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Why Do Our Birds Migrate. 



D. W. Dennis. 



It is insectivorous and "therefore" a migrant, is a common phrase in 

 literature about migrants ; it is the purpose of this brief paper to take 

 the therefore out of of this sentence ; to maintain that what a bird eats has 

 nothing to do with the great bird movement from the south to the north 

 in the spring and back again in the fall after breeding. 



The Pennsylvania reed bird, the bobolink, doubtless stops at the reed 

 swamps in Pennsylvania for refreshments on its way south ; the South 

 Carolina rice bird, another name for the bobolink, takes toll of the rice 

 swamps ; but no one thinks that the reeds or the rice are the cause 

 of the migrations. Surely if they had not wings, they could hardly fly 

 from the equator to Manitoba, but this does not make their wings the 

 cause of the journey ; nor is their food the cause. 



It is stoutly maintained that climate is the cause. This, like wings 

 and food, renders the journey possible; but it cannot in all cases cause 

 it, for many water birds, like the gannet and the petrel, go to their breed- 

 ing grounds from colder to warmer water and many from warmer to 

 colder. They go to inhospitable, inaccessible rocks that they may nest in 

 a place of safety, as I believe. 



I was impressed at Wood's Hole in the summer of 1901 to see tern 

 flying by in great numbers every morning. Later I visited their breeding 

 grounds at Penikese ; they were flying by Wood's Hole to get food for the 

 day ; they had not come to Penikese for food, for they came in such num- 

 bers that they overtaxed the fishing grounds for more than twenty miles 

 to the eastward. They had not come for climate, for they had come from 

 all available areas, colder as well as warmer. Perhaps it is admitted that 

 they came to lay their eggs and rear their young safe from destructive 

 mammals, including boys. 



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