Gull Research Organisation

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 August

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 August, the primary moult is in its last stage, with all juvenile primaries dropped and new second generation primaries up to P8. Most birds have the greater, median and lower lesser coverts moulted in the complete moult last months, with moult still going on in the (outer) lesser coverts. In the mean time, the partial autumn moult starts this month, with 2CY michahellis dropping again some of the outer median coverts and the upper tertials. The final extend of this partial autumn moult in 2CY birds can be seen in the October section.

Moult stage and pace of remiges and rectrices

We have limited surveys on primary moult stage of 2CY michahellis from the end of the month. The figures can be viewed in the table below. We described 82 2CY birds in detail on two occasions at Etaples, Calais region.

By the end of July, the average primary moult score is P6 fully grown by 28^th July. The most advanced birds by late July show an obvious short wing, with P10 dropped and P7 already fully grown. One bird has P8 fully grown. The low SD values (standard deviation) in the July tables imply a small range of variation.
By the end of August, 2CY michahellis show an average increase of one primary in NW France: the average PMS is 7.9 (n = 29) on August 22 and the average PMS is 8.1 (n = 53) on August 25.

Compared to argenteus, these michahellis figures show that the differences in average PMS are very limited and the individual variation result in large overlap.

The majority of 2CY michahellis have started the moult in the rectrices and the secondaries by July. By the end of August, moult in the secondaries is almost finished, with a gap in the inner half of the secondary row. At first, the secondaries are moulted in descending order, from the outermost secondaries inwards, towards the body. When these outermost secondaries are fully grown, another moult wave starts from the tertials outwards, in ascending order. The stage of secondary moult is nicely illustrated by image 15 to 18. The tail-feathers are moulted centrifugally. As can be seen in the same images, all the rectrices have been replaced and in some individuals, the outermost rectrices R6 are still growing by the last week of August.

Moult stage and pace of wing-coverts

The complete moult in the wing-coverts may start by late April, with the majority of 2CY michahellis moulting median wing-coverts by early May. During the summer months, the median and lower lesser coverts are replaced, the tertials are replaced from the upper tertials downwards, new greater coverts grow in in two waves: from the outermost feathers inwards and from the inner greater coverts outwards. The two waves meet at about coverts #7 and #8. The lesser coverts are replaced last, finishing with the feathers in the carpal edge and the upper rows of lesser coverts. It's late August then and the complete moult in the wing-coverts and tertials is at its end.

In the mean time, 2CY michahellis start moulting inner median coverts and the upper tertials for another cycle: the partial moult in autumn is initiated. This partial moult may overlap with the replacement of the last lesser coverts, by late August. As can be expected, birds include the most vulnerable and oldest wing-coverts first in this partial moult, so this partial moult normally starts with the outermost and inner median coverts, the inner greater coverts and the upper tertials. This is nicely demonstrated by several images in this August section: image 1 shows a bird with missing outer medians, image 11 shows a bird with missing upper tertials and outer medians and image 13 shows a bird with fresh inner greater coverts. These are all illustrative for individuals in which complete moult overlaps with partial moult. The complete moult will be finish by the time the last outer primary P10 is fully grown. See Gull Topography for explanations of feather tracts.

The box below enlarges upon the partial moult in autumn in 2CY michahellis.

Partial moult in 2CY Yellow-legged Gull. What exactly does it mean?

Feathers wear, bleach, break and deteriorate by use and climatologically exposure. Birds have to replace the feathers to renew their complete plumage, normally in cycles and in most northern hemisphere species at least once a year. Second calendar year Yellow-legged Gull is no exception, and the complete plumage is replaced in summer. The complete moult starts with shedding the innermost primary P1 and finishes with a fully grown outer primary P10. In autumn, a second moult wave is started, including body-feathers for most: some of the wing-coverts and tertials are moulted to a next generation feathers. Some individuals include tail-feathers in this moult.
These two images clearly show what is meant by the partial moult and illustrates the notations used in our surveys. Wing-coverts are labeled from the body towards the outer wing and the tertials are numbered from upper feather downwards. Best clue for recognition of fvresh feathers are the grey bases and neat white fringes, compared to the bleached adjacent feathers.
In these images, the following feathers are included in the partial moult: tertials #1-#2 (tt1, tt2) are new, the lower tertials are still old. In the greater coverts, #2 (gc2) has been replaced and #5 is missing. In the median coverts #1-#2 (mc1, mc2) have been replaced, #4 is missing, #6 has been replaced and all feathers from #8 outwards are new. The inner lower lesser coverts (illc) #1, #4-#7 are new, #8-9 are old, #10 is missing. In the upper lesser coverts (lc) only one innermost feather has been renewed. The exact generation of the new wing-coverts and especially the scapulars is very difficult to ascertain. 2CY michahellis has an extensive partial post-juvenile moult, where many wing-coverts are replaced. In complete moult in summer (2CY), these wing-coverts are replaced for third generation feathers. In the partial autumn moult in 2CY, as described in this box, some wing-coverts are renewed again, to fourth generation.
Scapulars are moulted 'continuous' as it seems, although at a lower pace in winter. By May, 2CY michahellis may show already 95% third generation scapulars and a vast majority is moulting again in June and (still?) in August. Some scapulars may thus apply to third generation feathers (especially in the lowest row), but likewise some apply to fourth (maybe fifth) generation scapulars. In the picture, the abraded lower scapulars with brown centres (ls) are probably old third generation feathers, the fresh plain grey feathers in the lower upper scapulars are probably fourth generation. In the mantle (m), similar grey feathers are growing in.

Moult stage and pace of scapulars

Moult to third generation scapulars may start as early as mid-January in 2CY michahellis. By June, all present birds show active moult in the scapulars, with largest numbers for the class 75%-99% third generation scapulars (n = 24). By the end of July, this moult in the scapulars is completed, with fresh feathers in the lowest scapular row.
Most individuals do not show obvious moult gaps in the scapulars and mantle by August. The last replaced scapulars still show warm buff or pale grey centres and obvious white fringes. We do not have sufficient data to draw conclusions on the exact moulkt stage of the scapulars and mantle.
By July and August, the variation in scapular patterns is tremendous, with some birds already showing an (almost) complete grey saddle: the grey scapulars and mantle contrast with the barred lesser coverts. Other individuals show strongly barred scapulars, resulting in a much more immature appearance.

Tables

*Primary moult score of 2CY michahellis* Yellow-legged Gull, at Etaples, NW France (50.43N, 01.37E) on August 08 2003.**
.	P6 fg	P7 fg	P8 fg	n:
P9-P10	-	-	-	-
P10 old	1	2	-	3
no old P	-	28	6	34
n:	1	30	6	37
n = 37; m new P = 7.1; SD new P = 0.42; m old P = 0.1; SD old P = 0.28. P9-P10 = P9-P10 are still old and present. fg = fully grown. In our field surveys, a primary is 'fully grown' when it exceeds the previous feather in the folded wing. Actually, such 'fully grown' feathers may have to grow a little, but under field circumstances, it's very difficult to find out if the waxy sheath, which is the standard measurement for fully grown primaries, is still present.

*Primary moult score of 2CY michahellis* Yellow-legged Gull, at Etaples, NW France (50.43N, 01.37E) on August 10 2003.**
.	P6 fg	P7 fg	P8 fg	n:
P9-P10	-	-	-	-
P10 old	4	8	-	12
no old P	-	27	19	46
n:	4	35	19	58
n = 58; m new P = 7.3; SD new P = 0.58; m old P = 0.2; SD old P = 0.41. Further comments / notes: see previous table.

*most recent fully grown primary in 2CY Larus michahellis,* Etaples, NW France.**
	August 22 2000	August 25 2000
p6	-	-
p7	5	-
p8	22	49
p9	2	4
p10	-	-
n:	29	53
m:	7,9	8,1
fully grown: In the year 2000 field surveys, a primary is scored 'fully grown' when it reaches the estimated fully length, which is very subjective in the field. In later researches, we redefined 'fully grown' to primaries, which exceed the previous feather in the folded wing. Actually, such 'fully grown' feathers may have to grow a little, but under field circumstances, it's very difficult to find out if the waxy sheath, which is the standard measurement for fully grown primaries, is still present.

most recent fully grown primary in 2CY Larus argentatus s.l. (but presumably argenteus), on August 23 & 26 at Boulogne-sur-Mer, NW France and on August 28 at Scheveningen, the Netherlands.
	August 23 2000	August 26 2000	August 28 2000
p6	6	-	3
p7	18	16	34
p8	40	27	20
p9	7	1	-
p10	-	-	-
n:	71	44	57
m:	7,7	7,7	7,3
SD:	0,77	0,53	0,57
Notes: see previous table.

Yellow-legged Gull michahellis 2CY HES 884278 August 25 2000, Boulogne/Mer, France. Ringed in Switzerland.

Yellow-legged Gull michahellis 2CY GO.41 August 2010, Malaga, Spain. Picture: Gabi Martin.
Ringed in Malaga.

Yellow-legged Gull michahellis 2CY G.86F August 24 2010, Malaga, Spain. Picture: Hans Larsson.

Yellow-legged Gull michahellis 2CY PDYZ August 14 2009, Tarragona, Catalonia, Spain. Picture: Chris Gibbins.

2cy michahellis in August, ringed in S France. (75783 bytes)

Yellow-legged Gull michahellis 2CY 171Z August 08-11 2003, Etaples, France. Ringed in S France.

Yellow-legged Gull michahellis 2CY S4E6 August 04 2009, Szeged, Hungary. Picture: Csaba Barkóczi.

Yellow-legged Gull michahellis 2CY SL51 August 09 2006, Leipzig, Germany. Picture: Jürgen Streudtner.

Yellow-legged Gull michahellis 2CY SL53 August 01 2006, Zadar, Croatia (44.07 N 15.14 E). Picture: A. Monoki.

Yellow-legged Gull michahellis 2CY, August 14 2009, Tarragona, Catalonia, Spain. Picture: Chris Gibbins.

2cy michahellis in August. (78445 bytes)

Yellow-legged Gull michahellis 2CY, August 10 2003, Etaples, France. P8 fully grown and no old primaries left.

2cy michahellis in August. (81845 bytes)

Yellow-legged Gull michahellis 2CY, August 08 2003, Boulogne/Mer, France. P7 fully grown, no old primaries left.

2cy michahellis in August. (59534 bytes)

Yellow-legged Gull michahellis 2CY, August 10 2003, Etaples, France. P8 fully grown.

2cy michahellis in August. (59684 bytes)

Yellow-legged Gull michahellis 2CY, August 10 2003, Etaples, France.Barred individual (second generation-like wing-coverts and scapulars.

Yellow-legged Gull michahellis 2CY, August 08-11 2003, Etaples, France. Two birds: one grey and one barred scapulars.

Yellow-legged Gull michahellis 2CY, August 10 2003, Etaples, France. P8 fully grown and secondaries still missing.

2cy michahellis in August. (70884 bytes)

Yellow-legged Gull michahellis 2CY, August 10 2003, Etaples, France.P7 fully grown and innermost secondary still juvenile.

Yellow-legged Gull michahellis 2CY, August 09 2003, Etaples, France. P7 fully grown and innermost secondaries still juvenile.

Yellow-legged Gull michahellis 2CY, August 23 2010, Malaga, Spain. Picture: Hans Larsson.

2cy michahellis in August. (47130 bytes)

Yellow-legged Gull michahellis 2CY, August 09 2003, Etaples, France.

Yellow-legged Gull michahellis 2CY, August 07 2006, Chevroux, Switzerland. Picture: Stephane Aubry.

michahellis remiges & rectrices.

Yellow-legged Gull michahellis 2CY, August 25 2000, Etaples, France.

Yellow-legged Gull michahellis 2CY, August 25 2000, Etaples, France.

Yellow-legged Gull michahellis 2CY, August 25 2000, Etaples, France.

Herring Gull to compare.

Herring Gull argenteus 2CY, August 25 2000, Boulogne/Mer, France. Have a look at the 2CY Herring Gull section.