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 November

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 November, 2CY michahellis show an almost similar plumage as 2CY October birds. There is hardly any additional moult in November and the main differences can be found in the state of wear of the feathers. Wing-coverts included in the partial moult start to show slight wear in the fringes as well by November.

Moult stage and pace of remiges and rectrices

All 2CY michahellis have finished the complete moult in the primaries, secondaries and rectrices by early-October. By the winter months, moult in the rectrices may be seen again in few 2CY michahellis. Birds grow in plain white tail-feathers or white feathers with limited black vermiculation. Active moult in the tail-feathers can also be seen in 3CY michahellis in partial spring moult (May).

Timing and strategy of partial moult

The complete moult take all the summer months, in which 2CY michahellis moult all the scapulars, wing-coverts, tertials and flight-feathers. In the July and August sections the progress of this complete moult is described. 
From late-August, the complete moult in the wing-coverts finishes with replacement of the last central greater coverts and finally the feathers in the carpal edge (outer lesser coverts). As those last lesser coverts are replaced for second generation feathers, the partial autumn moult starts in 2CY michahellis, starting again with the upper tertials and outer median coverts. By early-November, this partial moult finishes.

In most individuals, the moult strategy in the partial moult follows a common strategy: 2CY michahellis start the partial moult with shedding the outermost median coverts, followed by the upper tertials. This moult stage can be found commonly in late August, but may be found in late September birds as well (image 4733). Most extensive replacement takes place in the median and lower lesser coverts in October (see e.g. image 6630). Moult in the greater coverts is often confined to the inner feathers and moult in the tertials is often confined to the upper three feathers. 2CY michahellis hardly replace lesser coverts, and if they do, there is no distinguishable sequence.

It's hard to label the feathers to exact generation. As can be seen in the 1CY michahellis October section, the post-juvenile moult in michahellis can be very extensive. Most michahellis moult inner wing-coverts to second generation in 1CY October. They replace these wing-coverts again in the complete moult in July-August. Then again, inner wing-coverts are replaced by the partial moult in 2CY michahellis in September, but not necessarily the same wing-coverts as in the post-juvenile moult.

Moult stage and pace of scapulars

By November, scapular moult continues at very low pace. Due to the considerable moult in the scapulars in 1CY birds in August, in 2CY birds in April-May, in July and again in September, we exclude the scapulars from further analysis. 

Movements

By November, only few 2CY michahellis can be found along the coasts of SW Netherlands and NW France. The majority returns to lower latitudes. Those which remain, probably belong to michahellis from the colonies of Marseille and the Mediterranean coast.

Tables

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