L. michahellis: 1cy December

General description:

By December, 1cy michahellis shows more or less the same moult stage as birds from November. Active moult is nearly completely suspended now winter starts. Remarkably, in mid winter, the majority of michahellis from SW Netherlands and Le Portel (NW France) still show completely juvenile wing-coverts (but sample size is insufficient to draw any conclusions). This contradicts with the figures from July - September, so different individuals (and even different populations?) may be involved throughout the months. On some locations in the Netherlands, like landfills, inland gravel pits along the river Meuse and along the coast (like the Maasvlakte, near the port of Rotterdam) small groups can be found daily.

Mid-winter identification:

Identification of 1cy Yellow-legged Gull is rather straightforward in birds with moulted wing-coverts and tertials, although some 1cy cachinnans may look pretty similar, especially when males are involved. To compare these plumages, have a look at the 1cy cachinnans section. Yellow-legged Gull has extensive moult in the under-parts by December, with the second generation head already turning white in some individuals. The 1cy partial moult (post-juvenile moult) in the under-parts includes the head, neck, breast, belly and flanks. The under-tail coverts are normally excluded from this partial moult. 
The mantle and scapulars consist of second generation feathers, which are slightly worn at the fringes in the upper scapular region. These feathers were moulted late July and in August, hence are already more than four months old. In the lowest row of the scapulars, the recently moulted feathers have a neat fringe but the buffish hue on the centres start to fade away. In some 1cy michahellis, the next moult in the upper scapulars takes place, with feathers now replaced for the second time: moult to third generation.

Normally, best clues for 1cy michahellis:

• strong and powerful bird. Strong breast, large bird, especially males.
• heavy bill with an obvious gonydeal angle.
• angular head with sloped forehead.
• advanced moult stage in under-parts and scapulars.
• ill-defined window on the inner primaries confined to the inner-webs of the primaries.
• wedge-shaped tail-band, narrow on the outer rectrices (R6), where almost completely reduced to the inner-web of R6.
• dark outer greater coverts with the white fringe not reaching the base of the feather on the outermost greater coverts.

Moult stage and pace:

All 1cy michahellis  have shed and replaced the juvenile feathers in the scapulars and mantle feathers. In turn the mantle and scapulars feathers are completely second generation. The ordinary pattern is a pale based centre with dark bars or an anchor pattern.

The covert and tertial moult vary to a large extend at Etaples, with a remarkable high proportion of birds in January showing all the wing-coverts and tertials still juvenile (remarkable higher numbers than expected on the figures from October, where only 19-27% of the 1cy birds had all the wing-coverts and tertials juvenile). Year 2002, more research at this location has to be executed to confirm the first findings. An example of a bird with all the wing-coverts and tertials still juvenile can be seen in image 7990.

Other birds have various amount of replaced feathers in wing-coverts and tertials (as can be seen in image 7963). Limited data on moult doesn't allow us to draw any conclusions on the average 1cy michahellis moult stage by mid December.