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 - 3CY 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 May the numbers of 3CY michahellis slightly increase at Etaples in NW France and by June, several 100's can be found in the region (Etaples, Dannes, Boulogne-sur-Mer, see theLe Portel Page).
The general appearance of 3CY michahellis is rather straightforward. Most birds are easily recognized between 3CY argenteus, with darker grey upper-parts, pitch black primaries and adult-like bare parts coloration: a red orbital ring and yellow legs. An example of the average michahellis can be found in the first image, an individual ringed near Marseille, S France, showing some worn grey wing-coverts, moulted in the partial moult.

Moult stage and pace of remiges and rectrices

As stated earlier, the complete moult starts by mid-May, with 3CY birds dropping the innermost primary P1. By mid-June, the complete moult is in progress: the primary moult score is about 4.9-5.5. 3CY birds are about two primaries behind compared to 2CY birds (which have only P7-P10 old by mid-June). The outer primaries and secondaries are second generation, replaced about half a year ago, the white crescents are worn away. 
We didn't described enough 3CY birds in detail to draw firm conclusions. By mid-May, primary moult started in 3CY birds. The table below presents an extrapolation of figures of 2CY and 3CY. Based on moult scores from July, we estimate the primary moult score of 3CY michahellis.

The rectrices have the white tips worn way as well. By June, the partial spring moult has finished, and a small minority of 3CY michahellis have included some rectrices in this moult. Hence, it's not uncommon to find 3CY birds showing plain white tail-feathers, in some birds creating a 'blocked' tail pattern. The complete moult in the tail-feathers has not started yet by mid-June.

Timing and strategy of body & covert moult in June

We didn't described enough 3CY birds in detail to draw detailed conclusions, the sample size has been too small. A few preliminary conclusions on 3CY michahellis:

• Head-streaking, which was obvious during the winter months and concentrated on the ear-coverts, around the eye and up to the crown from September to March, has been replaced by snow-white fresh head-feathers. The head and under-parts are white by May and still white in June.
• 3CY birds show a combination of adult-like grey scapulars, contrasting with adjacent barred lesser coverts. It's difficult to score missing feathers in the complete grey upper-parts, hence we have no scapular moult scores. In general, obvious moult gaps are lacking in June. In some individuals, the scapular region contains some old and abraded feathers, sometimes showing a barred pattern, others are completely bleached white with only a slightly darker shaft-streak. However, most birds have the entire back adult-like grey.
• In several sections of 1CY and 2CY 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). Wing-coverts are replaced again in the compelte moult in 2CY and inner wing-coverts are included in the partial moult in autumn in 2CY. In 3CY birds, the wing-coverts are predominantly second generation, especially the outer greater coverts and most of the lesser coverts (in the carpal edge). The median coverts and lower lesser tract contain a mix of third or even fourth generation wing-coverts.
  The complete moult has started, obvious in the primaries with moult score 4.9-5.5. As the inner two or three primaries are dropped, the moult in the wing-coverts starts as well. The ordinary moult strategy and sequence start in the outer median coverts, the inner medians and greater coverts, the upper tertial and the outer lower lesser coverts, as is illustrated in this individual.
• The upper tertials are often included in the post-juvenile moult and the partial autumn moult of 2CY as well. Some of the tertials, like the inner median and inner lower lesser coverts, may appear adult-like, sometimes plain grey. However, these grey third and fourth generation tertials may still show a delicate diffuse brown pattern.
  By mid-June 3CY michahellis include the upper tertial in the complete moult. 

See Topography Section for explanation of feather tracts.

Table