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 unbroken 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 



