. The book of birds, common birds of town and country and American game birds . y shown in the migration of therobin (page 192). This bird differs frommost others in that throughout its entirecourse northward it adopts springs time-table for its own. The robins average temperature ofmigration is 35° F. ; that is. it puts inan appearance soon after the snow be-gins to melt and streams to open, butbefore vegetation has made any conditions occur in the centralMississippi Valley about the middle ofFebruary, and it is the first of Marchbefore spring and the robins cross north-ern Missou
. The book of birds, common birds of town and country and American game birds . y shown in the migration of therobin (page 192). This bird differs frommost others in that throughout its entirecourse northward it adopts springs time-table for its own. The robins average temperature ofmigration is 35° F. ; that is. it puts inan appearance soon after the snow be-gins to melt and streams to open, butbefore vegetation has made any conditions occur in the centralMississippi Valley about the middle ofFebruary, and it is the first of Marchbefore spring and the robins cross north-ern Missouri and arrive together insouthern Iowa. Thence a whole monthis consumed by the birds in their slowprogress—13 miles a day — to centralMinnesota. There their pace quickens,to keep up with the northward rush ofspring, and another 10 days at doubledspeed brings them to southern Canada. Here they must make an importantchoice. To the north and northeast liesa land that awakens slowly from its win-ters sleep, and where the sun must wagea protracted contest against the cold of. MAP SHOWING SUMMER AND WINTER HOMES OE THE BIRD THAT HATES DARKNESS The summer home of the Arctic tern is along the Arctic coast of North America; itswinter home within the Antarctic Circle, 11,000 miles away. During eight months of the yearthe bird lives where the sun does not go below the horizon. The track of the tern in itsround journey of 22,000 miles is unknown (see page 190). 191 192 OUR GREATEST
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