456 W. P. Pycraft: 



to enable the young' chicks to escape as soon as possible from 

 the many enemies incidental to a terrestrial breeding ground. 



Assuming that my contention that all birds were originally 

 arboreal and were reared high up among the branches of 

 trees, is proved, or at least shown to be extremely probable, I 

 purpose to pass on to show that the several forms of precocial 

 and altricial young are the result of adaptation, the end 

 being to reduce the great infant mortality attendant on jDre- 

 cocious development among the tree-tops. 



The chances of death which would beset precocious nest- 

 lings whose nursery is in the tree-top are many and obvious. A 

 large number would fall to the ground through losing their 

 hold on the branches before the wing-quills had sufficiently 

 developed to serve the purpose of flight ; others would fall 

 through weakness, the habit of dispersing themselves among 

 the branches of the trees in which the nest was placed result- 

 ing in a loss of regular food-supply owing to the difficulty of 

 being on the spot when the parents returned with food. Thus 

 the more sedentary members of the family would stand the 

 best chance of being regularly fed ; but among these the 

 danger of falling by accident would be an ever present one. 

 Once on the ground it is probable that they would sj)eedily 

 perish, for it is certain that the earliest birds were entirely 

 arboreal, and either would not or could not seek for lost off- 

 spring amid the thick undergrowth. 



ISTow two courses were open whereby this infant mortality 

 could be reduced. Either the eggs could be deposited on the 

 ground, or the activity of the young curtailed. The Game- 

 birds, Ducks, and Geese, Rails, Cranes, and Plovers may serve 

 for examples of these species which have descended from the 

 trees to the ground for nesting purposes, and although as a 

 consequence, the young have undergone considerable modifi- 

 cations in adaptation to the new environment, these changes 

 are not so striking as those which have taken place among 

 the young of the tree-dwelling species. They are, however, 

 just those which might have been predicted ; embracing* 

 peculiar habits of concealment aided by protective coloration, 

 and a reduction in the size of the wings and feet, now no 

 longer required solely as grasping organs. 



