PREFACE TO SECOND EDITION. 
Eleven years have passed since my " History of the Birds 
of Europe not observed in the British Isles" was completed 
in four volumes, and the large edition then printed having 
been sold, another is demanded. 
It is very gratifying to find that my efforts to advance 
the knowledge of European ornithology have been so suc- 
cessful. In responding to the demand for a- second edition, 
I should be ungrateful to my many friends did I not use 
every exertion to make it as perfectly up to the knowledge 
of the present day as possible. 
Eleven years is a long time in the history of modern 
science, and many and extensive alterations have been 
requisite. Some birds have been altogether omitted, either 
because their occurrence in Europe has been never definitely 
proved, or having become undoubted visitors to the British 
Isles, they will in future belong to the historians of British 
ornithology. I have taken the liberty of exercising a dis- 
cretion in this matter, for the record of a straggler to these 
isles cannot always be supported by the requisite proof, nor 
the appearance of a single individual deemed sufficient to 
exclude it from my work. 
