GEOGRAPHICAL DISTRIBUTION 



OF 



BRITISH BIRDS. 



Introductory Remarks. 



Geographical Distribution is a brancli 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 isolation 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. 



The greatest difficulty which presents itself, in attempting to estimate 

 the number of visitors to our Islands, is to be found in the vagueness of 

 the records of their supposed visits. These records display, for the most 

 part, a lamentable want of knowledge of the nature and value of evidence. 

 The mere statement that a certain bird Mas shot at a certain place on a 



