Notes on Migration in General 



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Notes on the Migration of Birds. 

 In Great Britain we see three phases of migration: The 

 summer residents, including such birds as the swallow and 

 cuckoo, which arrive in spring from warmer countries to the 

 south, and remain throughout the summer to breed, returning 

 again in the autumn to their former haunts. 



(2) The winter residents, such birds as the jack-snipe and 

 bean-goose, which arrive in winter from their summer breed- 

 ing grounds further north. These return to their old haunts 

 in spring. - - 



(3) The birds of passage, such birds as the sandpipers, 

 which rest for a short time on our shores during their journey 

 south in autumn,. 



It is the rule that all birds breed in the colder regions- of 

 their migration. 



The chief factor determining migration is the necessity of 

 a greater food supply, and next to this comes a change of 

 temperature.' 



As shown above, the general rule is that birds migrate 

 towards the Equator in autumn, and from it in spring.,. 



One very interesting result of the systematic investigations 

 of the British Bird Migration Committee is the discovery that 

 the courses of migrants often become circular. 



How do birds know where to go ? They seem to have an 

 extraordinary sense of direction, flying straight to their desti- 

 nation. It is an inherited instinct, and they have lingering 

 memories of landmarks that have long vanished. They cross 

 the Mediterranean by definite routes, either by the islands of 

 -the Grecian Archipelago, or across Corsica and Sardinia, or 

 over Gibraltar to Cetua, places that in the geological past 

 were connected by land. 



As a rule, the smaller birds keep nearer to the ground, and 

 in most cases many species travel together, but the cuckoo 

 and nightjar, with a few others, are very exclusive birds, and 

 prefer to migrate alone. It is supposed that the birds start at 

 night and feed by day, but this has not been fully confirmed. 

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