DEVELOPMENTAL, ECOLOGICAL, AND LIFE HISTORY INFLUENCES ON PREDATOR-INDUCED PLASTICITY IN SONGBIRDS

Predation is a ubiquitous ecological force that plays a major role in the evolution of phenotypes. Where the predation risk is predictable and variable, prey species are expected to evolve plasticity in traits that reduce the likelihood of being killed and eaten by predators. Such plasticity may be especially critical for the survival of dependent offspring because they are particularly vulnerable to predators and suffer high levels of predation across taxa. Yet the fitness effects of predator-induced plasticity can vary across life stages, differ between parents and offspring, or be mediated by interactions with other species in the community. The importance of each of these factors for mediating the fitness consequences of predator-induced plasticity in natural systems is poorly understood. In this dissertation, I explore these issues using experiments and observational data in a suite of songbird species. In chapter 1, I examine how plastic responses to increased nest predation risk influence offspring morphology, flight performance and survival after they depart the nest as fledglings. When nest predation risk was elevated, young departed the nest with shorter, but more fully feathered wings. Ultimately, plastic responses to increased nest predation risk did not reduce flight performance or survival of young after they departed the nest. In chapter 2, I test whether parental responses to increased nest predation risk better reflect strategies to mitigate predation risk for offspring or enhance parental fitness at a cost to current offspring. I show evidence that variation in parental responses to increased nest predation risk across species better reflects adjustments in parental effort that maximize parental but not necessarily offspring fitness. In chapter 3, I explore how species interactions vary with nest predation risk and examine the consequences for offspring survival. I show that in years with higher nest predation risk, cavity nesting birds nested together in individual trees more often and experienced greater offspring survival compared to nests in trees with only one nest. In chapters 4-5, I examine the potential for parent-offspring communication to influence parental responses to nest predation risk. In songbirds, offspring use conspicuous, loud begging displays to solicit feeding from parents. Consequently, offspring may be able to shape parental responses to nest predation risk to favor offspring over parental fitness. Yet parental responsiveness to begging varies among species and increased offspring begging may exacerbate nest predation risk by helping predators locate nests. In chapter 4, I explore the evolutionary drivers of parental responsiveness to begging by comparing parental responsiveness across species with diverse life history and ecological traits. Parents were more responsive to offspring begging in species with smaller nestlings at greater risk of starvation on average. However, I found less evidence that annual adult survival or nest predation rates drive parental responsiveness to begging. In chapter 5, I examine whether variation in nest structure across