GEOGRAPHICAL DISTRIBUTION 



OF 



BRITISH BIRDS 



Introductory Remarks. 



GEOGRAPHICAL DISTRIBUTION is a branch of the science of Zoology 

 which has very greatly increased in interest since the theory of 

 Evolution has been generally accepted. It was Darwin's opinion, 

 which recent research has invariably confirmed, that without isola- 

 tion the differentiation of species is impossible, and of all possible 

 modes of Isolation, Geographical Isolation is the most important. 



The number of species which have been included in the list of 

 British Birds at various times considerably exceeds four hundred, 

 but of these many have been admitted on most untrustworthy 

 evidence. 



The sources of error are various. In some cases a mistake has 

 been made in the naming of the examples, in others the examples 

 have been correctly named, but they were not obtained in the 

 British Islands, having been changed either by accident or by 

 design by a careless or fraudulent birdstuffer, or by a collector 

 ignorant of the value of scientific accuracy. 



A third and very frequent source of error, which it is often 

 impossible to avoid, is caused by the escape of imported birds 

 from aviaries, or the attempts which have been from time to time 

 made to introduce new species into this country by importing 

 birds from abroad and turning them out in the most favourable 

 localities. We may also include under this head the birds which 

 are occasionally helped over the ocean by alighting on the rigging 

 or frequently the decks of the ships which are always scattered 

 over the high seas. 



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