and the Maritime Provinces. 277 



would hasten to occupy any section which offered food for them, and both 

 insects and plants would do this. The birds which occupy the new section 

 would in time remain and breed there, even if they did not do so at first. 

 Now let us remember that even during that season of cold there still were 

 seasons, and that with each recurring winter the ice advanced somewhat 

 toward the south. The ice and cold near it would drive the birds back- 

 ward again, and naturally they would return to their birthplace and their 

 young would as naturally follow them. With the retreating cold in the 

 following spring, the birds which had formerly bred further north would 

 naturally return to their former breeding-ground, and the young to their 

 birthplace, and all with their progeny would again have to retreat before 

 the cold in the autumn. Thus an incipient migration began, which in 

 time became hereditary, or, to use a synonymous term, instinctive. 



Of course these migrations were very short at first, only a few miles 

 in length, for the change in the climatic conditions must have been slow ; 

 yet they were the beginning of migration with all its seeming mystery. 



One of the difficulties with which this theory has to contend is that 

 some birds now pass over large bodies of water ; but we can have little 

 doubt that they at first went around them, and little by little, as the migra- 

 tory instinct became more strongly fixed, they learned to cross the water. 

 Many of our species now, in going as far south as northern South America, 

 reach that place by going around the Gulf of Mexico and the Caribbean 

 sea by the way of Mexico and Central America. 



That birds have a strong love for localities, no one who has studied 

 them at all can doubt, and they will return to breed in given localities even 

 though they are constantly persecuted there. Twenty-five years ago I found 

 the gannets and razor-billed auks breeding on Bird rock in the Gulf of St. 

 Lawrence. There they were slaughtered by hundreds by the fishermen. 

 This persecution had been carried on for years, and has doubtless con- 

 tinued ever since ; yet according to reports of recent visitors the number 

 of the birds has not greatly diminished. 



The instinct for migration once established, this love for locality in 

 which they have bred will induce these birds to return to it year after year, 

 while the young return as near as their parents will permit them to their 

 birthplace. 



Now why is it that birds migrate northward with such regularity as 

 regards time ? The answer is easy to one who has seen them leave their 

 winter quarters. Birds breed very regularly, all of any particular species 

 beginning to lay within a few days of each other. It is the beginning of 

 the enlargement of the reproductive organs, which shrink much after the 

 breeding season is over, that induces birds to begin to migrate northward ; 

 and at this time the males generally begin to sing, so that when we hear 

 their songs we know that they will soon migrate. 



