Yellow-legged Gull - Larus michahellis

(last update: October 08 2013)

Delfín González
Gabriel Martín
Antonio Gutierrez
Amir Ben Dov
Mars Muusse

Yellow-legged Gull michahellis 3CY, August 09 2003, Etaples, France (50.42N, 1.34E).

In 3CY birds, the old second generation flight-feathers are replaced by new, more adult-like third generation feathers. This is most obvious in the (outer) primaries. The old second generation P10 is brown, abraded and will be replaced by glossy-black fresh third generation P10 showing an obvious mirror. 

The primary moult stage in the central bird (top image): P9-10 are old second generation and P6 is full-grown. P7 is at the length of P5. The complete moult in the secondaries has started as well and is normally initiated at the division between primaries and secondaries (S1, next to P1). The primaries are dropped in an almost constant interval, but moult in the secondaries may evolve much quicker: the first outermost secondaries (S1 to S3) are normally shed one by one with reasonable intervals, but the inner secondaries are almost dropped simultaneously, leaving large gaps in the inner-arm by the end of August.
Note also the adult-like coloration of the bare parts, with clear yellow legs, yellow iris and adult-like bill pattern, much more advanced than average 2CY in August.

Bottom picture: almost same moult stage. Note faint black on outer-web of P4, common in 3CY michahellis, but not commonly shown in older plumages.