In 2cy Larus fuscus fuscus, there is a large variety in moult stage in July and it's difficult to describe a 'typical' plumage for this age class. The images in the August Section and the photo's right illustrate the variation from slightly delayed moult, to 'average' and well-advanced birds. Delayed birds may be very difficult to separate from 2cy intermedius and heuglini. Advanced 2cy fuscus strongly resemble 3cy graellsii and intermedius. More details can be found on the page "Discusfus".

Primary moult in 2cy January - July

The general appearance of 2cy July fuscus is strongly dependent on the extend of the moult in the wintering quarters. On the wintering grounds, the scapulars are replaced immediately followed by the wing-coverts. Images from January and February, and wear in the coverts suggest this wing-covert moult cycle to follow the same sequence as in the complete moult (basic moult), starting with the innermost and outermost median coverts. From these two loci, moult waves start and meet at the central median coverts. In the mean time, inner greater coverts, upper tertials and lower lesser coverts are dropped. The wing-covert moult ends with replacement of the central greater coverts and outer lesser coverts in the carpal edge. 
A February individual nicely demonstrates this sequence. The coverts are all or almost all replaced by late January to mid February. Considering the wear of these wing-coverts in spring in some 2cy Scandinavia fuscus, the wing-coverts must have been moulted within a very short contracted period in these birds, as the abrasion and bleaching of the feathers is almost equal in the complete panel. Only after finishing the moult in the wing-coverts, 2cy fuscus start to moult the fight feathers from February onwards according to Lars Jonsson (1998), which is supported by the February bird, with P1-P10 still present despite ongoing wing-covert moult. Jonsson described ten 2cy fuscus from late January in Israel and none of these had shed a single primary.

In museum collections, Jonsson found four birds: one 2cy fuscus from late January, growing P1 and P2. Two other birds from April, found in Angola also showed moult in the primaries (moult scores 13 and 46) and another bird from Aden almost finished its primary moult in early May (moult score 39). For explanation of moult scores: see Topography Section.

Primary moult starting in February just fits in the fuscus picture, as this replacement takes over 4 months n large white-headed gulls. Thus, 2cy birds are just in time to finish this moult to migrate north again by late-May - June.

Primary moult stage in July

This is the general picture of a complete moult cycle taking place on the wintering grounds and generally explain the plumage of July 2cy fuscus in Scandinavia. Actually, some birds already start to moult a few wing-coverts in a subsequent moult, now to third generation. This is still the average picture, and is illustrated by C5UJ and C6XV. An example of 2cy fuscus which did not succeed in finishing the complete primary moult on the wintering grounds is CNMR, with P10 still old. The moult cycle may be very advanced in some birds, as illustrated by some ringed birds on this page, C3VS, CJUC and MC24. 
2cy fuscus are readily easy identified, when birds have replaced all primaries, replaced all wing-coverts to plain blackish brown coverts and almost pitch black mantle and scapulars. In short, this is reminiscent of a complete moult, which other taxa show in 2cy summer months (May-October). 

Variation in 2cy July fuscus is extensive. From 1995 to 1998 Jonsson described 2cy fuscus after arrival at Gotland, south Sweden, and these birds showed a wide range of variation. Most 2cy birds finished moulting all of the flight feathers by late April and May, others arrested moult in the primaries prior to migration. However, a mjnority of 2cy fuscus return in Scandinavia with all flight feathers still juvenile. Unfortunately, Jonsson doesn't further enlarges upon his diagnostic criteria to separate such birds from 2cy intermedius, which can be found in S Sweden in good numbers.

Jonsson's figures are in line with the findings of Visa Rauste (1999), who estimates 60-70% of 2cy birds to return in Finland with complete new flight feathers. He examined 19 2cy fuscus in Finland; 15 individuals had replaced all the primaries. Rauste found a minority of 2cy fuscus returning with several juveniel primaries (20 out of 64 birds, fig 32) and he also found soem 2cy fuscus to show all primaries still juvenile (although the figure is 0 out of 64 birds in fig 32). These last mentioned birds start primary moult in Finland. 

After arrival in Finland, most 2cy fuscus (70-80%) initiate the next moult cycle, many birds now moulting the inner primaries to 3rd generation. Interestingly, it may thus be possible to see two 2cy fuscus, both moulting the inner primaries. One bird moulting to 2nd generation, the other moulting to 3rd generation. Rauste examined one colour-ringed bird which continued moult in the outer primaries and in the mean time started moulting the inner primaries (P1-P2 fresh 3rd generation, P3 missing, P4-P8 2nd generation, P9-P10 growing 2nd generation).

All colour-ringed 2cy fuscus at Tampere (July 2002 & August 2003) in Finland showed advanced moult in the primaries. Most birds moulted P1-P9 or P1-P10 on the wintering grounds during the previous spring as 2cy. Late July and early August a typical 2cy starts shedding the inner primaries for the second time, growing in third generation primaries. Remember that these birds are still only one year old.

Figure 32 from Visa Rauste: Kennzeichen und Mauser von "Baltischen Heringsmöwen" Larus [fuscus] fuscus und "Tundramöwen" L. [fuscus] heuglini, Limicola 13 (1999): 153-188.
Progress of primary moult in fuscus (n=64) and heuglini (n=66) during the 2cy summer. The figures in the lower part give the number of retained juvenile primaries (10 = still complete juvenile primaries, 0 = firts moult completed); the upper part shows the progress of the second moult (only in fuscus), the figures give the number of renewed third generation primaries (an upward stroke on the symbol means that these birds have completed the first moult, but it is unknown if they have started the second).

Secondaries and rectrices in July

Average 2cy fuscus have replaced the complete tail and all of the secondaries on the wintering grounds. By August the tail-feathers appear already worn at the tips and the brown sub-terminal band might be slightly bleached towards paler brown. This can be seen in all pictures of ringed 2cy fuscus. 
Considering the advanced primary moult stage of most 2cy fuscus, it would be odd to suppose secondaries to be still juvenile. Secondaries are replaced as well, together with the outer primaries. Sometimes birds moult secondaries without starting primary moult (a phenomenon maybe stronger related to heuglini). Jonsson about secondary moult in 2cy fuscus in Sweden: "Although it is more difficult to judge in the field how many of the secondaries have been moulted, they generally appear to be largely moulted, but a few juvenile secondaries sometimes remain". The number of observation of fuscus in Finland (in our case) are too low to draw any conclusions, but early figures are in line with this opinion. At least one bird had some inner secondaries still juvenile (the only 2cy bird we caught). The tail-feathers are easily judged in the field and appeared second generation in all ringed 2cy birds.

Wing-covert moult in July

It's the kind of birds represented in image 3598 that show most juvenile wing-coverts, especially the upper rows of lesser coverts, the carpal edge (outer lesser coverts) and the central greater coverts, which are moulted in descending order. Such birds may actually not be fuscus. 
Average fuscus has all wing-coverts moulted on the wintering grounds prior to northbound migration and those second generation feathers appear already pretty bleached with paler brown centres and abrasion on the fringes. Quite some birds are missing the outer or innermost median coverts again in July, indicating they started a partial moult to third generation wing-coverts. Some advanced birds continue the replacement of wing-coverts which was initiated in spring. See: C3VS (inner greater and inner median coverts) CJUC (inner greater and central median coverts) and MC24 (outer lower lesser coverts).

In general these third generation feathers are all dark, blackish and can be found in almost all the images presented on the right-hand side. Advanced birds show many third generation wing-coverts, as can be seen in August images 3323 and 3353: Most of the median coverts, the inner greater coverts, most of the lower lesser coverts and the outer lower lesser coverts have been replaced by third generation coverts. As can be seen in the images, the old second generation wing-coverts are bleached and abraded at the fringes.

Identification

Of all plumages, 2cy fuscus probably is the easiest to recognise, when average or advanced birds are involved. Diagnostic features for juvenile, 3cy and adult fuscus are much more difficult to find. Prime candidates for confusion are 2cy heuglini and intermedius/graellsii. Heuglini is excluded here as we have not enough experience to get a complete picture of the moult extend in this plumage. 

Intermedius can show a much more advanced 2cy plumage than endorsed by current literature. Like 2cy fuscus, 2cy intermedius may show complete replaced wing-coverts in July, replaced tail-feathers and some intermedius may even replace secondaries on the wintering grounds. So far, we are not aware of any certain (ringed) intermedius with replaced primaries in spring and this feature is probably most indicative for fuscus. Other characteristics, like pitch black scapulars, long-winged jizz, and advanced moult in other feather tracts can be found in intermedius as well (see for more details: Discusfus page).

Identification of 2cy fuscus may be easier when the outermost primaries are still juvenile (arrested primary moult), especially when a new moult wave to third generation primaries started at P1. Third generation P1 in 2cy July intermedius has not been described so far.  Juvenile P10 is never present in 3cy graellsii or intermedius.

Migration

Contrary most literature, Jonsson presumes that 2cy fuscus do regularly migrate north, but the position of the wintering grounds (either Mediterranean or Africa) of these returning birds is unknown. Jonsson estimates that "a substantial proportion of the total number of this age-class" is involved. The vanguard of second calendar year birds normally returns July 01, after a one-month journey north.
Jonsson doesn't further specify on the "substantial proportion" of 2cy birds, which is a pity. Indeed, literature mention that most of 2cy birds remain at the wintering grounds or rich feeding grounds on stop-overs. The picture of low number of 2cy in Scandinavia is reflected by ring-recoveries of 2cy intermedius, which normally do not spend the summer months in S Norway but further south along the Atlantic coast (Nils Helge Lorentzen, pers comm). The same seems to be true for Finnish fuscus. From April onwards, many colour-ringed 3cy and older birds find their way north again to Tampere dump, but only low numbers of ringed 2cy fuscus are encountered (Markku Kangasniemi & Hannu Hoskinnen, pers. comm.).

This is further confirmed by colour-ringed Finnish 2cy fuscus. Rauste (1999): "... mindestens 5-10% der Vögel (kehrt) im 2en KJ für kurze Zeit im Hochsommer in die Brutgebiete (zurück). Die meisten dieser Vögel wurden zwischen Mitte Juni und Ende August gesehen." Rauste stresses that, since a large proportion of 2cy birds do not return in Finland, moult sequences may develop in a different way in these birds than described from his field observations in Finland.

Literature

Lars Jonsson (1998), "Baltic Lesser Black-backed Gull Larus fuscus fuscus moult, ageing and identification", in Birding World Volume 11 number 8, 1998.

Visa Rauste (1999), "Kennzeichen und Mauser von "Baltischen Heringsmöwen" Larus [fuscus] fuscus und "Tundramöwen" L. [fuscus] heuglini", in Limicola 13 1999.