Identifying the diversity of contexts that can lead to hybridization is important for understanding its prevalence and dynamics in natural populations. Despite the potential of ecological succession to dramatically alter species co-occurrence and abundances, it is unknown whether it directly promotes hybridization and, if so, has long-lasting consequences. Here, we summarize 30 years of survey data across 10 populations to show that in western and mountain bluebirds, heterospecific pairing occurs during repeatable and transient colonization events at the early stages of species turnover. Despite mixed pairing occurring only during early succession, genetic data showed presence of hybrids at both early and late successional stages. Moreover, hybrids showed novel patterns of variation in morphology and behavior, emphasizing that even ephemeral contexts for hybridization can have important evolutionary consequences. Our results suggest that because ecological succession often brings together closely related competitors in disparate numbers but lasts for only a brief period of time, it may be a widespread but underappreciated context for hybridization.

Sensory pollutants such as anthropogenic noise and night lighting now expose much of the world to evolutionarily novel sound and night lighting conditions, which can have detrimental effects on humans and wildlife. In my first chapter, we exposed wild Western Bluebird (Sialia mexicana) nestlings to noise, light, and combination (i.e., noise and light) treatments. Nests exposed to noise and light together experienced less predation than control and light-exposed nests, and noise-exposed nests experienced less predation than control nests, yet overall nest success was only higher in noise-exposed nests compared to light-exposed nests. Although exposure to light decreased nestling body condition and evidence was mixed for the singular effects of noise or light on nestling size, those exposed to noise and light together were smaller across several metrics than nestlings in control nests. Our results support previous research on the singular effects of either stimuli, including potential benefits, such as reduced nest predation with noise exposure. However, our results also suggest that noise and light together can negatively affect some aspects of reproduction more strongly than either sensory pollutant alone. This finding is especially important given that these stimuli tend to covary and are projected to increase dramatically in the next several decades. In my second chapter, we used a field-based manipulation to explore the role of audition in biodiversity perception and self-reported well-being of hikers. We used a “phantom chorus” consisting of hidden speakers playing bird vocalizations to experimentally increase audible birdsong biodiversity during “on” and “off” blocks on two hiking trails and surveyed hikers to record their self-reported perceptions of avian biodiversity and concepts reflective of attention restoration. We found that hikers exposed to the phantom chorus reported higher levels of restorative effects compared to those that experienced ambient conditions on both trails, although the causal relationships differed for each trail. Specifically, increased restorative effects were directly linked to the phantom chorus on one trail and indirectly linked to the phantom chorus on the other trail through perceptions of avian biodiversity. Our findings add to a growing body of evidence linking mental health improvements to nature experiences and, via our field-based manipulation, we identified audition as an important modality by which natural environments confer well-being. Finally, our results suggest that maintaining or improving natural soundscapes within protected areas may be an important component to maximizing human experiences, especially as tourism and noise pollution in protected areas grow.

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