We conducted several studies of Roseate Terns Sterna dougallii around Cape Cod, Massachusetts, USA, during the post-breeding period (July-September) in 1990- 1998. We also reviewed reports and estimates of numbers in regional publications. We identified 20 discrete sites where Roseate Terns and Common Terns S. hirundo staged (rested in flocks during daylight hours) between 24 July and 22 September. All sites were on open beaches or sand flats, usually near the end of barrier islands or barrier beaches. Only one site was found where Roseate Terns were present in thousands, but three other such sites have been documented during the last 20 years. All of these major staging sites are on outer beaches of Cape Cod adjacent to cold Atlantic Ocean waters. Roseate Terns appear to disperse throughout the breeding area in July and August, re-aggregating on outer Cape Cod in late August and September prior to southward migration in mid-September. Roseate Terns ringed at eight colony-sites throughout the breeding area in north-eastern North America were identified at staging sites around Cape Cod. We found only two sites on Cape Cod where Roseate Terns roosted at night in 1998; one of these has been a major roost site for many years. The concentration of a large fraction of this endangered regional population into a small area during September makes it vulnerable to human disturbance (especially at night) and to North Atlantic hurricanes.

Atlantic seabirds

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Peter Trull, Scott Hecker, Maggie J. Watson, & Ian C.T. Nisbet. (1999). Staging of Roseate Terns Sterna dougallii in the post-breeding period around Cape Cod, Massachusetts, USA. Atlantic seabirds, 1(4), 145–158.