Alcid Patchiness and Flight Direction Near a Colony in Eastern Newfoundland

Abstract

Topographic features, including shape of the coastline and shape of the bottom, generate spatially predictable flow gradients that can concentrate seabird prey. We hypothesize that bathymetrically induced flow gradients influence the distribution, flight orientation, and patch scale of foraging alcids around colonies. Two potentially important sites were identified from hydrographic charts of the waters around the colony at Witless Bay, in eastern Newfoundland. One site was a bank 70 km southeast of the colony. The second was a strip of high topographic relief running along the western margin of the Avalon Channel, which carries the inshore branch of the Labrador Current southward past the colony. Surveys in 1985 showed that murres (primarily Common Murres, Uria aalge) and Atlantic Puffins (Fratercula arctica) were present in abundance at the offshore bank. Both species brought fish to the colony from this bank. Surveys also showed that the abundance ofmurres and puffins was greater along the coastal strip south and north of the colony than at similar distances east of the colony. Surveys in 1987 showed that murres and puffins on the water were aggregated at the scale of the first internal Rossby radius, which is the characteristic scale of flow gradients at water mass boundaries (fronts). Our results suggest that multiple rather than single focus spatial models are required to describe the foraging behavior of colonial alcids.