190 



OUR GRKATl^ST '1M<A\ l-.l.l'.KS 



6.000 miles south to Arj^cntina. while the 

 others make a 3.000-mile flight directly 

 south to their winter home in Hawaii. 



TIIK world's most i;x'l'K.\oRliIXARV 



tra\'i;ij;r 



The shore-hirds, 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 191). 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. 



AMiat 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 



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. 



TIIi; 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 northw^ard 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 



