Trek van Dwergsterns Sterna albifrons in de oostelijke Waddenzee in het najaar

During counts of visible migration off the Groningen Wadden Sea coast in autumn 1984-88, 1779 Little Terns were seen migrating. Most Little Terns in the Dutch Wadden Sea and along the North Sea coast are recorded in the second half of July and first half of August, but off the Groningen coast peak migration did not occur before the end of August (figure 1). Incidentally, also early September strong movements were observed (1984, September 8th and 10th, 101 and 369 birds respectively). Most observations seem to refer to local feeding populations. On some days strong movements of Little Terns, as well as Common/Arctic Terns, were induced by violent weather conditions, possibly because feeding possibilities were reduced by strong wind and water turbidity so birds were forced to move to less turbid areas or migrate further south. Migration off the Dutch North Sea coast peaks around in the first half of August and almost ends shortly afterwards. It is suggested that part of the Little Terns present in the eastern Wadden Sea migrate further south over land, by night.