BRITAIN^S BIRDS AND THEIR NESTS. 225 



faithfully, if unwittingly, promoting the welfare of another 

 species at the expense of their own. 



Yet we cannot but marvel at the extent of the deception,, 

 for towards the end of the period the Cuckoo is about 

 three times the size of its benefactors, and they may- 

 have to perch on its back to feed it ! 



The English name ' Cuckoo,' from the note of the 

 male, may be variously spelt, and has its equivalents in 

 most European languages. 



NIDICOLOUS NESTLINGS. 



Plate 69. 



We have already dealt with the difference between 

 nidifugous and nidicolous nestlings, and have summarised 

 the salient features of the former (page 89). Nidicolous- 

 nestlings are characteristic of the great Order Passeres, 

 to which we shall come presently. They are also found 

 in the following Orders: Picarise, Owls, Birds - of - Prey, 

 Cormorants, &c. ; Herons, &c. ; and Pigeons. These groups 

 are nearly all composed of tree or cliff nesting species. 



We have also referred to the intermediate position of 

 young Auks and Gulls, which are down-clad and open- 

 eyed, but comparatively helpless. Similarly, some ground- 

 nesting members of groups chiefly nidicolous have ' inter- 

 mediate' young. A case in point is the Nightjar family 

 (see page 204) of the Order Picariae. On the other 

 hand, the ground-nesting Passeres (Lark and Pipit families) 

 have strictly nidicolous young (see, especially, page 230). 



Nidicolous young present sufficient differences in char- 

 acteristics to require grouping before they can be de- 

 scribed. They naturally fall into four classes. 



(1) The type found in the Kingfisher, Cuckoo, Swift, 



2c 



