26o THE MIGRATION OF BIRDS. 



Where they go and what their ultimate fate is a 

 matter shrouded in mystery ! It teaches us, how- 

 ever, to realize the fecundity and the mortality 

 pertaining to Avian Life. 



The origin of this great East to West Migration 

 Wave must undoubtedly be sought in long-past 

 ages. That the movement is a deeply-rooted one is 

 evident from the persistence with which it is under- 

 taken, even by some few species of comparatively 

 weakly flight. Doubtless it originated from a 

 prevailing low winter temperature in Eastern 

 Europe and Western Asia, and a comparatively 

 high winter temperature in Western Europe owing 

 to Gulf Stream influence. Had it not been for the 

 latter current this great Wave w^ould undoubtedly 

 have drifted South instead of West. That this 

 difference of temperature exists is a fact no one will 

 attempt to gainsay. The winters of South Russia 

 and South-west Siberia, in the same latitudes as 

 the South of France, are as remarkable for their 

 normal severity as the winters of West Europe 

 within the same parallels of latitude are for their 

 normal mildness. That this is due to the warm 

 ocean current that flows along the coasts of the 

 latter is also an undoubted fact. There can be no 

 doubt whatever (after what we have already learnt 

 of Migration) that this difference of climate has had 

 a marked effect on Avian life, and been the initiat- 

 ing cause of this East to West Migration Flight. 

 Now in remote yet Post-Glacial Ages, the British 

 Islands, the entire German Ocean, the English 



