1893
Aug 5
(No 4)
Concord, Mass.

  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 go 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 [delete]particular[/delete]summer birds depend. Thus
a Warbler or Sparrow which breeds in Virginia
can safely take up its summer quarters there
a month or more [delete]before[/delete] 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 ready 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 [delete]times[/delete]dates of
migration in the South as compared with those
recorded at more northern stations - Mass 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 [delete]oth[/delete]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 their may be more or less passing. 
[margin]Thoughts on
Migration[/margin]