Mantle: as south-west Portugal.

Underwing: as south-west Portugal.

Structure: usually showing slightly finer bills with a more tapering tip and a weaker gonydeal angle; the bills though are still heavier than those of graellsii and not so slender at the tip.

Primaries: as south-west Portugal.

Bare parts: as south-west Portugal except that the gonydeal spot is rather weaker in intensity and is orange-red rather than red. Some full adults show a pinky tinge to the feet and lower part of the legs.

Direct comparison with adult Lesser Black-backed Gull: the obvious difference is the mantle, intermedius is clearly much darker and graellsii is at least one shade darker. In size they are similar in length but the Yellow-legged Gulls look slightly heavier on balance with a slightly bulkier chest in particular. The bills of Lesser Black-backed Gulls are slightly thinner with a more tapering tip but the difference is not as marked as in the Canaries. The leg lengths are very similar. Overall there is a remarkable similarity between the Yellow-legged Gulls from this area and the Lesser Black-backed Gulls with only mantle shade being the obvious discriminating feature. More subtle discriminating features are given elsewhere (see Central Canaries).

First-years: much more likely (75% against 5%) to show a dusky tail with obvious barrings and indeed close in this respect to those in northern Spain. Slightly greater tendency (25% against 20%) to show a pale base to the bill and (90% against 70%) for one bar on the inner wing. On the large samples available (about 400 birds), less than 1% showed large size, very pale heads, heavily mottled coverts, heavy bill, long thick legs, boxy head and thick neck like Mediterranean Yellow-legged Gull. Less than 1% were also pale and uniform enough to be considered as argenteus but even these had tertials like graellsii.

Direct comparison with first-summer Lesser Black-backed Gulls: Lesser Black-backed Gulls show whiter rumps and tails, a darker and more oily grey-brown overall appearance, a larger smudge around the eye, heavier streaking on the neck and the sides of the breast, two bars on the inner wing, the absence of a pale primary panel and a slightly lighter structure as for adults. The tertials of both forms are very similar.

Moult in first-summers: the great majority had not yet started primary moult but a small percentage (from 2-5% in flocks) had shed P1.

Second-years: the legs are still flesh or pale pink in about half (50%) of 12 birds closely studied with 25% showing straw-coloured legs and a further 25% showing a yellow tinge to the legs but with pink feet. Over half (60%) have bills that are mainly yellow with a black tip on the terminal quarter. About 25% have the bill with a significant pale base from one-quarter to one-half the length and 15% have the bill still almost entirely black. The tails are a gleaming white with a narrowing and weaker tail band. The head is usually mottled particularly around the eyes but the neck, breast and belly are usually almost all white. The underwing is fairly uniform except for faint stripes. The back and scapulars show a fairly clean grey with scattered brown speckles. The coverts (greater, median, lesser) are usually still dark brown and are heavily mottled. In flight little grey usually shows on the wings. The outer primaries, coverts and obvious secondary bar are a dark grey brown, the inner primaries pale brown and only the central inner wing shows any grey, usually heavily mixed with grey-brown.

Direct comparison with second-summer Lesser Black-backed Gull: besides the slight structural differences and the more marked differences in the shade of the back (as for adults), the Lesser Black-backed Gulls look more retarded with more mottling on the head, heavy streaking on the neck and heavy blotches on the sides of the breast. The back may also retain more brown feathers and the bill may be less yellow.

Third-years: more retarded than those further south and hence closer to those in northern Spain. The greater coverts are still heavily mottled and the legs are rarely a bright yellow, being usually a pinky-yellow colour. The bill is yellow for at least the basal three-quarters. The tip may show a small orange-red gonydeal spot or a black band. About 80% of birds show a small mirror on P10 but none show a mirror on P9. The black on the primaries sometimes extends to P3.

Information needed: moult in adults.

Comment: intermediate in appearance between the birds further south (south Portugal) and those further north (Cantabria). Bermejo (2001) also reported a cline from Andalucia/south Portugal to Cantabria in many aspects.