THE SHELDUCK AND SURFACE FEEDING DUCKS 211 



THE SHELDUCK AND SURFACE-FEEDING DUCKS 



[W. P. PYCRAFT] 



Systems of classification are apt to be somewhat arbitrary, and 

 rarely reflect the habits of the living animals they embrace. But 

 there are exceptions to every rule, and the division of the Ducks into 

 " surface-feeding " and " diving " species is one of these ; for this 

 division, though originally based almost entirely on habits, is confirmed 

 by evidence obtained from diverse sources. One is tempted to regard 

 the surface-feeding species as birds of the fresh waters, and of the 

 diving species as marine types ; but a little reflection will show that 

 this is by no means true. It is thus, then, plain that the obvious 

 structural features which distinguish these two groups are not to be 

 attributed to their haunts, but rather to the method of securing their 

 food. Those of the surface water will, it is true, dive under excep- 

 tional circumstances, as in the avoidance of enemies, or momentarily 

 when in play ; but they are not dependent on diving feats to secure 

 their daily bread. Such food as is obtained lower than the surface of 

 the water is procured by peculiar, semi-diving movements, wherein the 

 fore part of the body is submerged, leaving the hinder portion sticking 

 vertically out of the water, after the fashion of geese and swans. The 

 diving Ducks, on the other hand, have to dive for a living, and hence 

 it is that in them we find the legs relatively shorter, the thigh-bone 

 especially, whereby the carriage of the body when on land becomes 

 semi-erect and somewhat strained. On the water, however, the 

 advantage of this change in the fashion of the limb becomes at once 

 apparent, for it is now obvious, from the more backward position of 

 the legs, increased powers both of diving and swimming are attained. 

 This modification of the leg, however, is purely an adaptive character, 

 and therefore of no value to the systematist. Happily, however, it is 

 confirmed from an unexpected source, and one which excludes all 



