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 May

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:

From mid-April onwards, 2CY michahellis start dropping the inner primaries and the first wing-coverts. By May all 2CY michahellis are in active primary moult (except the odd individual). The wing-coverts which were included in the post-juvenile moult are normally left out of the first stage of the complete moult in summer and are replaced in a later stage. 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). 
By May, the numbers of 2CY michahellis have increased at Etaples in NW France with a few 10's of birds in the direct surrounding of the fish-market (about 75 on May 01 2003) and many immature birds using the near landfill of Dannes to feed on. 
The general appearance of 2CY michahellis is rather straightforward in 95% of the birds. Strong and powerful males are easily recognized between 2CY argenteus. Michahellis side-by-side argenteus can be viewed in this April picture. Examples of average May michahellis can be found in photo 03 and in photo 10. Those powerful birds (presumable males) show a combination of (some) grey adult-like scapulars, a pale head, contrasting with the neck-collar, dark-centred tertials and often substantial numbers of wing-coverts replaced in the first pre-basic (post-juvenile) moult and now, by May, active moult in the wing-coverts. Such features are indicative for michahellis and a combination of these characteristics would be very odd for argenteus and argentatus, by May. 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. 
In most birds, and especially when direct comparison is possible with argenteus, michahellis proofs to be ahead in moult. Nevertheless, 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 May LBBG pages here and the first image on this page.

The third and tenth images represent strong male michahellis, easily recognized by the jizz, grey scapulars and often the replaced wing-coverts. Some female michahellis may show very extensive grey scapulars, as this bird demonstrates. Another distinct 'group' of 2CY michahellis can be recognized and are represented by the bird in image 05. These birds may be similar in jizz and size (thus probably males) and are easily picked out of a group of argenteus Herring Gulls as well. They do not show third generation grey adult-like scapulars but have the third generation scapulars with barring or anchor patterning. The base colour is often brown-buffish in fresh feathers (by May - June) and the pattern, which can be bold and obvious, is normally repeated on the wing-coverts and result in a complete barred plumage in freshly moulted birds (although this completely replaced plumage can not be found in May birds but is obtained by the end of June. See the June Section for images). 
Some michahellis may appear exceptionally advance in moult, as the female in image 04 shows. Previous to the complete moult in summer, this individual has replaced many wing-coverts, tertials and even all the rectrices. Apparently, birds with advanced post-juvenile moult do not necessarily develop all-grey scapulars in an early stage, and therefore, by the barred patterns, do not look or appear more adult-like than others. 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.

Low tide: patrolling 2CY michahellis at the fish-market of Etaples, NW France, early-May.

Moult stage and pace:

In the tables below, figures are presented on May moult scores in several feather tracts of 2CY michahellis. We described 60 2CY birds in detail on two visits at Etaples, Calais region.

By early May, primary moult is in progress with an average primary moult score of 3.5 by mid-May. Most advanced birds by mid-May show an obvious gap in the inner primaries, already missing P5 (almost 10% of the birds). Out of 43 birds, none had all primaries still in place and none had P1 still in place. This moult stage is matched by argenteus from this location with bulk of the present birds missing up to P3 or P4 (table below).

The majority (> 80%) of 2CY michahellis have all the rectrices still juvenile. A minor 13% started the moult of tail-feathers by mid-May. As can be seen in previous sections, low but substantial numbers of michahellis do replace rectrices from October to March.

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 May. 
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. 

The table below present figures of active wing-covert moult by mid-May. There still is a minority of birds showing fresh second generation wing-coverts: 25% of 2CY michahellis showing fresh median coverts. Active moult is most obvious in these median coverts and the lower lesser coverts (see Gull Topography for explanations of feather tracts). Over 80% of 2CY michahellis has at least shed some median coverts by mid-May and and are thus in active moult (the complete moult in 2CY, also called second basic moult of the summer months has started). Out of 39 birds, no birds have a complete juvenile wing-coverts panel, as delayed birds were showing (old) second generation wing-coverts as well.

Moult in the scapulars and mantle, moult to third generation scapulars, may start as early as mid-January in 2CY michahellis. By May, all present birds are showing active moult in the scapulars, but still, a majority of birds (60%) has less than 25% (optical measurement of visible area) 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 upper scapulars which have been replaced by May, as is illustrated by this bird. Nevertheless, some birds may appear very advanced in scapular moult, with most of the back adult-like grey (see e.g. this presumed female).

If close views can be obtained, many 2CY michahellis show a red or orangey-red orbital ring by May; see again this female and this female, but on the other hand also this male.

Tables: