AVIAN TIDAL WAVES. 



49 



autumn there is a vast tidal wave of bird emigration 

 from the northern division of the American continent to 

 the southern and central divisions (which last includes 

 the West Indian Islands), and vice versa, every spring ; 

 just as occurs at the same seasons in the Old World 

 from Europe and Asia right away down to the nethermost 

 limits of Africa and the more southern divisions of the 

 eastern hemisphere. Silently and mj/steriously, this avian 

 game of " musical chairs " begins as the first cold shadow 

 of winter spreads over the north polar region ; and from 

 this circumpolar starting point the tidal wave of birds 

 flows southwards along the main land-tracts of the earth, 

 gaining in amplitude as it sweeps southwards in every 

 direction. Again in the spring another mysterious 

 summons starts the return wave flowing in a northerly 

 direction. 



Practically everyone in England, old enough to realize 

 an3rfching at all, is perfectly aware that cuckoos, swallows, 

 nightingales, and many other such-hke birds, arrive and 

 depart at certain times of the year : but there are doubtless 

 an enormous majority who regard this simply as a special 

 peculiarity appertaining to the British Isles — a kind of 

 dispensation of Providence to enable the Britisher to 

 realize that autumn and winter are upon him, or to give 

 him a pleasant thrill of expectation at the outward and 

 visible evidences of approaching spring and summer. 

 They have never thought, or never realized, that this same 

 nightingale is cheering the watcher anxious to hear its 

 notes once more in Copenhagen, Germany, and parts of 

 Russia, and, if we are not too particular about small 

 tspecific differences, even in far distant Persia. Nor, 

 perhaps, have they realized that the dweller in the United 

 States of America or Canada has, in just the same way, 

 his harbingers of spring, which arrive from the south, 

 and that he is no less joyful at their advent. 



And so it is, even on our little Swan Island, where at 

 least forty of its fifty species are there to escape the rigours 

 of more northern chmates, or simply put in an appearance 



D 



