Movement ecology of an intercontinental migratory bird during spring stopover

Emily Beth Cohen

Abstract

Movement ecology is a component of nearly all aspects of animal behavior and an animal's decision to move is likely influenced by a complex combination of exogenous and endogenous factors. Therefore, an examination of the causes and consequences of organismal movement provides a conceptual framework for understanding complex behavioral strategies. My dissertation research is focused on the movement ecology of an intercontinental migratory songbird during spring migration. I adopted experimental approaches to study the factors influencing how a songbird migrant, red-eyed vireos ( Vireo olivaceus ), makes decisions in unfamiliar landscapes from the initiation of spring stopover. I simulated the arrival of nocturnal migrants at unfamiliar stopover sites to study the influence of multiple factors including energetic condition, sex, time program, habitat, landscape and conspecific song on movement patterns and stopover duration. To do this, I used radio-telemetry to follow the detailed movements of red-eyed vireos at stopover sites while quantifying vegetation structure and composition, food availability and avian predators and competitors. I found that arrival energetic condition and habitat strongly influenced movement. In addition, migrants moved further and faster during an initial "searching" period during which they selected habitat types with greater food availability where they captured more prey. Migrants arriving with reduced fuel stores also remained longer at stopover sites and only migrants arriving early in the spring stayed for extended periods of time. Conspecific song did not serve as a cue for the quality of a habitat type but it did influence within-habitat selection. Finally, I applied the results of these experiments to build individual-based models of movement according to behavioral rules and habitat-specific fuel deposition rates to measure the fitness consequences of migrant-habitat interactions during spring stopover. I applied the model and found fuel deposition rate increased as the amount of hardwood in the landscape increased and the degree of spatial aggregation of habitat decreased. The experimental and individual-based modeling approach adopted in this research provides much needed information about how migrants make decisions in unfamiliar landscapes during stopover as well as the fitness consequences of those decisions.