University of California Press
Sanderlings (Calidris alba) breed within a small latitudinal range in the arctic while spreading in winter virtually throughout temperate and tropical marine beaches of the world. This paper examines spatial variation in Sanderlings nonbreeding density across the New World, documents annual cycle differences between populations wintering in California and those wintering in Peru and Chile, and then explores demographic and ecological factors underlying Sanderlings migration to different wintering grounds. Densities during the nonbreeding season are higher on the Pacific coast than on the Atlantic at all censused latitudes in the New World, and reach a peak in southwestern Peru and northwestern Chile adjacent to the Humboldt Current. Populations wintering in California spend a larger fraction of the year on the wintering site than do those wintering in Peru and Chile. Adults replace primaries during prebasic molt in both regions, as do first-winter Sanderlings in Peru and Chile. First-winter birds in California do not molt primaries. Comparisons of weight and time-activity budgets near the northern and southern ends of the winter distributions along the Pacific coast of the western hemisphere indicate that resource conditions are more favorable for Sanderlings in the south.
Copyright 1985 by the American Ornithologists' Union