The structural characteristics identified for the adult Atlantic Yellow-legged Gulls apply to the first-years. A heavy blunt-ended bill, bulky chest and broad wings are all frequently found in the young Southern Atlantic Yellow-legged Gulls and weaker features in the young Cantabrican Atlantic Yellow-legged Gulls. All juveniles show flesh-coloured legs. The features for the Southern Atlantic Yellow-legged Gulls are summarised below.
Features of all birds include:
- obvious dark brown-black outer primaries (darkest part of plumage);
General plumage and bare part features (80%+ of birds) include:
- dusky heads with obvious dark spot around the eye (82%);
- bright white rumps, tails white with broad dark subterminal band (87%);
- all black bills (88%)
- tertials with dark grey-brown centres and narrow pale fringes (88%).
Other general tendencies (55-79% of birds) include:
- a grey-brown mantle colour (62%); remainder have a ruddy tinge (34%) or a more obvious reddish-brown colour (4%);
- some contrast (64%) between the underwing coverts and the rest of the underwing;
- a pale primary window (74%); in most cases (51% of total), it is, however, indistinct;
- a scaley mantle texture (55%) rather than a uniform one;
- an inner wing with one bar (63%), that is with a clear secondary bar only;
Seasonal changes are:
- by late March/April, duskiness on heads diminished but nearly all retain dark eye spot; a few show pale base to bill; legs are less bright, some showing a pale straw tinge; the first hint of grey appears on the mantle and scapulars; primary moult commences in a small minority in late March but by the end of April half have shed at least one feather with the most advanced having P3 growing/P4 missing.
- by May, only a small minority still have all primaries intact with the rest evenly distributed in moult up to P6 growing/P7 missing. Other more frequent features by now are a ruddier mantle colour, whiter heads, paler bases to bills and more obvious pale primary windows.
- by late July, most have completed primary moult but a few are retarded enough to show P8 growing and P9 missing.
Overall, there is a tendency towards graellsii with dark grey-brown mantles, tertials with dark grey-brown centres and narrow pale fringes, dusky head markings, all-black bills and gleaming white tails. However, some features do not match graellsii well but do match michahellis as described by Dubois & Yésou (1984): the inner wing is frequently rather weakly striped, a contrasting underwing pattern is often found and there is usually at least an indistinct pale primary window.
Regional variations (within the dark form) are tendencies for:
- an inner wing with two bars (secondary plus greater coverts) in south Portugal and the central Canaries; exceptionally dark plumage with blotches on head and heavy breast and belly streaking in the Azores (Dubois 2001; Bakker 2000).