12 ANIMAL LIFE UNDER WATER 



from above, while the half-open portion is re- 

 flecting the reddish-yellow colour around, and 

 so appears to blend with the granite rock. 



White objects on the surface are also con- 

 cealed by reflection. The top illustration on 

 the plate opposite page 4 shows how the body 

 of the lesser black-backed gull reflects the colour 

 below and is, in consequence, inconspicuous 

 against the surface of the water. 



But it is not necessary that the plumage of 

 a bird should be .white for it to secure conceal- 

 ment by reflection, for black-plumaged birds 

 become mirrors under the water owing to reflec- 

 tion from the air bubbles retained in their 

 plumage. 



Opposite are two illustrations of the same 

 water-hen. The bird is shown swimming on the 

 surface in the area of total reflection. The 

 lower half of the bipalatinoid-shaped object, 

 as already explained in the case of the gull, is 

 the body of the bird below the surface of the 

 water. The upper half is merely reflection. 



In the top photograph the light streak where 

 the body of the bird cuts the surface is well 

 marked. In the lower illustration the streak of 

 light between the reality and reflection is not so 



