470 
Dr. A. L. Thomson : Results of a Study of [Ibis, 
the question can he 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 farther southwards. 
And until this is known, very little of the true nature of 
migration can be understood. 
Some of the questions which may be answered in due 
course by the marking method are as follows, and most of 
them 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 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-marking, one must 
remember that it is only supplementary 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 migration. 
O 
There are various kindred points relating to distribution for 
instance, and interesting evidence of the rate of mortality is 
occasionally afforded. Furthermore, it might be a valuable 
aid to the study of plumage sequences to acquire a collection 
of birds which had lived entirely free and natural lives and 
of which the ages were accurately known. 
