300 The Bird 
that the conspicuous white of the under surface of the 
second bird is, when normally lighted up by the sun, 
neutralized by the shadow of the bird, and the darker 
upper parts are softened and toned down by the strong 
direct light; while if the entire bird be unshaded, although 
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Fig. 238.—Sooty Tern on her nest. 
coloured like the environment, the dark shadow beneath 
will reveal it clearly. 
Whether or not birds really appreciate the value of 
the protective colour of their plumage, it is certain that 
a quail or ptarmigan will remain crouching on a brown 
bit of turf, until all hope of evading danger is gone; while 
birds which are very evidently not protectively coloured 
are invariably more wary and difficult of approach. When 
