Great Black-backed Gull (Larus marinus)

(last update: July 12, 2015)

Great Black-backed Gull 2cy April

Moult timing in first winter birds: August-January

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 in September illustrates that 40% (n = 10) do show the first signs of moult, i.e. new upper scapulars. By October, over 90% (n = 13) replace the upper scapulars and 38% has started moult in the lower scapulars as well. By November the category "Total scapulars" did not hold a single ringed bird scoring "0% 2nd gen scaps". In other words, all the 27 ringed birds in November had replaced at least one or more (upper) scapulars for 2nd gen feathers.

By December, again all ringed birds had at least some new upper scapulars, with many birds categorised ">75% of the upper scpaulars replaced". There may be a bias towards southern populations, as all images on this site are from birds ringed in S Norway or colonies further south like Denmark and France. It remains pure speculation, but it would be interesting to know where very fresh juvenile birds in November, like THIS ONE hatched. Birds similar to this one, but still fresh by 2cy March, are represented by THIS POWERFULL bird, which is believed to have travelled from far northern Europe. A far northern hatching colony does not necessarily reflect late moult in scapulars. In February we photographed this Russian bird from Murmansk, yet with obvious avergae moult scores in the scapulars.

Despite its southern hatching location, this 1cy bird black JJ77, showed only very limited scapular moult by December, and from all 8 ringed birds in December, it was obviously most retarded.

Tables:

below: graph corresponding to data from table 1. n=13. Distribution of replaced scapulars in April 2cy 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).

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.

The group of birds which score 100% 2nd gen scapulars gradually grow; remember however that 1st cycle birds, especially in March-April, grown fresh upper scapulars again, most probably 3rd gen feathers (feather condition was not scored by us). Figures in the graph may be read reverse, the presence of juvenile feathers decrease over time.