Systematic notes on Palearctic birds. No. 22, Fringillidae, Emberiza schoeniclus. American Museum novitates ; no. 1795

Abstract

"In summary it can be said that, while it is convenient to arrange the various races of Emberiza schoeniclus into three groups, the boundary between them is very arbitrary in some parts of the range. In other regions the bill characters vary a great deal individually, and it is best not to use them for subspecific discrimination, and many races are slightly differentiated or relatively so in both bill characters and coloration. If these, as well as those that are purely intermediate, are eliminated, only a very few remain, namely, nominate schoeniclus, pyrrhulina, pyrrhuloides, intermedia, and korejewi. Pallidior and pyrrhulina are very far removed geographically and probably owe their general similarity to parallel adaptation. In view of the fact that all the races with a large, though not necessarily identical, bill occur in the more southern and generally drier parts of the range, the tendency towards large bills also seems an instance of parallel adaptation. In this connection, it is of interest to note that the forms inhabiting the most arid regions have the largest bill of all, as in Turkestan, Seistan, the Syrian Desert, the Tarim Basin, and the Zaidam"--P. 13.