INTRODUCTI ON.
The task of compiling a list of the known species of Birds becomes
very difficult when the Passeriformes are approached, and I have
found an extraordinary increase in the number of the Muscicapiclce
and Pycnonotidce, since I wrote the fourth and sixth volumes of the
‘ Catalogue of Birds ’ in 1879 and 1881.
Apart from the work involved in picking up the threads since the
‘ Catalogue’ was finished, the question of Classification presents grave
difficulties in the case of the Passeriformes. A good deal of sterling
work has been done daring recent years, but we are still far from
a satisfactory system as regards the Passerine birds. Although the
late Mr. Seebohm afterwards admitted that he ought to have included
Pratincola, Cossypha, etc. in the fifth volume of the ‘ Catalogue,’ that
does not account for all the difficulties of the question; but I have, of
course, not enumerated such genera as these among the Flycatchers.
There remain, however, many doubtful forms in the Museicapidce, and I
have followed Mr. Eugene Oates in some of the modifications which he
has introduced in his excellent volumes of * Aves ’ in the * Fauna of
British India.’ Genera like Cryptolopha, Parisoma, Polioptila, etc. may
just as well be Sylviidce as Sencornis, Acanthiza, and Hypolais; and it
seems extremely difficult to draw a line between the Flycatchers and the
Warblers. In face of the uncertainty which surrounds the classification
of the Old-World Passeres, I have adhered, in the present volume,
mainly to the order of Yol. IY. of the ‘ Catalogue.’
Proofs of this volume have been sent to many of my colleagues
abroad, and the assistance they have rendered me requires my sincere
recognition. I have tried everywhere to acknowledge the original