CORMORANT AND OTHER DIVERS 37 



water to cause a " flash " from the sheen on its 

 plumage. 



The back of the great northern diver is 

 covered with numerous white spots. These 

 white spots do undoubtedly sparkle, even at a 

 considerable depth, like a swinging shoal of fry. 

 I have shown the power of white as a reflector 

 under the water. 



Those who are unfamiliar with the plumage 

 of the great northern diver I would refer to the 

 illustration opposite page 17 in Vol. VI. of 

 Morris's " History of British Birds." Morris's 

 description is : 



" Breast white, back dusty, spotted all over 

 with oblong, oval and round spots of white ; each 

 feather has two spots, one on either side of the 

 shaft near the tip, forming rows." 



The plumage of the great northern diver 

 appears to me, par excellence, an example of 

 aggressive concealment. The white breast con- 

 ceals the bird's approach while it is in the 

 area of total reflection, and under the water 

 the back simulates a shoal of small shining 

 fish. 



The L white-billed northern diver is a bird that 

 only accidentally leaves the Arctic circles. The 



