44 



THE BIOLOGY OF BIRDS 



" sexual selection." Now, each and all of these interpreta- 

 tions and others more subtle still may be quite legitimate ; 

 our only caveat is that their acceptance should not be on too 

 easy-going terms. We must remember, for instance, as is 

 well explained by H. C. Tracy (1910), that striking coloration 

 may develop for purely physiological reasons under con- 

 ditions of comparative immunity from attack, and may 

 prove a rather embarrassing legacy in subsequent ages when 

 the conditions have changed. 



Utilitarian interpretations are not convincing without 

 experiment, but there is no reason whatever for severely 

 refusing to consider the utility of coloration, especially as the 

 consideration may suggest experiment. From a paper by 

 Dr. J. C. Mottram (1916) we take a utilitarian classification 

 which had primary reference to Lepidoptera. 



Colour 



AND 



Pattern 



Unrelated to 

 THE Visual 

 Perception 

 OF Other 

 Animals 



For the absorption of Light Rays. 

 For the absorption of Heat Rays. 

 Excretory Products, etc. 



Related to 



THE Visual 

 Perce p t i o n 

 OF Other 

 Animals 



To the eyes | Protective 

 of enemies/ coloration 



Inconspicuous To the eves (Coloration 

 TO Other ofnrev concealing 



* ' attack 



Animals 



To the eyes \ , 

 of friends J 



Conspicuous 

 TO Other 

 Animals 



To the eyes 

 of enemies 



'Attracting and 

 repelling and 

 warning co- 

 loration 



■^oVprer^l''"'"-' 



To the eyes jSocial signals 

 of friends /Sexual signals 



