During the summer of 1990, large numbers of Cormorants Phalacrocorax carbo and Little Terns Sterna albifrons were seen on the islet of Rottumeroog in the eastern Dutch Wadden Sea. Between 9 and 15 July 1266 Cormorants were seen flying eastward and 419 westward, while at least 175 were roosting. Most of the birds were in immature plumage. Sightings of colour ringed Cormorants have shown that the first born young of the Dutch breeding birds move north and east after the breeding season towards Denmark and the southern Baltic region. On 25 July at least 1135 Little Terns were roosting on Rottumeroog, with birds still coming in after dusk. On 2 August 900 and on 6 August 600 Little Terns were still present. More than 1000 Little Terns have never been counted before in the Dutch Wadden Sea The number of about 1200 comprises about 25% of the Little Tern population breeding north and east of the Netherlands. From Rottumeroog the Little Terns migrate southwards along the Dutch coast to the Zeeuwse Delta area, where the largest numbers are found shortly after the peak occurrence in the Wadden Sea.


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Guido O. Keijl, & Eduard V. Koopman. (1991). Veel Aalscholvers Phalacrocorax carbo en Dwergsterns Sterna albifrons op Rottumeroog, in juli en augustus 1990. Sula, 5(4), 146–149.