CHAPTER III 



THE GEOGRAPHICAL DISTRIBUTION 



OF BIRDS 



HE distribution of life over the globe is known as biogeography. With 

 that branch of the subject dealing with the distribution of animals 

 (zoogeography) we are of course at present only concerned with 

 the distribution of birds. Although earlier attempts had been made 

 to correlate certain observed facts of avian distribution, it was not until about 

 the middle of the last century that the subject was placed on a logical and scien- 

 tific basis. These earlier attempts failed because it was undertaken to delimit 

 life areas by degrees of latitude and longitude, or by the lines of political division, 

 while in the light of present understanding it needs but a moment's reflection to 

 disclose the fact that the distribution of life on the earth must depend upon 

 natural causes and conditions, and only occasionally and quite by accident to 

 coincide with the political divisions. 



Inasmuch as most birds possess the power of flight, which enables them to 

 pass easily and quickly from one area to another, or, within certain limitations, 

 even from one hemisphere to another, it might be inferred that their distribution 

 would be relatively uniform, but such is far from being the case. If a person 

 reasonably familiar with the bird life of eastern North America should journey 

 around the world, first crossing this continent, and thence by way of Central 

 America through South America, and by way of Polynesia to New Zealand, 

 Australia, Asia, Europe, and Africa, he could not fail to be impressed with the 

 marked differences in the birds coming under notice. In a few Ceases, such as 

 afforded by the pelagic and far- wandering Albatrosses, Petrels, Gulls, Terns, and 

 Tropic-birds, he might find the same species at several widely separated points 

 in the journey; in many instances he would note the presence of familiar groups, 

 as Ducks, Woodpeckers, Kingfishers, Hawks, Owls, but in the vast majority 

 of cases the species would be entirely different, while in not a few, whole families 

 and orders would appear and disappear in succession. 



It is not always easy to account for the presence or absence of certain genera 

 or other groups of birds in this or that part of the world, especially when it 

 appears that the conditions of environment in localities whence they are absent 

 are apparently similar to those obtaining where they are present, and were it not 

 for the aid rendered by geology and paleontology we should often be left without 

 an adequate explanation. It is no doubt true that certain groups of birds now 



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