third calendar year: May
During winter and especially early spring, 3cy LBBG undergo a partial moult in the winter quarters. This moult typically involved the upper-parts, the under-parts and the head. Also, the bare parts develop to more adult-like coloration. By May, the tail, primaries, secondaries, wing-coverts and tertials often still consist of old feathers (retained from previous autumn). Wing-coverts strongly contrast with the renewed grey upper parts (and sometimes the median covert row).
However, not every 3cy LBBG follows this sequence, and we have encountered many returning birds with a variable amount of new tertials, coverts and even rectrices. Some 3cy LBBG return with few new primaries (arrested moult) as well. It's still preliminary to classify LBBG with arrested moult in the primaries and allocate them to certain populations. First figures indicate both intermedius from Scandinavia and local breeding Dutch intergrades may arrest moult in 3cy in spring. Advanced moult on the wintering grounds (incl primary moult) is normally associated with nominate fuscus.
During the month of May an unknown number of 3cy birds return to the colony, either for a short visit or to linger around for longer periods. The first arrive around mid-April, the majority around mid-May. There may be good reasons for 3cy birds to return to their native colony, e.g. lack of food supply on the wintering grounds, to learn the best feeding grounds around the colony, exploit best breeding places, etc. Some 3cy birds will even attempt breeding. But there are risks involved as well taking on a long journey back to the breeding grounds.
3cy graellsii from Rotterdam port (SW Netherlands) visit the colony in May, but numbers are low. Some 3cy birds stay at NW France, at dumping sites and do not return to the actually breeding sites, although it's only a short distance.
Most 3cy LBBG stay at the edge of the colony or social roosting places.
One theory tells the brown feathers may protect 3cy birds against furious attacks of territory holding adult males. These brown feathers may be signs for breeders that these 3cy birds do not participate in mating. Nevertheless, severe fighting is not uncommon. Still, 3cy birds daily return to the colony and it seems they watch the steps of the elder birds. They may also predate on eggs, young rabbits, etc in the colony.
Moult of primaries
In May, moult activity is very low. Birds start shedding the innermost primaries. At the end of May all local birds at least show a gap of P1 and P2, some birds have already shed P4. Adult and sub-adult LBBG will start their primary moult from mid-June, dropping P1 and P2, although some birds may start as early as May. Compared to 3cy birds, they have a delay of one or two primaries. New third generation primaries in 3cy LBBG are adult-like in having grey centers and white tips, contrasting with the old plain black-brown second generation primaries. Remarkably, from the second half of May 'new' birds arrive at the colony, showing delayed primary moult compared to average 3cy. Out of ten birds on the last day of May, four birds still retain all primaries.
Compared to older birds, the third generation primaries show smaller tips. P9 normally lacks a mirror and the mirror on P10 is small. P3 and P4 show more black marks (often resulting in a complete sub-terminal band on P4, where most adults only have black on the outer web).
Except for the primaries, there are almost no other feathers shed, although some inner median coverts may be shed.
Moult of tail-feathers
Some birds start moulting the tail, but May is very early. Most common at this age is a worn second generation tail, i.e. a tail with a broad black/brown tail-band. Only a few birds are actively moulting some tail-feathers, starting with the innermost pair. This pair is on top and often bleached and the tips worn away. About 30% of 3cy birds moulted one or more pairs last winter, resulting in a blocked pattern of white and non-white tail-feathers. This winter-moult involves tail feathers randomly, creating an unpredictable black and white tail in spring. Birds returning with a complete white tail are no exception.
Moult of coverts
Most 3cy birds still show brownish second generation wing-coverts (greaters and lessers at least) while upper-parts and bare parts look very adult-like. In May, moult in the coverts is normally not found in birds staying near the colony. Birds outside the colony may already start moulting at the end of May. New coverts are easily recognized since this third generation feathers are typically uniformly grey, like in adults. Some third generation feathers however (moulted in the previous autumn like the medians, mantle and scapulars) may be like second generation feathers in pattern (see e.g. picture of BLB L-97134), but those moulted in summer are much more adult-like. The old retained second generation feathers show at least some brown in the centre and show white fringes, but the exact pattern gets lost by wear.
More about arrested and suspended moult
The average moult stage for second summer LBBG can be seen in the pictures. But some odd individuals turn up as well, for instance with fresh white tips on P1-P7, while P8-P10 are still second generation (and P10 obviously lacks a white mirror). It seems that, in both graellsii and intermedius, arrested moult is a rare phenomenon, but may occur. See bottom images.
In his article about identification of fuscus LBBG (Birding World, 1998), Lars Jonsson writes about 3cy birds: "Second-summer fuscus is the most likely to be seen as a vagrant... Overall, they are much blacker than the corresponding plumages of graellsii and intermedius and they show much more adult-looking wing coverts. Also, fuscus very typically shows a staggered or incomplete renewal of the greater coverts, where a few brown feathers are retained in an otherwise rather blackish row. On the whole, the more complete renewal of the wing coverts during the pre-breeding moult is markedly different to that of intermedius and graellsii, which typically return for their second summer with a new dark grey 'saddle' but old wing coverts (although quite often the median row will have been renewed, forming a grey band on the middle of the wing)." And further: "I would positively identify a second-summer Lesser Black-backed Gull in May showing predominantly dark wing coverts and very fresh inner six to eight primaries as a fuscus."
Although this all is very true for fuscus, it may be an over-simplified analysis of the variation in 3cy intermedius returning in May. Most pictures shown here, probably show graellsii LBBG or Dutch intergrade LBBG as they were taken near or in colonies in the Netherlands. But on several occasions, groups of true migrants from Scandinavia can be found at the beach and several "puzzling" individuals were encountered of which a few are shown here. It seems that at least one of the key features to look for (i.e. arrested moult) occurs in intermedius as well and at least an estimated 4-10% of 3cy LBBG may show this features in spring. And this may be a low estimation, since birds with arrested moult are exactly the birds "in a hurry" and may not take long rests at the stop-over points. It's interesting to see in what way fuscus-like features have to accumulate to make identification as fuscus acceptable.
When intermedius shows arrested moult in the primaries, combined with advanced moult in the upper-parts, these birds can easily be mistaken for fuscus. At Le Portel, France, three such LBBG were present early May 2001, including a very dark, gentle (female) intermedius. The bird's characteristics strongly approached those said to be diagnostic for fuscus. Very dark (blackish) gentle (female?) second summer intermedius, which show very advanced moult in the upper-parts, combined with arrested moult in the primaries do occur and approach fuscus in both coloration and general structure. Now we have come across few such LBBG, it's hard to select diagnostic features to distinguish between these two taxa.
Arrested moult or suspended moult?
In discussions about arrested moult, suspended moult is included as well. Strictly, the difference between arrested and suspended moult lies in the continuation:
Suspended Moult: A bird starts moulting the flight feathers in the ordinary way (from P1 outwards). At a certain point, the moult stops (is arrested, e.g. when migration starts). After arrival, the bird catches up moulting the rest of the flight feathers, which can be recognized as fresher.
Arrested Moult: A bird starts moulting the flight feathers in the ordinary way. At a certain point, the moult stops. After arrival, the bird starts moulting P1 again, thus doesn't continue moulting the rest of the flight feathers.
In some cases moult continuation is combined and two moult waves start: one wave at P1 and one wave at the place where moult was arrested, prior to migration. This is visible as two gaps in the wing (beware of secondary moult in the outer secondaries (S1, S2, S3).
Arrested moult: in autumn or spring?
It may be important in identification to know whether moult was arrested prior to migration (in autumn) or moult was arrested later on in winter, prior to northbound migration. Whatever, it might be very difficult to judge the correct age of flight feathers by their abrasion and wear. In this discussion, it must be said that there is a difference between pigment fading (black feather parts fade to brown, but grey stays grey) and bleaching (all feathers parts, including the paler parts turn pale). Where this discussion ends is still open.
Dutch 3cy LBBG at the Maasvlakte
Do the birds we see in the Netherlands represent average Dutch LBBG and do they truly mirror characteristics found in average LBBG? There are about 25.000 breeding pairs at the Maasvlakte. The average reproduction is 1 young: 25,000 1cy birds leave the colony. Already 50% die in the first year (12,500 left) and another 25% die in the second year. Hence, after two years only 9,000 birds remain. If you were able to count all colonies present on the Maasvlakte and surroundings in one moment, you would still miss many birds (1,000's). From the ringed 300 a year, only 9 where seen again the following year (by only 4 observers). But another year later, around 16 birds were recovered, then in their 3cy. Many seem to spend the summer south, where there is no rivalry over nesting places and enough food supply. Others simply linger around, at sea or at other feeding stations like dumping sites.
LBBG 3cy: graellsii