Slightly smaller than the European Herring Gull, the Lesser Black-backed Gull has a dark grey to black back and wings, yellow bill and yellow legs.
The similar looking but larger Great Black-backed Gull is easily identified by its pink legs.

As a rule, adult gulls attain their adult plumage and reach sexual maturity in two to five years, depending on the species.
Juvenile gulls do not look like their parents, but instead have a distinctive streaked brown plumage.
Over the years their plumage changes from brown to, usually, white or white-blue.
In general, males average larger than females and have slightly to distinctly bigger bills and larger heads.
The Lesser Black-backed Gull attains adult plumage at an average age of four years.

Juvenile Black-backed Gulls are difficult to distinguish from juvenile European Herring Gulls.
However, in Lesser Black-backed Gull the blackish tertials have white fringes to the individual feathers rather than the chequered white notches shown by juvenile Herring Gull.
Note also that, compared with juvenile European Herring Gull, juvenile Lesser Black-backed Gull has a dark, rather sooty plumage with a darker area around the eye.

First 4 photos: On the ferry to the island of Texel, The Netherlands, 18 April 2012
Last photo: IJmuiden Beach, The Netherlands, 23 September 2020