The influence of research scale on bald eagle habitat selection along the lower Hudson River, New York (USA)

As the concepts of landscape ecology have been incorporated into other disciplines, the influence of spatial patterns on animal abundance and distribution has attracted considerable attention. However, there remains a significant gap in the application of landscape ecology theories and techniques to wildlife research. By combining landscape ecology techniques with traditional wildlife habitat analysis methods, we defined an 'organism-centered perspective' for breeding bald eagles (Haliaeetus leucocephalus) along the Hudson River, New York, USA. We intensively monitored four pairs of breeding eagles during the 1999 and 2000 breeding seasons, and collected detailed information on perch and forage locations. Our analysis focused on three critical habitat elements: available perch trees, access to foraging areas, and freedom from human disturbance. We hypothesized that eagle habitat selection relative to each of these elements would vary with the spatial scale of analysis, and that these scaling relationships would vary among habitat elements. We investigated two elements of spatial scale: grain and local extent. Grain was defined as the minimum mapping unit; local extent was defined by the size of an analysis window placed around each focal point. For each habitat element, we quantified habitat use over a range of spatial scales. Eagles displayed scale-dependent patterns of habitat use in relation to all habitat features, including multi-scale and threshold-like patterns. This information supports the existence of scale-dependant relationships in wildlife habitat use and allowed for a more accurate and biologically relevant evaluation of Hudson River breeding eagle habitat.