OUR GREATEST TRAVELERS 



193 



the ice - masses in Lake Superior and 

 Hudson Bay. To the northwest stretches 

 a less forbidding region, ah"eady quick- 

 ening under the influence of the Cliinook 

 winds. 



THE E/\STERN ROBINS MOVE SLOWLY, THE 

 PACIFIC MUCH EASTER 



Most of tlie roljins from JMissouri that 

 pass througli western Alinnesota 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 iXIay 6, 

 when their 7\laska-bound relatives are al- 

 ready J ,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 rcmge 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. Llence 

 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 



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 Saskatchewran, 

 central British Columbia, and southeast- 

 ern Alaska, \\'hile 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-groinid 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 CLiEE SW;\LL0WS 



While the Alaska-breeding robins start 

 oiT 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. 

 Bv the first of May he arri\'es in central 

 Missouri, which the robins left 60 days 

 earlier, and yet he reaches northwestern 

 Alaska onlv 10 davs 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 a\-erage of 30 miles a day. The 

 next 10 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 fo'" 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 

 Iiome, and yet is averaging only 25 miles 



