YOUNG BIRDS AND RECORDS OF THE PAST 127 



As a consequence of this reduction the young are, so to 

 speak, prematurely born, or rather the embryonic period 

 of development has become relatively shortened, and the 

 young accordingly emerge from the shell in the helpless 

 state to which we have already referred. That the 

 number of species which are ushered into the world 

 in this helpless state far outnumbers those which make 

 their entry in a further advanced condition speaks volumes 

 for the benefits derived from the shortening of embryonic 

 life, even though this may lengthen the time during which 

 the young must be cared for, and so increase the parental 

 burdens. As examples we may cite the vast host of song- 

 birds, their nearly related types represented by the parrots, 

 cuckoos, kingfishers, bee-eaters and their kin, the pigeons, 

 storks, birds of prey, and the cormorants and their near 

 allies. 



The amount of food-yolk once reduced, a return to 

 the older fashion of active young was impossible ; and 

 this explains why the young of so many species hatched 

 on the ground are as helpless as those reared in the topmost 

 boughs of the highest trees. These young are descendants 

 of birds whose young in turn had become adapted to the 

 requirements of an arboreal nursery ; and though this was 

 later forsaken it is obviously impossible, as we haveremarked, 

 to make a return to the earlier precocious condition. 



After what has been said so far, it is somewhat surprising 

 to find precocious young, belonging to species which are 

 essentially birds of the marsh and beach, reared in arboreal 

 nurseries ! The green sandpiper {Toianus ochrofus), for 

 example, will make use of deserted nests of other species 

 — blackbirds, hawks, squirrel-dreys — at heights varying 

 from 3 feet to 30 feet from the ground. Similarly the 

 noddy {Anous stolidus) and the white tern {Gygis Candida) 



