BRITAIN'S BIRDS AND THEIR NESTS. 287 



suppose that the earhest birds lived and nested on the 

 ^ound, and that our present-day Game-birds, already 

 described, are perhaps the most 'generalised,' and the 

 nearest to the ancestral forms. But in the embryos 

 of these very Game-birds we find claws on the ' fingers ' of 

 the wing, which remind us of those used by the young 

 of that curious South American bird, the Hoatzin, in 

 crawling about the trees. The Hoatzin is noteworthy in 

 being a tree-nester, with active nidifugous young. The 

 oldest fossil bird known, the Archasopteryx, also possesses 

 such claws. From these and other facts some have 

 supposed that arboreal habits are really of very great 

 antiquity — that, in fact, birds were evolved from tree- 

 jumping reptiles. The birds that remained in the trees 

 gradually came to have nidicolous nestlings, for nidifugous 

 young would be subject to great mortality in an aerial 

 abode. Before this occm-red, however, the Game-birds and 

 others came down, and they have retained the active nidi- 

 fugous nestlings, which are at no disadvantage on the 

 groiind. Pipits and others, however, have come down at 

 a comparatively recent date, after the transformation from 

 nidifugous to nidicolous young had been effected. 



Such, at any rate, is the theory, and it is certainly 

 a very good one. Whether it stand or fall, or how it 

 must be modified, is a matter for further research and 

 thought, for the subject has been grievously neglected. In 

 this book, dealing primarily with birds' nests, eggs, and 

 young, we have tried to emphasise the importance of the 

 too long neglected study of young birds. We believe in, 

 and would have others believe in, the importance of the 

 questions concerning nestlings. This will surely be con- 

 ceded : that these questions are wrapped up with the most 

 far-reaching problems of the origin and history of bird- 

 life, which we can now study only from the records written 



