The Birds’ Calendar 

of them is confined to their spring passage. It 
is a peculiar fact, for which I can find no ex- 
planation, that some species seem to choose a 
different route for the fall migration from that 
in the spring—passing to the north through the 
Atlantic States, and even near the coast in 
spring, but taking a more inland course on their 
return. The added fact that the fall migration 
is made in smaller flocks, and apparently with 
fewer delays on the route, accounts for their es- 
caping observation even when their course is the 
same. Strictly speaking, all birds not permanent 
in one place throughout the year are migrants ; 
but, for convenience in distinguishing this group 
from the other two, the term is commonly ap- 
plied only to those that neither summer nor 
winter with us, and can be seen only in transit. 
The approach of warm weather—the new 
impulse of life—starts them in successive flocks 
northward. Moving by easy stages, so that 
their advance accords with the later opening 
of spring in more northerly latitudes, they 
stop for a brief season here and there, and 
it is often several weeks before they reach 
their final destination. Evidently no one 
species moves in a body, as they seem to come 
in successive ‘‘ waves.’’ In making a tour of 
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