8 HOW BIRDS ARE NAMED 



our eastern bird, the former being no more a subspecies, of the latter, 

 than the latter is of the former. In other words, to continue to apply 

 only generic and specific names to the Eastern Robin would imply that 

 it was a species, while the use of a trinomial for the Western Robin 

 would imply that it was a subspecies. As a matter of fact, we know that 

 there is but one species of true Robin in North America, consequently, 

 in accordance with the logical and now generally accepted method, 

 we apply to that species the name Planesticus migratorius, and this is 

 equally applicable to Robins from the West and from the East. The 

 eastern subspecies is, therefore, known by the trinomial Planesticus 

 migratorius migratorius, the western subspecies by the exact nomencla- 

 tural equivalent, Planesticus migratorius propinquus, and the more 

 recently described small, pale Southern Robin, as Planesticus migra- 

 torius achrusterus. Thus we have one Robin which is represented by 

 three subspecies. It may be asked, why give names to these geograph- 

 ical races? Why not call Eastern, Western and Southern Robins by 

 one name without regard to their climatic variations? To which it 

 may be replied, that subspecies often differ more from each other than 

 do species. For example, it would clearly be inadvisable to apply the 

 same name to the small, pale Song Sparrow of Arizona, and the large 

 dark Song Sparrow of Alaska. (See figures beyond.) Seen without 

 the connecting forms from the intervening regions and they apparently 

 are specifically distinct, but the application to each of a subspecific 

 name, or trinomial, not only indicates that they are different, but it 

 shows also that they are representative forms which are joined by a 

 series of intergrades; a contribution of the first importance to the study 

 of evolution. 



For much the same reason, we should recognize by name those 

 birds, which, like the Robin, show less pronounced climatic variations. 

 Here we have species in the earliest stages of development from a 

 common ancestor, and in naming them we are, in effect, giving 'a handle 

 to the fact' of their evolution by environment. The study of the distri- 

 bution and migration of birds and the mapping of natural life-areas are 

 also intimately connected with this recognition by name of geographical 

 variations. 



Since it is evident that a species may vary much or little according 

 to the extent of its range, the governing conditions, and its tendency 

 to respond to them, no fixed rule can be drawn which shall state just 

 what degrees of difference are deserving a name. It follows, therefore, 

 that in some cases ornithologists do not agree upon the validity of a 

 bird's claims to subspecific rank.* 



In North America, however, questions of this kind are referred to 

 a Committee of the American Ornithologists' Union, and its decisions 

 establish a nomenclature which is accepted as the standard by other 

 American ornithologists and which is adopted in this volume. 



Finally, the student should be warned not to permit this matter of 



*See Allen. Auk, 1890, pp. 1-9. 



