EFFECTS OF EXPERIMENTAL NOISE EXPOSURE ON SONGBIRD NESTING BEHAVIORS AND NEST SUCCESS

Anthropogenic 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 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