Andy,
I am not suggesting that every odd gull is a hybrid, just keeping an open mind about a bird like this.
Yellow-legged Gulls have been pairing up with Lesser Black-backed Gulls and, to a lesser extent, Herring Gulls in the Netherlands yearly since 1987 and in Belgium since 1996. The hybrid offspring they produce also return to the colony when mature and produce backcrosses. Nowadays, about 10 YLGulls breed annually in the Netherlands, usually in mixed pairs. In Belgium, about 3 to 4 YLGulls interbreed, and about 10 hybrid gulls pair up with other gull species each year. Spain now has a small population of Lesser Black-backed Gulls too, and these birds regularly pair up with the local Yellow-legged Gulls. For instance, there were 17 mixed pairs on the Berlengas in 1996. I do not know the situation in France, but I do not see why it would be any different. Interbreeding is also going on in the UK, by the way.
Therefore, I think it is not too unreasonable to keep an open mind.
Also, I would plead for studying Yellow-legged Gulls not just on local patches but also in the breeding range, summer and winter. Maybe you have? I certainly have, and the OP bird looks a bit dodgy to my eyes - that is all I am saying.
I fully realise that the discussion is a bit pointless since the bird is not wearing a ring, so we can never be sure about its identity.
I am not suggesting that every odd gull is a hybrid, just keeping an open mind about a bird like this.
Yellow-legged Gulls have been pairing up with Lesser Black-backed Gulls and, to a lesser extent, Herring Gulls in the Netherlands yearly since 1987 and in Belgium since 1996. The hybrid offspring they produce also return to the colony when mature and produce backcrosses. Nowadays, about 10 YLGulls breed annually in the Netherlands, usually in mixed pairs. In Belgium, about 3 to 4 YLGulls interbreed, and about 10 hybrid gulls pair up with other gull species each year. Spain now has a small population of Lesser Black-backed Gulls too, and these birds regularly pair up with the local Yellow-legged Gulls. For instance, there were 17 mixed pairs on the Berlengas in 1996. I do not know the situation in France, but I do not see why it would be any different. Interbreeding is also going on in the UK, by the way.
Therefore, I think it is not too unreasonable to keep an open mind.
Also, I would plead for studying Yellow-legged Gulls not just on local patches but also in the breeding range, summer and winter. Maybe you have? I certainly have, and the OP bird looks a bit dodgy to my eyes - that is all I am saying.
I fully realise that the discussion is a bit pointless since the bird is not wearing a ring, so we can never be sure about its identity.