io8 POPULAR SCIENCE MONTHLY. 



THE SIGNIFICANCE OF THE CONDITION OF YOUNG 



BIRDS AT BIRTH. 



BY W. P. PYCRAFT, A.L.S., F.Z.S. 



IT is a matter of common knowledge that the young of birds are 

 ushered into the world in very different degrees of development, 

 according to the species to which they belong. The helplessness of 

 the callow young of the crow-tribe, for example, stands in strong con- 

 trast to the activity displayed by the young of the game-birds. Again 

 the young of birds are remarkable for the very wide degrees of varia- 

 tion which obtain in the matter of clothing on their escape from the 

 shell, variations which range from absolute nakedness to abundant 

 feathering, albeit feathering of a peculiar type. 



Out of these commonplace facts the systematic ornithologists, on 

 the one hand, and the philosophical zoologists, on the other, have 

 woven theories which have undergone many changes; but, so far, we 

 venture to think, all have missed the point. A survey of the work 

 of the systematic ornithologist will show that on more than one 

 occasion the condition of the young at birth has been made either 

 the corner-stone of a classification, or one of the main supports thereof. 



For the one purpose or the other these young have been duly 

 labeled and classified. In consequence, they may be contemplated 

 from two different points of view : ( 1 ) According to their helplessness 

 or otherwise, and (2) according as they are clothed or otherwise. 

 When the young emerge from the shell in a fully active state, they 

 are known as nidifugous or prascocial; those, on the contrary, which 

 are quite blind and helpless on leaving the shell are known as nidicolous 

 or altricial young. The nidicolous young may be, as we have already 

 remarked, absolutely naked, in which case they are said to be 

 psilopgedic. If, on the other hand, they are clothed, they are said to be 

 ptilopsedic. All nidifugous young are ptilopsedic. The nidicolous 

 young, being helpless and often blind, are assiduously fed by the 

 parents, whilst among the nidifugous types, the young either feed them- 

 selves under the guidance of their parents, or accompany them in the 

 search for food, and are fed by the way as the food is procured. 



Two very different standards of thought have inspired those who 

 selected the condition of the young at birth as a basis of avian classi- 

 fication. The older naturalists, adopting what we now regard as the 

 purely artificial standards of their time, grouped birds according as 



