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 - adult September

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

September is one of the best months to study michahellis at Le Portel and Etaples, NW France. At the beach of Le Touquet, near Etaples, large groups congregate and use the beach as a resting place. They frequent the Dannes landfill as feeding place and many depend on the local fish-market of Etaples for food supply. The ports of Boulogne-sur-Mer and the beach of Le Portel are other good spots to find adult Yellow-legged Gulls. See Le Portel page for locations.

The difference between sub-adult and adult birds is sometimes very difficult. We used the plain grey greater primary coverts as criteria in our scores. For details on differences between michahellis and cachinnans, see e.g. the article by R. Klein & D. Gruber in Limicola, April 1997.

Moult of remiges and rectrices in September

All the old primaries have been shed and new central secondaries grown in almost simultaneously. By the end of the month the average adult michahellis show eight new fully grown primaries and an almost completed secondary moult: S1 to ±S8 are fully grown, the central secondaries are growing and the inner secondaries are still missing. The tail-feathers are fully grown or moult is nearly completed: the outer rectrices which still have to grow an inch or so.

In this section, two tables are included with the results of primary moult scores from Le Portel. In the first table, the SD value is strongly influenced by the observation of a single adult showing P5 as the last fully grown primary. Leaving this single score out the survey, the SD value would be 0.52, which is more in line with results from the previous months and the survey from the same day that is presented in the second table. After leaving the odd single bird out, the average primary moult score by the end of the month is 7.9 with n = 64 and SD = 0.53. As can be seen in the table, adults and near-adults are about one feather behind compared to 3CY birds and about two primaries behind compared to 2CY birds.

Moult in the wing-coverts

The complete wing-covert moult is in progress throughout August and is finished by September. The ordinary moult strategy and sequence started in the outer median coverts, the innermost medians and innermost greater coverts, the upper tertial and the outer lower lesser coverts. By mid-August, the median and lower lesser coverts have been replaced and adult michahellis are missing the outer greater coverts and some lesser coverts. By late-August, the outer greater coverts have been replaced as well and the gap in the greater coverts will be closed at greater coverts #7-#8 in birds following the ordinary moult strategy, see e.g. here (missing greaters) and here (closing the gap at #7-#8). Moult in the central greater covert is completed by mid September and the fresh feathers still show a delicate pale grey fringe (see e.g. here).
By early-September, the most advanced birds have replaced all the wing-coverts and may start again a new additional cycles of wing-covert moult: the partial wing-covert moult in autumn. They normally start at the oldest wing-coverts, i.e. the median coverts and lower lesser coverts. See e.g. here.

The tertial moult is finished by the end of September. Normally the upper two tertials show wear in the tips while the next four tertials are very fresh with broad white tips.

The last feathers in the lowest row of lower scapulars are growing in and by the end of September the complete scapular and mantle region is pretty neat without moult gaps in the average adult michahellis, as can be seen in the images from the end of September (e.g. here, missing one central lower scapular).

Timing and strategy of body moult in September

The winter head becomes more obvious in August and September, where streaking is concentrated around the eye, on the ear coverts and to the nape, sometimes running down in the neck. Isolated small dark spots can also be found in the lower neck. Moult of the flank feathers was started already at the end of July. By August, feathers in the breast and vent are moulted as well. All under-parts are snowy white lacking the fluffy loose feathers which were visible in the summer months. 

See the Topography Section for explanation of feather tracts.

Naked parts

Adult michahellis shows limited black on the bill. The colour of legs and bill hardly turns duller than in full summer plumage. The iris is clear yellow lacking pigmentation; the orbital ring coral red.

Tables