Lesser Black-backed Gull (graellsii & intermedius)

(last update: 09-06-2013)

third calendar year: October

Movements

Most LBBG have left the colonies and surrounding feeding grounds near the Maasvlakte (the Netherlands) and migrate south towards France, Portugal and Morocco. By October many remain on continental NW Europe, as north as the south of the Netherlands along the coast at Westkapelle, 65 km south of the Maasvlakte (see map). By the end of October, birds changed their plumage for adult-like upper-parts and under-parts. The primaries and secondaries are third generation (adult-like). Wing-coverts and tertials have been renewed into (at least) third generation feathers and mantle and scapulars are most fourth generation now.

LBBG in 3cy by mid-October

• The bill shows a bill-band of various size. The average birds (80%) show an ”adult” bill with a broad band over the upper and lower mandible (see this image).
• The bare parts coloration is not as intense as in adults, more lemon and orange.
• The head is heavily streaked by freshly moulted streaked feathers.
• The under-parts are streaked, sometimes only in the hind-neck.
• Mantle and scapulars resemble adults now (being fourth or even fifth generation).
• Tertials exist of newly moulted third generation feathers. The tertials are adult-grey with a white top. Some birds show a more blackish centre on the new third generation tertials 3, 4, 5 and 6.
• The wing-coverts are plain, grey adult-like third generation feathers (or sveral coverts may be a generation older, depending on previous moult sequences). In only a very few you can find some barring. When so, this barring is found on the inner greater coverts, tertials 2-4 and the inner median coverts. Sometimes (in 5%), a few feathers in the greater coverts have not been replaced (see this image) and create brown interruptions in the new grey row. The old greater coverts normally are number 5-7 (counted from the body). About 95% of 3cy LBBG follows the normal moult sequence: start with the inner 3-4 then continuing with the outermost feathers and moulting these inwards.
• The primary score at the end of October averages 46 with at least P7 fully grown on any bird (see table below). The third generation primaries are very adult-like but P10 often shows an obvious smaller mirror, often not reaching the sides of the feather and situated further from the top.
• Secondaries: about 60% shows replaced third generation secondaries by the end of October.
• The under-wing coverts are white.
• The new tail is completely white or with very restricted black markings (20%) on the outer webs.

Arrested moult in 3cy LBBG

Some 3cy birds show arrested moult: new inner primaries, up to p6, p7 and p8, with the outermost primaries still old (P7, P8 and P9 respectively). Arrested moult or near arrested moult can be be recognized by the lack of an obvious gap of at least one missing primaries between the fully grown outermost primary and the next innermost old primary. But one has to be cautious: the gap in the primaries of 3cy birds caused by active moult is smaller than is shown in adults and about 70% of 3cy birds do not miss a full primary when it is in active wing-moult. Especially when the outer primaries are moulted, this feature is very common. A few example are presented on this page.

1. Birds with a moult gap of less than one primary:
This photo shows a 3cy intermedius ringed in Denmark with P8 already longer than P7 and the outer primaries P9 and P10 still present. P8 still has to grown a few inches, while P9 is still present. A 3cy bird with some characteristics found in intermedius is shown in this photo. Again, this bird has P7 fully grown and P8 still growing. P9-P10 are still old.

2. Birds with arrested moult:
This photo shows a presumed intermedius in 3cy with P8 fully grown and P9-P10 still old second generation. And this photo shows another dark grey LBBG, presumable intermedius with arrested moult at P8. This bird has most of the upper-parts and under-parts adult-like as is commonly found in 4cy birds. 

Remarkably, in such birds, the primary moult will probably be arrested or has been arrested at P8. In the October sub-adult LBBG section more birds are presented with arrested moult.

Several of the birds with arrested moult have all grey upper-parts, small tips on the outer primaries and reduced mirror on P10. In general, 4cy are hard to exclude for a 100%, as the old P10 is often missing. 

As long as immature coverts and tertials appear in the upper-parts, identification directly points to 3cy LBBG (e.g. pronounced black shaft streaks, spaghetti pattern in the coverts, club patterns on the outer lesser coverts in the carpal edge). When the upper-parts appear all grey, LBBG may not be aged so easily. But still the primaries may be indicative for 3cy: the primary tips are very limited, often absent on P7-P10. P10 normally shows a white mirror, but this mirror is reduced to a relatively small spot and often not reaching to the feather edge. Another strong clue advocating 3cy are the retarded old second generation primaries. If P10 is still present, this P10 is very abraded, bleached and lacks of course the P10 mirror. See for instance those -near- arrested moults in image 13, 14, 15, 19 and 20. Another feature can be seen in preening birds or birds stretching the wings, the outer secondaries may show some spaghetti pattern. The fresh tail feathers often show black markings, especially on the outer webs. Finally, the bare part coloration may point to immaturity, with extensive black on the bill (a clear bill-band), the basal half of the bill black or pinkish, the legs pinkish yellow and sometimes an off-yellow iris.

Tables

LBBG 3cy Belgium: graellsii / Dutch intergrade

LBBG 3cy the Netherlands: graellsii / Dutch intergrade