Lesser Black-backed Gull (graellsii & intermedius)

(last update: 09-06-2013)

third calendar year: September

In most typical graellsii LBBG nearly all feathers are being replaced now. Birds require fresh plumage with adult-like upper-parts and under-parts. On average, coverts and tertials are moulted into third generation feathers and mantle and scapulars become fourth (even fifth) generation, after the moult to third winter plumage.

From head to toe you can see the following changes:

• The bill will acquire a bill-band due to the hormonal changes (third winter bill coloration). There is quite some variation: some birds will get a blackish base to the bill, while others only get a sharply defined band across the gonys. The average birds (79 %) show an ”adult” bill with a nice broad band over the upper and lower mandible. The bill colours become paler, more lemon and orange. The legs turn pale pinkish yellow or off-yellow.
• The head becomes heavily streaked as freshly moulted streaked feathers grow in, replacing the white old, worn feathers. Some birds acquire an almost greyish head.
• The under-parts are also moulted. Nearly 100% of the birds show streaked under-parts, some having streaking in the hind-neck only.
• Most 3cy LBBG finish the moult of mantle and scapulars (completed by mid September). The upper-parts resemble adults now (being fourth or even fifth generation).
• Tertials exist of newly moulted 3^rd generation feathers. They are moulted downwards, giving a contrast between the new upper tertials and the old lower tertials (with the central tertials missing). The difference is obvious with these new tertials adult-grey with a white top, contrary the blackish centred old tertials with black markings in the tip. Some birds show a more blackish centre on new 3^rd generation tertials. If so, it's prominent in tertials #3-6. At the end of September almost all 3cy have six new tertials, while some birds are still moulting the final tertials.
• The wing-coverts have been moulted all to third generation, but some 3cy LBBG have a moult-gap in the coverts or still have some old coverts. 95 % follows the ordinary moult sequence: first the inner 3-4 followed by the outermost feathers (which are replaced inwards). Only 5% follows a random strategy and leave a few feathers in the greater coverts not replaced. The under-wing coverts are replaced by adult-like white feathers in a sequence similar to the upper-wing.
• The primaries are moulted outwards and the primary-score at the end of September averages over 40 (n = 153) with p6 full-grown on all bird, as shown in the table below. The third generation primaries are very adult-like but p10 often shows an obvious smaller mirror
• The secondaries are shed inwards, starting next to the primaries. In adults secondary moult starts from the moment p6 is half way to fully grown. In 3cy, only a few birds show secondary moult in September. The 3cy moult of secondaries is not related to moult of primaries. As shown in the bottom table, birds with fully grown p8 or even p9 can still show complete old second generation secondaries. Such birds were found as late as October 10 2001.
• The tail is new, third generation in most cases (90%), but still in active moult in some birds (5%) or complete third generation, white or with very restricted black markings (5%). Old worn rectrices seen in September, without any black markings, are probably third generation as well, moulted early in spring. Variation within 3cy and 4cy birds is huge and advanced 3cy can be aged wrongly as delayed 4cy birds.
  

Tables 3cy LBBG in September

LBBG 3cy Belgium: graellsii / Dutch intergrade

LBBG 3cy the Netherlands: graellsii / Dutch intergrade