190 
6,000 miles south to Argentina, while the 
others make a 3,000-mile flight directly 
south to their winter home in Hawai. 
THE WORLD'S MOST EXTRAORDINARY 
TRAVELER 
The shore-birds, such as the golden 
plover, present the longest migration 
routes among land-feeding birds; but 
even their surprising records are sur- 
passed by some of the birds which glean 
their living from the waters. The world’s 
migration champion is the Arctic tern 
(page t91). It deserves its title of Arc- 
tic, for it nests as far north as land has 
been discovered; that is, as far north as 
the bird can find anything stable on which 
to construct its nest. 
Indeed, so Arctic are the conditions 
under which it breeds that the first nest 
found by man in this region, only 7% 
degrees from the Pole, contained a downy 
chick surrounded by a wall of newly 
fallen snow that had been scooped out of 
the nest by the parent. 
When the young are full grown the 
entire family leaves the Arctic, and sev- 
eral months later they are found skirting 
the edge of the Antarctic continent. 
What their track is over that 11,000 
miles of intervening space no one knows. 
A few scattered individuals have been 
noted along the United States coast south 
to Long Island, but the great flocks of 
thousands. and thousands of these terns 
which alternate from one Pole to the 
other have never been met by any trained 
ornithologist competent to learn their 
preferred path and their time schedule. 
The Arctic terns arrive in the far north 
about June 15 and leave about August 
25, thus staying 14 weeks at the nesting 
site. ‘They probably spend a few weeks 
longer in the winter than in the sum- 
mer home; and, if so, this leaves them 
scarcely 20 weeks for the round trip of 
22,000 miles. Not less than 150 miles in 
a straight line must be their daily task, 
and this is undoubtedly multiplied sev- 
eral times by their zigzag twistings and 
turnings in pursuit of food. 
The Arctic terns have more hours of 
daylight and sunlight than any other ani- 
mals on the globe. At their most north- 
ern nesting site, the midnight sun has 
OUR GREATEST TRAVELERS 
already appeared before their arrival, 
and it never sets during their entire stay 
at the breeding grounds. During two 
months of their sojourn in the Antarctic 
they do not see a sunset, and for the 
rest of the time the sun dips only a little 
way below the horizon and broad day- 
light continues all night. The birds 
therefore have 24 hours of daylight for 
at least eight months in the year, and 
during the other four months have con- 
siderably more daylight than darkness. 
THE MOVEMENTS OF THE ROBIN 
The number of miles traveled per day 
by a migrating bird varies greatly in dif- 
ferent parts of the migration journey. 
These variations are intimately con- 
nected with corresponding variations in 
the speed of the northward march of 
spring, and are based primarily on two 
facts: First, that the interior of a conti- 
nent warms up faster than the coasts; 
second, that spring is hastened in western 
North America by the Japan current, 
while it is as decidedly retarded in the 
east by the polar current. 
The results of these two causes are 
strikingly shown in the migration of the 
robin (page 192). This bird differs from 
most others in that throughout its entire 
course northward it adopts spring’s time- 
table for its own. 
The robin’s average temperature of 
migration is 35° F.; that is, it puts in 
an appearance soon after the snow be- 
gins to melt and streams to open, but 
before vegetation has made any start. 
These conditions occur in the central 
Mississippi Valley about the middle of 
February, and it is the first of March be- 
fore spring and the robins cross northern 
Missouri and arrive together in southern 
Iowa. Thence a whole month is con- 
sumed by the birds in their slow prog- 
ress—13 miles a day—to central Minne- 
sota. There their pace quickens, to keep 
up with the northward rush of spring, 
and another 10 days at doubled speed 
brings them to southern Canada. 
Here they must make an important 
choice. To the north and northeast lies 
a land that awakens slowly from its win- 
ter’s sleep, and where the sun must wage 
a protracted contest against the cold of 
