Great Black-backed Gull (Larus marinus)

(last update: July 12, 2015)

Great Black-backed Gull adult September

By September, adult GBBG are still in active moult, most birds growing the central primaries and dropping. As can be seen in so many large white-headed gulls, approximately when P6 is growing, birds start moulting secondaries and rectrices. Of course the tertials (which in a way could be interpreted as inner "secondaries" as well) are included in the moult process much earlier in the season, but when P6 is growing, a new moult wave starts in the outermost secondary (S1), the feather next to P1. The first phase of the secondary moult progresses slowly, one feather at the time, but when the new outer secondaries are visible, a much larger moult gap soon appears in the central secondaries. At the same time, the moult wave that started in the upper tertials continues as well, and the two moult waves meet approximately at S16.

Rectrices (tail feathers) will be moulted in September as well, this process is centrifugal, starting ate the inner feathers and progressing outwards. The exact location of the last remaining old feather is difficult to interpret, but this is not necessarily R6 (the outermost feather). Leaving R5 as last old feather is a common startegy.

An indication of the primary moult of GBBG, and compared to YLG (michahellis) and HG (argentatus) is presented in the tables below:

Tables:

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Great Black-backed Gull (Larus marinus) 6cy J7RH September 10 2011, Boulogne sur Mer, France (50.44 N - 01.35 E). Picture Jean-Michel Sauvage.

Great Black-backed Gull NOS 367624 (Larus marinus) adult: September 18 2004, IJmuiden, the Netherlands (52.27N - 04.33E).
Primary P7 is fully grown while P10 still has to be shed.

Great Black-backed Gull (L. marinus) NOO OA13312 September 24 2006, IJmuiden, the Netherlands. Picture: Ruud Altenburg.

Great Black-backed Gull (Larus marinus) adult: September 30 2001, Le Portel - Boulogne sur Mer, France (50.42 N - 01.34 E).
Group of Great Black-backed Gulls and Herring Gulls (L. argentatus) at Le Portel.