OCCURRENCE OF POLAR SEABIRDS AT SEA IN RELATION TO PREY CONCENTRATIONS AND OCEANOGRAPHIC FACTORS

The distribution and abundance of breeding and foraging seabirds is usually a reflection of the availability of prey in the marine ecosystems on which the birds depend. At the scale of hundreds of km, differences in marine communities may be reflected in variation in the species composition of resident seabirds. At small scales, environmental features such as fronts or ice can influence where birds will aggregate to forage. Features at which prey become concentrated near the surface are of particular importance to bird species dependent upon small planktonic organisms. Concentrations of foraging seabirds frequently indicate the presence of such features, or of areas of unusually high prey biomass. Thc absence of birds does not mean that concentrations of potential prey are absent. "Assembly rules." by which one might predict aspects of the marine environment that birds should use in selecting foraging areas are proposed.