Interseasonal movements and non-breeding locations of aleutian terns onychoprion aleuticus

Abstract

Few observations have been made of Aleutian Terns Onychoprion aleuticus outside of summer breeding colonies. We investigateed the non-breeding distribution of Aleutian Terns by collating published and unpublished records of observations during the migration and wintering periods, and by implementing a geolocator tracking study at the largest known breeding colony in North America (Yakutat, Alaska). We deployed 114 geolocator tags in 2010 and recovered six tags over the course of six years. Using light level data, we conducted spatial analysis of tern migration cycles from 2010 to 2013. Results revealed one of the longest distance terrestrial vertebrate migrations ever recorded, with a one-way migration distance of > 16 000 km between Alaska and the Southeast Asia/Oceania region. We found that core winter ranges occurred in coastal Thailand, the Philippines, three areas within Indonesia, and Papua New Guinea. Five of the six recovered geolocators contained data spanning multiple years and provided evidence of both wintering-and breeding-site fidelity. Our effort to more completely document the extent of the Aleutian Tern winter range is a foundational step toward understanding both the natural history and the ecological stressors that could affect this under-studied, locally-imperiled seabird.