Yellow-legged Gull - Geelpootmeeuw (L. michahellis): adult August

(last update: 08 december 2003)

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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.

General description:

August 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 sub-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 August:

This is the last month research on remaining old primary scores can be executed, as the group of birds with all primaries shed still does not influence the mean and SD-value significantly. The weighted mean value for the end of August at Etaples and Le Portel is 1.59, with n = 133 and SD = 0.69. Again the narrow range of remaining primaries is obvious, expressed by the low SD value. As the table shows, the average remaining old primary score is 1.6, with still one week to go in August. Extrapolation will result in a remaining primary score of about 1.5 for August 31. By the end of July this score was still 2.35 with n = 106 and SD = 0.63. 
Linear regression analysis of first, provisional data collected for Yellow-legged Gull, Lesser Black-backed Gull and Herring Gull (data from NW France and SW Netherlands) show some differences between the three species. Michahellis is an early moulting species, as can be expected as it starts breeding relatively early. It is on average about a full primary ahead of the two other species. Furthermore, compared to argenteus Herring Gulls, it also is somewhat quicker in moulting the primaries (shedding primaries at a higher pace) and therefore the figure shows a steeper regression line (larger regression coefficient in the formula). In future, pages on these differences will be added on his site.
The secondaries are shed from the first week of August onwards. The outermost secondaries (about S1-S4 are shed first and at the time S1 and S2 start growing, the central secondaries are shed quickly one after another in the first weeks of September. Compared to 2cy michahellis, adults are about one and a half month delayed in secondary moult, but the sequence is similar. In the inner-arm, close to the tertials, a small block of about four feathers remain unshed, probably to guarantee a certain level of maneuverability. The innermost secondaries are shed in the same period as the central secondaries. 
Rectrices moult is in progress throughout the month with complete new feathers visible at the end of August.

Moult in the wing-coverts:

Moult in the wing-coverts is very obvious in adult michahellis in NW France by early August. A large amount of the (central) greater coverts and median coverts are shed and some of the secondaries are visible almost to the base, even when the wing is folded. Simultaneous moult starts in the central tertials.

In the scapulars, the upper scaps and upper lower scaps have been replaced; moult progresses in the lowest row of scapulars. Moult in the scapulars is limited. The mantle and scapular region is moulted throughout the summer period, but you hardly find large moult gaps of adjacent missing feathers in these tracts. This seems reasonable as most energy has to be put in replacement of the remiges, rectrices and coverts. Nevertheless, the lowest row of lower scapulars (lls, see the Gull Topography Section) may show missing feathers, especially in the central lls and in the rear lls. Randomly, some upper scapulars may be included in moult as well but often only at a slow pace, one-by-one. The outer lls may appear very worn by August.

Adult michahellis may include the upper two tertials in the partial moult in autumn. This may explain the moult pattern in some adults by the end of August. The majority of adult michahellis drop the 3rd and 4th tertial, while #5-6 look very abraded. The tips of the upper two tertials show wear as well but are not as abraded as the lowest tertials. The moult sequence in August normally progresses from the 3rd tertials downwards. Some individuals may continue to include the upper two tertials again in the partial moult of October.

The average adult michahellis in August has a few innermost greater coverts replaced by new feathers and has growing new feathers from the outer-wing inwards, resulting in a large moult gap in the central greater coverts. The moult sequence in the greater covert bar is similar to that of e.g. Lesser Black-backed Gull and Herring Gull. The inner three or four greater coverts are shed first and are growing at the time another moult wave is initiated at the outer greater coverts. Subsequently, the greater coverts are growing in two moult waves: one from the outer-wing inwards and one from the inner greater coverts outwards. The two waves meet at greater covert #7 or #8. By the time the two moult waves meet, the inner greater coverts may show slight wear at the tips already. This is the common moult sequence as can be found from late July to October, but other sequences may be shown as well, including a quite random "jumpy" sequence in the greater coverts, with every other one replaced.

The median covert moult is slightly ahead of the greater covert moult and by the end of August adult michahellis close the moult gap in the central median covert. This can for instance be seen in a sequence like in image 8: The inner five median coverts are fully grown, #6 is slightly shorter and has to grow an inches or so. Another moult wave is growing from the outer-wing inwards, with the last fully grown feather at about #11, while #10 falls a little short, #9 even shorter and #7 just visible. It's obvious that the two moult waves will meet at #6-#7.
The lower lesser coverts (llc) normally follow the same moult sequence as the median coverts, but are slightly behind in time. 
The lesser coverts are moulted more randomly and especially the outer lesser coverts (the carpal edge) may show abraded remaining coverts throughout this month. The wing-coverts in the carpal edge are the last replaced coverts, at the end of the basic moult.

Timing and strategy of body & covert moult in July

The winter head becomes more obvious in August where streaking is concentrated around the eye, on the ear coverts and to the nape, sometimes running down in the 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. Some adult still show head moult around the eye (e.g. image 4).

See the Topography Section for explanation of feather tracts.

Naked parts:

Some birds develop black markings on both the upper and lower mandible by the end of the month.

Tables:

 

Adult michahellis: Deiva Marina, NW Italy, August 08 2001

prim score 0: 20: 21: 22: 23: 24:  25: 26: 27: 28: 29: 30:  
1* 3 0 2 2 2  13 16 8 9 2 2  

*: prim score 0 (1 bird) was left out the statistical analysis.

n: 59 m: 25.9 SD: 2.16
fully grown 0: p4: p5: p6:                  
1 13 45 1             n: 59 m: 4.8 SD: 0.45 

Notes:
1. Compare the moult score of western and eastern Italian michahellis in July and August. Eastern birds are more advanced.
2. 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.

 

 
Primary moult score of adult michahellis Yellow-legged Gull, at Etaples, NW France (50.43N, 01.37E) on August 08 2003.
. P4 fg P5 fg P6 fg ? fg n:
P7-P10 - - - 1 1
P8-P10 5 6 - 6 17
P9-P10 - 9 4 - 13
n: 5 15 4 7 31
n = 31; m old P = 2.6; SD old P = 0.56.
P7-P10 = P7-P10 are still old and present.
? fg = fully grown not known. Fully grown primary score most probably P6 or less.
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 adult michahellis Yellow-legged Gull, at Etaples, NW France (50.43N, 01.37E) on August 09 2003.
. P4 fg P5 fg P6 fg ? fg n:
P7-P10 - - - - -
P8-P10 5 12 - 12 29
P9-P10 - 18 8 8 34
n: 5 30 8 20 63
n = 31; m old P = 2.5; SD old P = 0.50. 

 
Primary moult score of adult michahellis Yellow-legged Gull, at Etaples, NW France (50.43N, 01.37E) on August 10 2003.
. P4 fg P5 fg P6 fg P7 fg ? fg n:
P7-P10 - - - - 2 2
P8-P10 5 22 - - 28 55
P9-P10 - 22 24 - - 46
P10 old - - - 1 - 1
n: 5 44 24 1 30 104
n = 104; m old P = 2.6; SD old P = 0.55. 

 

Remaining old primaries in adult michahellis, Etaples, NW France.
  0 P10 P9 P8 P7 n: m: SD: 
August 22 2000 6 20 43 3 0 72 1,60 0.71
August 25 2000 5 17 38 1 0 61 1,57 0.67

 

 

ad LBBG in winter, ringed in the Netherlands. (65647 bytes)Yellow-legged Gull (michahellis) 19cy & 21cy C 53597 August, September & November, Boulogne-sur-Mer, NW France. Picture: Jean-Michel Sauvage.
adult michahellis Yellow-legged Gull in August. (85671 bytes)Michahellis 365D, August 11 2003, Etaples, France. 
Ringed in S France, seen at the same location in successive summers. 
adult michahellis Yellow-legged Gull in August. (33772 bytes)Photo 4252: michahellis adult, August 10 2003, Le Portel, France.
Injured bird. 
adult michahellis Yellow-legged Gull in August. (69721 bytes)Photo 7209: michahellis adult, August 09 2003, Le Portel, France. 
adult michahellis Yellow-legged Gull in August. (66616 bytes)Photo 7624: michahellis adult, August 11 2003, Le Portel, France. 
adult michahellis Yellow-legged Gull in August. (65168 bytes)Photo 7673: michahellis adult, August 11 2003, Le Portel, France. 
adult michahellis Yellow-legged Gull in August. (27843 bytes)Photo 001: Michahellis adult, August 25 2000, Etaples (France). 
adult michahellis Yellow-legged Gull in August. (67746 bytes)Photo 002: Michahellis adult, August 25 2000, Etaples (France). 
adult michahellis Yellow-legged Gull in August. (59460 bytes)Photo 003: Michahellis adult, August 25 2000, Etaples (France). 
adult michahellis Yellow-legged Gull in August. (27643 bytes)Photo 004: Michahellis adult, August 25 2000, Etaples (France). 
adult michahellis Yellow-legged Gull in August. (103910 bytes)Photo 005: Michahellis adult, August 25 2000, Le Portel (France). 
adult michahellis Yellow-legged Gull in August. (32276 bytes)Photo 00 7: Michahellis adult, August 25 2000, Etaples (France). 
adult michahellis Yellow-legged Gull in August. (25497 bytes)Photo 00 8: Michahellis adult, August 25 2000, Etaples (France).
adult michahellis Yellow-legged Gull in August. (40832 bytes)Photo 7336: michahellis adult, August 10 2003, Etaples, France. 
adult michahellis Yellow-legged Gull in August. (22168 bytes)Photo 00 6: Michahellis adult, August 25 2000, Etaples (France). 
adult michahellis Yellow-legged Gull in August. (34905 bytes)Photo 7358: michahellis adult, August 10 2003, Etaples, France. 
adult michahellis Yellow-legged Gull in August. (76779 bytes)Photo 7346: michahellis adult, August 10 2003, Etaples, France. 
adult michahellis Yellow-legged Gull in August. (75874 bytes)Photo 7348: michahellis adult, August 10 2003, Etaples, France. 
adult michahellis Yellow-legged Gull in August. (72502 bytes)Photo 7375: michahellis adult, August 10 2003, Etaples, France. 
adult michahellis Yellow-legged Gull in August. (94882 bytes)Photo 7564: michahellis adult, August 10 2003, Etaples, France. 
adult michahellis Yellow-legged Gull in August. (71876 bytes)Photo 7366: michahellis adult, August 10 2003, Etaples, France. 
adult michahellis Yellow-legged Gull in August. Photo 00 9: Michahellis adult, August 25 2000, Etaples (France).
adult michahellis Yellow-legged Gull in August. (65917 bytes)Photo 0 10: Michahellis adult, August 25 2000, Etaples (France).