Yellow-legged Gull - Larus michahellis

(last update: May 16, 2011)

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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.

L. michahellis: adult July

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 2nd, 3rd and 4th 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:

 

Adult michahellis remaining old primaries, July 11 2002 Etaples, NW France. n = 66, m = 6.3, SD = 1.03
P4 / <P5 old 4
P5 old 7
P6 old 29
P7 old 19
P8 old 6
P9 old 1
P4 / <P5 old: at least P5-P10 are still old and these scores are added by the definite P4-P10 birds. Those <P5 birds refer to sleeping adults.

 

adult michahellis remaining old and fully grown new primaries, July 28 2001 Etaples.
  p? p3 new p4 new p5 new p6 new n =
p6 old 1         1
p7 old 14 2 4     20
p8 old 14 3 5 4*   26
p9 old       1 1 2
p10 old         1 1

m (average): 2.4 remaining old primaries, SD = 0.69
p?: many birds sleeping, fully grown primaries hidden by tertials, so often p4 or less.
The survey was done at resting and preening adults; presumed sub-adults (with at least black central markings on the outer primary coverts) were left out of the score.
*: including two birds with p5 longer than p4, but still not fully grown (also called p4+).

 

adult michahellis remaining old and fully grown new primaries, July 29 2001 Etaples.
  ? p2 new p3 new p4 new p5 new n =
p7 old 16 1 2 3*   22
p8 old 20     8** 3*** 31
p9 old 2       1 3

m (average) = 2.3 remaining old primaries; SD (standard deviation value) = 0.58.
?: many birds sleeping, fully grown primaries hidden by tertials, so often p4 or less.
*: including one bird with p4 longer than p3, but still not fully grown (also called p3+).
**: one bird with p4 longer than p3 but still not fully grown (also called p3+).
***: one bird with p5 longer than p4 but still not fully grown (also called p4+).

 

adult michahellis scores: Lignano, Venice July 27 - 29 2001.
prim* score 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
3 5 4 9 8 19 33 28 46 22 13 5 8 9 4
    n: 216, m: 25.3, SD: 2.88
fully** grown p0 p3 p4 p5 p6                    
6 9 75 114 18           n: 222 m: 4.53 SD: 1.02    
About 75% is missing the complete median covert bar.
About 25% is missing / moulting tail-feathers.

*: prim score = primary moult score, see Topography for explanation. However, in this table a different score was used, with shed feathers scoring 0. So, both old feathers and recently shed feathers score 0, fully grown feathers score 5, still the primary score runs from 0 to 50.
**: Note: 6 bird did not miss a single primary. Those are left out the primary score.


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).

 

adult michahellis in April. (61415 bytes)Yellow-legged Gull (michahellis) adult, July 09 2010, Maagan Michael, Israel. Picture: Gal Shon. Complete moult.
adult michahellis in April. (61415 bytes)Yellow-legged Gull (michahellis) adult, July 09 2010, Maagan Michael, Israel. Picture: Gal Shon. Complete moult.
michahellis adult July 28 2010, Malaga, Spain.
Picture: G. Martin.
adult michahellis in April. (61415 bytes)Yellow-legged Gull (michahellis) adult, July 09 2011, Tel Aviv - University Garden, Israel. Picture: Amir Ben Dov.
Mixed pair of michahellis x armenicus.
adult michahellis in July. (62792 bytes)michahellis adult.
adult michahellis in July. (41288 bytes)photo 1: michahellis adult, July 11 2002, Etaples, NW France. From unknown origin, ringed green, blue, metal on left leg.
adult michahellis in July. (54509 bytes)photo 2: michahellis adult, July 11 2002, Etaples, NW France. The typical adult which is slightly behind in primary moult: P5 is still old and P2 is replaced. This individual is in active tail-feather moult.
adult michahellis in July. (45393 bytes)photo 3: michahellis adult, July 11 2002, Etaples, NW France. P6 is still old and P3 is growing.
adult michahellis in July. (54638 bytes)photo 4: michahellis adult, July 11 2002, Etaples, NW France.
Typical adult.
adult michahellis in July. (74548 bytes)photo 5: michahellis adult, July 11 2002, Etaples, NW France.
All wing-coverts abraded.
adult michahellis in July. (101300 bytes)photo 6: michahellis group, July 27 2001, Etaples (France). Wings raising adult with P7-P10 still old and many outer greater and median coverts shed.
adult michahellis in July. (95615 bytes)photo 7: michahellis group, July 27 2001, Etaples (France). An adult with P7-P10 still old, the greater coverts shed and the median coverts recently replaced.
adult michahellis in July. (97582 bytes)photo 8: michahellis group, July 27 2001, Etaples (France). Three sub-adults left and a wing raising adult with P7-P10 old.
adult michahellis in July. (98374 bytes)photo 9: michahellis group, July 27 2001, Etaples (France). Note the difference in moult progress.
adult michahellis in July. (99830 bytes)photo 10: michahellis 5cy?, July 27 2001, Le Portel (France). Note the black central markings on the primary coverts, a sign of immaturity.
adult michahellis in July. (92394 bytes)photo 11: michahellis group, July 27 2001, Etaples (France). Left to right: Two wing raising adults and one 3cy with P8-P10 old.
adult michahellis in July. (115395 bytes)Photo 12: michahellis adult, July 7 2001, IJmuiden, the Netherlands. 
adult michahellis in July. (93487 bytes)photo 13: michahellis adult, July 30 2001, Le Portel (France). P8-P10 still old and p6 just over P5.