CANON TRISTRAM 163 



The actual causes that determine the actual time, year by 

 year, at which certain species migrate will of course be difficult 

 to ascertain. I will say, however, that they will be found to depend 

 on those climatic changes which most affect the particular species. 

 The changes of colour or the fall of certain leaves, the change to 

 the pupa state of certain insects, the prevalent winds or rains, 

 or even the decreased temperature of the earth or water, may 

 all have their influence. (Nature, 1874.) 



Next comes Canon H. B. Tristram, a diligent 

 student of birds and bird problems during his long 

 life of eighty-six years, who late in the last century 

 advanced his theory that all animal life originated in 

 the Arctic regions; that when that portion of the 

 globe grew too cold for comfort the birds were driven 

 south. And that was the genesis of the instinct of 

 migration. Then we have the addition of the glacial 

 epoch notion advanced by others; how, when it 

 passed away, the birds, remembering their ancient 

 natal home, returned to or as far towards it as the 

 conditions would allow to breed; then, when the 

 short Arctic summer ended, they had to fly south 

 again. Seebohm, the ornithologist, took up this 

 notion with enthusiasm, and having extended it by 

 inventing a succession of glacial epochs, went to 

 Africa, where many wonderful things are found, to 

 look for evidence. It was said that as he had sailed 

 with four glacial epochs and returned with only three 

 he must have accidentally dropped one overboard on 

 his voyage home. 



But although laughed at by some, others think 

 there is something in this theory, and some even 

 believe that it holds the field. 



