Great Black-backed Gull (Larus marinus)

(last update: July 12, 2015)

Great Black-backed Gull 2cy March

Description of 1st summer plumage

First-summer (Mar-Aug) as first-winter, but head and underparts generally whiter. Mantle, back and scapulars grey with black subterminal bars and shaft-streaks. Upperwing and tail paler with wear. Bill black with smudgy, greyish- or fleshy-tinged base and pale tip to both mandibles. Eye dark. (source: Malling Olsen, K. & Larsson, H. 2004 Gulls of Europe, Asia and North America. London: Christopher Helm).

Moult in summer months.

The above description from Malling Olsen may be true for birds in March and April, but 2CY Great Black-backed Gulls in the summer months are obviously different from first-winter plumage birds.
Great Black-backed Gull is an early moulting species, at least that's what birds show that stay in NW France along The Channel coast and moult timing may even start earlier than 2CY Yellow-legged Gull michahellis (see tables in 2CY May section for marinus, michahellis and argentatus). New 2nd generation feathers may superficially resemble the old and worn juvenile feathers in pattern (transversal barring), but they are very fresh, especially visible at the fringes and the tips, and the base tone is warm buffish or pale brown rather than the silvery white tones in juvenile feathers, Only after several weeks these warm toned 2nd gen feathers will turn paler as well and become more contrasting again.

In early summer there is an obvious difference between fresh warm toned 2nd gen feathers and old bleached juvenile feathers, sometimes resulting in a messy looking bird, also due to missing feathers creating moult gaps in the covert rows. Such birds look different from first winter birds.
Later in summer (July-August) the process of complete moult is very obvious in the outer primaries and in this respect birds of course look very different from first winter birds.

Larus marinus JY481 2CY, February 10 2013, Boulogne-sur-Mer, France (Jean-Michel Sauvage). Classic late winter bird with most scapulars replaced, but wing-coverts and tertials still juvenile. Note pattern on juvenile central greater coverts: predominantly silvery white with widely spaced brown bars. Complete moult not started yet.

Larus marinus 3U4 2CY, May 27 2014, Whiting, USA (Amar Ayyash). Complete moult started early in this bird, with only P8-P10 old juevniel primaries in the left wing (P7 also still present in right wing). Note warm toned fresh 2nd gen median coverts and all central greater coverts missing. Messy looking bird.

Larus marinus 2CY, July 30 2014, IJmuiden, the Netherlands (Mars Muusse). P9-P10 old juvenile. Note vermiculated pattern on fresh 2nd gen greater coverts, different from the widely spaced bar pattern on juvenile greater coverts.

Larus marinus NOS 337783 2CY, August 14 2013, Boulogne-sur-Mer, France (Jean-Michel Sauvage). Complete moult in last stage with P7 fully grown and no old primaries left, resulting in short-winged appearance. Again, note vermiculated pattern on central greater coverts.

Larus marinus NOS 337783 2CY, November 06 2013, Boulogne-sur-Mer, France (Jean-Michel Sauvage). Same bird as previous image. Complete moult finished, note mirror on underside of P10. Compare to August, and notice a subsequent "partial autumn moult" has changed the plumage slightly, again fresh feathers appear in the wing panel. The upper tertial and innermost greater coverts GC1-2 have been replaced again; also new are median coverts MC2,10,11,13,15, and lower lesser coverts LLC1-3,6,8-12, and about 10x lesser coverts. Five of these fresh feathers indicated by red lines.

Tables:

Note: nla 6038628 from Holland is the only bird in our sample (n=232) not ringed as pullus, but ringed in October in IJmuiden, Holland, hence no provenance on origin.

below: graph corresponding to data from table 1. n=24. Distribution of replaced scapulars in March 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.