28 CIRCULAR 363, U. S. DEPARTMENT OF AGRICULTURE 
one area throughout the year. Thus, at the southern part of the 
range there is merely a concentration in winter, the summer individ- 
uals 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 
vare readily ascertained, since, for example, in the section about 
Washington, D. C., the breeding robin is the southern variety (7urdus 
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 (7. 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. 
VARIABLE MIGRATIONS WITHIN SPECIES 
The difference in characters between subspecies has been used by 
students of migration to discover other interesting facts concerning 
variations of the migratory flight between closely related birds that 
breed in different latitudes. The familiar eastern fox sparrow 
(Passerella iliaca iliaca), for example, breeds from northwestern 
Alaska to Labrador, and in winter is found concentrated in the south- 
eastern part of the United States. It thus travels a long distance 
each year. On the west coast of the continent, however, slix sub- 
species of this bird breed in rather sharply delimited ranges, extend- 
ing from the region of Puget Sound and Vancouver Island to Unimak 
Island, at the end of the ‘Alaska Peninsula. One of these, known as 
the sooty fox sparrow (P. 7. fuliginosa), breeds in the Puget Sound 
area and makes practically no migration at all, while the other races, 
nesting on the coast of British Columbia and Alaska, are found in 
winter chiefly in California. The races that breed farthest north are 
in winter found farthest south, illustrating a tendency for those birds 
that are forced to migrate to pass over those so favorably located that 
they have no need to leave their breeding areas, while the northern 
birds settle for the winter in the unoccupied areas farther south 
(fig. 12). 
Another example of the same kind is found in the case of the 
Maryland yellowthroat (Geothlypis trichas) of the Atlantic coast. 
