30 THE FLIGHT OF BIRDS 



we are not conscious of any difference between the 

 voluntary and the involuntary. In the case of a 

 bird the line is still harder to draw, not only because 

 we cannot get within his mind, but because the 

 movements which we are bound to label voluntary, 

 since they cannot be mere unconscious reflexes, are 

 so largely instinctive. When the young Swallow 

 takes the first plunge from the parental nest and 

 trusts himself to the air, he finds at once that he 

 can fly ; the power of flight is instinctive. A child 

 has to learn by much practice to co-ordinate his 

 muscles ; no other young creature is so devoid of 

 instinctive skill. The young Swallow, though he 

 can co-ordinate his muscular activities well enough 

 to fly with some success, has, of course, much to 

 learn. At the outset he misses most of the flies and 

 gnats, and his parents have to come alongside and 

 put their captures in his mouth. But he seems by 

 instinct to spread his tail when it should be spread, 

 and, no doubt, though it is hard to see this, he takes 

 a harder stroke with one wing than the other, when 

 a harder stroke is required. For fore-and-aft balance 

 he depends largely on his tail. He has not a long 

 neck that he can bend or straighten out, and his legs 

 are so short and light that no movement of them can 

 have much effect. For lateral stability he must, as 

 far as voluntary adjustments are needed, depend 

 mainly on unequal wing-strokes.* That birds do 

 take unequal strokes has been clearly proved by the 

 camera in the case of Pigeons, Owls, Gannets and 

 some others (see PI. n). This inequality, sometimes 

 so conspicuous in a photograph, the human eye has 



* See Chap. V. 



