496 BIRDS. 



In most cases, however, birds pair, and the mates are true 

 to one another for a season. The pairing is often preceded 

 by a courtship in which the more decorative, more vocal 

 males win their desired mates, being to some extent chosen 

 by them. Darwin attributed the captivating characteristics 

 of the males, well seen in peacocks and birds of paradise, 

 or as regards musical powers in most of our own British song- 

 sters, to the sexual selection exercised by the females ; for if 

 the more decorative or the more melodious males always 

 got the preference in courtship, the qualities which contri- 

 buted to their success would tend to predominate in the 

 race. He believed, moreover, that characteristics of male 

 parents were entailed on male offspring. Wallace regarded 

 the differences between males and females in another way, 

 arguing that natural selection had eliminated the more con- 

 spicuous females, for brightness would be disadvantageous 

 during incubation. It seems likely enough that both con- 

 clusions are to some extent true, while there is much to be 

 said in favour of a deeper explanation, to which Wallace 

 inclines, that the differences between the sexes are natural 

 and necessary expressions of the constitutional differences 

 involved in maleness and femaleness. 



Nests. — After pairing, the work of nest-building is begun. 

 Almost all birds build nests ; the well-known habit is a 

 characteristic expression of their parental care. Other 

 creatures, indeed, such as sticklebacks among Fishes, and 

 squirrels among Mammals, besides numerous Insects, build 

 nests, but the habit is most perfectly developed among 

 Birds. As is well known, each species has its own peculiar 

 style of nest, and builds it of special materials. Generally 

 the nest is solitary, hidden in some private nook. The per- 

 fection of art which is reached by some birds in the making 

 of their nests is marvellous ; they use their bills and their 

 feet, and smooth the inside by twisting round and round. 

 Usually the hen does most of the work, but her mate some- 

 times helps, both in building the nest and in hatching the 

 young. 



The nest is a cradle rather than a house, for its chief use 

 is to secure an approximately constant warmth for the young 

 which are being formed within the eggs, and to afford pro- 

 tection for the helpless fledglings. At the same time, the 



