Seasonal movements and pelagic habitat use of murres and puffins determined by satellite telemetry

We tracked the movements of Common Murres (Uria aalge), Thick-billed Murres (U, lomvia), and Tufted Puffins (Fratercula cirrhata) using surgically imp lanted satellite transmitters. From 1994-1996, we tagged 53 birds from two colonies in the Gulf of Alaska (Middleton Island and Barren Islands) and tw o colonies in the Chukchi Sea (Cape Thompson and Cape Lisburne). Murres and puffins ranged 100 km or farther from all colonies in summer, but most ins trumented birds had abandoned breeding attempts and their movements likely differed from those of actively breeding birds. However, murres whose movem ents in the breeding period suggested they still had chicks to feed foraged repeatedly at distances of 50-80 km from the Chukchi colonies in 1995. We detected no differences in the foraging patterns of males and females durin g the breeding season, nor between Thick-billed and Common Murres from mixe d colonies. Upon chick departure from the northern colonies, male murres--s ome believed to be tending their flightless young--drifted with prevailing currents toward Siberia, whereas most females hew directly south toward the Bering Sea. Murres from Cape Thompson and Cape Lisburne shared a common wi ntering area in the southeastern Bering Sea in 1995, and birds from Cape Li sburne returned to the same area in the winter of 1996. We conclude that di fferences in foraging conditions during summer rather than differential mor tality rates in winter account for contrasting population trends previously documented in those two colonies.