Yellow-legged Gull - Larus michahellis

(last update: October 08 2013)

Coordinators:
Delfín González
Gabriel Martín
Antonio Gutierrez
Amir Ben Dov
Mars Muusse

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Larus michahellis - 2CY June

This website deals with the Yellow-legged Gull taxon michahellis, which is a common migrant from July to December in NW Europe. After extensive expansion of the breeding population during the last three decades, it nowadays can be found breeding in Belgium, the Netherlands and Britain in mixed couples with both Herring Gull (argenteus) and Lesser Black-backed Gull (graellsii). There are subtle differences between the populations from the Mediterranean, Atlantic coast of Portugal and Morocco and from the islands in the Atlantic. Most pronounced differences can be found in the taxon atlantis, now regarded as full species by some authors and birds along the Atlantic coast of the Iberian peninsular: lusitanius. Both atlantis and lusitanius are treated in their own sections on this website.

General description:

By June the primary moult is obvious as the outer flight-feathers are dropped now. Most birds look shabby, with obvious gaps in the median and greater wing-covert rows. The feathers which were included in the post-juvenile moult are normally left out of this spring moult until July. The exact figures are hard to obtain, as birds which do drop these earlier moulted feathers are not recognized of course (unless birds are ringed and reported several times). However, irregular moult sequences are not found in the tertials, as in most birds replacement in the tertials follows the ordinary sequence, from tertial #1 downwards. The majority of 2CY michahellis is easily identified by (some) adult-like grey scapulars, darker grey than in Herring Gull, almost blue-grey, and different from the silvery grey third generation feathers in argenteus. Check out the 2CY argenteus images in the May Section and June Section.

By June, 2CY michahellis in complete moult (second pre-basic moult) can be found commonly around the harbour of Etaples in NW France with a few 10's of birds in the direct surrounding of the fish-market and many immature birds using the near landfill of Dannes to feed on.

Identification:

The general appearance of 2CY michahellis is rather different from 2CY June Herring Gulls from Belgium, the Netherlands, especially regarding the pattern on fresh scapulars and wing-coverts. However, some local Herring Gulls from NW France may look very similar, have a look at these ringed Herring Gulls: this, this and this one. 
Strong and powerful male michahellis are readily easy recognized between 2CY argenteus. Examples of average May michahellis can be found in photo 4928 and in photo 1734. Those powerful birds (presumable males) show a combination of almost completely white under-parts, some grey adult-like scapulars, extensive moult in the wing-coverts and by June, an average moult score of 6.0 (P6 has been dropped, see table below). Such features are indicative for southern breeding taxa, as michahellis is, but doesn't necessarily exclude French Herring Gulls. Michahellis moult timing may show overlap with argenteus from southernmost populations and local argenteus (argenteus breeds in the industrial area of Boulogne/Mer). 
Some Lesser Black-backed Gulls graellsii and intermedius may resemble miniature michahellis, as this taxon may show advanced moult in wing-coverts and tertials as well. However, ID is often straightforward as its mainly the smaller taxon intermedius showing most advanced moult in LBBG. Furthermore, LBBG has a much broader tail-band, darker inner primaries and the last required scapulars often show much darker grey centres. Check out the 2CY June LBBG pages here. Remember that many LBBG winter far south (NW Africa), suspending moult during migration in June, thus showing only small moult gaps, contra extensive moult in June michahellis, showing obvious large moult gaps in the wing-covert rows. 
Remember that our surveys took place in Etaples (location information on the Le Portel Page), where you find michahellis from the western Mediterranean: mainly from S France, a few from Italy, Switzerland and NE Spain.

Grey-based scapulars or barred scapulars:

Images 1734 and 4928 represent strong male michahellis, easily recognized by the jizz, and showing barred wing-coverts and scapulars. The base colour is often brown-buffish in fresh feathers (by May - June) and the pattern, which can be bold and obvious on the scapulars, is normally repeated on the wing-coverts and result in a complete barred plumage in freshly moulted birds. 
Some female michahellis may show barred scapulars as well, but at Etaples, birds showing extensive grey scapulars are often smaller birds, so presumed females, as this bird demonstrates. The causality is one-way: smaller birds often show grey scapulars, but large birds do not necessarily have to show barred scapulars, as this bird and this bird show. 
Some michahellis may appear exceptionally advance in moult, as the female in image 1357 shows. This bird already show plain grey wing-coverts in the medians as well. has Probably, previous to the complete moult in summer, this individual has replaced many wing-coverts and tertials to second generation feathers. By June these coverts aremoulted again and may appear adult-like. Remember that birds with advanced post-juvenile moult do not necessarily develop all-grey scapulars in an early stage but may grown in fresh barred feathers as well. Therefore, by the barred patterns, these advanced birds do not necessarily look or appear more adult-like than others, as this bird demonstrates: all wing-coverts have been replaced, but they all appear immature. We don't know whether development of plain grey third generation scapulars or barred third generation scapulars is gender related, but on average, it seems the smaller birds (presumable females) develop more often grey scapulars than barred.

Moult stage and pace:

What's the average moult in June? We described 24 2CY birds in detail on two visits at Etaples, Calais region and the following pattern can be extracted:

By mid-June, primary moult is now visible in the folded wing. The average primary moult score: P6 missing and P7-P10 the last juvenile primaries. Most advanced birds by mid-June show an obvious gap in the central primaries, already missing P7 (almost 20% of the birds). Out of 41 birds, none had a score below "P3 missing", a figure matched by the approximately 200 Herring Gulls L. argentatus s.l. from the same location and from the Netherlands (one week later). The average moult stage of L. argentatus from this location almost equals michahellis, with bulk of the present birds missing P5 or P6 (table below). Interestingly, the primary moult score of local argenteus is slightly higher than argentatus s.l. average, as preliminary figures of metal-ringed French argenteus show.

The majority (about 75%) of 2CY michahellis have all the rectrices still juvenile. From April onwards, moult in the rectrices is still postponed but next month, when the inner 4 primaries are grown, the moult in both secondaries and rectrices will start.

In several sections of 1CY michahellis it's mentioned that birds include wing-coverts in the post-juvenile moult (unlike argentatus / argenteus where this post-juvenile moult is confined to the scapulars). To distinguish between 2CY birds which have still suspended moult (after the post-juvenile moult) and birds which have really started to replace wing-coverts, we separate between old second generation feathers and fresh second generation feathers in the table below. This is much easier said than done as the old second generation feathers may have been required as early as late-August and these wing-coverts may be extremely similar to the abraded juvenile wing-coverts. Close views under excellent light conditions are necessary to distinguish between the two by June, see e.g. this individual.
Except the difference in timing of moult, these new second generation feathers may show a different pattern as well, with fresh second generation feathers moulted from April and May onwards looking 'less immature': the base colour of the feathers is not buff-brown but buff-grey or feathers may be "grey-based" and the pattern may be less well-defined.
Its interesting to see that the wing-coverts which were included in the post-juvenile moult are left out of the first stage of the complete moult in early summer (until June at least) and are replaced in a later stage. This is nicely demonstrated by a Swiss metal-ringed michahellis Sempach 885629. The exact figures of such moult sequences are hard to obtain, as birds which do drop these earlier moulted feathers are not recognized of course. However, irregular moult sequences are not found in the tertials, as in most birds replacement in the tertials follows the ordinary sequence, from tertial #1 downwards.

The table below present figures of active wing-covert moult by mid-June. The progress in wing-covert moult is obvious with moult gaps in almost all wing-covert tracts, unless all coverts in  arow have been replaced completely. Leaving older second generation median coverts in place, while moult progresses in other tracts is a very common phenomenon, as 9 of 14 birds demonstrate. This is even more clear in the lower lesser coverts, where the figure is 7 out of 7. A few individuals have completely finished moult in the greater coverts, but all birds present are actively moulting lesser coverts. See Gull Topography for explanations of feather tracts.

As can be seen in many images of May, June and July 2CY michahellis, the sequence of moult in the lower lesser coverts is sometimes hard to obtain correctly. Post-juvenile feathers are maintained over a longer period and result in a 'jumpy' moult pattern and only after these old post-juvenile feathers are replaced for new third generation feathers, the lower lesser covert row appears neat and tidy. It's the end of July then...

Moult to third generation scapulars may start as early as mid-January in 2CY michahellis. By June, all present birds show active moult in the scapulars, with largest numbers for the class 75%-99% third generation scapulars (8 birds). 50% of the birds (n=24) have over 50% of the visible area (optical measurement) of the scapulars renewed. Previous sections of 2CY michahellis show the most commonly seen moult sequence in the scapulars, starting with the lower upper scapulars and finishing with the rear lowest scapulars. So not surprisingly, its mainly the lower scapulars which have been replaced by May, as is illustrated by this bird. Nevertheless, some birds may still moult upper scapulars.

Some 2CY michahellis showed a red orbital ring by mid-April to mid-May. This coloration might be initiated by hormones in early spring. By June and July, the red coloration has weakened and the orbital ring looks immature again.

Tables: