Roseate (Sterna dougallii) and Common Tern (S. hirundo) Use of Staging Sites during the Post-breeding Period in Coastal Massachusetts

Blake, Katherine
Jon Atwood, PhD
Department of Environmental Studies
Despite many studies of tern breeding biology in the northeastern U.S., little attention has been given to behavior after nesting is completed and before fall migration begins, known as the post-breeding period. This is an important time in the avian life cycle and especially critical for the young of species such as Roseate (Sterna dougallii) and Common (S. hirundo) Terns that remain dependent on adults for weeks after fledging. Specific objectives of this project were: (1) to identify, characterize and map important staging sites of Roseate and Common Terns in Southeast Massachusetts, particularly Martha's Vineyard, Nantucket, throughout Buzzards Bay and Cape Cod (2) to investigate factors that may influence use of staging sites, including time of the post-breeding period, time of day, tide and an interaction of time of day and tide and (3) to contribute to collaborative work on movements of color banded adult Roseate Terns between MA staging sites. In two years of study (2007-2008) terns were observed staging at 35 sites across Cape Cod, Nantucket and Martha's Vineyard between July and September. Three sites were suspected of being used as overnight roosting sites in 2008. Terns were present in the thousands at 15 sites and tens of thousands at four sites; one site at times supported a sizable fraction of the Northwest Atlantic population of the Endangered Roseate Tern. Analysis from detailed ground surveys of five sites and four aerial surveys (2008) showed staging site use differed by site, time of the post-breeding period and between years. Similar to patterns of dispersal identified in previous studies (Trull et al. 1999), terns appeared to congregate in the largest concentrations at sites along the outer Cape in mid to late September, just prior to southward migration. Time of the post-breeding period, time of day and tide accounted for a significant amount of variation in tern abundance at some sties.