760 



PHYLUM CHORDATA : CLASS AVES — BIRDS 



sociable, gregarious birds. A few, like the fowls, are polygamous ; 

 the cuckoo is polyandrous. 



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, according to Darwin, 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 

 songsters, 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 contributed 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 in 

 the course of natural selection the more conspicuous females had been 

 eliminated, brightness being disadvantageous during incubation. It 

 seems likely enough that both conclusions are to some extent true, 

 while there is much to be said in favour of a deeper explanation, to 

 which Wallace inclines, that the secondary differences between the sexes 

 are correlated with the fundamental 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 pecuhar style of nest, 

 and builds it of special materials. Generally the nest is solitary, 

 hidden in some private nook. The perfection 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 sometimes 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 protection for the helpless 

 fledglings. At the same time, the nest secures the comfort of the 

 parent-bird during the days and nights of brooding. 



The variety of nests may be illustrated by mentioning the burrowed 

 nests of sand-martins and kingfishers, the ground-nests of game-birds 

 and gulls, the mud-nests of house-martin and flamingo, the holes 

 which the woodpecker fashions in the tree-stem, the platforms built by 

 doves and eagles, storks and cranes, the basket -nests of most singing- 

 birds, the structures delicately woven by the goldfinch, bullfinch, and 

 humming-birds, the sewed nest of the tailor-bird, the mossy nests of 

 the wrens, the edible nest of the CoUocalia. which is chiefly composed 

 of mucin secreted by the salivary glands. 



Egfgs of birds. — When the nest is finished, the eggs are ready to 

 be laid. After they are laid, the patience of brooding begins. With 

 the great care that Birds take of their N-ouiig we may associate the 

 comparatively small number of the eggs ; but there are probably other 



