20 CIRCULAR 363, U. 8. DEPARTMENT OF AGRICULTURE 
stretch of country that is crossed by advancing spring in 68 days. In 
this case, however, it does not mean that individual robins are neces- 
sarily slow, for probably the northward movement of the species 
depends upon the continual advance of birds from the rear, the first 
individuals arriving in a suitable locality remaining to nest, while the 
responsibility of the northward movement of the species is continued 
by those still to come. | mals: Bal, 
Special interest attaches to the great variation in the speed at which 
birds travel in different sections of the broad flyway extending from 
the Gulf of Mexico to the Arctic Ocean by way of the Mississippi and 
Mackenzie Valleys. The blackpoll warbler furnishes an excellent 
example (fig. 11). This species winters in north-central South Amer- 
ica and migrates in 
April across the West 
Indies to Florida. 
From this point some 
individuals fly north- 
west to the Mississippi 
Valley, north to Mani- 
toba, northwest to the 
Mackenzie River, and 
thence almost due west 
towestern Alaska. In 
tracing the long route 
of these birdsitis found 
that a fairly uniform 
average speed of 30 to 
35 miles a day is main- 
tained from the Gulf to 
Minnesota. Then 
comes a spurt, for a 
week later the black- 
polls have reached the 
central part of the 
Mackenzie Valley, and 
by the following week 
-— they are observed in 
FIGURE 10.—Blue goose, a late but rapid spring migrant that winters [01 thw estern Alaska. 
on the coast of Louisiana and breeds on Baffin and Southampton During the latter part 
Islands and flies between summer and winter areas practically f a 6 ‘i d 
without stops. Photograph by Paul W, Hoffman. or the journey, there- 
fore, many individuals 
must average more than 200 miles a day. They use 30 days 
in traveling from Florida to southern Minnesota, a distance of 
about 1,000 miles, and scarcely half that time to cover the remain- 
ing 2,500 miles to Alaska. It should be noted that the increased 
speed is directly associated with the change in direction, the north- 
and-south course in the Mississippi Valley being accomplished 
slowly, while the northwesterly course across Canada is made at 
a much greater speed. Increased speed across western Canada to 
Alaska is also shown by many other species. A study of all species 
traveling up the Mississippi Valley indicates an average speed of 
about 23 miles a day. From southern Minnesota to southern Mani- 
toba 16 species maintain an average speed of about 40 miles a day. 
