PREFACE xi 



of papers to be found in the Proceedings and Trans- 

 actions of learned societies. Wherever it has been 

 possible, I have verified what I have learnt from 

 books by the methods explained in the concluding 

 chapter. Discussions with mathematicians, in par- 

 ticular with Mr. T. J. Bowlker and Mr. R. C. Gilson, 

 to whom my most cordial thanks are due, have 

 greatly helped me in dealing with the difficult 

 problems of flight. Mr. A. H. Macpherson has 

 very kindly put at my service the results of some 

 of his observations on the song and on the migration 

 of birds. I have also to thank Mr. F. E. Beddard, 

 without whose encouragement I should not have 

 begun this work. In important cases I have 

 mentioned in footnotes the source to which I am 

 indebted for facts or theories, and at the end of each 

 chapter I have given a list of some of the best books 

 and papers on the subject treated of. Those of my 

 readers who wish to proceed to a more special study 

 of any of the different branches of ornithology will, 

 I hope, find these references an assistance. 



On many parts of the subject I have delivered 

 lectures to the Hailevbury Natural Science Society. 

 In this book I have followed much the same lines, in 

 the hope that it may prove useful to lovers of birds 

 here and elsewhere. Technical terms, except such as 

 are unavoidable, I have dispensed with, and, as far as 

 possible, I have explained difficulties, never, inten- 

 tionally, wrapped them in the obscurity of big words. 

 There is only one species of ornithologists with whom 



