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 2CY, September 30 2001, Dannes / Boulogne-sur-Mer, NW France.

A rather contrastingly patterned 2CY michahellis with scapulars and almost the complete median covert row replaced for adult-like grey feathers. The head and under-parts have been moulted. Primary P10 is fully grown, resulting in a primary moult score (PMS) of 50. See Gull Topography for explanation of PMS.
The old coverts and tertials show a contrast between the black-brown centres and the white fringes and tips.
The partial moult in autumn is in progress with the upper tertials been replaced for at least third generation grey feather. The exact generation is difficult to proof when dealing with unringed birds which have not been followed over the last two years. As can be seen in several 1CY sections, many michahellis include upper tertials in the post-juvenile (first pre-basic) moult, so the moult in 2CY autumn birds may result in new upper tertials of fourth generation.
The lower tertials are still older, either second or third generation feathers. As can be seen in the 1CY sections, not many birds include all tertials in the post-juvenile moult, so the majority of 2CY michahellis have second generation lower tertials (only moulted once during the complete moult last summer).
The inner greater covert are included in the partial moult as well and appear grey, as the upper tertials. Most obvious moult is going on in the inner and central median coverts with almost the complete row of new grey feathers. In the lower lesser coverts and in the inner lesser coverts, several feathers are new or missing, and the new feathers appear grey as well. The upper lesser coverts were replaced recently in the complete moult, which finishes by August, and in this individual, those upper lessers are excluded from the partial moult in autumn so far.