Juveniles typically show a buff-brown wash on the crown and ear-coverts, while throat and hind neck are white. The buff extends on the sides of the breast and on the mantle and scapulars, where the feathers become more ginger-toned and show white fringes. The tertials are brown, as are the median coverts and lower lesser coverts. The greater coverts and upper lesser coverts are grey. The white tail shows a clear black tail-band.

The partial autumn moult (post-juvenile moult into so-called "first winter") starts right from the moment the nests are abandoned and is normally completed by September. This partial moult includes the head and under-parts and often some median and lower lesser coverts are moulted to second generation feathers as well. Most of the buff-brown colour is replaced: the head becomes whiter with only a dark patch on the ear-coverts and around the eye, extending over the crown. The mantle and scapulars are moulted to second generation feathers which in turn are all grey. If median and lower lesser coverts are involved, they are replaced by all-grey feathers as well, similar to the juvenile outer greater coverts. The tertials are normally excluded and remain brown. Observation of 1cy birds in December reveal that a substantial number of birds are still in active moult, replacing the wing-coverts and lower scapulars. Therefore, it seems to be likely that the partial autumn moult in 1cy birds may continue into the next spring moult in 2cy. Exact data are not presented here, but in several images of 1cy December birds on this page, this extensive partial moult can be seen (e.g. here and here).

During the wintering months, from October to January, moult is normally suspended or may continue at a very low pace.

Next moult takes place in early spring (from February to April into so-called "first summer") and includes again the body and head, hence a partial moult again. By now, the hood is more or less developed, although often with white flecking. A few individuals may include the central tail-feathers in this partial moult.

The complete moult in 2cy birds takes place from June into October, and starts with the inner primaries. The second generation inner primaries are dark from below with small greyish tips 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 darker red. In general, birds resemble adult birds in many respects once this moult is completed. 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.

Next moult starts in December and goes on into April. When this moult is completed, birds show the "adult summer" plumage. 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.

Measurements in mm’s wing: 280-315, tail: 104-124, bill: 30-37, tarsus: 42-47; n = 12.

Ringed Black-headed Gulls in the first week of January 2002 at Le Portel and Etaples (NW France):
Helsinki ST 167.479. This bird was ringed as pullus at the nest, June 28 1995, Korsnäs, Finland (62.55N,21.03E).
Black 5RU. This bird was ringed at the same spot as an adult on January 03 2002 (same day as the day of recovery).
Black 6RW. This bird was ringed as an adult on January 03 2002.
Black 5RV. This bird was ringed as an adult on January 03 2002 (day before the recovery).
Black R023. This bird was ringed as 2cy in 1995 and was reported since for more than 20 times at the same spot. 
Green CC66. It had also a metal ring number ST-172.055 and was ringed as full-grown adult, hatched before 1993. Ringing date: 30.4.1995 at Rautalampi, Finland (62.43N,26.45E).

photo 7525: Black-headed Gull L. ridibundus 1cy, December 24 2002, Amsterdam, the Netherlands.

photo 7517: Black-headed Gull L. ridibundus 1cy, December 24 2002, Amsterdam, the Netherlands.