Song sparrows, meadow larks (_Sturnella_), blue jays (_Cyanocitta
cristata_), and some other species make such short migrations that
the movement is difficult to detect, as individuals may be found in
one area throughout the year. Thus, at the southern part of the range
there is merely a concentration in winter, the summer individuals
being entirely sedentary. Speculation is useless on the distances
of individual migration without definite evidence concerning the
precise winter quarters of birds that summer in a particular part of
the breeding range of the species, but from the records of banded
birds important evidence is becoming available. Eventually it may be
possible to say definitely just how far the song sparrows that nest
in northern New England and the Maritime Provinces of Canada travel
to their winter quarters, and whether the blue jays of New York and
the upper Mississippi Valley remain throughout the winter in their
breeding areas, or move farther south and relinquish their places to
individuals from southern Canada.
An illustration of what is now known on this subject is found in the
case of the robin. This bird occurs in the Middle Atlantic States
throughout the year, in Canada only in summer, and along the Gulf
coast only as a winter resident. On the Atlantic coast its movements
are readily ascertained, since, for example, in the section about
Washington, D. C., the breeding robin is the southern variety
(_Turdus migratorius achrusterus_), which is found there from the
first of April to the last of October, when its place is taken (in
smaller numbers) by the northern robin (_T. m. migratorius_), which
arrives about the middle of October and remains until the following
April. It is probable that a similar interchange of individual robins
occurs throughout a large part of the rest of its range, the hardy
birds from the north being the winter tenants in the abandoned summer
homes of the southern birds.
The red-winged blackbirds that nest in northern Texas are almost
sedentary, but in winter they are joined by representatives of other
subspecies that nest as far north as the Mackenzie Valley.