626 BIRDS. 



Many birds, apart from those who have been educated, 

 have "vfords," expressing pleasure, pain, sense of danger, 

 presence of food, and the hke. But there is a difference 

 between this power of utterance and the possession of 

 language, which implies the expression of a judgment, e.g., 

 food is good. 



The vocal organ of Birds is not situated in the larynx as it 

 is in Mammals, but in the syrinx — a song box at the base of 

 the windpipe. In this syrinx there are vocal membranes or 

 folds of skin; their vibration as the air passes over them 

 causes sound ; the note varies with the muscular tension of 

 the folds, with the muscular state of the complex associated 

 parts, and with the column of air in the windpipe. 



Courtship. — Birds usually pair in the springtime, but tliere are many 

 exceptions. Some, such as eagles, live alone except at the pairing 

 time ; others, notably the cloves, always live together in pairs ; many, 

 such as rooks, parrots, and cranes, are 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, argiiinti^ that 

 in the course of natural selection the ]nore conspicuous females had 

 been eliminated, brightness being disadvantageous durin^^ 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 betw een the sexes 

 are natural and necessary expressions of the fundamental constitutional 

 difierences involved in nialeness and femaleness. 



Nests. ^M\ex 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 sticklebacls 

 among Fishes, and squirrels among Mammals, besides numerous 

 Insects, budd nests but the habit is most perfectlj- developed amonc 

 Ends. As is well known, each species has its o«n iieculnr stvle ol^ 

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

 hidden in some private nook. The perfection of art which it i° i"^^! 

 by some birds in the making of their nests is marx'ellous • the\- u-*""^?! • 

 bills and their feet, and smooth the inside by twisting round and^*^ T 



