. Common birds of town and country . ssibility of resting is shown in this map. This isthe same distance as traversed by the Atlantic plover, but the latter can get to land when introuble. The dotted lines along the Arctic coast show the breeding range of the bird. 25, thus staying- 14 weeks at the nestingsite. They probably spend a few weekslonger in the winter than in the sum-mer home ; and, if so, this leaves themscarcely 20 weeks for the round trip of22,000 miles. Not less than 150 miles ina straight line must be their daily task,and this is undoubtedly multiplied sev-eral times by their z
. Common birds of town and country . ssibility of resting is shown in this map. This isthe same distance as traversed by the Atlantic plover, but the latter can get to land when introuble. The dotted lines along the Arctic coast show the breeding range of the bird. 25, thus staying- 14 weeks at the nestingsite. They probably spend a few weekslonger in the winter than in the sum-mer home ; and, if so, this leaves themscarcely 20 weeks for the round trip of22,000 miles. Not less than 150 miles ina straight line must be their daily task,and this is undoubtedly multiplied sev-eral times by their zigzag twistings andturnings in pursuit of food. The Arctic terns have more hours ofdaylight and sunlight than any other ani-mals on the globe. At their most north-ern nesting site, the midnight sun hasalready appeared before their arrival,and it never sets during their entire stayat the breeding grounds. During twomonths of their sojourn in the Antarcticthey do not see a sunset, and fur therest of the time the sun dips only a little. MAP SHOWING SUMMER AND WINTER HOMES OF 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 359}. 361 THE NATIONAL GEOGRAPHIC MAGAZINE way below the horizon and broad day-light continues all night. The birdstherefore have 24 hours of daylight forat least eight months in the year, andduring the other four months have con-siderably more daylight than darkness. THE MOVEMENTS OE THE ROBIN The number of miles traveled per dayby a migrating bird varies greatly in dif-ferent parts of the migration variations are intimately con-nected with corresponding variations inthe speed of the northward march ofspring, and are based primarily on twofacts : First, that th
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