A fundamental understanding of how gull plumages change with age is extremely useful when it comes to identifying birds in the field; and it makes gull ID much less intimidating! Gulls acquire their adult plumage in stages, taking a few years. As a general rule, larger gulls take more years to reach full maturity than smaller ones. Indeed, you could lump each gull into one of three age categories, which we may as well call ‘two age-groups’, ‘three age-groups’ and ‘four age-groups’. ‘Two age-groups’ gulls include Blackheaded Gull. There is a juvenile plumage, followed by a body moult to a first-winter plumage (the wings are like the juvenile). (Note: Juvenile and first-winter are thought of as one age group). After the bird’s first birthday, there is a full moult resulting in an adult winter plumage. From then on in the gull’s life, the bird will still moult but the main change in appearance will be in the pattern of the head (in the case of Black-headed Gull, right, acquiring a brown head in summer, and a dotted head for winter). ‘Three age groups’ gulls such as Common Gull follow a similar pattern, but for the second winter of the bird, there is a distinct second-winter plumage. After two years will the adult plumage be attained. ‘Four age-groups’ gulls include all the large ones such as Herring Gulls and the blackbacked gulls. As with the last category, there is an additional year of increasingly adult-like plumage before the full adult plumage is reached. Mostly, four age groups can be recognised in the population (or five, when the juveniles are transitioning to first-winters).