Avian Migration in the Anthropocene: Anthropogenic Impacts, Methodological Approaches, and New Directions

Abstract

Migratory birds face a multitude of threats and stressors in the Anthropocene. During migration, birds must contend with habitat alteration and loss, extreme weather intensified by climate change, human infrastructure in migratory paths, and artificial light at night altering the dark nocturnal environment in which they evolved to migrate. The combination of these threats and stressors has led to widespread declines in migratory bird populations, with North American populations declining by ~2.5 billion individuals since 1970. While the threats to migration have developed rapidly in the Anthropocene, so too have the technologies that migration researchers have at their disposal to study impacts, and design solutions, to mitigate impact, protect, and restore migrant populations. In this dissertation, I study these recent technological advances, describe how they may be used to advance our understanding of avian migration, apply them to assess the impacts of light pollution on nocturnal migrants, and then identify a conservation strategy that may be important in restoring depleted migrant populations. First, in chapter 1, I compare the use of two cutting-edge methods, nocturnal flight call monitoring and weather radar, to study and quantify migration behavior in a previously understudied region, finding that each method performs well in our study region. Next, in chapter 2, I provide a perspective on how nocturnal flight call monitoring may be used to advance the study of avian migration, detail recent technological advancements in the use of this method, and identify remaining limitations and biases for this method that should be areas of future research priority. In chapter 3, I then apply nocturnal flight call monitoring to examine how nocturnal avian migrants may be altering their behavior as they interact with sources of artificial light at night, finding that migrants may be altering their flight paths to avoid areas with unnatural light. Lastly, in chapter 4, I mine the North American bird banding dataset to examine a basic, but deeply important, question of migration ecology; does age structure of the migrant community shift during migration? I find that age structure shifts spatiotemporally both within a single migration season, and over the last 53 years, with wide-ranging implications for our understanding of migration biology, ecology, behavior, and conservation. Overall, my dissertation work serves to advance our knowledge of avian migration, the methods we have at our disposal to study this phenomenon, and the tools that may be available to conserve and restore depleted populations.