This bird was ringed in Sweden: Stockholm 6143424 and it shows the common appearance of adult ridibundus in winter, although some adults may show remarkable amounts of black on the head already. Actually, in some individuals the partial moult may start by December (southern breeders?). This Swedish adult has been present at IJmuiden several winters now, again in 2004. Ringed as pullus on 26 June 1999 at Mankarbo, Tarnholmen Sweden (60.11N 17.22E), and seen earlier 3 September 2000 at IJmuiden and 25 January 2001 at IJmuiden.

From June into October the complete moult in Black-headed Gulls start with the inner primaries. The second generation inner primaries are dark from below with small greyish tips, in this individual from P1 to P6, best visible from above. From P3 outwards (sometimes from P5 outwards) the second generation primaries show much white, except on the outer-web of P10. The under-wing coverts are pale grey, the tail is moulted to all-white feathers and the bill and legs turn dark red. Only a few individuals can be recognised as 2cy (second calendar year) birds in October by the primary coverts, which may still show some dark markings. Otherwise, most 2cy Black-headed Gulls from October are indistinguishable from adults. This individual is in all respects in complete adult plumage.

Next moult starts in December and goes on into April. It’s a partial moult including the body and head: the head becomes typically brown with obvious eye-crescents. Some birds develop a pinkish wash on the breast, a phenomenon maybe related to diet. When this moult is completed, birds show the "adult summer" plumage.