THE DIPPER. 233 



two walked gradually into the water, and, having dis- 

 played their wings, spread them upon the surface, and 

 by these means appeared entirely to support them- 

 selves. 



"In this position they continued for some time, 

 at one moment spinning themselves, as it were, two or 

 three times round, and at another desisting, and re- 

 maining perfectly motionless upon the surface ; at 

 length, they almost insensibly sank." 



This last sentence is an extremely valuable one, 

 especially as the writer had no idea that he was eluci- 

 dating one of the problems of natural history. It is 

 evident that this bird, like those which have already 

 been described, has the power of contracting its body 

 at will, so as to make itself heavier than the water. 

 This being the case, the Dipper would have no diffi- 

 culty in walking under water, the supposed buoyancy, 

 on which so much stress was laid, not existing at the 

 time, and only resumed when the bird wishes to return 

 to the surface. 



The food of this bird is almost wholly composed of 

 aquatic insects, molluscs, etc., though it will occa- 

 sionally eat small fish. It has already been mentioned 

 that in searching for prey, the Dipper makes its way 

 up the stream. The reason for this proceeding is 

 evident. Did the bird walk down the stream, it would 

 not see the various insects that are carried towards it 

 by the force of the water. Moreover, whenever it 

 turned over a stone in search of prey, the hidden 

 insect would be swept away from it ; while, as the 

 bird keeps its head up the stream, the prey is carried 

 into its mouth. Within the stomachs of those Dippers 



