CHAPTER III 



The Evolution of Migrations 



It has been pointed out above that migrations are 

 being elaborated today and that we can see some- 

 thing of the process. Further, there is no reason to 

 beheve that the forces now at work are different 

 from those in operation in the early days of bird 

 evolution when the necessity for migration must 

 first have arisen. We may therefore commence by 

 examining, once again, the present state of certain 

 affairs in the northern section of the globe. 



There are some few species of northern birds that 

 we call migratory to which the term is not as un- 

 reservedly applicable as it is to the great majority. 

 The most outstanding of these is the mallard. 

 Although many migrants annually leave a few 

 individuals behind them in the fall there is reason 

 to believe that in most cases the laggards are 

 suffering from some anatomical defect that either 

 makes them heedless of the calls of migration or 

 unable to migrate. But a percentage of mallards, 

 under certain conditions quite a large one, appears 

 to be actually loath to leave the north. The species 

 is invariably the last to vacate the Province of 



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