CHAPTER 15 



SKUAS 



Sailing on obscene wings athwart the noon . . . 



Samuel Taylor Coleridge 



INCIPIENT or casual clepto-parasitism among birds can be seen by 

 anyone who visits the Serpentine on a cold winter afternoon and 

 watches the gulls and diving ducks. 



Children often throw large chunks of bread into the water which are 

 hastily seized by the tufted ducks. While they are attempting to swallow 

 these unwieldy pieces the gulls dash at them and try to harry them or 

 startle them into dropping the bread into the w^ater. The ducks 

 frequently dive to escape from the gulls, which hover over the water and 

 pounce again immediately after the ducks surface. Quite often, owing 

 to their wonderful powers of flight, their dash and persistence, the gulls 

 manage to appropriate the bread for themselves. This behaviour is the 

 result of the unnatural conditions prevailing on the Serpentine, where 

 all the birds are crowded together round an artificial source of food, 

 but it proves how, in certain circumstances, species which are not 

 normally clepto-parasites can modify their behaviour in that direction. 

 A more curious episode of this type was once observed in the farmyard. 

 A cockerel, wdth great dash and daring, rushed up to a cat and seized 

 and swallowed the mouse with which it was playing. 



The only real British bird clepto-parasites are the skuas, but it is 

 perhaps worth mentioning one or two foreign species which have 

 developed a slightly different form of the same habit. 



The American wigeon {Anas americana) — a rare vagrant in Britain — 

 associates with coots and robs them of the weeds which they obtain by 

 diving under water but subsequently bring to the surface to eat. This 

 is probably an extension of a commensal relationship similar to that 

 which exists between our wigeon and brent geese. 



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