The images below are of 4 Lesser Black-backed Gulls Larus fuscus graellsii (Dutch intergrade), all ringed in July 2011 as pullus in the colony of IJmuiden (Forteiland), the Netherlands.
4th-calendar year Lesser Black-backed Gulls can be notoriously difficult to age because they can look very adult like, especially when seen in rest.
This is proven by Green Y.AWL which looks very much like an adult: hardly to no brown in the coverts, large white tips to the primaries, a large mirror on P10, a fully white tail and no primary moult yet (in line with most adults at this time of year).
The others show much more sub-adult features: much brown in the coverts, small to none white primary tips, a small mirror on P10, dark markings in the tail and inner primary P1 dropped.
Here a comparison of the main features per ringed individual:
|Code||Tertials||Coverts||Primary tips||P10 mirror||Bill markings||Tail||Primary moult|
|Y.AWH||Brown||Mix of brown and adult, much black on the primary coverts.||Small white spots.||Small||Black on upper mandible only.||Small black spots.||P1 dropped.|
|Y.AWL||Adult||Adult looking, black on primary coverts.||Large white spots.||Large||Black on both mandibles.||Fully white.||None.|
|Y.AWN||Adult||Predominantly brown.||No white spots.||Very small||Faint black markings on both mandibles.||Small black spots.||P1 dropped.|
|Y.AZA||Adult||Adult looking.||No white spots (or very worn).||Large||Faint black markings on both mandibles.||Much black.||None.|
All photos were taken at the end of May/beginning of June 2014 in the gull colony of IJmuiden where they were ringed.