How Birds Are Named. 



A further study of our eastern Robin shows that in the southern 

 part of its breeding range (the Carolinas and Georgia), it varies from 

 the northern type in being smaller in size and much paler and duller in 

 color; and to this second geographical variety is applied the name 

 Merida migratoria achrustera, (achrustera, meaning less highly colored). 



It may be asked, Why give names to these geographical races? Why 

 not call eastern, western and southern Robins by one name, Merula 

 migratoria, without regard to their climatic variations? 



In reply, two excellent reasons may be given for the recognition of 

 subspecies by name; first, because in some cases they differ from one 

 another far more than do many species, when it would clearly be in- 

 advisable to apply the same name to what are obviously different 

 creatures. For example, it has lately been discovered by Mr. E. W. 

 Nelson that the small, black-throated, brown-breasted, Quails or Bob- 

 whites of southern Mexico, through a long series of intermediates in- 

 habiting the intervening region, intergrade with the large, white- 

 throated, black-and-white breasted, Bob-white of our northern states. 

 It would be absurd to call such wholly unlike birds by the same name, 

 nor could we give a full specific name to the Mexican Bob-white since 

 at no place can we draw a line definitely separating it from the northern 

 Bob-white. Furthermore, the use of only two names would conceal 

 the remarkable fact of the intergradation of two such strikingly differ- 

 ent birds; a fact of the first importance to students of the evolution of 

 species. 



For much the same reason we should name those birds which show 

 less pronounced variations, such as are exhibited by the Robin. Here 

 we have a species in the making, and in tracing the relation between 

 cause and effect, we learn something of the influences which create 

 species. Thus, climate has been definitely proven so to alter a species, 

 both in size and color, that, as we have seen in the case of the Song 

 Sparrows, marked climatic changes are accompanied by correspond- 

 ingly marked changes in the appearance of certain animals. In nam- 

 ing these animals we are, in effect, giving a 'handle to the fact' of their 

 evolution by environment. 



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