THE BOOK OF MIGRATORY BIRDS 67 



when the tops of the Rocky Mountains and the Mexican 

 and Central American Cordilleras were capped with snow 

 and ice, glaciers streaming far down their sides towards 

 the sea, several species found their retreat cut off either 

 by sea or ice. It is my belief that at this time and for 

 this cause our American horses and camels and elephants 

 perished. Their remains are found in vast beds in the 

 warmest parts of the United States, bordering on the Gulf 

 of Mexico. They had reached an impassable barrier, and 

 not being fitted (specialised) they inevitably perished. A 

 different geographical formation in Asia enabled the same 

 creatures to make good their escape to warmer regions. 



As there was a minimum and there will be a maximum 

 to the ice age, so there has been a minimum and there 

 will be a maximum to migrations. The ice fronts of the 

 polar regions must be the limits of the feathered tribes. 

 Mammalian life will find its migratory limit far short of 

 those points. 



In common with other species there is little doubt that 

 earliest man himself was of a migratory habit. The 

 human family was put to the same test as others, and came 

 out of it triumphant. The obstacles which he was forced 

 to cope with resulted in his great mental development that 

 placed him far in the van in this struggle for existence. 

 He invented clothing, made better dwellings, discovered 

 the uses of fire, and became a domesticator of the wild 

 animals, or, taking lessons from some others, stored away 

 food for the inclement season. Thus the most improved 

 race abandoned migration, and a great advance on civilisa- 

 tion was accomplished. 



In answer to Mr. Gregor's question as to the "logical 

 reason" of the spring migration, I conclude that this 

 characteristic of certain species dates from the pleistocene 

 era of the tertiary period and has two causes food supply 

 and comfort. 



Of the first category the examples are numerous and 

 present in everybody's mind. As to the second, a forcible 

 case would be that of the caribou of Newfoundland, which 



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