Baltsvluchten van Noordse Sterns Sterna paradisaea op open zee

On 4th June 1991, in the southeastern North Sea at 55°13.3’N, 06°35.8’E, (i.e. 128 km west of Rømø) a compact flock of 26 adult Arctic Terns Sterna paradisaea was seen swimming with 2 more individuals foraging nearby. When disturbed by the approaching vessel, aerial displays were observed, described as ’low-flight’ and ’high-flight’ in Cramp (1985). The two terns which had been foraging joined the group, each carrying fish. Most terns appeared to have a partner with which the display was performed. It is unlikely that breeding birds from the North Sea area would perform displays far out at sea in June. It is noted that there is quite a time lapse between the peak of migration in the southern North Sea (late Apr-early May) and arrival on high arctic breeding grounds (late June), while these high arctic breeders have very little time left to reach breeding condition and to copulate after arrival. The sighting could suggest that for these high arctic popidations the last part of their long way north lakes much lime during which pair bond is renewed (or even established) and foraging lakes place in order to arrive in good condition.