170 A HISTORY OF BIRDS 



appears to be made at all times of the year, and by both sexes, 

 but especially during the courting season, when two or more 

 birds join fogether keeping the most perfect tune. 



Pigeons and Night-jars when on the wing can produce at 

 will a curious snapping sound by bringing the wings together 

 smartly over the back ; and this appears to be most frequently 

 indulged in during the period of courtship. 



Similarly, certain small South American Passerine birds, 

 known as Manakins, have the shafts of the secondary quill 

 feathers curiously thickened to an extraordinary degree, so as 

 to form solid, horny lumps. Therewith, by bringing the two 

 wings sharply together over the back, a peculiar noise, not 

 unlike the crack of a whip, is produced. One of the Game- 

 birds — the Black Penelope (Penelope nigrind) of Guatemala — 

 while on the wing will occasionally pitch suddenly earthwards 

 with outstretched wings, and at such times a crashing, rushing, 

 sound is produced, which has been likened to the sound of a 

 falling tree. This is peculiar inasmuch as there seems to be 

 no modification of the wing feathers which would account for 

 such a noise, while, on the other hand, certain relatives of this 

 bird have the three outermost primary quills curiously excised 

 along their inner webs, yet, as far as is known, they produce no 

 peculiar sounds. 



Better known, and more easily verified, is the strange " drum- 

 ming" or "bleating" practised by various species of Snipe, 

 and especially the Common Snipe {Gallinago media), during 

 the courting season. It is now known that these remarkable 

 sounds are produced by both sexes, and by means of the tail 

 feathers. Mounting to a great height, these birds suddenly 

 turn and descend with prodigious speed, meanwhile holding the 

 tail fully expanded. The outermost pair of feathers are, how- 

 ever, specially modified, so that, in the first place, during this 

 descent, they stand at right angles to the long axis of the body, 

 and well away from all the rest of the tail feathers. This alone, 

 however, would not produce the sound, which is due to the fact 

 that the shafts of the feathers are somewhat thickened and 

 peculiarly curved, while the vane or web of the inner side of 

 the feather is of great width, and structurally differs from the 

 vanes of the other feathers. This difference consists in a 

 greater number of booklets, and in the larger size of those 



