Great Black-backed Gull (Larus marinus)

(last update: October 12, 2011)

Great Black-backed Gull 1cy October

Description of 1st winter plumage

First-winter (Sep-Mar) similar to juvenile, but head and upper breast whiter with narrower dark streaks (especially around eye and on hindneck); forehead normally white. May show dark ear-spot. Mantle and scapulars pale grey to buff with blackish subterminal bars or anchor-shaped spots; often intermixed with juvenile feathers. Bill similar to juvenile, but some develop paler base from early winter. Pale individuals have whitish underparts, narrower dark subterminal marks on upperparts and narrow dark covert-markings. With wear may bleach as described under Herring Gull, but rarely as extreme (an extremely pale spring bird shown by Grant (1989a) could to my eyes be partly leucistic, as the upperparts appear unmarked, which is atypical even in very worn birds). (Malling Olsen, K. & Larsson, H. 2004 Gulls of Europe, Asia and North America. London: Christopher Helm).

Moult into first winter

Juvenile moult to first winter plumage partial Aug-Nov, including mantle, scapulars, and (probably) parts of head and body. Often no sign of moult into Nov/Dec. (Malling Olsen, K. & Larsson, H. 2004 Gulls of Europe, Asia and North America. London: Christopher Helm).

Although Malling Olssen states "often no sign of moult into Nov/Dec", this is not supported by data of ringed birds. The table presented below illustrates that over 90% of the 1cy birds in October (n = 19) do show (at least) the first signs of moult, i.e. new upper scapulars.
By October, over 90% (n = 19) replace the upper scapulars and about 25% has started moult in the lower scapulars as well.

All wing-coverts, tertials and flight feathers still juvenile by October, except for the odd bird in any larger group.

Tables:

below: graph corresponding to data from table 1. n=19. Distribution of 2nd generation scapulars in October 1cy GBBG, separated into Upper Scapulars, Lower scapulars and for Total scapular region. Classification in 6 classes, running from 0% (no 2nd gen scaps) to 100% (all scaps in a region are 2nd gen).

It is clear from the column "Total scapulars" that less than 10% of the October birds scored "0% 2nd gen scaps", in other words, over 90% of those 19 ringed birds had replaced at least one or more (upper) scapulars for 2nd gen feathers.