THE TRAVELS OF BIRDS 



dates of the arrival and departure of all the 

 migratory birds which visit him. 



In this time-table we will notice that the early 

 birds those which come in March are much 

 less prompt than the later ones those which 

 come in May. This is because the weather of 

 March is so much more uncertain than that of 

 May. In some years, near New York City, 

 snow covers the ground and the ponds are frozen 

 almost until April. In others, the snow melts 

 and the ice disappears before the middle of 

 March. But by May i, the weather is more 

 settled. The first week in May of one year is 

 much like the first week in May of another year. 



So it follows that the exact time of the arrival 

 of the birds is more or less dependent on the 

 weather. But it is not the weather which in- 

 duces them to start. What can the Baltimore 

 Oriole in Central America know about the 

 weather near New York City? Not a thing. He 

 leaves Central America without regard to the 

 weather there or any other place. But his jour- 

 ney may be delayed by bad weather or hastened 

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