Gull Research Organisation

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 3CY michahellis.
The general appearance of 3CY michahellis is rather straightforward. Most birds can still be recognized by the plain grey upper-parts, combined with barred wing-coverts. The bare parts are typically a red orbital ring and yellow legs. An example of the average michahellis can be found in the first image, an individual ringed near Marseille, S France, showing active moult in the wing-coverts and only the outer two primaries are still old second generation.
For details on differences between michahellis and cachinnans, see e.g. the article by R. Klein & D. Gruber in Limicola, April 1997.

Moult stage and pace of remiges and rectrices

The complete moult started by mid-May, when 3CY birds dropped the innermost primary P1. By early July, the average score has strongly increased: P7-P10 are still old secnd generation and all inner primaries are missing or new. Since the tips of P5 and P6 normally extend beyond the tertials (especially the abraded July tertials), the moult gap of missing P5 and P6 is obvious.
3CY michahellis continue shedding primaries throughout the month, and by the end of July, the average primary moult score is 8.5, hence 50% have only P9 and P10 old, the other 50% has P8-P10 old. With this score, 3CY birds are about two primaries behind compared to 2CY birds (which have a score of 9.2: 45%of 2CY have shed all primaries by late July).
As in adults, the gap between full-grown primaries and remaining old primaries is in general about three feathers, but often slightly more as the table shows. This large moult gap is typical for michahellis, and not found in e.g. Dutch argenteus.

By the time P4 is fully grown, 2CY birds normally start the complete moult in secondaries and rectrices. The ordinary moult strategy in 3CY birds may be slightly later (starting when P5 is fully grown. Note however that individual variation may exist, particularly in 3CY michahellis rectrices moult as this moult may follow an irregular pattern in earlier months. The partial spring moult has finished in June and a small minority of 3CY June michahellis have included some rectrices in this partial moult. Hence, it's not uncommon to find 3CY birds showing plain white tail-feathers, in some birds creating a 'blocked' tail pattern already, prior to the complete moult. On average, the common sequence is centrifugal moult: starting with the inner tail-feathers and continuing symmetrically outwards to both outer feathers.

Secondary moult hasn't started yet in late-July, but is initiated in early-August. The images on this page showing birds with open wings illustrate that all outer secondaries are still present. By early August, the outermost secondaries (S1 & S2, at the division between secondaries and primaries) are normally dropped individually, but the central secondaries are shed almost as in small groups, creating large gaps of missing secondaries, nicely illustrated by this flying 2CY bird and this stretching 3CY August michahellis.

Timing and strategy of body & covert moult in July

Wing-covert moult in 3CY and sub-adult michahellis vary between individuals. See e.g. 365D, showing extensive moult in the wing-coverts (the sequence is mentioned in the accompanying text). Such birds contrast strongly with e.g. this bird, which has almost all the wing-coverts old.

Tables

The surveys were done at resting and preening 3CY sub-adults (with at least no white mirror at P10 and at least some obvious second summer feathers).

oldest primaries \ full-grown primaries in 3CY michahellis, Etaples, July 29-30 2001. n = 92, m = 8.5, s = 0.58
.	p4	p4+	p5	p5+	p6	p6+	?	n = 92	%
p=0	-	-	-	-	-	1	-	1	1%
p10	-	-	-	-	1	-	-	1	1%
p9	-	3	16	15	7	1	2	44	48%
p8	8	12	9	-	-	-	15	44	48%
p7	-	-	1	-	-	-	1	2	2%
Notes: Aggregated scores of two dates. Average on both dates 2.49 remaining primaries. * Oldest primary: the first primary to be shed next. * P=0: no old primaries in the outer wing (1 individual); p7 means p7-p10 are still old and p7 will be the next primary to be shed (2 individuals). * p4 as full-grown primary: p1-p4 are new. P4+ means p4 is the last full-grown primary but already, p5 is longer than p4 but just not yet full-grown, thus p4 last full-grown primary. * ?: no full-grown primary is visible (e.g. in resting individuals). In most cases this can be read as 'p5 yet not full-grown', because in most cases p5 would be visible in a resting bird because this primary is slightly longer than the longest (primaries covering) tertial.

Yellow-legged Gull - Larus michahellis

General description

Moult stage and pace of remiges and rectrices

Timing and strategy of body & covert moult in July

Tables