(8 images) Herring Gull DA 2129502cy (argenteus), April 20 2002, Boulogne-sur-Mer, France (50.42N,01.34E). 

A ringed 2cy bird seen in April, June and July; ringed with a French ring: Museum Paris DA 212950. It was ringed as 1cy on November 20 2001 at Wimereux (50.46N, 01.36E), only 6 km north of Boulogne. This bird was registered 'Yellow-legged Gull, L. cachinnans' by the ringer, which it may well be; but we believe some characteristics might point to argenteus. At first impression DA 212950 is surprisingly reminiscent of 2cy of the michahellis taxon (see the third April image!!!), and for two months, there were strong indications for both argenteus and michahellis, with a slight bias to argenteus.
It's a strong and powerful bird, with the general jizz of michahellis. The head proportions strongly indicate michahellis in the third image, but it also adopted the jizz of argenteus as can be seen in the last images from July. The inner primaries show relatively large paler patches and create a window not unlike the window in argenteus, though not really well-defined. Another indication for argenteus is the checkered 'piano-key' pattern of the outer greater coverts. Michahellis normally show extensive dark bases on the outer greater coverts. The recently moulted rear lower scapulars show an ill-defined pale brown pattern on a largely white base as can be found in many 2cy argenteus (though Dutch argenteus may moult these feathers slightly later in the season and such moulted lower rear scapulars are normally found in May. By April quite some argenteus show juvenile rear lower scapulars). 

For comparison a few other Paris-ringed birds are added on this website:
- A 2cy argenteus, ringed in France, Paris DA-216321.
- A 2cy argenteus, ringed in France, Paris DA-216323.
- An adult argenteus, ringed in France, Paris DA-..... .
- An adult michahellis, ringed in France Paris EA-543054 seen in the Netherlands.

Although these above mentioned characteristics may point to argenteus, other points strongly advocate michahellis. The tertials are extensively dark-based, and together with the primaries are the darkest feathers on the bird. The tail-feathers show a wedge-shaped tail-band, contrasting with the vermiculated base of the rectrices and the almost completely white upper-tail coverts. One of the strongest points for michahellis are the second generation wing-coverts which were included in the post-juvenile moult. About ten second generation coverts can be found in the lesser coverts. British, Dutch and Belgium argenteus normally show a complete juvenile wing-covert panel throughout spring, until May. About 50% of the upper scapulars have been replaced for third generation feathers, strongly resembling second generation scapulars in their pattern. Four lower scapulars have been moulted as well. 

April 20 2002

April 20 2002

April 20 2002

3 images above: DA 212950, April 20 2002, Boulogne-sur-Mer, France (50.42N,01.34E). 

3 images below: DA 212950, June 13 & 14 2002, Boulogne-sur-Mer, France (50.42N,01.34E).

The same bird Paris DA 212950 is depicted below. By June, the plumage looks completely different with almost all the scapulars moulted to third generation feathers, showing a bold pattern of black bars on a buffish-brown base. When you compare the left wing of this bird in the April and June pictures, it shows that the lesser coverts which were included in the post-juvenile moult are left out of this spring moult, while adjacent feathers are freshly replaced second generation lesser coverts. These earlier moulted second generation coverts are shed by July. The tail is still completely juvenile and the primary moult arrived at P6 with P7 still juvenile and P4 fully grown. 
The left wing is slightly behind in moult, both in the wing-coverts and in the tertials. The upper three tertials have been replaced, while the lower tertials are still juvenile. Greater coverts #1-3 are new second generation feathers and the central greaters are missing. In the outer-wing, the greater coverts are growing inwards, with the inner coverts shorter than the outer feathers. All median coverts have been replaced and the two inner medians which were included in the post-juvenile moult are still present (although one is slightly out of position and subsequently a gap appears in the median row, see the image below). Interestingly, in the left wing the moult in the lower lesser coverts row is ahead compared to the right wing. There are no juvenile lower lesser coverts left, but the exact sequence of moult is hard to ascertain with many feathers of uneven length and many feathers missing. The lesser covert moult is well in progress with the feathers included in last year's post-juvenile moult still in place.

June 13 2002

June 13 2002

June 14 2002

June 14 2002

2 images below: DA 212950, July 10 2002, Boulogne-sur-Mer, France (50.42N,01.34E). 

Again, DA 212950 still present in July. By July the tail-feathers are moulted with only the juvenile R6 present (outermost tail-feather). All other rectrices have been shed and are growing, not visible yet. Primary moult arrived at P6 which is fully grown, while P9-P10 are still juvenile.
The moult-state of the left wing can be seen in the pictures: tertials #1-5 are second generation while #6 is still juvenile. All greater coverts are new second generation feathers. All median coverts were already replaced by June. The innermost lower lesser covert is still missing, all other feathers are replaced. The lesser covert moult is in progress with four feathers (which were included in last year's post-juvenile moult) still in place; about 60% of the lesser coverts is missing. The moult to third generation scapulars is almost completed: in the lowest scapulars two feathers are missing and one feather has a pale white base, this feather is probably still second generation. All other feathers are third generation, very similar to second generation feathers in their bold anchor pattern.

July 10 2002

July 10 2002