The Body of a Bird 



295 



birds in colour when confined in a bird-house where the air 

 was constantly moist. Correlated with the effect upon 

 colour is often a difference in size, and in many instances 

 among birds the more northerly individuals are larger, 

 those inhabiting warmer regions being less in stature. 



Among wild birds, the Quail, or Bob-white, shows an 

 almost imbroken series from the northern, light-coloured 

 variety, ten inches in length, to the Cuban bird, very 



Fig. 235. — Siberian Black Lark, male bird in the spring. 



much darker in shade and measuring only eight inches 

 from beak to tip of tail. The race of Bob-whites seems 

 very susceptible to climatic influence; as in Mexico there 

 are nearly a dozen different geographical races, each in- 

 habiting a distinct portion of the country. Many other 

 wide-spread groups of birds, such as the Song Sparrows, 

 vary in a similar manner. It is strange what a marked 

 effect this greater or less amount of moisture has upon 

 birds, even in very limited districts. A South Ameri- 

 can pipit, the individuals of which spend their lives on 

 very circumscribed plots of earth, exhibits two colour 



