102 THE FLIGHT OF BIRDS 



they fly. Very striking is the contrast between the 

 shrill whistling of the wings of the slow-flapping 

 Swan and the whir or swishing sound that accom- 

 panies the flight of a flock of Starlings. It has been 

 thought that the particular note depended on the 

 pace at which the wing moved through the air, but 

 in reality it is due to the vibration of the feathers. 



Wing music is often very beautiful ; it is a grand 

 thing to get near to a large flock of Golden Plover 

 and hear and see them go scudding by. There is 

 also pleasure in watching an Owl when he comes 

 near, and in realizing the complete silence of his 

 flight. At the edge of the outer web of his first 

 primary wing-feather, the hooklets of the barbules 

 are missing, and the barbules themselves are mere 

 vestiges. Consequently the edge of the feather has 

 the softness of down, and this, no doubt, has much 

 to do with the ghost-like silence of the Owl's flight. 

 The Nightjar also is a very silent flyer, though in 

 his wing -feathers the hooklets are nowhere missing. 

 Still his plumage is remarkable for its softness, and 

 this probably accounts for the absence of whir as 

 he plies his wings. 



