BIRDS IN FLOCKS 261 



even thousands ; and their ways are very fascinating. They 

 are in constant movement from the hedge to the field, or 

 from one part of the field to another, moving with a simul- 

 taneous flash of wings, and a jerkier and more erratic flight 

 than the ordinary wheelings and long glissades of the starling 

 flocks. They seem responsive to a hundred thrills of im- 

 pulse for which we can detect no obvious reason ; but probably 

 it is their fine sense of hearing which gives them so many 

 superfluous alarms, and often prevents them from feeding 

 quietly for more than a few seconds together. We remember 

 watching a large flock of hen chaffinches feeding one winter 

 day in a stubble-field on a high wooded hill above some weirs 

 on the Thames, which were murmuring loud in flood. The 

 noise of the river came beating up through the woods on a 

 gusty breeze, and the birds were continually flying up from 

 the field into the shelter of the surrounding beeches. At last 

 a sudden tremor seized not only the chaffinches on the stubble, 

 but a long-tailed tit searching in a bush close by us ; and a 

 moment later a flaw in the wind brought up the noise of the 

 weir in a deep roar. It seemed that the birds had caught 

 the vibration of the approaching sound before it became 

 audible to human ears ; and most of the sudden movements 

 of birds feeding in flocks are probably due to subtle sounds 

 or cessations of sound, which are unperceived by the human 

 listener, but are perfectly perceptible to their acute and 

 watchful senses. 



In the silence of the golden September afternoons in the 

 stubble-fields even our own heavy hearing becomes keener, 

 so that it is easier for us to conceive of the acute senses' of 

 birds and wild animals. If the field is empty for a while of 

 wandering flocks, the silence at first seems absolute, when 

 we stand still or lie down on the faintly aromatic haulm. 

 Gradually our ears are opened ; we can hear the far-off 



