Floating on Air

Grey Heron (Ardea cinerea) flies past some Black Headed Gulls (Chroicocephalus ridibundus) floating in and above the water at Strumpshaw Fen, Norfolk, England. The blue background at first appears to be sky but this is refuted by the reflections of the Gulls that reveal the watery truth. But after alll, isn't flying just floating on air?
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