INTRODUCTION 27 



choice seems to be controlled only by the size of their gullets and the capacity of 

 their crops. Most diving ducks are, however, much less independent, and their dis- 

 tribution is from time to time deeply affected by slight changes in freshness or salt- 

 ness of lagoons and the consequent luxuriance of various crops of water-plants and 

 mollusks. 



It follows, of course, that most of the fresh-water ducks are easy to maintain in 

 confinement on ordinary grains, while such species as Scaups, Golden-eyes, Scoters, 

 Eiders, and the fish-eating Mergansers are only kept alive with infinite care and 

 trouble. Among the surface-feeders, Shovellers do not live well, because their natu- 

 ral food consists of a large proportion of very minute animal and plant life. 



There is a greatly increased proportion of animal matter in the summer food of 

 ducks, and the young for the first few weeks depend upon animal food, chiefly the 

 larva? of insects, for sixty to ninety per cent of their entire diet. 



COURTSHIP AND NESTING 

 As I shall notice under the Mallard, and may repeat here, the term "courtship" 

 will be used to cover the whole series of events resulting from the "mating hunger," 

 all activities, in fact, which lead up to the building of the nest. The term "display" 

 will be used merely to describe those social plays which result finally in the choice of 

 a mate, and where display is well developed it is probable that the female does actu- 

 ally select her own mate, although we still lack experimental evidence on this point. 



Under courtship we should consider the search for the mate, the fighting, or rivalry 

 of males, etc., but "courtship" must not be used in an anthropomorphic sense. We 

 must always bear in mind that the birds' activities are exercised mostly in an un- 

 conscious manner, and without real understanding, although their general behavior 

 may remind us very greatly of our own. 



Display antics have occupied the attention of field observers a great deal of late 

 years. They are well worthy of study because they are extremely complex, and very 

 characteristic of the species. There is no doubt that these postures hark back a long 

 way in the relationship of the various subfamilies of Anatidoe. I do not think they 

 were described before Naumann's great work on the birds of middle Europe about 

 a hundred years ago. Besides being interesting in themselves, they are often very 

 beautiful, and tend to exhibit the grace or agility of the performer in its highest 

 degree, and to show off the striking parts of his plumage. 



It would be interesting to inquire into the origin of display, but this would draw 

 us into a general discussion of the evolution of sex, and the origin of secondary sex 

 characters, a subject that would lead us far afield. We must admit that in some way 

 these sex postures are closely associated with the choice of mates, for they are very 

 elaborately developed in many different families of birds, are almost as pronounced 

 in reptiles, and are highly organized in insects. It is hard to understand whether 



