Great Black-backed Gull (Larus marinus)

(last update: July 12, 2015)

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 = 23) do show (at least) the first signs of moult, i.e. new upper scapulars. And about 40% 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.

top: marinus 1cy JH837 September 20 2010, Boulogne sur Mer, France (50.44 N - 01.35 E). Picture Jean-Michel Sauvage. All scapulars still juvenile. Class: US=0%, LS=0%, TOT SCAPS=0% .

below: marinus 1cy JP873 October 23 2012, Boulogne-sur-Mer, NW France. Picture: Jean-Michel Sauvage. Five upper scapulars replaced, note the buffish tone in the fresh 2nd gen scapulars. Class: US=1-25%, LS=0%, TOT SCAPS=1-25%.

Tables:

below: graph corresponding to data from table 1. n=33. Distribution of replaced 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 have been replaced).

It is clear from the column "Total scapulars" that less than 10% of the ringed October birds scored "0% 2nd gen scaps", in other words, the other 90+% of those 33 ringed birds had replaced at least one or more (upper) scapulars for 2nd gen feathers.

below: Great Black-backed Gull JA804 illustrates differences in colour and pattern between old juvenile 1st generation scapulars and fresh buffish 2nd generation feathers. Bird ringed as pullus on June 12 2012 at Salvøy, Karmøy, Rogaland, Norway (59°17'54"N 005°12'27"E). Picture: Jean-Michel Sauvage, September 28 2012, Boulogne-sur-Mer, NW France.

below: Distribution of replaced scapulars for "Total scapular region" for months August in hatch year until commencement of first complete moult in April. Classification in 6 classes, running from 0% (no 2nd gen scaps) to 100% (all scaps, including long rear scaps, have been replaced). Only ringed birds, n=238.