CHAPTER VII 

 civilization's effect on the bird supply 



TWELVE hundred kinds of wild birds have 

 been positively identified in North America. 

 About one-third of this number are called 

 sub-species, or climatic varieties. To illustrate the 

 meaning of " sub-species," it may be stated that in 

 Texas the plumage of the Bob-White is lighter in 

 colour than the plumage of the typical eastern Bob- 

 White, which was first described to science; therefore, 

 the Texas bird is known as a sub-species of the type. 

 Distributed through North America are nineteen 

 sub-species of the eastern Song Sparrow. These 

 vary from the typical bird by differences in size and 

 shades of marking. In a similar way there are nine 

 climatic variations of Screech Owls, six Long-billed 

 Marsh Wrens, and fourteen Horned Larks. It is 

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