PREFACE 



Any attempt to elucidate the problems connected 

 with the Migration of Birds must, in the present 

 state of knowledge, contain some theory and specula- 

 tion, but the diligent observations of an army of 

 careful workers yearly add facts, which though they 

 may appear insignificant when considered alone, 

 tend in the aggregate to confirm or repudiate the 

 conclusions of past workers. I have endeavoured 

 to bring together some of the more important 

 theories, and to give prominence to ascertained 

 facts ; I have also striven to check desire on my 

 own part to wander into realms of pure speculation, 

 though conscious that I have not always evidence 

 to support my suggestions. 



The numbers in brackets ( ) in the text refer 

 to the books or papers mentioned in the list at 

 the end of the volume, which is in no ways an 

 attempt at a full bibliography. I have quoted 

 freely from the works of past and living ornitholo- 

 gists. To these I offer apologies if I have mis- 

 construed their arguments, and acknowledge my 

 indebtedness to those whose observations or writing 



