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 
