Factors influencing breeding distributions of harlequin ducks, Histrionicus histrionicus, in northern Labrador : a multi-scale approach

Considerations of spatial and temporal scales are important for understanding the distribution of highly mobile migratory birds, because habitat selection can involve hierarchical processes from the landscape to nest site scale. The aim of this thesis was to evaluate the importance of predation, intraspecific competition, biophysical habitat features and prey abundance in determining the distribution of breeding Harlequin Ducks Histrionicus histrionicus in northern Labrador. This was assessed at several spatial scales, both within and among years. Results indicate source-sink metapopulation structure at the landscape scale, with glacially carved river canyons containing sub-populations. Availability of cliff nesting habitat and, subsequently, abundance of birds of prey is a likely mechanism determining demographic differences among sub-populations of Harlequin Ducks along the source-sink gradient. Habitat and prey availability did not differ among source and sink populations, suggesting birds of prey may limit Harlequin Ducks from otherwise suitable habitat. A spatially explicit Geographical Information System (GIS) model supported these results, indicating spatial segregation of Harlequin Ducks and birds of prey at the landscape scale. Spatial segregation also was found at the home range scale within local populations where intermediate densities of both taxa were present. A variety of biophysical features and prey availability were important for home range selection within source populations. Tradeoffs among habitat quality and predation risk were important in sink and 'intermediate' populations. These results provide empirical support for aspects of several theoretical areas, including application of a metapopulation framework to migratory birds, coexistence of predators and prey through spatial dynamics, spatial and landscape influences on population dynamics and demographics, and the importance of considering multiple spatial and temporal scales in ecological research. Results also will be important for conservation and management of Harlequin Ducks, a species at risk in eastern North America, particularly for identifying key spatial areas in which to focus conservation efforts