OUR GREATEST TR.W^ELERS 



193 



the ice - masses in Lake Superior and 

 Hudson Bay. To the northwest stretches 

 a less forbidding region, already quick- 

 ening under tlie 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, thev 

 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 iJritish Columbia 

 are already far north at the advent of 

 spring and do not need any hurried mi- 

 gration to reach .\lberta on time. .\s a 

 fact, they average only 8 miles a day, the 

 slowest rate for the s])ecies. 



It may be fairly asked, I low do we 

 know that the .Alaska robins have come 

 all this long distance from the central 



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. 



Alost 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 WARULERS AND CLIFF SWALLOWS 



While tlie Alaska-breeding rol)ins start 

 oft' in February and spend nearlv 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 hitter's 90-day schedule has been 

 shortened b\- the warbler to 30 davs. 



The black - poll warbler furnishes a 

 striking example of .speed acceleration 

 during the latter jiart of migration. .\s 

 indicated on the map of his migration 

 route (page 183), between .Vpril 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 nuist strike out for 

 the north very early, since by March 10 

 it is alread} 2,500 miles from the winter 

 home, and yet is averaging only 25 miles 



