xvi INTRODUCTION. 



by Dr Thienemann at Rossitten. A light ring of 

 aluminium bearing a number and an address is put on 

 the foot of a captured, uninjured bird, which is then 

 set free ; the recovery of the ring — in a small percentage 

 of cases — supplies an item of precise information in regard 

 to migrational movements. 



Study of Development. 



To follow the individual development of the bird 

 within the egg — to see it ' climbing up its own genealogical 

 tree' — requires technical methods and skill beyond the 

 reach of the ordinary observer. But that is no reason 

 why he should not share in the study of development. 

 The study of nestlings and young birds has only begun, 

 and it is a study as fascinating as it is promising. Mr 

 Pycraft has recently shown how much scientific interest 

 there is in looking into the mouths of fledglings, and there 

 are many peculiarities of juvenile structure [and behaviour 

 that demand investigation. There is still much to be done 

 in continuous observation of plumage changes in growing 

 birds. And even if the observer cannot penetrate with 

 success into the secret processes going on within the shell, 

 there is much on the outside that will keep him thinking 

 for many a day. These rows of eggs, lying in such 

 perfect order in the cabinet, suggest a finished, scientific 

 task ; but, if we may use such a phrase, they bristle with 

 unsolved problems — e.g. as regards shape and size, coloiir 

 and markings. 



Evolution of Bieds. 



The study of birds reaches its highest level when 

 it asks the evolutionist's questions — Whence and how ? 

 There was a time, as every one knows, when there were 



