The Geographical Distribution of Birds 



By Lynds Jones 



What do we mean by the ''Geographical Distribution" of birds? Are not 

 birds to be found everywhere, over both land and sea? Are they not, then, uni- 

 versally distributed? As a class they certainly are, but not as species nor even 

 orders. Parrots are not found in frigid regions, nor are snowflakes and snowy 

 owls found in the tropical regions. Our \\^ood Warblers and Vireos are not found 

 outside of America, while there are no birds of Paradise anywhere in America. 

 We shall see that most of the birds found in the eastern hemisphere differ from 

 those foimd in the western, speaking broadly, but that many of the island birds 

 are different from birds of continents. 



Since most birds migrate shorter or longer distances in search of a place to 

 rear their young, and return again to warmer regions to pass the winter months, 

 the question at once arises: What is the geographical distribution of such mi- 

 gratory birds? That is not so difficult as it may seem at first glance. We have 

 only to inquire what governs the movements of the species in question in such a 

 Avay that its appearance at certain places at certain known times may be confi- 

 dently expected. The study of migration and breeding has shown that the impulse 

 to move northward in the spring to the old nesting-places where the young are 

 reared is more reliable than the impulse to move southward on the approach of 

 cold. The birds are more certain to appear at their old summer homes in spring 

 than they are to be found at any particular place during the winter. But if there 

 be any objection to this view it will yet remain true that where a bird. rears its 

 young should more properly be called its home than the place to which it is forced 

 by the approach of cold or the lack of food. In either case, therefore, we may 

 regard the home of the bird, and, therefore, treat its distribution geographically 

 as the place where it habitually rears its young. Having settled the question as 

 to what shall determine the distribution of the separate species, it remains to study 

 the physical conditions of the earth for the sake of finding what it is that deter- 

 :mines the limits to which the different species may go. 



We know that the distribution of land and water over the earth has not al- 

 ^vays been the same as it is now, but that many places that are now covered with 

 water were once dry land, and that in many places where there is now^ land there 

 used to be water. Xow, America is wholly separated from Uro- Asia- Africa, but 

 once they were connected together by a broad neck of land where Bering Sea now 

 lies, and there may have been another neck of land connecting Europe with Ice- 

 land and Greenland and so with North America. Now^ Australia and New 

 Zealand are wholly separated from all other lands, but they were not so long ago. 

 So of the larger islands in general, they have not always been isolated as now, but 

 connected with great land masses, sharing with them the animals which roamed 

 over the whole vast regions. For in the earlier times before Man had appeared 

 upon the earth, before the great Glacial Period, the whole earth was tropical in 



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