Great Black-backed Gull (Larus marinus)

(last update: October 12, 2011)

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=8. Distribution of 2nd generation scapulars in December 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 not a single bird scored "0% 2nd gen scaps", in other words, all those 8 ringed birds had replaced at least one or more (upper) scapulars for 2nd gen feathers; but this was already the case by November.

Below: progress in scapular moult in 1cy & 2cy L. marinus from August to April.
The group of birds which score 100% 2nd gen scapulars gradually grow; remember however that 2cy birds, especially in March-April, grown fresh upper scapulars again, most probably 3rd gen feathers. Figures in the graph are not adjusted for this; and the graph may be read reverse, the presence of juvenile feathers dimish through time.