The Possibilities of Bird-Marking. 207 



there a second home to which they annually returned after the cessation 

 of the conditions referred to had allowed them to recolonise their original 

 more northerly area, the routes followed by the individuals remaining those 

 followed by the species at the time of this supposed first great movement. 

 Then we have the more recent theory (cf. Pycraft, History of Birds, 1910, pp. 

 100-105) that the migrational habit arose from the gradual northward spread 

 of the species from its supposed original southern area in search of fresh 

 feeding and breeding grounds, the birds withdrawing to this original area 

 each winter. Without discussing these theories, let us note how their proof 

 or disproof would necessarily rest on a knowledge of the facts concerning the 

 relation of particular summer-quarters to the corresponding winter-quarters- 

 and of the routes connecting them. Thus it is often suggested that the 

 members of a species "summering" farthest north winter farthest south, and 

 that those midway are more or less stationary : but the observer only sees a 

 general southward movement, and we must single out typical individuals 

 for study before we can answer the question — that is to say, we must mark 

 them. Again, we have several 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, we may not be able to say 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, the immigrants passing on 

 over their heads and journeying farther southwards. And until we know 

 this, we know very little of the true nature of migration. 



Here are some of the questions which may be answered in due course 

 by students who follow the marking method, and most of these questions 

 have an important bearing on one or other unsolved 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 definite routes, and if so, what is the nature of these routes ? And 

 these questions might be multiplied indefinitely. 



While urging the importance of bird-marking, we must remember 

 that it is only supplementary to other methods, and must not be practised 

 to their exclusion. But the marking method has at present a special 

 importance, due to the fact that much progress has been made on other 



