432 ZOOLOGY 



are long the neck must be of corresponding length to allow the 

 head to reach the ground. Long legs are often coupled with a 

 wading habit; though in the ostrich and some of the land birds 

 length is associated with the running habit. 



The feet, — including the number and position of toes, the 

 character of the claws, and the presence of the web, — are a good 

 index of the manner of life. The amount and arrangement of 

 the web varies greatly in the different water birds. The beak 

 and the feet, though separated by the extreme length of the 

 animal are really three appendages which work together. Aside 

 from the prime functions of the feet in walking and swimming, 

 the beak and claws work in close cooperation in getting food, in 

 offense and defense, and in the nest-building operations. Both 

 claws and beak are strikingly adapted to the food habits. 



By means of the syrinx (§437) most birds produce sounds. 

 In the higher birds (oscines) the sounds may become highly 

 organized and melodious. Such songs are for the most part 

 related to mating and the breeding season. The call-notes are 

 more permanent though not so full of melody. By these the 

 birds express such simple emotional states as fear, anger, con- 

 tentment, and excitement. They are a simple language well 

 understood by the other members of the species. It is probable 

 that the mating songs are similarly expressions of the exuberant 

 emotions of the mating time, which become sustained and 

 elaborated from the pleastu-e they come to give the producer. 

 In other words they represent a passage from the useful to the 

 esthetic even for the bird himself. 



The succession of instincts which in the spring will cause 

 even one-year-old birds to go with remarkable precision through 

 the migration, courtship, mating, the selection of a suitable 

 place and materials for nest making, egg-laying, incubation, 

 feeding and protecting the young, and finally their introduction 

 to the world, is at once the marvel and despair of the naturalist. 

 In all these respects there is the greatest variation. Some mate 

 yearly, others mate for life. Some conceal their nests with 

 greatest ingenuity and build it with great care, while others lay 

 their eggs in the barest possible places. They may lay one egg 

 or a score. Incubation of the eggs may be performed by the 



