Using migration monitoring data to assess bird population status and behavior in a changing environment

Across the world, researchers use migration banding stations to document bird migration and study the phenomenon. In this dissertation, I focus on ways of analyzing bird migration banding data and the utility migrating birds as indicators of ecosystem health that make these monitoring efforts more useful to answering ecological questions and managing migratory species. In Chapter 1, we provide background on hierarchical modeling and an overview of our findings. In Chapter 2, we developed and validated new methods to estimate daily changes in migratory population size while controlling for changes in detectability due to environmental conditions. In Chapter 3, this modeling technique was then employed to evaluate the continental-scale and the local-scale determinants of migratory population size for ten species of migrants using a Key Biscayne, FL site for migratory stopover in the fall. Species showed diverse relationships between abundance and local weather conditions. Wet conditions on the breeding grounds consistently increased migratory onset and dry conditions on the non-breeding grounds from the previous winter consistently reduced population size across all species. In Chapter 4, we looked at how daily changes in migrant density influenced the stopover behavior of seven songbirds at the Key Biscayne stopover site. Density-dependence had positive and negative effects on mass gain across species, the chance of that effect being negative increased with the average daily stopover population size of the species. Density-dependence was hypothesized to be a function of overall migrant abundance at the site, with only highly abundance species showing negative effects. Finally, in Chapter 5 migrating birds are used to tell us about contaminant exposure in their breeding and non-breeding environments. We found higher amount of mercury in fall than the spring and there was evidence that fall mercury exposure was altering migratory behavior. These patterns provide the first evidence that Hg exposure alters migratory physiology in songbirds. Overall, this dissertation suggests that migration monitoring is useful for both basic and applied research and provide a tool for understanding the complicated life cycles of migratory animals.