Great Black-backed Gull (Larus marinus)

(last update: July 12, 2015)

Great Black-backed Gull 4cy August

Comparing plumages when birds are in complete moult in July-August

July and August, mid-summer, all birds are in complete moult. The combination of very worn old feathers and recently replaced new feathers, together with moult gaps in many feather tracts make many birds look like fluffy messy feather balls rather than birds. By late July, many local populations see a new cohort of very fresh juveniles added to the group.

Although most of the breeding population are situated in Scadinavia (from a west European view), this is a surprsingly early and fast moulting species.

Great Black-backed Gull (Larus marinus) JU827 1CY, August 28-30 2014, Boulogne sur Mer, France (Jean-Michel Sauvage).	Great Black-backed Gull (Larus marinus) JA697 1CY, September 06 2008, Westkapelle, The Netherlands (Ies Meulmeester).
ID 1CY birds in July-August: birds recently left the colony in very fresh and crisp juvenile plumage. Easily told from 2CY birds by the full hand of pointed, first generation primaries showing a paler window in the inner feathers. No moult in primaries, no moult in secondaries and no moult in tail.
Great Black-backed Gull (Larus marinus) JT631 2CY, July 30 2014, IJmuiden, the Netherlands (Mars Muusse).	Great Black-backed Gull (Larus marinus) 2CY, July 09 2013, Katwijk, the Netherlands (Mars Muusse).
ID 2CY birds in July-August: messy looking birds, showing moult gaps in many feather tracts by July. Inner primaries are new, overall dark grey but with arropw head at tips. New 2nd generation central primaries have relatively small white tips and have darker outerwebs, gradually dissolving in paler innerwebs and are brownish, not blackish as in in 3CY birds. Moult in primaries, and by late July often starts moult in secondaries and tail as well. New feathers in coverts are heavily barred, often densely marbled in the greater coverts; new feathers not adult-like plain blackish as in most 3CY birds. Iris dark.
Great Black-backed Gull (Larus marinus) DKC 3096165 3CY, July 27 2015, Boulogne sur Mer, France (Jean-Michel Sauvage).	Great Black-backed Gull (Larus marinus) 3cy, July 24 2013, IJmuiden, the Netherlands (Mars Muusse).
ID 3CY birds in July-August: combination of adult-like features and immature markings. Told from one year younger 2CY birds by pattern on fresh inner primaries, which appear adult-like grey with bold white tips. Central primaries have blackish outerwebs, sharply set from grey innerwebs and have bold white tips as well. Moult in primaries, and by last days of July often starts moult in secondaries and tail as well. New feathers in coverts are adult-like blackish. Iris remains dark. Told from one year older 4CY birds by the pattern on the old feathers. Old outer primaries are faded brown, often with a small mirror on P10. Secondaries are old 2nd generation, showing large blackish centres on all feathers and dark shaft running to very tip. Old, second generation tail with distal band and proximal barring. Secondaries on 4CY birds are still old in July, retained 3rd generation, with blackish centres and broad white tips, like in adults (but pattren on secondaries in 4CY variable). By August new rectrices grow in, normally with less black in 3rd generation tail, some tail-feathers almost completely white. 4CY birds normally have more adult-like bill pattern.
Great Black-backed Gull (Larus marinus) JW209 4CY, August 28 2013, Boulogne sur Mer, France (Jean-Michel Sauvage).	Great Black-backed Gull (Larus marinus) 4CY, July 30 2014, IJmuiden, the Netherlands (Mars Muusse).
ID 4CY birds in July-August: exact ageing can be difficult in many birds, and these are better left grouped as 'sub-adults'. Still, the combination of old and new feathers may give hints, especially the pattern on old feathers. New 4th generation inner primaries growing in by July are adult-like dark grey, and there is slightly more black on the central primaries in this age class than in full adults. Upperparts and new coverts appear adult-like blackish as well, but new central tertials and new central greater coverts often show lining or markings again. Best clue for ageing 4CY birds are old retained feathers: old 3rd generation outer primaries have (medium) mirrors on both P9 and P10. Secondaries are blackish with pale tips. Old wing-coverts and old outer primary coverts have extensive brown centres, and the condition is often obviously worse than in adult birds. Many birds show old lower tertials and the lesser coverts; these old feathers are worn but the brown markings in these locations are obvious in many birds.
Great Black-backed Gull (Larus marinus) 5T9 5CY, July 07 2015, Ipswich, MA (Billy Clifford).	Great Black-backed Gull (Larus marinus) JC0S 5cy, August 02 2008, Boulogne sur Mer, France (Jean-Michel Sauvage).
ID 5CY birds in July-August: exact ageing can be difficult in many birds, and many 5CY birds will probably go unnoticed and are labelled 'adult'. Birds with overall adult plumage, both in old and new feathers, which combine this adult-like plumage with single patterned feathers in greater primary coverts or a single spot in the tail are very likely 5CY birds.
Great Black-backed Gull (Larus marinus) JV3C 8CY, August 25 2012, Boulogne sur Mer, France (Jean-Michel Sauvage).	Great Black-backed Gull (Larus marinus) adult, July 30 2014, IJmuiden, the Netherlands (Mars Muusse).
ID 5+CY birds in July-August: exact ageing only when ring data are available.

Great Black-backed Gull (L. marinus) 4cy JB42 August 28 2003, IJmuiden, the Netherlands.
P4 fully grown, P8-P10 still old. Tail completely white.

Great Black-backed Gull (L. marinus) 4cy E703 August 12 2004, Westkapelle, the Netherlands. Ringed in 2001, isle of Terschelling, the Netherlands.

Great Black-backed Gull (Larus marinus) sub-adult: August 2000, Le Portel - Boulogne sur Mer, France (50.42 N - 01.34 E).
Clearly an immature GBBG, which is replacing the greater coverts. Compared to 2nd calendar years, adults and near-adults are a few primaries behind in moult.

Great Black-backed Gull (Larus marinus) sub-adult: August 11 2003, Boulogne/Mer, France (50.42 N - 01.34 E).

Great Black-backed Gull (Larus marinus) sub-adult: August 11 2003, Boulogne/Mer, France (50.42 N - 01.34 E).

Great Black-backed Gull (Larus marinus) sub-adult: August 2000, Etaples, France (50.34 N - 01.34 E).
Another individual showing the combination of adult-like blackish scapulars and barred coverts and tertials. Note the black markings on the bill.

Great Black-backed Gulls (Larus marinus) sub-adult: August 2000, Etaples, France (50.34 N - 01.34 E).
Primary p7 almost fully grown and p10 still present.