Non-breeding season movements of six North American Roseate Terns Sterna dougallii tracked with geolocators
* Correspondence author: firstname.lastname@example.org
1 Massachusetts Division of Fisheries and Wildlife, 1 Rabbit Hill Road, Westborough MA 01581, USA;
2 I. C. T. Nisbet & Company, 150 Alder Lane, North Falmouth MA 02556, USA;
3 Division of Science, Pennsylvania State University, Reading PA 19610, USA;
4 British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK;
5 Current address: Migrate Technology Ltd, P.O. Box 749, Coton, Cambridge, CB1 0QY, UK.
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.
The western North Atlantic population of the Roseate Tern Sterna dougallii breeds on nearshore islands from Québec and Nova Scotia (Canada) to New York (USA). This population declined from a peak of approximately 4,400 pairs in 2000 to 3,200 pairs in 2012-13, close to its size when it was first listed as endangered in the USA in 1987 (U.S. Fish and Wildlife Service 2010; Nisbet 2014). Although this species is intensively managed and studied at North American nesting colonies, it is poorly known outside the breeding season, when most mortality probably occurs (Nisbet 2014). Prior knowledge of Roseate Terns was summarised by Cramp (1985), Gochfeld et al. (1998) and Ratcliffe et al. (2004). Birds from all parts of the western North Atlantic range stage around Cape Cod (41-42°N 70-72°W) in July-August before migrating south in September (Trull et al. 1999; Jedrey et al. 2010). Prior to this study, most information about migration routes, stopover locations and areas used in the (Northern Hemisphere) winter was derived from ringing recoveries (Nisbet 1984; Hays et al. 1997; see Discussion); one roost site in eastern Brazil has been described (Hays et al. 1999) and five others have been named but not described (Lima et al. 2005; De Luca et al. 2006). Subsequent to this study, Roseate Terns have been photographed at three additional locations in northern Brazil, and photographs have been posted on the web site www.wikiaves.com (see Front Cover photo). Here, we report a study of the movements of North American Roseate Terns using geolocators. We use tracking data for six individuals to identify their dates and routes of migration, and to identify stopover and wintering areas that could be used as locations for future studies and potential conservation actions.
We thank the U.S. Fish & Wildlife Service (especially M. Amaral) for financial support, the New Bedford Harbor Trustee Council for logistical support, P. Szczys for sexing the birds, J. Spendelow, R. Veit, S. Luecke, H. Goyert, M. Servison, E. Lencer, N. McGrath, J. Hatt, K. Parsons, S. Hecker and S. Mitra for help in the field and/or information, T. Boswell for help with GIS, S. Scully for data assistance, R. Jessop and the Victorian Wader Study Group for supplying Darvic, P. Pyle for help with the Cover Photo caption, and two reviewers for helpful comments on an earlier draft.
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