262 



BRITISH BIRDS. 



Fig. 1. 



THE DOWN-STROKE OF THE WING. 

 The fact that a bird moves its wing forward at the same time 

 that it moves it downward is well-known. But the extent 

 of the forward movement is, I think, hardly realised. On 



first thoughts it may 

 seem odd that a bird 

 should be able to 

 propel himself by 

 such a movement as 

 this. When the wing 

 has to propel as well 

 as to hft, the bird 

 gives it an upward 

 incline from the front 

 of the back margin, 

 and. being held in 

 this position, it can- 

 not but propel as 

 weW as support him. 

 In these two photo- 

 graphs this point is 

 not brought out, since the pigeons are only raising themselves 

 from the window-ledge on which they had been standing. 



Figure 1 shows the down- 

 stroke still in its full force. The 

 primaries are bent upward, 

 and the first primary is con- 

 spicuously more bent than its 

 neighbours. This can only 

 be due to its greater phancy, 

 and there is every reason to 

 believe, though the photo- 

 graph does not make this 

 clear, that it takes place simul- 

 taneously and to an equal 

 extent in both wings. It 

 cannot, therefore, be of any 

 assistance in steering. But it 

 is clear that the straightening 

 out of the feathers when the 

 down-stroke slackens must be 

 ec(uivalent to a continuation 

 of the stroke, and help to give 

 it an easy and comfortable 

 finish. The separation of the 

 primaries probably prevents a too sudden escape of the air 



Fig. 



