46 BULLETIN 185, U. S. DEPARTMENT OF AGRICULTURE. 



together in southern Iowa. Thence a whole month is consumed by 

 the birds in their slow progress (13 miles a day) to central Minnesota. 

 Their pace then 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 winter's sleep, 

 and where the sun must wage a protracted warfare against the cold of 

 the ice masses in Lake Superior and Hudson Bay. To the northwest 

 stretches a less forbidding region already quickening under the 

 influence of the Chinook winds. 



Most of the robins from Missouri that pass through western Minne- 

 sota elect to turn to the northwest, and now they must not only keep 

 pace mth the rapidly advancing season but must do so on a long- 

 drawn diagonal. Their daily average rises to 50 miles (four times 

 that in southern Iowa) and later, when the course of the birds 

 bound for western Alaska becomes nearly due west, the rate in- 

 creases to 70 miles a day — more than six times the speed mth which 

 the journey began. The Alaska-breeding robins are the only ones 

 that develop high speed. Robins bound for Newfoundland move 

 leisurely along the Atlantic coast at the proverbially slow rate of the 

 oncoming of spring in, New England, and, scarcely exceeding 17 miles 

 a day, they finally arrive at their destination the first week in May, 

 when their Alaska-bound relatives are already 1,200 miles farther 

 north. 



An interesting migration route is that of the robins nesting in 

 southern Alberta, which arrive too early to have come from the 

 south and southeast; hence they must have come from the south- 

 west, though this route has necessitated their crossing the main 

 range of the Rockies while the mountains were still in the grasp of 

 winter. Robins remain aU winter on the Pacific coast, north to 

 southwestern British Columbia, which has about the same winter 

 temperature as St. Louis, 700 miles farther south. Hence the win- 

 tering robins of British Columbia are already far north at the advent 

 of spring and do not need any hurried migration to reach Alberta on 

 time, so that they average only 8 miles a day, the slowest rate for 

 the species. It may fairly be asked. How do we know that the 

 Alaska robins have come all this long distance from the central 

 Mississippi VaUey, instead of the far shorter distance from British 

 Columbia ? It happens that the robins of the two sides of the conti- 

 nent slightly differ in color and in pattern of coloration. Birds of 

 the western style are not known north of southwestern Saskatche- 

 wan, central British Columbia, and southeastern Alaska, while the 

 whole country to the northward is occupied by birds whose charac- 

 teristics prove that they came from the southeast. 



