Estimating Bald Eagle Occupancy and Density in the Chesapeake Bay Watershed

Bald eagles (Haliaeetus leucocephalus) are a newly recovered species, and as such, little is known about their modern population dynamics and how these dynamics interact with their ecology. With the recent expansion of eagle populations, managers have begun to question assumptions about bald eagles, including their sensitivity to disturbances. Discerning how eagles react to both outside influences and internal factors is crucial for eagle conservation, especially in focal areas of importance, such as the Chesapeake Bay. I used seven years of monitoring data from the Virginia Department of Game and Inland Fisheries (VDGIF) to determine the occupancy (chapter 1) and density (chapter 2) of bald eagles in concentration areas in the Bay (Rappahannock, James, Potomac, York Rivers) and their associations with habitat characteristics. I used robust occupancy models to assess habitat associations within concentration areas (chapter 1). Additionally, I used Royle-Nichols n-mixture models to find average abundance and multiply this across the number of units in the study area to determine effective density (chapter 2). Bald eagle occupancy (chapter 1) was seasonally variable, with different covariates influencing eagles at different times of the year. Patterns of occupancy by non-breeding populations (summer months) responded to salinity, land cover, and recreational disturbance. Patterns of occupancy by bald eagles in winter (breeding season) responded to salinity and were age-specific. In both seasons, less saline waters (tidal fresh and oligohaline) were more frequently occupied than more saline waters (mesohaline). Density models (chapter 2) suggested that canopy cover may be important. However, the models I used appeared inappropriate for the data, they did not converge, and therefore my results were generally uninformative for this metric. Chapter one occupancy analyses show high rates of bald eagle occupancy and a relative resistance of eagles to recreational disturbances, which suggests that this population is growing, which may lead to increased management concerns in the future. Chapter two analyses revealed that archived data from mandated monitoring of sensitive species are valuable to the scientific community; however, if the models used are not appropriate for the data collected, the ability to answer research questions is limited