PREFACE vii 



For the sake of convenience the work has been 

 divided into two parts ; the first treating of physical 

 and cHmatic changes, and their effects on Birds and 

 species generally ; the ancient Emigration of birds to 

 the British Area, and its modern progress ; lastly of 

 Island Avifaunas and their bearing on the entire subject. 

 The second part deals with the Migration of Birds with- 

 in the British Area ; the Routes those birds follow ; 

 the conditions of their Flight ; the spring and autumn 

 aspects of the phenomenon ; and lastly, with the very 

 curious and interesting subjects of Local Movement 

 or Internal Migration, and Irruptic Movement. 



I earnestly hope that the present work may assist in 

 solving some of the many intricate problems connected 

 with the present and past Geographical Dispersal of 

 Life, and the Migration of Birds ; for then its purpose 

 will be amply attained, and the labour involved in its 

 construction ever recalled with pleasure. 



Charles Dixon. 



