These surprising birds of a seagull are not only sea. They live also on the fresh rivers. Also they are called also a seagull only freshwater. In my city there are many seagulls. They also fly having widely spread wings and shout. Difference only that they eat not sea fish, but river. And as always elicit bread at people.
At these seagulls even plumage same, as at sea birds.
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From @viki27