FIRST INSIGHTS INTO THAYER'S GULL LARUS GLAUCOIDES THAYERI MIGRATORY AND OVERWINTER PATTERNS ALONG THE NORTHEAST PACIFIC COAST

Investigating the seasonal movements of migratory seabirds is essential to our understanding of their basic life history and conservation needs. Using satellite telemetry, we studied the migration and non-breeding distribution of Thayer's Gulls Larus glaucoides thayeri, a little known North American gull. Four adult birds that were tracked from a colony in the Canadian high Arctic migrated south overland, crossing multiple mountain ranges to arrive at the coast between southeast Alaska and northwest British Columbia. The subsequent wintering distribution differed greatly among individuals occupying ranges as far north as Yakutat Bay, Alaska (59.7 degrees N) and as far south as Monterey Bay. California (36.7 degrees N). Gulls spent 62%-82% of the overwinter period in waters overlying the inner continental shelf (mean sea surface temperature 8.4-11.7 degrees C; mean distance to coast 2.6-8.8 km, mean depth 19-102 m), in areas of generally low human activity. Their remaining time was spent primarily onshore in coastal (15%-20%) or inland areas (4%-23%) composed of natural vegetated habitat with low human population density. Little time was spent in agricultural (0%-5%) or urban (0%-1.5%) environments. Our tracking study provides new insights into the basic natural history of this species. This knowledge should help in the development of conservation strategies for the management of Thayer's Gull populations.