442 The Outline of Science 



There are birds, too, which commonly use the old nests of other 

 species, with or without additions of their own, although they 

 are not always incapable of building for themselves if faced with 

 the necessity. This habit is not uncommon in the case of birds 

 of prey; the Kestrel, for example, often uses the old nests of 

 crows and pigeons. The Green Sandpiper, belonging to a very 

 different order of birds, uses the old nests of thrushes and other 

 tree-nesting birds and even squirrel's "dreys"! although most 

 of its own kin are typical ground-nesters. 



14 

 Chicks and Nestlings 



It is impossible to leave the main question of nesting habits 

 without some reference to the striking differences observable 

 among the newly hatched young of birds. These fall into two 

 well-marked groups in accordance with the condition and stage 

 of development at the date of leaving the egg. Technically these 

 groups are the nidifugous and the nidicolous, terms which we 

 may translate as nest-quitting and nest-dwelling, though perhaps 

 something of the distinction is conveyed in the two ordinary 

 names "chick" and "nestling." The chick of the domestic fowl 

 is notoriously a nest-quitter; so also are ducklings, whether 

 domestic or belonging to one of the many wild species, and so 

 likewise the young of the plover kind. All these birds leave the 

 egg prepared to take an immediate active part in life; they are 

 open-eyed and lively, able to walk and, in appropriate cases, 

 to swim and capable of rinding their own food with no more 

 than the guidance and protection of the parent. Contrast these 

 with, say, young thrushes helpless, blind, almost naked, and 

 rather repulsive-looking creatures, which would die miserably 

 without the food their parents so assiduously bring. The differ- 

 ence is, indeed, a most striking one, but some of the nest-dwelling 

 young are not quite so unlike the more active chicks ; the nestlings 

 of the birds of prey and of the owls, for instance, are clothed in 



