adult: January - April

LBBG in the Netherlands: January

A small proportion of the NW European LBBG spend winter along the coast of the Netherlands. In the south, along the coast at Westkapelle (see map), small groups can be found well into January. 

left: intermedius, January 05 2001, Westkapelle, the Netherlands. right: intermedius, January 05 2001, Westkapelle, the Netherlands. left: intermedius, February 07 2003, Boulogne/Mer, France (50.42 N - 01.34 E).

The complete moult has been finished by January, as the images in the first box show. Both individuals in picture 01 & 02 are believed to be adults, originating from intermedius colonies. Quite a proportion of the present LBBG at Westkapelle show this structural characteristics: neckless, short fine bill, short tibia and therefore appear short-legged and long-winged -as in the second picture (P6 reaching further than the tail-tip). Often, intermedius may be characterized as a compact birds. In both pictures, the yellow legs and bill combined with a large mirror on P10 suggest full adultness.
In the upper-parts, there is no sign of sub-adult brown feathers. A few coverts have a brownish wash, but these are probably older adult coverts. They can be found in the median covert row, the upper tertials and inner greater coverts, normally the tracts which have been replaced first, now already showing slight wear and tear. Furthermore, the inner wing-coverts and upper tertials are the most exposed feathers in the wing.

LBBG, Vuurtorenvlakte, Maasvlakte, the Netherlands, March 30 2002. An adult bird found dead, hit by a car.

The wing-tip pattern in both adults is totally different: just small white tips and a indistinct white mirror on P10 in the first picture. The second bird has an extensive white tips, on P10 merging with the white mirror and a large mirror on P9. The tip and mirror on P10 are hardly separated, just a small black sub-terminal band divides the two. Birds present in the colony, and probably willing to mate, may still show an all-dark P10, lacking a mirror. The other extreme is a large mirror on P10, merged with a tip and a considerable mirror on P9, covering both the inner and outer-web. In general, large mirrors on P9 and P10 are associated with adult males.

LBBG returning to the colonies in the Netherlands

End of March; many adult LBBG of the Maasvlakte (see map) already return to the breeding grounds and try to find nesting locations in the colonies. Successful adults are very faithful to nesting locations and partners and can be found breeding on exactly the same spot (inch-perfect!) year after year. Adult males, returning early in the colony normally wait for the same partner, establishing dominance over a last-year's successful territory. If the female arrives later in the season, other female try to mate with such dominant males, but once his partner arrives, the bond will soon be established and those (often young) females are kicked out the territory. 
By the end of March, 1.000s of LBBG (probably mostly originating from intermedius populations in Scandinavia) migrate east-northeast along the coast-line of the Netherlands and make short stop-overs at the beach. Well over 90% of the birds are adults and trains of birds glide motionless over the beaches of the Wadden Isles into the Danish Wadden Sea.

LBBG, April 16 2001, Nachtegalenkeet Maasvlakte, the Netherlands. An image showing the difference in grey tones between two adult LBBG, breeding in the Netherlands.

At the Maasvlakte, most major position are taken again in the colony by another type of LBBG: Dutch intergrades. The are slightly darker than typical graellsii from Britain, but not as dark as the average intermedius from Scandinavia. They carry the genetic heritage of both taxa. The exchange of gene pools hasn't stopped yet. Still, in the colonies at Maasvlakte we see foreign ringed birds, breeding together with local Dutch birds. Not surprising, these foreign birds often seem to be females.
In the mean time birds born in colonies at Maasvlakte spread to other colonies abroad as well. The very prosperous colony at the Belgium port of Zeebrugge was initiated by both British and Dutch LBBG, as several colour-ringed birds proved. 

Primary Moult Scores in adult LBBG:

Year 2003 we did some preliminary research on primary moult scores in adult LBBG. In total, we scored about 1400 birds from early April to mid October. This research will be used to do some more fundamental research in tear 2003-2004. First results for April are quite simple: we scored 49 birds on April 05 and we scored 45 birds on April 19. All these birds had P1 still present, hence PMS = 0. Nevertheless we did see several adult LBBG in the colony, which had P1 shed by April 19. Some notes: the scorse on April 05 2003 were done at Naaktstrand, on preening, bathing and arriving birds, through 20x-60x telescopes. Active moult would be noticed, but to detect arrested moult in such circumstances is pretty difficult. Next year, we try to start our surveys with catching birds and examine the exact primary stage in the inner primaries by taking photographs. 

Tables & Graph

Table above, data for the Netherlands (2000-2010), results for April (aggregated week): number of remaining old primaries in adults.
REM10 = 10 primaries still old (hence, complete moult not started yet). First signs of complete moult commencement in WEEK 18 (starting 30 April).

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 April (arrested moult excluded). Sample size for this graph is 879 ringed birds.

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

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).

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.

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.

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

LBBG in the Netherlands: colour ring projects

For over 10 years we have colour ring projects in the Netherlands. By far the largest project involves LBBG breeding in two colonies near the port of Rotterdam: one large colony at Maasvlakte and the second at Dintelhaven (eastern Maasvlakte). Although the other colony is well visible from either side, only separated by water, birds appear to be very faithful and try to nest in the colony where they were raised. Only limited number of ringed birds can be found in the 'wrong' colony.

First LBBG were ringed with white rings, first with letter digit digit, later with letter letter digit. At the colony 'Maasvlakte', orange rings were used. First years (1991-1992) codes were letter digit digit, later letter letter digit. From then on, all ring codes started with E (Europoort Rotterdam), followed by three letters or digits. 
At the colony of 'Dintelhaven' green rings were used, the same repertoire. In the right column of this page you can find some examples of ringed adult LBBG from both locations.

At the port of IJmuiden, near Amsterdam, Fred Cottaar started another LBBG colour ring project on roof top breeding birds. In this project, red and white rings were used with three different codes: a single letter or single digit or bars.
Such codes can also be found on other colours, originating from the isle of Texel, the Netherlands.
Recently, Fred Cottaar caught adult LBBG on the nest and they received red rings, starting with E and followed by three digits.

Another recently started colour-ring project in the Netherlands can be found in the industrial area of Moerdijk (inland breeding LBBG). This project was started by Roland-Jan Buijs and he used mint green rings with two black letters. Because this population breeds in tall grass, Roland-Jan used tibia rings.

Subsequently, an interesting English project was started by David Sowter in 1997. 

Purpose:

Despite regular culling and disturbance the Lesser Black Backed Gull colony at Tarnbrook Fell has continued to thrive.  This study is intended to determine the extent to which movement of Lesser Black Backed Gulls between the three sites, which are inter-visible on a good day, may play a part in the breeding success of the Tarnbrook colony.  It is also hoped to establish whether there are common feeding, roosting and migration sites and what part they play in the movement of gulls between colonies for breeding.

Method: 

In the pilot year, 1997, 200 juveniles were ringed at each of the three sites using green darvic with a single white letter code: R, T, and W.  For each of the five years 1998- 2001, 2500 birds will be ringed at each of the three sites with black darvic rings with yellow site letter plus a three letter/number combination  (left leg) so individual birds can be identified in the field by year and site.  Individual BTO metal rings (right leg) will also identify birds.

To develop and analyze data based on personal observation and records achieved through co-operation with local bird clubs and through the BTO network and the large gull coordinator, Peter Rock.

Sites:

Ribble Estuary Nature Reserve: ( 53 42’ N : 2 55’ W - SD 3924) in co-operation with Mike Gee/Dick Lambert, English Nature Wardens and SW Lancs Ringing Group.  Dick and the SW Lancs Ringing Group have carried out some ringing for most years since the mid-1980’s.  The site is within salt marsh near the mouth of the River Ribble and is subject to periodic flooding by high tides, which decimates the breeding success in some years.

Tarnbrook Fell, Forest of Bowland: (54.01N  2.35W - SD 6258) with permission and sponsorship from Grosvenor Estates, Abbeystead and Mr R Banks the Abbeystead Estate manager;  Mr R Challenor for Mallowdale estates and NW Water for Brennand estates.  Dr John Coulson and associates have been undertaking studies and control measures at this site since at least the mid-1980’s.   The colony, which is within heather, grass and peat-hag moorland at a height of 450-530 metres, has continued to maintain high numbers or expand despite culling and managed disturbance over a number of years.

South Walney Nature Reserve: (54.03N 3.12W - SD 2162) in co-operation with Rob Shaw and Nick Littlewood, the warden of the reserve.  There has been ringing of gulls on this dune site at the south end of Walney Island since at least the early 1960’s.

Colour Ring combinations:  
R is Ribble;  
T is Tarnbrook Fell ; 
W is Walney Island.

1997: GREEN showing WHITE single letter for site.
1998 - 2002: BLACK showing YELLOW 4 letter/number combinations.

Please send details of sightings with date, location, details of gulls and activity to:

David Sowter: 5 The Grove Penwortham Preston PR1 0UU. 01772 749220. davidsowter@freenet.co.uk

All responses will be acknowledged.

Especially these kind of project, with many LBBG colour ringed, may give full insight in variation of LBBG plumages from different locations. See also the Distribution Section.