Adult October

adult: October

Last update of this page: 06-04-04 22:43

Movements

By October, all LBBG have left the colonies and surrounding feeding grounds near the Maasvlakte (the Netherlands) and migrate south towards France, Portugal and Morocco. In November and to a lesser extend December, a couple of hundreds remain on continental NW Europe, as north as the south of the Netherlands along the coast at Westkapelle, 65 km south of the Maasvlakte (see map). As it seems, every year a larger group of LBBGs stay "at the most northern latitude as possible", i.e. migrate south only when winter conditions force them to.

By late November 2000 (a rather mild winter) ringed individuals from Scandinavia, Denmark, the Netherlands, Belgium and the U.K. were present at Westkapelle. When winter really started in December 2000, this group moved south as well to unknown wintering grounds, probably the Atlantic coast of West and South-West Europe.

Primary moult timing and strategy

By October the majority of adult Lesser Black-backed Gulls moulting the outer primaries. There is a clear difference between presumed birds lingering around and birds which will probably migrate further south quickly. The difference can be found in the primary moult strategy.

Some adult have a large moulting gap in the central primaries (for example p8-p10 old and only p4 fully grown and p5 still slightly shorter than p4) by the first days of September. It is hard to believe these birds will travel large distances non-stop as such moult gaps are highly inefficient for this migration pattern. Probably these birds, which can be found moulting in a period roughly from late August to late November stay in the area throughout their primary moult. They migrate further south either forced by cold winter or when the primaries moult arrives at the far outer primaries.

The other group is represented by birds with a very small moult gap in the primaries or with a very low primary moult score, indicating that primary moult will probably suspended until arrival at the wintering grounds.

Tables

Remaining old primaries for adult LBBG year 2001 (the Netherlands)
	0	1	2	3	4	5	6	7	8	9	10	n:	m:
Oct 8-12	101	136	173	83	30	22	25	7	8	3	3	591	2,17
(aggregated Maasvlakte & Westkapelle) n: total; m: average

Adult LBBG primary scores, Naaktstrand - Maasvlakte, the Netherlands, October 19 2002
.	p8 old	p9 old	p10 old	no old	total old
p5 f.g.	2	-	-	-	2
p6 f.g.	3	68	20	-	91
p7 f.g.	-	19	60	39	118
p8 f.g.	-	-	2	22	24
total f.g.	5	87	82	61	235
Notes: 1. f.g. (fully grown): including primaries which are not completely fully grown, but all primaries of which the tip exceeds the previous primary in the folded wing. 2. old primaries: total (n) = 235, average (m) = 8,8 standard deviation (SD) = 0,86. 3. new primaries: total (n) = 235, average (m) = 6,7 standard deviation (SD) = 0,66. 4.Adult LBBG scored in a group of 1.500 birds (of which 90% LBBG). A remarkable homogeneous group regarding grey-tone of upper-parts, after three days of western winds. 5. a few ringed birds in this group: orange CA9 (P10 old, P7 f.g.) ringed as pullus in the Netherlands on July 01 1995, now 8cy. green EA34 (P10 old, P7 f.g.) ringed as pullus in the Netherlands on July 02 1993, now 10cy. green EV62 (P10 old, P7 f.g.) ringed as pullus in the Netherlands on June 21 1997, now 6cy.

Adult LBBG primary scores, Dannes (region Calais), NW France, October 19 2002
.	p6 old	p7 old	p8 old	p9 old	p10 old	no old	total old
p4 f.g.	-	1	-	-	-	-	1
p5 f.g.	1	1	5	1	-	-	8
p6 f.g.	-	-	2	30	11	-	43
p7 f.g.	-	-	-	23	37	30	90
p8 f.g.	-	-	-	1	8	83	92
total f.g.	1	2	7	55	56	113	234
Notes: 1. f.g. (fully grown): including primaries which are not completely fully grown, but all primaries of which the tip exceeds the previous primary in the folded wing. 2. old primaries: total (n) = 234, average (m) = 9,1 standard deviation (SD) = 0,98. 3. new primaries: total (n) = 234, average (m) = 7,1 standard deviation (SD) = 0,86. 4.Adult LBBG scored in a group of 2.000 birds (of which 30% LBBG). A heterogeneous group regarding grey-tone of upper-parts. 5. a few ringed birds in this group: orange EV89 (P8 f.g.) ringed as pullus in the Netherlands on July 02 1997, now 6cy. green E774 (P9 = P8 f.g.) ringed as pullus in the Netherlands on July 04 1995, now 8cy. white R23 (P9 old, P6 f.g.) ringed as pullus in the Netherlands on July 06 1991, now 12cy. blue ASAY (P8 f.g.) ringed in Belgium.