470 Dr. A. L. Thomson : FesxUs of a Shi<J>/ of [Ibis, 



tho question can be answered. Again, there are many cases 

 of species which are found all the year round in the British 

 Isles, but yet are known in autumn both as immigrants from 

 the north and as emigrants to the south, and vice versa in 

 spring. Now, except by marking one can hardly hope to be 

 sure whether it is our own summer birds that emigrate, 

 leaving the newcomers to occupy the area for the winter, 

 or whether our own birds are resident while the immigrants 

 pass on over their heads and journey i'arther southwards. 

 And until this is known, very little of the true nature of 

 migration can bo understood. 



Some of the questions which may be answered in due 

 course bv the marking method are as follows, and most of 

 them have an important bearing on one or other nnsolved 

 problem of bird-migration : — To what extent do birds return 

 to their birthplaces to breed, and under what circumstances 

 are new areas colonised ? Do birds have definite winter- 

 quarters, and if so, do they seek them year after year? 

 Do young birds seek the same winter-quarters as their 

 parents ? Do birds of the same summer area (and same 

 species) seek the same winter area? What relation do the 

 winter-quarters of the northerly-breeding members of a 

 species bear to those of the southerly-breeding members ? 

 Do migrants travel by different routes, and if so, what is the 

 nature of these routes? And these questions by no means 

 exhaust the subject. 



While urging the value of bird-maiking, one must 

 remember that it is onl}- supplcmentar}' to other methods, 

 and must not be practised to their exclusion. In passing, 

 too, it may be noticed that bird-marking may incidentally 

 serve other ends than those connected with mioration. 

 There are various kindred points relating to distribution for 

 instance, and interesting evidence of the rate of mortality is 

 occasionally aftbrded. Furthermore, it might be a valuable 

 aid to the study of plumage sequences to acquire a collection 

 of birds wdiieh had lived entirely free and natural lives and 

 of which the ages were accurately known. 



