160 THE FLIGHT OF BIRDS 



recuperate after the labours of the day. For most 

 birds, however, the danger is reduced to a minimum. 

 While they sleep perched on a branch the weight of 

 their bodies keeps their legs bent at the ankle, and 

 when the ankle is bent the toes grip automatically. 

 Were it not for the automatic grip of the toes, the 

 bird would fall and be at the mercy of any prowling 

 enemy. 



Call-notes and Song. 



When the bird became able to move with speed and 

 make long journeys, some new power was required 

 to bring the sexes together and to prevent a pair 

 that had mated from becoming separated. Hence 

 it is that birds are loud-voiced, though reptiles are 

 nearly all of them dumb. To a mere call-note, a 

 very humble origin, it is probable that we can trace 

 the beautiful songs of the Nightingale and the 

 Blackcap. For many of the migrant birds in par- 

 ticular a loud, easily recognisable call-note was an 

 urgent need. After a flight of some thousands of 

 miles cock and hen must somehow find each other. 

 The Nightingale, when he has passed the Mediter- 

 ranean and reached his northern home, trumpets 

 forth to all the world the fact that he has arrived. 

 His future mate hears the call, and together they set 

 about the all-important business of nesting. And 

 thus we see that all a bird's activities must be viewed 

 in connection with the fact that he has wings and 

 is capable of long flights. 



The End. 



