Lesser Black-backed Gull (graellsii & intermedius)

(last update: 20-2-2011)

second calendar year: August

In Lesser Black-backed Gulls, nearly all feathers are being replaced by August. There may be great differences, both between individual and in time: between the beginning and the end of the month. Many birds change from a grabby immature into a fresh bird with adult-like upper-parts and under-parts. From head to toe you can see the following changes.

• The bill becomes paler. Variation in bill colour is very obvious now. All-black bills (still present in 20%) show pink bases while some birds (advanced) may show a pink-yellow bill with only a small sub-terminal band. The average birds show a pink bill with a dark distal half.
• The iris turns paler brown or whitish, the advanced birds already show a yellowish white iris.
• The head varies from all-white without any speckling or streaking to 'dirty' and heavily streaked on a grey background.
• The under-parts moult into white feathers, with dark streaks on the flank and at the sides of the breast. Quite some birds show all-white worn under-parts by late August, with only some streaking on the flanks.
• The mantle and scapulars consist of old worn second or third generation feathers, being plain with a darker shaft-streak and sub-terminal band, and fresh third or fourth generation feathers, being adult-like (though slightly paler than pure adult-grey) and often with a darker shaft-streak or central wedge.
• At the end of August, the majority of 2cy LBBG shows many third generation mantle-feathers, creating a grey triangle on the back. 
• The differences in the amount of adult-grey feathers on mantle/scapulars are obvious: some 2cy just have a few grey feathers on the mantle while others have moulted all mantle and scapulars into adult-like third or fourth generation feathers.
• Most 2cy LBBGs still moult their mantle and scapulars at the end of August (well into September), so the area of grey on the upper-parts may still grow creating the grey saddle, as often seen in 3cy birds returning in spring.
• Tertials on a 2cy  LBBG in August can exist of old juvenile as well as fresher second generation feathers or (for advanced birds) newly moulted third generation feathers. The juvenile tertials are very worn pale brown, while second generation feathers are all black with a broad white tip (normally with a thumb-print pattern or vermiculation at the sides). New third generation tertials are adult-like grey but may lack the obvious white tip. By August, many birds miss at least some tertials, often the upper tertials. When present, the upper tertials are normally the most recently moulted ones.
• The wing-coverts are in active moult, so gaps in the covert bars are very common. Normally, moult starts with the median coverts. While moulting these medians, birds start to shed the greaters (and may shed the lessers as well). The inner median coverts are normally moulted from the body to the outer-wing (up to #5 app.), while the outer medians grow towards the body. Normally the meet at the 7^th or 8^th median covert, counted from the body. The same applies to the greater coverts, where moult normally starts with the inner coverts. Wing covert moult ends with the outer lesser coverts. Often, these feathers may be a clue for the age of a bird.
• A common state of moult on a 2cy LBBG by mid-August is:
  new inner medians (second generation), a few new inner greaters (second generation), missing outer and central greaters, missing at least the inner half of the lessers and retained outer lessers. The second generation greater coverts are normally blackish with no or faint barring. Second generation medians and lessers contrast with first (juvenile) generation feathers; they are black centred with a whitish fringe or show barring or anchor patterns.
• The primaries are moulted outwards and at the end of August all present birds (n = 130) showed at least a fully grown p6. The average moult score by the end of the month is 40, with p7 fully grown, p8 half-way and p9 just visible. But some birds scored 35, while some advanced individuals showed scores of 50. Compared to the old juvenile primaries, new primaries are darker (jet black) and have a rounded top. The inner primaries are paler than the outers, often p1 and p2 with a darker shaft on a brownish background.
• The secondaries are shed inwards, from the moment p5 is half way to fully grown, often creating large gaps from p1 inwards. They are shed simultaneously (a few, about 5, remain juvenile, and are visible as a block at approximately S5-10 and S16-17). Secondaries grow fast; birds with primary moult score 40 already have at least 5 new secondaries, which are black centred.
• The under-wing becomes paler, as juvenile under-wing coverts are replaced by white or black-and-white (contrasting) 2^nd generation feathers.
• The tail is second generation in many birds, still in active moult on some, but fully grown in many. The new feathers are all-black or white with a broad irregular black band. In many birds the second generation tail shows more black than on the juvenile. By November, some 2cy LBBGs show predominantly white tail-feathers and probably some 2cy moulting the tail-feathers in July are replacing second generation feathers for third generation rectrices.
• Structurally, LBBG show much individual variation. One bird can easily be as large and robust as a Greater Black-backed gull, while another (like female intermedius) is only slightly larger than Common Gull (L.canus), gently built with an attenuated rear.
• The more constant colour of the legs is flesh-coloured to pink; only a very few have a hint of yellow.
• Those birds with advanced mantle and scapulars may look like 3cy birds as they return in the Netherlands by May next year.

Tables:

The tables below show primary scores of 2cy LBBG in August. In the Netherlands, we have seen colour-ringed and metal-ringed birds from British, Belgian, Dutch, German and Scandinavian projects, thus from graellsii, intermedius and Dutch intergrade populations. We therefore do not specify data to taxa level. 
2cy LBBG were identified on primary pattern and upper-part coloration. Primaries are scored fully-grown when a primary exceeds the previous feather in the folded wing. Note that this also includes feathers which would be scored 'just not fully grown' (score 4) in other researches. We choose this score since it proved to be very difficult to establish the presence of waxy sheath on the feather-base in field surveys.
When judging the old primaries, be aware of the dark print on outer primaries, created by the shed, previous feather. Such prints may contrast strongly with the bleached primary tips.