OUR GREATEST TRAVELERS 
the ice- masses in Lake Superior and 
Hudson Bay. To the northwest stretches 
a less forbidding region, already quick- 
ening under the influence of the Chinook 
winds. 
THE EASTERN ROBINS MOVE SLOWLY, THE 
PACIFIC MUCH FASTER 
Most of the robins from Missouri that 
pass through western Minnesota elect to 
turn to the northwest, and now they 
must not only keep pace with the rapidly 
advancing season, but must do so while 
traveling on a long-drawn-out diagonal. 
Their daily average rises to 50 miles— 
four times that in southern Iowa—and 
later, when for the birds bound for west- 
ern Alaska the course becomes nearly 
due west, the rate increases to 70 miles a 
day—more than six times the speed with 
which the journey began. 
The migration map of the robins shows 
that these Alaska-breeding birds are the 
only ones that develop high speed. The 
robins bound for Newfoundland move 
by easy stages along the Atlantic coast at 
the proverbially slow rate of the oncom- 
ing of spring in New England, and, 
scarcely exceeding 17 miles a day, they 
finally arrive at their destination May 6, 
when their Alaska-bound relatives are 
already 1,200 miles farther north. 
One of the most interesting things in- 
dicated on the map is the migration route 
of the robins who nest in southern Al- 
berta. They arrive too early to have 
come from the south or the southeast; 
hence they must have come from the 
southwest, though this has necessitated 
their’ crossing the main range of the 
Rockies while the mountains were still 
in the grasp of winter. Robins remain 
all winter on the Pacific coast, north to 
southwestern British Columbia, which 
has about the same winter temperature 
as St. Louis, 700 miles southward. Hence 
the wintering robins of British Columbia 
are already far north at the advent of 
spring and do not need any hurried mi- 
gration to reach Alberta on time. As a 
fact, they average only 8 miles a day, the 
slowest rate for the species. 
It may be fairly asked, How do we 
know that the Alaska robins have come 
all this long distance from the central 
193 
Mississippi Valley, instead of the far 
shorter distance from British Columbia? 
It happens that the robins of the two 
sides of the continent are slightly differ- 
ent in color and in pattern of coloration. 
Birds of the western style are not known 
north of southwestern Saskatchewan, 
central British Columbia, and southeast- 
ern Alaska, while the whole country to 
the northward is occupied by birds that 
evidently have come from the southeast. 
The heavy, solid line on the map shows 
the approximate meeting-ground of the 
two forms. 
Most migrants except the robins, 
ducks, and geese wait in their warm 
winter quarters until springtime is far 
advanced, and then, traveling swiftly, 
occupy only a few days in their vernal 
migration. The black-poll warbler is one 
of the best examples. 
THE WARBLERS AND CLIFF SWALLOWS 
While the Alaska-breeding robins start 
off in February and spend nearly 90 
days in going from central Missouri to 
western Alaska, the black-poll warbler 
remains in his tropical home during Feb- 
ruary and March, and is not seen in 
southern Florida until about April 20. 
By the first of May he arrives in central 
Missouri, which the robins left 60 days 
earlier, and yet he reaches northwestern 
Alaska only 10 days later than the robins. 
The latter’s 90-day schedule has been 
shortened by the warbler to 30 days. 
The black-poll warbler furnishes a 
striking example of speed acceleration 
during the latter part of migration. As 
indicated on the map of his migration 
route (page 183), between April 20 and 
April 30 he goes from central Missouri 
to central Iowa, a distance of 300 miles, 
or an average of 30 miles a day. The 
next ten days the rate rises to 100 miles 
a day, while during the last few days of 
migration a velocity of 300 miles a day 
is attained. 
In contrast, notice the dates, distances, 
and speeds indicated for the cliff swal- 
low on its migration-route map (page 
185). The swallow must strike out for 
the north very early, since by March 10 
it is already 2,500 miles from the winter 
home, and yet is averaging only 25 miles 
