This could be a pure cachinnans and even though one may argue that most of the features seen in this bird also fit argentatus, there are firm clues that at least one of the parents must have been a cachinnans. Even though the upperparts are rather pale; iris rather pale; head relatively striated; and the black band on P5 rather narrow, it would not surprise me if it still fits within the phenotypic variation found in true cachinnans. However, a hybrid or backcross is not easy to rule out.
The winter streaks in head are needle-thin and very distinctive without the typical coarse spotted argentatus appearance; cachinnans can have such streaks in autumn as also seen on Netfugl.
Characters in favor of cachinnans are e.g. the relative and thin long legs compared to the adjacent Herring Gulls, a bill which is relative slim without pronounced gonys angle, a dark red orbital ring, reminiscence of a cachinnans neck boa with dark spots on lower neck, and upperparts which are marginally darker than on nearby argentatus.
The winter streaks in head are needle-thin and very distinctive without the typical coarse spotted argentatus appearance; cachinnans can have such streaks in autumn as also seen on Netfugl.
Characters in favor of cachinnans are e.g. the relative and thin long legs compared to the adjacent Herring Gulls, a bill which is relative slim without pronounced gonys angle, a dark red orbital ring, reminiscence of a cachinnans neck boa with dark spots on lower neck, and upperparts which are marginally darker than on nearby argentatus.
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