Third-year: Undisclosed Site, Essex - February 2009
Firstly aged as a third-year due to the brown feathering in the tertials and wing coverts and the dark marks on the bill.
Compare the upper-part colour and tone with the surrounding Herring Gulls, darker and bluer than the bird on the left but closer to the bird on the right, though still perhaps with a slightly bluer cast.
The head shape is a little squarer with the peak at the hind crown; the Herring Gull to the right showing a peak almost above the eye.
The bill is rather heavy and blunt tipped whilst the legs are distinctly pale yellow. The eye is pale but not as pale as the Herrings.
Yellow-legged Gull - Larus michahellis
Third-years
Third-year: Hole Haven Creek, Essex - January 2009
Note the long winged appearance; square looking head; deep blunt tipped bill and dark blue-grey upper-parts.
Third-year: Hole Haven Creek, Essex - January 2009
Compare with the near-adult Herring Gull at the front.
The upper-parts are darker blue-grey; the primaries project further; the head is clean unmarked white and hefty bill with deep Gonys expansion.
As can be seen it was a rather large bird.
Third-year: Paglesham Lagoon, Essex - December 2006
The square head with peak at the hind crown is obvious here as is the deep hefty looking bill whilst the upper-parts are clearly a few shades darker than the background Herring Gull.
 Paglesham Lagoon (3).JPG)
Third-year: Undisclosed Site, Essex - 19th February 2011
Aged as 3rd-winter by the retained dark feathering in the tertials and wing coverts and the dark marks on the bill and the small primary tips.
The upper-parts are dark grey and legs nicely yellow whilst the head is completely unmarked white as would be expected by this time of year. Note the pale eye.
Third-year: Undisclosed Site, Essex - 26th March 2011
Very similar to the bird on 19th February 2011
The bill is large and heavy with an obvious bulbous tip and dark marks. The legs are yellow but not fully flushed up yet.
The greater coverts show a brownish wash whilst the tertials show the strongest sings of immaturity. The primary tip spots are still relatively small.
Note the overall juzz of the bird; large headed, full and barrell chested and long tapering rear end. The upper-part tone is a good couple of shade darker than Herring Gull and has a more 'blue' quality.
Third-year: Undisclosed Site, Essex - July 2011
Closely resembling adult however there is still dark feather to the tertials and wing coverts whilst the primaries large any noticeable white tips or spots.
There is a large white mirror visible to the under of P10 on the far wing,
Third-year: Undisclosed Site, Essex - July 2011
Comparison image with an adult Herring Gull.
Although these birds are of different ages upper-part tone and structural differences can be easily seen.
The Yellow-legged Gull is large square headed and full chested with long rear end, older generation primaries still retained.
Third-year: Undisclosed Site, Essex - December 2011
The legs have attainted a good yellow flush and the upper-parts are mid toned however note the sturdy bill with blunt bulging tip, pale eye with red orbital ring and the slender tapering rear end.
Aged as third-year due to combination of white tipped black primaries and retained dark markings in the wing coverts and tertials,
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WINTER BIRDS
Third-year: Undisclosed Site, Essex - 29th August 2009
This summer bird is a little strange in that although it has completely grey upper-parts that would be expected of a third-year the primaries large mirrors and white tips, save for the finest of white tips to P10. The primaries also look rather brown.
In addition the bill has a broad black band, though the edges of the red Gonys spot are visible. The bill though is typical Yellow-legged Gull, hefty, bulbous and blunt tipped.
This could be a retarded third-year, retaining older second-year primaries, or a very advanced second-year; there's not much obvious visible wear and tear to the primaries.
Third-year: Undisclosed Site, Essex - 29th August 2009
The same bird as in the previous image: here there is an obvious white mirror visible to the under-side of P10 which is more supportive of a third-year though again the change of angle has not revealed any white primary tips.
Note the graellsii Lesser Black-backed Gull sat down at the back and compare upper-part tones.
SUMMER BIRDS : April - September