30 BRITISH BIRDS. 



LOXIA CURVIROSTRA AND LOXIA PITYOPSITTACUS. 

 COMMON CROSSBILL and PARROT CROSSBILL. 



(PLATE 13.) 



English ornithologists, having voluntarily cramped their ideas by putting 

 on the straight jacket of a binomial nomenclature, have for the most part 

 treated the Common and Parrot Crossbills as distinct species. The facts 

 of nature do not warrant such a conclusion in the least. A large series of 

 examples from Europe, Siberia, China, Canada, and Mexico show some 

 differences in size, especially in the bill, which varies almost as much as 

 that of the Lesser Redpole or the Reed-Bunting. Crossbills from the 

 pine-forests of Europe have the largest bills ; those from Mexico have 

 nearly as large bills, but the upper mandible is slightly weaker. Ex- 

 amples from the larch- and spruce-forests of Europe and Asia have both 

 mandibles weaker; whilst those from Canada have still smaller bills, and 

 approach very near to the Himalayan Crossbill in this respect. The 

 length of wing varies much less, being as under : 



Length of wing. Height of bill. 



L. pityopsittacus . . 4'3 to 4rO inches. '6 to '5 inch. 



L. mexicana . . . 4-1 3'7 '55 '4 



L. curvirostra . . . 3*9 3'7 '5 -4 



L. americana . . . 3'5 3'3 '35 '3 



L. himalayana . . 3'1 3'0 '35 '3 



It is probable that in a sufficiently large series the measurements of 

 each of these supposed species would be found to overlap that next to 

 it, and that all these forms are conspecific and nothing but local races. 

 It is not known that they differ in colour or in any other respect 

 except in size, thickness of bill, and choice of food. The two last- 

 named peculiarities are probably cause and effect. In ' Naumannia ' for 

 1853, p. 78, is a plate of twenty bills of Crossbills to illustrate a paper 

 by Brehm, who attempts to discriminate between six species of Parrot 

 Crossbill and eight or more species of Common Crossbill. Scotch 

 examples are intermediate between the Parrot and Common Crossbills 

 of the continent; they probably feed on both kinds of cones. The fact 

 that the tropical form of the Old World is a small weak -billed race, whilst 

 that of the New World is larger and stronger-billed than its northern 

 representative, is probably also merely a question of food. The synonymy 

 of the two forms which are found in our islands is as follows ; 



