Lesser Black-backed Gull (graellsii & intermedius)

(last update: May 17 2015)

LBBG (probl nominate fuscus) 3cy, May 05 2001, Dannes, NW France. 

Second picture (over exposed to show the covert moult stage): Note that the old brown coverts are plain brown without a pattern, while new coverts are plain blackish. It stands next to an average graellsii; note the very dark upper-parts. The white tail has a few very small dark spots.
There is an obvious difference between second and third generation primaries. P1-P6 show white tips on fresh primaries. P7-P10 are still second generation remiges and typically, P10 lacks a white mirror. P2 has a paler outer web, and as can be seen in the preening bird, the grey centre is not as black as the sub-terminal band.
The scapulars are almost black. In the mantle, some older feathers have a round black centre and a dark brown fringe.

The outer lesser coverts are dark brown, the inner lesser coverts are almost black. The median and greater coverts contain such older brown-hued feathers as well, but there are no moult gaps: it seems all moult was suspended prior to migration.
The innermost 6 secondaries are probably third generation, the outer are second generation. The under-wing coverts are entirely white.
The two upper tertials are fresh, #3 has a brown hue on the centre and #4-6 were moulted more recent than #3.
In the lower neck, faint fine streaks are hardly visible.
At least the outer primary coverts are brownish with pale tips (as could be expected as in many cases the primary covert moult follows the corresponding primary moult). Such a dark plumage combined by arrested moult and slender expression strongly favors the Baltic race fuscus.

In both graellsii and intermedius, arrested moult is a rare phenomenon. When intermedius show arrested moult in the primaries, combined by advanced moult in the upper parts, these birds can be mistaken for fuscus. At Le Portel, three such kind of LBBG were present early May 2001 (and another at the Maasvlakte, the Netherlands), including a very dark, gentle (female) intermedius.

Characteristics separating intermedius from fuscus:
The article of Lars Jonsson in BW 11-8 (1998) gives excellent insight in the features and moult strategy of Baltic fuscus. However, it remains to be seen whether these points fully exclude intermedius. Very dark and gentle (female?) 2^nd summer intermedius, which show very advanced moult in the upper-parts, combined with arrested moult in the primaries do occur and approach fuscus in both coloration and general structure. Research spring 2001, an estimated 4% of immature (as it seems predominantly 3cy) LBBG may show arrested moult. 

Summer 2001, a discussion page called discusfus has been added to create a forum for discussing intra-specific characteristics in immature LBBG races. Soon, more will be added about arrested autumn moult in graellsii and intermedius.