CHAPTER V 



THE CLASSIFICATION OF BIRDS 



LASSIFICATION is the orderly grouping together of those beings or 

 things that have certain characteristics in common. Zoological classi- 

 fication, therefore, is the grouping together of animals in accordance 

 with their affinities and interrelationships so far as these have been 

 ascertained, and consequently avian classification is an attempt to express, as 

 nearly as present facts warrant, the lines along which it is supposed the birds have 

 been developed. It may be regarded as the higher phase of ornithological study, 

 requiring for its successful prosecution the widest knowledge, the keenest discrimi- 

 nation, and the most careful interpretation. The only satisfactory manner in 

 which such a classification can be graphically displayed is by means of a so-called 

 genealogical tree, the trunk and limbs of a tree, as it gradually divides into smaller 

 and smaller branches, illustrating well the manner in which groups of birds are 

 assumed to have developed, each from an earlier or ancestral stock. It is obvi- 

 ously impossible to show this relationship by arranging them in a linear sequence, 

 although the exigencies of book making may render such disposition necessary. A 

 linear arrangement may go well for a short distance, one group following another 

 in an apparently natural succession, but sooner or later a point is reached where 

 it is necessary to begin again at the base of another branch or stem, and so in the 

 system of classification here adopted it is not necessarily to be presumed that 

 each group is always related in equal degree to that which immediately precedes 

 or follows it. 



I have already pointed out that, although the Class of Birds is not sharply 

 circumscribed by what may be called essential characters, the fact that they 

 alone possess an outer covering of feathers makes their recognition easy under 

 any and all circumstances. There can never be any doubt in the popular mind 

 about the identification of a bird as such, a condition far from being true in many 

 other coordinate groups of the animal kingdom. For present purposes, there- 

 fore, the Class of Birds may be said to be clearly differentiated, but when we 

 come inside the Class a wholly different state of affairs is presented, for there is 

 perhaps no group of similar scope in which the members are relatively so uniform 

 in structure and appearance as are the birds. Their classification is thus nat- 

 urally beset with many difficulties. As Mr. Ridgway well says : " Accepting evo- 

 lution as an established fact, and it is difficult to understand how any one who 

 has studied the subject seriously can by any possibility believe otherwise, - 

 there are no 'hard and fast lines,' no gaps, or 'missing links' in the chain of 



45 



