FIELDCRAFT

Bird Watching (UK) - - Your Birding Month -

AGING GULLS

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).

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