The Body of a Bird 213 
in this and in many other so-called protectively coloured 
birds, other factors, such as the direct effect of light on 
Fig. 250.—Snowy Owl. Aggressive coloration in an Arctic Owl. 
the plumage, enter into the causation, can only be solved 
by future thorough investigation. 
Albinos are occasionally found among widely different 
