On the Differences between Nestling Birds. 457 



The Game-birds (Gallina?,), appear to be the only group in 

 which the young- combine protective coloration with the power 

 of precocious flight. This latter has been gained by forcing 

 the growth of the inner quills of the hand — the quills which 

 became functional at a slightly later date — during the earlier 

 ancestral arboreal phase. That precocious flight has not been 

 more generally adopted seems at first somewhat strange. A 

 little reflection, however, will show that excessive activity on 

 the ground would 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 to render return possible. 

 Evidence indeed is forthcoming to prove that such precocious 

 flight is actually harmful. Thus Mr. Ogilvie-Grant, writing of 

 the Common Pheasant, tells us that the mother, on any alarm, 

 with 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 trusting to 

 their protective coloration. Quiet restored, the parent returns, 

 often only to recover but three or four of her chicks, the others 

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



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

 retaining their arboreal nesting habits, have minimized the 

 danger of the young falling to the ground by curtailing their 

 activity until the power of flight has been fully attained. 



This process of curtailment 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 

 outnumber 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 perfectly naked, others 

 enveloped in a thick coat of down, whilst, in some, the down 

 is developed soon after hatching ; and in others not at all. 

 The fact that this expedient of curtailment has been inde- 



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