher nests experienced a reduction in v hatching success and subsequent metrics, such as number of nestlings or fledglings relative to control boxes, during the first study year. The year in which we witnessed the decline in nest success for ash-throated treatment individuals coincided with a significant drought year, suggesting that combinations of multiple stressors lead to nest abandonment. In recording provisioning behaviors during the fledgling stage, no difference in provisioning was found between treatment and control ash-throated flycatcher nests. We contrast these species-specific responses to recent observational work on both species in New Mexico and other studies that have examined fitness consequences of noise. Lastly, we stress the importance of these findings in addressing current conservation practices of nest box placement with respect to roads.
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