Photo 8708: Black-headed Gull L. ridibundus 2cy, January 04 2002, Le Portel / Boulogne-sur-Mer, France (50.42N,1.34E).

The partial autumn moult (post-juvenile moult into so-called "first winter") started right from the moment the nest was abandoned last summer and ended last September. In this bird, the partial moult included the head and under-parts. The buff-brown juvenile coloration on the head and in the lower hind-neck has been replaced: the head is most white now with a typical black spot on the rear ear-coverts and a dark patch around the eye, in this bird slightly extending over the crown. The mantle and scapulars have been replaced for second generation feathers which are all grey. 
Moult in the wing-coverts and tertials is in progress. The upper tertials were replaced very recently with a shiny glossy cast on the feathers and the fringes very neat. The new second generation feathers appearing plain grey. Note the worn fringes and the dark brown centres in the lowest tertials, indicating that those feathers are still juvenile. The inner greater coverts have been replaced recently as well and are plain grey, as in the upper tertials. The central and outer greater coverts are still juvenile, slightly brownish hued on the grey centres and worn at the fringes. In this individual, the partial moult in the wing-coverts included most of the inner median and lower lesser coverts, which are replaced for plain grey second generation wing-coverts. Note the black tail-band, typically for juvenile tail-feathers.

Normally, moult is suspended during the wintering months, from October to January, with the next moult taking place in early spring (from February to April: moult into so-called "first summer" plumage). However, as can be seen in several images on this website, some birds continue moult (particularly in the greater coverts) in these months, although probably on a slightly lower pace. In this way, the partial autumn moult gradually overlaps with the next partial moult of spring, which in turn may continue in the complete moult in summer. 
The partial spring moult normally includes the body and head. The hood will be more or less developed, although often with white flecking. A few individuals may include the central tail-feathers in this partial moult.

The common appearance of adult ridibundus in winter, although some adults may show remarkable amounts of black on the head already, as in some individuals the partial moult may start by December.

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 P7, 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.