|3cy fuscus: August
This page contains images from a short trip to Stockholm, Sweden and to the landfill of Tampere, Finland in 2002. For comparison, have a look at the images of ringed graellsii and unidentified graellsii / intermedius presented in the Lesser Black-backed Gull sections of August, September, October and November-December and on the page "Discusfus".
In general 3cy nominate fuscus resembles adult birds in many respects, especially in the wing-coverts, tertials, scapulars and mantle. The soft parts are very adult-like as well with the iris yellow (although sometimes peppered black), the bill yellow with a red spot on the lower mandible and the black bill-band largely reduced to a faint dark line. The legs may vary from whitish yellow to deep yellow. Black on the bill seems to be a good indication for 3cy birds.
By August, arrested moult in 3cy fuscus is a common feature and can be seen in almost all birds, although one may wonder how to recognize birds which have replaced all the primaries at the wintering grounds. The large majority of certain aged 3cy fuscus (ringed birds) seen by us at Tampere proved to have arrested primary moult. Images of 3cy fuscus shown by Lars Jonnson in his identification article on Baltic Lesser Black-backed Gulls in Birding World (1998 Volume 11 No 3) all show arrested moult as well. One may conclude that a substantial majority of 3cy fuscus has the primary moult suspended prior to northbound migration.
Primary moult strategy and timing
Nominate fuscus is an exception amongst gull species regarding moult. Most of the moult takes place after arrival at the wintering grounds, not in summer. To construct a picture of primary moult in fuscus, some problems arise. There is hardly data on moult from the winter quarters, and the picture has to be constructed on how birds look like once they get back in Europe. Second problem is the variation in extent of primary moult. Many birds replace all or almost all primaries in winter, but apparently, some may wait to spring and follow a strategy commonly seen in graellsii. In subsequent years, one may wonder if the variation diverges further, resulting in 'lazy' moulting birds and rapid (though standard for fuscus) birds. In general, primary moult in the first three years (1cy - 3cy) can be roughly described:
1cy July - September: fuscus at the breeding grounds. Most birds still in complete juvenile plumage, with first generation (juvenile) primaries (see juvenile section). They migrate south and arrive in the Mediterranean or further south in Africa with juvenile primaries.
2cy October - May: fuscus moult most of the primaries (or all 10) to second generation. Quite some birds replace P1-P9 for second generation primaries and still have P10 juvenile (see e.g. C5UJ, CNMR). In a very small number of 2cy birds, this moult is completely lacking. These individuals start moulting the primaries in the same way as other large gulls in NW Europe (from May onwards; not noticed in ringed birds, but see putative fuscus: 3745).
2cy June: according Jonsson (1998), a substantial part of fuscus migrate north and arrive in Scandinavia by July. Data from Finland suggest a majority stay in the winter quarters or at stop-over sites and don't make the complete journey north in summer.
2cy July - August: fuscus may initiate a primary moult wave which only include several primaries, up to the moment migration southwards takes place and moult is suspended. There are two strategies:
A: they may continue moult from the primary where moult was suspended, prior to migration (see e.g.: 2808). Typically, primaries in the outer-hand are involved in these birds;
B: they may start all over with P1, in some birds leaving the P10 still juvenile. In this case, moult was 'arrested' in the outer-wing (CNMR).
By moulting the inner primaries, some birds show three generation of primaries in the wing: the inner primaries being fresh third generation, the central primaries second generation and P10 still juvenile and very abraded.
Finnish data suggest only a very low number of birds start their first moult cycle in summer. In these birds, moult in the primaries may be suspended completely or moult may include the inner primaries (up to P3 in some birds) by July and August.
2cy August - September: fuscus arrest primary moult and migrate south to the wintering grounds.
2cy October - 3cy April: there is only limited data on this period. Jonsson (1998) examined two 2cy birds found in Africa in October; both were actively moulting the outer primaries. Probably, these bird replaced juvenile primaries for fresh second generation feathers, as most advanced 2cy summer birds moult P2 or P3.
All 3cy that return in Europe in June showed fresh (third generation or older) tail-feathers and secondaries, so in winter the complete set of tail-feathers and secondaries must have been renewed. If the same strategy is followed as the previous winter, birds start their moult in the tail-feathers, then the secondaries and finally the primaries. This may help to explain why moult is arrested in the outer primaries: the primaries are (again) the last tract to be moulted in fuscus.
3cy April - May: many fuscus in 3cy return to the breeding grounds. Most arrive May - early June. Prior to spring migration, 3cy fuscus arrest primary moult again in the outer primaries, resulting in the obvious moult step when they return in Sweden by late-April and early-May. The obvious mirror on P10 can be explained by the late requirement of this second-generation P10, which is therefore more adult-like in appearance. As was already the case in spring, moult continues in waves, rather than in the ordinary sequence P1 to P10 and these waves result in clear divides between the fresh and the old primaries halfway the wing. This is shown by e.g.: C5XM.
3cy June - August: By July and August, moult in the primaries is initiated again after suspension and often include the inner primaries again (see C5XE, C0XC), up to P6 in some birds. However, it's common to find 3cy July birds with all primaries present (e.g. C2A5, C3A4, C4XR, C5XM, C9NN). Some birds show second generation outer primaries, probably a common feature in birds which previously arrested moult in 2cy and showed juvenile outermost primaries in summer. See e.g.: C8XC, CNMR, C0NM. Fuscus may continue moult by two strategies:
A: they may continue from the primary where moult was suspended, prior to migration (only a small minority seem to follow this line);
B: they may start moulting again from P1 (e.g. C2WJ, C6NS, C6WM). In this case, birds carry three sets of primaries: the fresh 4th generation inner primaries, the 3rd generation central primaries moulted last February and the second generation outer primaries moulted last winter after they were excluded in spring 2cy.
Second generation outer primaries in 3cy fuscus can be recognized by rounded tips, no mirror (or a small mirror) on P10 and bleached pale brown feathers (C0NM, C3RH).Second and third generation P10 may be very alike, although second generation P10 is often brownish, where third generation P10 is typically glossy black (see CNMR).
3cy September: birds migrate south, most birds with at least two but commonly three sets of primaries. During migration, moult is suspended.
3cy October-December: fuscus continue moult on the wintering grounds following the same strategy as last winter. The irregular step-wise moult may be repeated in the next years, but the difefernces between older generations / sets of primaries is difficult to ascertain in the field, and has yet to be proven.
This moult sequence in nominate Lesser Black-backed Gull Larus fuscus fuscus was already described by Stresemann & Streseman in 1966 in Journal für Ornithologie. They described a periodische Staffelmauser, a step-wise moult in fuscus. Large white-headed gulls in north and northwest Europe replace the remiges during the breeding season and finish this moult in autumn prior to (compared to fuscus, a relative short distance) migration. Fuscus is an exception as it doesn't start the remiges moult before arriving at the wintering grounds in Africa and the Mediterranean. For a long-distance migrant like fuscus, this seems to be a suitable strategy. The same pattern can be found in long-distance migrants like Terns (Sternidae).
fuscus fuscus C1SM 3cy, August 06-09 2002, Tampere, Finland (61.33N 24.59E).