SQUIRRELS AND RATS 217 



in numbers in the autumn; but if this be so, one 

 wonders why they do not die at home. I think that at 

 this season there is a widespread migratory movement, 

 and that many perish by the way. 



The squirrel is also, I think, a would-be migrant 

 occasionally. I have read an account of a great 

 squirrel migration in North America, in which the 

 animals perished in the water, like migrating lem- 

 mings in Norway, when attempting to cross a river. 

 I have some reason to think that it is always in the 

 autumn when squirrels first make their appearance 

 in newly-planted woods at long distances from any 

 place where the animal inhabits. 



Rat migrations are common in England all over 

 the country : they are regular local movements, and 

 may not have the same cause as the seasonal migra- 

 tions of birds, although they invariably occur in the 

 spring and autumn. We know, however, that there 

 have been great migrations of the brown rat in the 

 past; that early in the eighteenth century it invaded 

 Russia from China, and spread all over Europe and 

 the world. But to go to books is to find that great 

 migrations of mammals, big as well as little, have 

 often occurred ; that even the royal tiger is a colonist 

 in India, and was unknown in that land when its 

 sacred writings were composed. An account of the 

 migration of the larger animals in Africa and North 

 America would make a big volume. 



To go back to bird migration: I trust that these 

 observations of mine, made so many years ago, will 



