226 STRA Y FEA THERS FROM MANY BIRDS. 



So far as concerns the birds of the Arctic and north 

 temperate regions of the globe, there can be little doubt 

 that glacial epochs have been the grand means of 

 segregation. Species after species must have perished 

 in those eventful stirring times when they were gradually 

 subjected to the extremes of an Arctic and a Tropical 

 climate, and during the time of their enforced pilgrimage 

 to and residence in more southern regions, and the 

 consequent change of habits, change of food, and ex- 

 posure to new perils, made all the more deadly through 

 want of experience in combating them. Then came the 

 great and gradual exodus back again, as the glacial ice 

 retreated north, during which period many species were 

 exterminated, others were split up into eastern and 

 western races, and new and old world species, and many 

 more were left behind in the Tropics to develop into 

 southern representatives of these northern species, where 

 they remain to this day, permanent residents among 

 more ancient forms, and living evidence of some of those 

 grand revolutions through which our globe has passed 

 during its long eventful history. 



Although we are unable to state with certainty the 

 causes of the death of species even during prehistoric 

 time, there are many birds that have become extinct 

 within the past hundred years or so, the reason for 

 which is known to naturalists. One of the most 

 familiar instances is the Great Auk or Gare Fowl, a bird 



