420 MIGRATION 



of our grouse have flown across the Channel ? The 

 answer to this supposed doubt on the part of the reader 

 for the necessity of the assumption of a former land- 

 connection is, that there is no instance on record of a 

 red grouse having been captured on the continent, or of 

 a willow-grouse having ever strayed to our islands ; and 

 it is a well-known ornithological fact that in a great many 

 instances a very narrow channel of deep sea bounds the 

 geographical range of birds. Migration across the sea 

 seems to take place only where it has become a fixed 

 habit, formed ages ago. Birds are very conservative. 

 To an immense extent they do as their forefathers did. 

 One cannot expect a very high development of the 

 reasoning faculty in them. The lower the power of the 

 reason the greater is the blind force of hereditary 

 instinct. Like other conservatives, birds have to suffer 

 the penalties of not being able to adapt themselves to the 

 changed circumstances of the times. There can be no 

 doubt that thousands of birds perish in their attempt to 

 follow the old routes which their ancestors took. I have 

 been assured repeatedly by naval officers that they have 

 seen many instances of flocks of birds being drowned at 

 sea, and I have myself picked up birds that have been 

 washed ashore after a storm. 



The origin of migration probably does not date back 

 to a period before the glacial epoch. As birds gradually 

 began to increase and multiply to an extent sufficient 

 to produce a struggle for existence, in the form of a fight 

 for food, they seem to have adopted a custom, which 

 they still retain, of leading away or driving away their 

 families every autumn to seek food and a home else- 

 where. As the circle of bird-life constantly widened, 

 in due time the abundance of food tempted many birds 

 to stray into the Arctic regions, to breed during the long 



