xii CONTENTS 



CHAPTER V 



THE GENERAL HABITS AND FUNCTIONS OF BIRDS 



PAGES 



The flight of birds Flightless birds The fitness of 

 birds for an aerial existence Various modes of 

 flight Gliding flight : how performed Flight by 

 active strokes of the wings : how performed The 

 movement of the wings Soaring or sailing flight : 

 how performed Terrestrial and aquatic motion 

 of birds Birds unable to progress upon the 

 land Running, walking, and hopping move- 

 ments Progress in water The food of birds 

 Modifications of the bill Common to various 

 distantly related groups Social, gregarious, or 

 solitary instincts of birds Mimicry in birds 

 Protective colours and resemblances of birds 

 Forest birds Desert birds Marsh and swamp 

 birds Moorland and mountain birds Arctic 

 birds Variation in birds Of external structure 

 and colour Dimorphism in birds Sexual dimor- 

 phism Dimorphism independent of sex Struc- 

 tural dimorphism 178-211 



CHAPTER VI 



THE LOVE DISPLAYS OF BIRDS 



Bird music Vocal music of birds Variety in song 

 Capriciousness of song The origin and purpose 

 of avine song Individual variation in the song 

 of birds Imitation Do birds sing by instinct 

 or imitation? Vocal sounds of birds The in- 

 strumental music of birds Made by ordinary 

 appliances Made by special modifications of 

 the plumage The drumming of the Snipe 

 Modifications in the wings of the Humming-Birds 



