Spatial and temporal ecology of a colonial waterbird: the distribution and abundance of nesting common eiders (Somateria mollissima) in Labrador

Abstract

Understanding patterns of animal distribution and abundance and their causes is at the heart of ecological investigations with implications for conservation, resource management, theoretical development and testing. Surveys to evaluate the localized distribution and abundance of common eiders (Somateria mollissima) nesting in Labrador were conducted from 1998 to 2003. Information was compiled and analysed with respect to clutch size, nest initiation, nest density, abundance, population trend, spatial distribution, colony dynamics, as well as interspecific and abiotic habitat relationships. Eiders showed a north south-clinal variation in nest initiation with birds in the south laying earlier then birds in the north. There was significant interaction between annual and regional variation in life history parameters (nest initiation, clutch size, egg volume) and regional differences in nest abundance and nest density, with the lowest densities in Hopedale, while Nain and Rigolet were comparably high. Overall, eider populations were increasing. Colony dynamics and local population turnover were investigated, and colonization rate was greater than extinction rate, but these varied by region. Interspecific relationships were investigated and significant positive associations were found between nesting eiders and nesting Larids (Larus argentatus and L. marinus), and gulls seemed to track eider colonies over time, but eiders did not track gull colonies. No evidence of a significant relationship between nesting eiders and intertidal resources were found. Negative relationships were documented between nesting eiders, landscape features and ice. This was attributed to increased access to breeding islands by terrestrial predators; however other factors such as colder conditions, or reduced access to prey because of ice obstruction or ice scour might be at play. The effect of spring ice on nesting eiders in Labrador has profound implications for understanding the biological consequences of long-term global climate change. This thesis represents some of the first published information on eider ecology in Labrador, a focal species with ecological and cultural importance, and this research has implications for the regional, national, international conservation and management of common eiders. Findings were interpreted in the context metapopulation theory, source sink population dynamics, conspecific attraction, and the ideal free distribution.