LECTURES. 33 
the idea that the shallow water covers what was in former times land 
there would be no advantage to the flying bird in crossing it rather 
than deeper seas as if its strength failed death by drowning must 
ensue in either case. There fis a great difficulty in tracing these 
routes, for though special birds may be marked for recognition, 
so great is the mortality among them that any given one has 
only a chance of fully completing the journey, also it is inevitable 
that it must be shot to be recognised, and once having the bird, it is 
impossible to say what would have happened if it had been allowed to 
live. One very well-marked route we do know, however, which is, 
from North Russia through Lapland and Scandinavia to Britain. 
This route is not in a Southerly direction, but it is to a warmer 
climate. This question of routes is now receiving attention from a 
commission appointed to inquire into the matter. 
So far then, we have accounted for the original route, now we 
should find some reason why this route is persisted in. As in the 
case of the nest-making and singing and fear of enemies, we have 
done away with the old theory of instinct,— have suggested that 
tradition and imitation play an important part. These same forces 
act in the same manner on the migratory instinct. Birds usually 
migrate in large numbers, and though the young may precede their 
parents by a few days they are soon overtaken, also the young fly 
nearer the ground and wili cross the sea by the shortest passage, 
where they can see land on the other side, skirting round the South 
coast to the Straits of Dover, whereas the parents who have been the 
return journey, at any rate with experienced travellers, go by a 
shorter route, though this necessitates crossing the sea at a wider part. 
We can to acertain extent see the migratory habit growing, as 
during the last roo years very many plantations of trees have been 
made in Scotland further North than any such plantations before 
existed, and we find that this is accompanied by a further migration 
North in the case of some birds. 
That routes can be considerably modified, and that the instinct 
does not descend in the unvarying form which was supposed, is 
shewn by the fact that some species have within the last few years 
been seen for the first time in the Faroe Isles and others in th 
Cape Verde Islands. It can only be supposed that some birds have 
joined another party and then guided other birds of the same class. 
One last remark and I have done. A few American birds ar 
seen in England but very rarely on the Continent, and they ar 
more common in this country than formerly, it is thought that the 
