THE CONDITION OF YOUNG BIRDS AT BIRTH. in 



possible, however, that protective coloration was preceded by the de- 

 velopment of precocious powers of flight, which have since been dis- 

 carded by all save the game-birds. Probably this rejection was 

 brought about because excessive activity on the ground was found 

 to be as fatal as in the trees; since the young, in escaping from one 

 danger, would be liable to run into another, or to stray too far away 

 to render return possible. 



At the present day, though the young of all the game-birds are 

 protectively colored they have yet preserved more or less perfectly their 

 earlier precocial powers of flight, the birds, when escaping danger, using 

 their wings either like the ostrich, as an aid in running, or in actual 

 flight, and there is evidence to show that the broods in consequence 

 suffer. As an example, the observations of Mr. Ogilvie Grant on this 

 subject may be cited. In writing of the common pheasant, he tells 

 us that the mother, on alarm, with a warning note to the young, at 

 once flies off and leaves them to take care of themselves. This they 

 do by scattering in all directions, and then squatting down and trust- 

 ing to their protective coloration for safety. Quiet restored, the 

 parent returns, often only to recover but three or four of her chicks, 

 the rest having strayed to such a distance that they are left to perish. 



Thus, then, the hypothesis of precocious flight seems by no means 

 an improbable one. Its development will be easy to understand when 

 it is remembered that the raw material therefor is furnished by that 

 aberrant member of the game-birds the hoatzin. The life-history of 

 this bird will be discussed later. 



We may pass now to a consideration of those species which, retain- 

 ing their arboreal nesting habits, have adopted the method of curtailing 

 the activity of the young. This process was accomplished by reducing 

 the food-yolk within the egg, and thus inducing an earlier hatching 

 period. We may approximately measure the extent to which this 

 reduction has been carried by the degree of helplessness displayed by 

 the newly hatched bird, and by the nature and extent of its clothing. 



The number of species which have adopted this expedient out- 

 number those which have not, and this speaks volumes for its success. 

 As examples, we may instance the passerine or song-birds, parrots, 

 cuckoos, birds of prey, cormorants and their allies, and the stork- 

 tribe. The young of these are all born extremely helpless, many per- 

 fectly naked, others enveloped in a thick coat of down, whilst in some 

 down is developed soon after hatching, and, in a few, not at all. 



Having once however reduced the amount of food-yolk, return to 

 the older fashion of nidifugous young became impossible, and this 

 explains why nidicolous young are still born to those parents which 

 have adopted the practice of depositing their eggs upon the ground. 

 It proves that the arboreal habit has been forsaken since the specializa- 



