Afwijkend gekleurde Grote Sterns Sterna sandvicensis op Griend en elders in West-Europa

This paper reports the recent observations (August 2010) of at least two aberrant coloured Sandwich Terns, caused by the mutation Brown, in The Netherlands, England and Scotland respectively. All sightings refer to birds that were ringed. The mutation is discussed. Although it is the most common genetic pigment disorder in birds, it is seldom seen in terns. The bird from The Netherlands was probably born at the island Griend (Wadden Sea). The two sightings in the UK could refer to the same individual. The times and dates of all sightings make it unlikely that the British and Dutch birds were one and the same individual that could have crossed the North Sea.