EVOLUTION OF BIRD-SONG 



cackling before wet weather" (ibid. vol. ii. p. 20). 

 Yarrell has stated that the term " storm cock " was 

 applied to the mistle- thrush because of that bird 

 " giving his song both before and during the occur- 

 rence of wind and rain." It appears to me, however, 

 that this thrush sings most during bright sunshine, 

 especially in the first three months of the year. 

 The domestic cock readily perceives an approach 

 of rain, and announces the fact by crowing. 



Dense fog is a powerful deterrent of song : I 

 have several times witnessed its almost immediate 

 effect in silencing singers. On one occasion this 

 was particularly noticeable. One day in January 

 several starlings, robins, and a brown wren were in 

 full song in a valley, when suddenly a low cloud swept 

 up the valley, shutting out the sunshine, and render- 

 ing indistinct or invisible the hedgerow elms. The 

 songs abruptly ceased. After the lapse of some 

 ten minutes the cloud passed away, the sun suddenly 

 shone, and all the birds recommenced their songs. 

 I had observed carefully only a few of these, 

 when another cloud obscured the scene as quickly 

 as its precursor, and at once the songs were aban- 

 doned. I waited during a longer period of misti- 

 ness, and then turned homeward ; yet I had not 

 gone beyond earshot of the place when the second 



