VARIATION IN MARINE DISTRIBUTIONS OF CASSIN'S AUKLETS (<i>PTYCHORAMPHUS ALEUTICUS</i>) BREEDING AT TRIANGLE ISLAND, BRITISH COLUMBIA

Abstract

Approximately 55% of the world's population of Cassin's Auklets (Ptychoramphus aleuticus) nests at Triangle Island, British Columbia. To improve our understanding of the biology of these birds during the breeding season, we tracked 112 radiomarked individuals over three years, 1999–2001. We flew high-altitude surveys to describe the at-sea distributions of the marked birds during the chick-rearing period. Using radiotelemetry point locations, we determined that the location of marine use areas, distance from colony, and water depth varied significantly across years. In 1999 and 2000, radiomarked birds were, on average, ∼50 km southwest of Triangle Island in waters approximately 1400–1800 m deep. However, in 2001, radiomarked birds were, on average, ∼80 km northwest of Triangle Island in waters ∼725 m deep. Intra-annually (i.e., between surveys spanning days or weeks), there were no such large-scale directional shifts in marine use area. The size of marine use areas (quantified using kernel home range [KHR] analyses) varied across the three years, from approximately 650 to 1,400 km2 (50% KHR) and from approximately 3,200 to 8,200 km2 (95% KHR). Variation des distributions en mer de Ptychoramphus aleuticus se reproduisant sur l'île Triangle, en Colombie-Britannique