Thought s on 
^p^ration 
To sum the matter briefly, migratory land birds — 
species or individuals or both — which breed the furthest 
south are the first to leave their winter quarters and to 
reach their summer homes. They are also the first to g’o 
South in autumn. The explanation is very simple, viz. the 
more southern breeding stations are ready for occupancy long 
before the more northern ones are freed from snow and ice, 
or at least are in condition to supply the requisite amount 
and kind of food on which the summer birds depend. Thus 
a Warbler or Sparrow which breeds in Virginia can safely 
take up its summer quarters there a month or more earlier 
than can another of the same species or habits at Anticosti 
or Labrador. And breeding so much the earlier of the two, 
it is rea.dy to take its young southward at a much earlier 
date in autumn. The logic of these conclusions is irresistible 
and all the available data relating to the dates of migra¬ 
tion in the South as compared with those recorded at more 
northern stations — Massachusetts, for example — attest 
the probable truth of the theory as a whole. 
The individuals of any particular species must, 
during the spring migration, continually pass and perhaps 
repass each other as the successive flights push northward 
over or by places which have already been populated by 
their summer birds. In autumn, on the other hand, the flights 
must follow one another at least until the confines of the 
winter habitat have been reached after which there may be 
more or less passing. 
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