22 



The name of the genus comes first, and is capitaHzed, the name 

 of the species second, and that of the subspecies third. As, 

 for example, the robin: Planesticns migratorius, There is but 

 one species of robin in North America. There is a recognized 

 western race of the robin known as Planesticns migratorius 

 propinquvs. Consequently, we apply to the eastern robin the 

 nomenclatural equivalent: Planesticus migratorius migratorius. 

 Then, again, there is a small pale southern robin now known as 

 Planesticus migratorius achrusterus} Here is but one robin 

 represented by three subspecies. The differences in size and 

 color are not very great. Why, then, recognize races at all 

 and dignify them by names? To this it may be answered that 

 as we advance in the study of ornithology we are driven to 

 trinomials by the fact that some species are now known to have 

 many geographic races, some one of which may differ far more 

 from some other . in size and color than do certain distinct 

 species, and yet there are connecting links between all of these 

 races. 



If we take another common and widelv distributed bird, the 

 song sparrow, we jfind that at least twenty-three races of this 

 species are now recognized, and if we compare the small, pallid, 

 desert song sparrow with the large, dark, Aleutian song sparrow 

 we find that these two races of one species dift'er in size, shape, 

 and color more widely than do such distinct species as the song 

 sparrow and Lincoln's sparrow. There is even more apparent 

 difference in appearance between these two races than the 

 novice will see between the eastern song sparrow and the fox 

 sparrow, — birds not only of different species, but also assigned 

 to different genera. Nevertheless, the pallid or desert song 

 sparrow and the Aleutian song sparrow are connected by a 

 chain of subspecies. 



Genera and species are not immutable. Many of the dis- 

 tinctions of the past represented mainly the gropings of the 

 human intellect in a new field. Now minute differences are 

 more carefully noted. Some of the former genera are now 

 regarded as species, and some of the former species are con- 

 sidered as mere races. There is perhaps no fixed and uni- 

 versally accepted definition of just what constitutes a sub- 



1 A fuller discussion of this subject will be found in the revised edition of the Handbook of 

 Birds of Eastern North America, by Frank M. Chapman, 1914, pp. 5-9. 



