Non-breeding season movements of six North American Roseate Terns Sterna dougallii tracked with geolocators

Abstract

Little is known of the endangered and declining western North Atlantic population of the Roseate Tern Sterna dougallii outside the breeding season, when most mortality probably occurs. We used geolocators to track Roseate Terns in 2007 and 2009 and retrieved six units with useful data. In the post-breeding period in July-August, all six birds staged around Cape Cod, close to the breeding site. They started southward migration from 28 August to 14 September and flew directly across the western North Atlantic Ocean to staging areas around Puerto Rico and the Dominican Republic. We identified five major areas and four minor areas in the West Indies and along the north and east coasts of South America where birds stopped over for 2-24 d during southward and northward migrations. Birds arrived at (Northern Hemisphere) wintering areas from Guyana/Suriname on the north coast of South America to eastern Brazil between 3 October and 2 November. They left wintering areas from 7-23 April and arrived back at the breeding area from 5-30 May. Although this study is based on data for only six birds, it identifies several stopover and wintering areas that should receive priority for future studies and potential conservation measures. Geolocators did not impair Roseate Terns' ability to raise young in the year the devices were attached, but lower than expected rates of return suggest that the geolocators reduced survival, and most of the birds that returned had lost body-mass and did not breed in the year of return.