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 July

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

Early July and from July 26-30 2001 we did small surveys on Yellow-legged Gulls at Le Portel (near Boulogne-sur-Mer) and Etaples (near Le Tourquet). In these surveys, we scored moult stages to determine timing of moult in primaries (and wing- coverts and body-feathers) in adult michahellis. Adult michahellis is readily easy identified by July, as only limited adult Herring and Lesser Black-backed Gulls are present. 

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 July

The tables below show the moult progress in a two week interval at Etaples, near Boulogne-sur-Mer, NW France (click here to find maps of locations and pictures of Le Portel surroundings). In the second week of July, the adult michahellis primary score is slightly over 6: 6.3 in the first table. By the end July, primary moult continues, only leaving the outer four or five primaries unshed. It's hard to draw any conclusions about the moult stage of new grown primaries in July, as in most birds the exact primary moult score could not be established. However, the score of remaining old primaries was established at 2.4, with n = 106, weight SD = 0.63, July 28-29 2001 at Etaples. The very narrow range of moult scores (expressed by the low SD value) is one of the most striking characteristics when scanning a group of michahellis. The spread around the mean value is often near perfect and in this respect differs strongly from e.g. Lesser Black-backed Gull, which has high SD values, in many cases caused by a mix of different populations. For more details on LBBGs, click here. A gap of three primaries is common in adults, as can be found in the tables as well; e.g. P4 fully grown, P5 almost fully grown, P6 almost at half of the final length, P7 just shed and P8 still old.
The secondary moult is just not started by the end of July. In immatures the secondary score is slightly advanced compared to adults and by the end of July, third calendar year michahellis drops the 2^nd, 3^rd and 4^th secondaries (the outermost secondaries). Near adults (4CY birds) are similar in moult pace to the adults and normally show a complete secondary row. The same is true for the rectrices. Normally, adults show a complete tail throughout July while average 3CY michahellis drop the central tail-feathers by the end of July. 

Moult in the wing coverts

Normally, adult michahellis do not include wing-coverts in the partial pre-breeding moult in spring. Consequently, the coverts start to show extensive wear by June; and by early July feathers can be very abraded. The feathers most vulnerable for wear are the upper tertials, the inner coverts and the rear lower scapulars. As can be seen in some of the images, e.g. image 12 and 10, some tertials and greater coverts have the top half strongly reduced, leaving only a protruding shaft-streak in some feathers. 
By July, some adults still have present all the abraded coverts, showing no gaps in the covert rows (see e.g. image 5). Other adults start moult, dropping the inner greater coverts and innermost and outermost median coverts. Adults with new median coverts can be found at Le Portel by early July as can be seen in image 4. The lesser covert moult sequence is more difficult to fully understand as feathers of this tract are dropped randomly. The start of greater covert moult is pretty obvious, as suddenly the white-tipped secondaries can be seen from underneath the greater coverts. Normally, those secondaries are hidden completely. 
By the end of July, the vast majority of adult michahellis have started wing-covert moult and may look very messy: the old retained feathers are very abraded and quite some feathers have been dropped, resulting in various moult gaps.

Timing and strategy of body & covert moult in July

In line with other large white-headed gulls in NW Europe, most obvious body feather moult starts with the head feathers around the eye and the flank feathers (see image 5). From the end of June and throughout July, feathers are dropped in the area around the eye and leaves the skin naked. The red orbital ring becomes even more obvious. Most other body feathers are retained and especially the flank feathers may look very abraded. 

See the Topography Section for explanation of feather tracts.

Tables

This table presents the results of a research done in the same period at Lignano, near Venice. As can be read from the table, adults in this region are ahead in primary moult-score compared to the birds from NW France. In line with what can be expected, moult in the rectrices is advanced as well, with about 25% moulting the tail-feathers. The moult of rectrices starts about a week or 10 days later at Le Portel (in the first week of August).