Lesser Black-backed Gull- Kleine Mantelmeeuw (graellsii & intermedius)

(last update: 17-4-2014)

adult Lesser Black-backed Gull: March

Colony at "quai de la loire" at Calais, NW France. This is a mixed colony of Lesser Black-backed Gulls and Herring Gulls, with Lesser Black-backeds dominating. Theer are now about 200 pairs breeding. Picture from April 14 2014 (Jean-Michel Sauvage).

LBBG graellsii in spring: open wings.

Pictures of several birds March 17-24 2015 at leiden, the Netherlands. These will probably breed in this area, sometimes called "Dutch intergrades" or "continental graellsii", and birds are a shade arker grey on upperparts than British graellsii, matching many intermedius from Denmark or S Norway.

Lesser Black-backed Gull EV adult, March 24 2015, Leiden, the Netherlands.	Lesser Black-backed Gull N03J adult, March 24 2015, Leiden, the Netherlands.

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 below: 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).

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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