'Water-boiling' display by Whooper and Bewick's Swans. From the mid 1980s, at Welney, Norfolk, we have noticed a regularly occurring display by Whooper Cygnus cygnus and Bewick's Swans C. columbianus feeding in high densities on waste potatoes tipped out for them. Usually, but not always, it follows an aggressive encounter with a conspecific, and entails the swan lifting itself clear of the water and


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