UC Davis

With increased development and expanding urbanization, there has been a rise in anthropogenic noise pollution. This alteration to the natural acoustic environment has significant impacts on a wide variety of species. However, not all species—nor individuals within a species—respond to noise pollution in the same way. Intrinsic factors such as sex, age, and behavioral tendency all contribute to intraspecific variation to responsiveness to environmental disturbances, including noise. Here, I explored how individual differences contribute to variation in response to noise during the breeding season. I did this by exposing nest boxes settled by established populations of tree swallows (Tachycineta bicolor) to experimental playbacks of traffic noise. First, I sought to determine whether relative differences in aggressive tendency of mated pairs explained differences in reproductive success under noise exposure. I found that in nest boxes exposed to low noise levels, pairs that were more similar in aggressiveness raised slightly larger nestlings than pairs that were more different in their aggressive tendencies, but under high noise, pairs that were more similar in aggressiveness exhibited a significant reduction in nestling size. I examined parental care to find a mechanism for this effect, but I found that noise exposure did not affect incubation, provisioning rate, nor vigilance behavior while at the nest box. However, I did find that aggressive tendency explained male provisioning rate, with a decrease in provisioning observed in highly aggressive males, but no effect in females. Upon observing an effect of mate pair similarity on reproductive success in the context of noise, I examined whether individual aggressiveness, sex and quality played a role in settlement decisions, and could potentially impact mate assortment, and thus reproductive success. In a second experiment, I began noise exposure at the breeding grounds prior to territory establishment. I found that for both males and females, aggressiveness significantly explained nest box choice in regard to noise exposure. Highly aggressive individuals avoided settling in boxes exposed to high noise levels. This resulted in positive assortative mating by aggressive tendency, with pairs in lower amplitude boxes exhibiting higher average aggressiveness than pairs in higher amplitude boxes. I found no relationship between noise and measures of adult quality (body condition, breast feather brightness, mantle feather saturation), and no measures of quality were correlated within mate pairs. Lastly, during the height of breeding of the settlement study, the tree swallow populations were exposed to an unprecedented spring cold snap, with temperatures dipping to approximately 15°C (59°F) during the day and 6.67°C (44°F) at night, resulting in high nestling mortality and nest failure. Therefore, my last chapter explored the effects this severe weather event on reproductive success in the context of noise. I evaluated what factors influenced nest failure, how mates rebounded after the storm, and whether noise exposure potentially exacerbated consequences to breeding. I found that nestling age played a large role in nest success, with most mortality observed in the mid-age nestlings, rather than the recently hatched nestlings, or nestlings close to fledging. We also saw impacts to time to fledging and growth from the cold snap, though we did not find evidence that exposure to noise exacerbated the effects from the cold snap. Nestlings that lived through the storm, exhibited a similar response to noise as found in prior studies, with nestling mass decreasing with exposure to noise. However, for nestlings that hatched later in the season, after the cold snap, we see no such effect of noise. Additionally, adults varied in their response to the cold snap. Second year females were the most likely adults to cease breeding after the cold snap, and females with brighter breast feathers renested after the cold snap the soonest. Overall, intrinsic differences between nestlings as well as adults explained variation in how our population of tree swallows coped with a sudden extreme weather event.