248 A HISTORY OF BIRDS 



Various intermediate stages in this process of "hobbling" 

 may be studied in the case of those species which, having 

 young of the precocious type, breed in colonies, often of vast 

 size, or on ledges of precipitous cliffs. The reduction of the 

 food-yolk, and the consequent premature hatching observable 

 in the young of such species, are undoubtedly advantageous. 

 This is the case in so far at least as the preservation of the 

 species is concerned, since, when reared in colonies affording 

 a free space to roam, they would, if active, become lost amid 

 a general crowd of nestlings, and hence soon starve — even if 

 the parent birds had acquired the habit of feeding indiscrimin- 

 ately any nestling in the colony which clamoured for food. In 

 the case of cliff-breeding species like the Guillemots and Razor- 

 bills, and many Gulls, this quiescence, at first enforced by sheer 

 inability to move and later adhered to by habit, saves an 

 enormous mortality through falls from the cliffs. 



Whilst a large number of birds have adopted the expedient 

 of curtailing the activity of the young, and thereby have in- 

 creased the burden of family cares, there are a few species of 

 Game-birds known as Megapodes, or mound-builders, which 

 have succeeded in reducing the ties of offspring to the smallest 

 possible limits — without descending to parasitism — by enorm- 

 ously increasing the size of the egg so as to include a pro- 

 portionately large amount of food material for the developing 

 embryo. As a consequence, the whole of the normal nestling 

 period is passed ivitliin the shell, and the young bird emerges 

 fully feathered and able to fly. The parental instinct seems 

 in consequence of this habit to have become well-nigh ex- 

 tinguished, for there is no brooding of the eggs, and little or 

 no care displayed for the chicks which are hatched after the 

 fashion of many reptiles — by the warmth generated by decay- 

 ing vegetable matter in which the eggs had been placed ^ 

 (Chap. XIII., p. 217). 



^Although numerous facts have been recorded concerning the disposition of 

 the eggs of the various species of Megapodes there appears to be no published 

 account of the discovery of young immediately after hatching and before working 

 their way out of the natural incubator in which these birds are hatched. 



From observations made at the Gardens of the Zoological Society on the 

 nesting of the Australian Brush-turkey (Cathctuyus lathami), it would seem 

 that the nestling remains in the mound raised by the parents for about thirty-six 

 hours, and then makes its way up to the outer world. During this time the quills 

 of the wing appear to complete their growth, since, though at the moment the 



