THE BIRD SUPPLY 

 difficult to explain why this variation in colour and 

 size is so pronounced in some species and yet is totally 

 absent in others of equally wide range. The Mourn- 

 ing Dove breeds in many localities from the southern 

 tier of Canadian Provinces southward throughout 

 the United States and Mexico, and yet everywhere 

 over this vast range the birds are the same in size and 

 colour. Nowhere do the individuals exhibit any 

 markings suggestive of climatic influences. 



Some birds are very rare and are admitted to the 

 list of North American species because of the fact 

 that during the years a few stragglers from other 

 parts of the world have been found on our continent. 

 Thus the Scarlet Ibis from South America, and the 

 Kestrel and Rook from western Europe, are known to 

 come to our shores only as rare wanderers who had 

 lost their way, or were blown hither by storms. 

 Eighty-five species of the birds now listed for North 

 America are of this extra-limital class. Among those 

 naturally inhabiting the country, some are, of course, 

 much more abundant than others, thus every one 



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