102 THE FLIGHT OF BIRDS 
they fly. Very striking is the contrast between the 
shrill whistling of the Fings 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. 
