THE LOVE DISPLAYS OF BIRDS 221 



male, and uttered during the season of courtship 

 and love only. Many of these strange sounds 

 are an accompaniment to the various dances, 

 displays, marches, evolutions, and antics that 

 we shall shortly describe. Others, of course, 

 are in no way connected with love or war, but 

 serve as alarm notes, or to indicate the where- 

 abouts of companions. In certain species the 

 vocal organs differ very considerably in the two 

 sexes, being then instances of audible sexual 

 dimorphism. The boom of the Bittern, for in- 

 stance, is one of the most extraordinary sounds 

 in nature, and seems to be entirely a sexual 

 production. Such a wild unearthly night-cry 

 has very naturally become surrounded by super- 

 stition ; the bird was thought to produce it by 

 inserting its bill into a reed, or burying it deep 

 in the mud. This boom consists of two perfectly 

 distinct sounds, and is said to be produced 

 as the bird inhales and exhales its breath. Then 

 we have the piercing cries emitted by the Divers, 

 well likened to the screams of tortured chil- 

 dren ; or the awe-inspiring notes of the Owls — 

 all love cries, and claiming to be classed as avine 

 music. Then the notes of the Goatsuckers are 

 equally curious, and have in many cases been 

 syllabled into such phrases as " Willy-come-go," 



