Effects of experimental anthropogenic noise on avian settlement patterns and reproductive success

The acoustic footprints of factories, roadways, etc. reach far beyond their physical infrastructure because high-amplitude, low-frequency noise can propagate many kilometers. Previous studies found that noise exposure decreases habitat quality and reproductive success for some species. However, few studies have linked the reduction in perceived habitat quality due to noise exposure to effects on avian settlement patterns and reproductive success. Here, we experimentally investigate the impacts of noise pollution during settlement on adult settlement patterns and subsequent reproductive success in tree swallows (Tachycineta bicolor). We found that tree swallow adults preferentially settled in quieter nest boxes (a 1 dBA increase delayed settlement date by 1.4 and 3.5 days for males and females, respectively). Egg-laying date (a proxy of female quality) also increased by 3.8 days for every 1 dBA increase in noise. These results suggest that lower-quality tree swallows settled in noise; however, more research is needed to confirm this result, as we did not measure adult quality directly. Our results also suggest a negative relationship between noise exposure during settlement and reproductive success, which cannot be explained by differences in adult quality alone. When controlling for egg-laying date, females that settled in noise-exposed nests laid 0.58 fewer eggs than controls. Finally, maternal noise exposure, but not egg-laying date, was negatively related to nestling body condition. These results are concerning, as they highlight multiple pathways through which traffic noise may result in negative impacts at the local, population level for free-living birds.