20 THE BIRDS OF THE BRITISH ISLES. 



largely of aquatic plants ; on private waters the bird is a 

 useful check to the troublesome American weed, Anacharis. 

 Insects are eaten, and, it is said, frogs, but these and toads it 

 will worry and discard, and it will kill the young of other 

 water fowl. 



The nest is a large structure of rank vegetation lined with 

 down, and is usually placed near water, on an islet if one is 

 available. The five to twelve greenish- white eggs, laid as a rule 

 in April, average in size 4-3 by 2*9 inches. The bird pairs for life, 

 and the cob shares in incubation, but usually guards the nest, 

 " busking," as it is called, when approached. In this terrifying 

 performance the wings and scapulars are further raised, and the 

 neck is drawn back until almost hidden by the wings ; the bird 

 forces itself forward in rushes with simultaneous strokes of its 

 feet, ploughing up the water. The ash-grey downy young are 

 at first carried on the parent's back. The male will at times 

 monopolise domestic duties, refusing to allow his mate to 

 relieve him during the long incubation. 



The bill, already described, is black at the tip and along the 

 cutting edge as well as at the base and on the lores. The legs 

 are black, the irides dark brown. The young in first plumage 

 are sooty grey, the legs are lead-coloured, and the bill, without 

 any berry, is greyish black. When over a year old and nearly 

 white, the bill is still fleshy rather than orange. White cygnets, 

 by no means uncommon, gave rise to the so-called Polish Swan, 

 which is now known to be a variety. Length, 60 ins. Wing, 

 27 ins. Tarsus, 4"5 ins. 



Common Sheld-Duck. Tadoma tadoma (Linn,). 



The Common Sheld-Duck (Plate 12) breeds near salt 

 water in northern Europe and Asia, It reaches north Africa, 

 India, and south China in winter. Its distribution in the British 

 Isles is general but uneven ; it is a sand and dune haunting 



