By July, most adult Lesser Black-backed Gulls are very busy feeding the now fledged young. By mid-July large flocks of 100's of 1cy birds leave the colonies simultaneously and gather on the sandy beaches. The adults keep on feeding the 1cy birds on these beaches, often until the end of the month. 
The moult score on adult LBBG may be influenced by the energy and effort which is put in the feeding of chicks. In the colony, we try to score primary and wing-covert moult in relation with number of eggs or fledged chicks. Year 2002 we didn't collect enough data on this subject. However, we can represent figures of primary moult in adult LBBG which still have a strong bond with the colony. They arrive at a nearby sandy beach to drink, wash and preen quickly, leaving again within 10 minutes to fly back into the colony. Primary moult score is presented in the next table.

Tables & Graph

Table above, data for the Netherlands (2000-2010), results for July (aggregated week): number of remaining old primaries in adults.
REM10 = 10 primaries still old (hence, complete moult not started yet).

Above: Scatter Plot for PMS in adult Lesser Black-backed Gulls. Number of remaining old primaries throughout the year (arrested moult excluded). Sample size is 6.171 birds.

Above: Scatter Plot for PMS in adult Lesser Black-backed Gulls. Number of remaining old primaries for July (arrested moult excluded). Sample size for this graph is 302 ringed birds + 399 unringed birds.

  Table above, data for the Netherlands (2000-2010), results for July (aggregated week): number of new, fully grown primaries in adults.
NEW0 = no new primaries visible (arrested moult excluded in this analysis). So either P1 still old, or P1 dropped, but the very tip still not visible.
NEW1 = P1 longest new primary. Range between "at least the tip of P1 is visible" until "tip of P2 still shorter than P1".
NEW2 = P2 longest new primary. NEW3 = etc.

Above: Scatter Plot for PMS in adult Lesser Black-backed Gulls throughout the year. Longest new primary is classified "fully grown". Sample size is 2.969 birds. Birds scored on NEW primaries (arrested moult excluded).

Above: Scatter Plot for PMS in adult Lesser Black-backed Gulls. Scoring on longest new primary, which is classified "fully grown" for July (arrested moult excluded). Sample size for this graph is 2 ringed birds + 121 unringed birds.

The earliest date for birds with missing primaries is 30 April 2006, which is not the earliest day in our complete sample. We scored 98 Lesser Black-backed Gulls prior to that date, some already in February. As can be expected, none of these was in primary moult, and this group was excluded in our further analysis as it will only result in a misfit for the onset of moult, using linear regression statistics.

The last scoring days were in November, with a larger sample (133 adults) on 04 November 2010. From that date we have the last birds with retaining old primaries (13 birds with 1, 2 or even 3 old primaries; 120 birds with no old primaries left). From other days in November, only 10 birds were scored (all ringed adults). They all had no old primaries left.

The first tine a new primary (P1) was visible, was on 08 May 2006. Prior to this date, birds were scored missing inner primaries, but the very tip was still not visible (and therefore not scored). As soon as the tip of P1 was visible, this was automatically scored "fully grown" For the other primaries to be scored fully grown, they had to exceed the previous primary in length (so P2 fully grown, only from when it is longer than P1).

Peter Stewart presents onset of primary moult by scores for caught adult Lesser Black-backed Gulls in the Severn Estuary, U.K., repeated in the table below. To read his results, see this PDF file.  

LINEAR REGRESSION

Onset of primary moult can best be illustrated by a sinusoid for the first few weeks and last weeks, but there appears to be linear dependency over much of the central moult period.

LINEAR REGRESSION FOR OLD REMAINING PRIMARIES

Complete sample: Linear regression (n = 6171, R2= 0.820, sign: P<0,000)
PMS = -0,381* WEEK + 17,967

Ringed adults: Linear regression (n = 2069, R2= 0.800, sign: P<0,000)
PMS = -0,325* WEEK + 16,270

Unringed adult: Linear regression (n = 4102, R2= 0.779, sign: P<0,000)
PMS = -0,513* WEEK + 23,031

LINEAR REGRESSION FOR NEW FULLY GROWN PRIMARIES

Complete sample: Linear regression (n = 2969, R2= 0.930, sign: P<0,000)
PMS = 0,302* WEEK - 5,933

Ringed adults: Linear regression (n = 1209, R2= 0.888, sign: P<0,000)
PMS = 0,252* WEEK - 4,747

Unringed adult: Linear regression (n = 1760, R2= 0.833, sign: P<0,000)
PMS = 0,442* WEEK - 11,906

Some details about colour rings (CRs)

Late June, early July are the weeks to catch pulls and colour ring them. This has been done for years now at Maasvlakte, the Netherlands and most images show ringed adults from these projects. Ring projects are going on for decades already and in Vest-Agder, S Norway, over 60.000 LBBGs have been ringed throughout the years. From 1995 on, blue colour ringed LBBGs from Scandinavia turn up. Some details:

At Westkapelle, the Netherlands (see distribution), LBBGs can be found well into November. Readings of (metal) ringed LBBGs revealed some originate  from Denmark, some from Sweden and some from S Norway. Although local Dutch individuals may occur as well, bulk of the present LBBGs in November are probably Scandinavian birds. Large colonies can be found in Vest Agder (S Norway) and this is the most northern colony from which ringed Scandinavian birds occur in the Netherlands. 

But though they may be seen in NW Europe well into November, others (from the same colony) proved to be more adventurous. For instance this known long distance migrant, much in line with Finnish colour-ringed LBBG fuscus. It's a 1cy LBBG X, metal ringed Stavanger 472418 date July 5 1984 at Rauna, Farsund, Vest-Agder, Norway 58.03N 06.40E and shot October 18 1984 in Owando, Kongo 00.27S 15.44E, 6553 km to the south 3 months and 13 days later.
Colour-ringed birds from the Maasvlakte have been reported to migrate over long distances as well: they were seen at interesting location e.g. USA and Finland.

In the Ring Recovery Section, we try to plot the races of Larus fuscus to give more detials on the various migration routes.