I don't think it's a European Starling. The tail feathers aren't right. It appears to be some type of swallow, known for their forked tails and migrations between Africa and Europe. The long tail feathers are indicative of a migratory species. I'm guessing that pigeons are representative of Brits.
Keep in mind that Banksy is British. Pigeons and European Starlings are both native species there. And, given his other political works, I doubt he's anti-immigrant. He seems to be showing us the insignificance and absurdity of our territorial disputes by equating us to animals.
I was looking at it from an American perspective, but your right that it would have made more sense in a European context. I think you may have taken my comment a bit more seriously than I did.
My only point was that sometimes these 'minor' differences are enough to cause the problems that people fear. It is not silly or ignorant to be cautious, or even fearful of an invasive species.
Some, but not all are dangerous. And caution must always be used if ecological disaster is to be avoided.
I'm not sure what he's trying to say.
So I did some googling. I couldn't find any invasive African birds, but it looks similar to an European Starling. They are contributing to the decline of native birds and crops.
And then there's the pigeon. Also an invasive species, but has been here a lot longer, and has no negative impact on local species. Has even helped to stabilize and restore some local falcon species.
Is Bansky trying to rally us against the African immigrants?