Appendix, amounts to 1626. Jerdon, from a much smaller area, described 1016. Hume's Catalogue of 1879 contained 1788 entries, of which he rejected 106 and regarded 74 as doubtful, leaving 1608, or nearly the same as the present enumeration. The precise number of species is naturally dependent on a personal factor, some writers being more liberal than others in admitting the claims to specific rank of races which are distinguished by small differences of plumage or measurement, or which are connected by intervening links with the typical form. Such races or subspecies, as they are called, have not, as a rule, been separately numbered and described in the present work, but they have received due notice and their characters have been explained.
A very considerable part of the present work is founded on the Catalogue of Birds in the British Museum, and on the specimens preserved in the Museum Collections. It is difficult to exaggerate the obligations of both Mr. Gates and myself to Dr. R. Bowdler Sharpe and Mr. W. Ogilvie Grant, the officers in charge of the Bird Department. In several cases the labour of compiling this and other volumes has been lightened by access to unpublished parts of the Museum Catalogue.
Prof. Newton's most useful 'Dictionary of Birds' has often furnished valuable information, and has occasionally prevented mistakes from being made; whilst for anatomical information I am greatly indebted to Dr. H. Gadow's contributions to the Dictionary and to his share of Bronn's great work. Some important details have also been personally communicated by Dr. Gadow and Mr. Beddard.
In addition to the many friends in India who have contributed to the previous volumes, thanks are due to Mr. F. Finn and Mr. A. L. Butler, both of whom have sent valuable notes. In this volume, as in the last, Mr. Oates's notes have been of great service, and he has added important information on some of the Birds of Upper Burma.