THE LOVE DISPLAYS OF BIRDS 223 



heard only during the season of courtship and 

 love. 



We have now to deal with that varied assort- 

 ment of sounds produced by mechanical means, 

 and forming the second of the two classes into 

 which we have divided avine music. This we 

 have termed Instrumental Music, because the 

 organs of voice take no part in its produc- 

 tion. These sounds are produced in a variety 

 of ways ; not only by the bill, but by certain 

 modifications of the feathers ; whilst in some 

 cases the ordinary plumage is so manipulated 

 as to obtain the required effect. We may first 

 draw attention to a few instances in which these 

 sounds are produced by ordinary appliances. 

 Many species of Woodpeckers have a habit of 

 tapping with the bill the trunks or branches of 

 trees ; and if these chance to be hollow a noise 

 is produced which can be heard for a consider- 

 able distance ; whilst the bird's head is moved so 

 rapidly that our eye can scarcely follow it. So 

 loud is this noise, under certain favourable cir- 

 cumstances, that it seems as though the trees 

 were actually being split asunder. These noises 

 are for the most part peculiar to the nesting 

 season, and most naturalists are agreed that they 

 are signals between the sexes. Some birds are 



