They follow the sun in a dailymigration that feeds their passengers and ensures their own survival. (?
它们每天跟着阳光迁移，不仅确保了自己生命的延续，而且也成为过往‘旅客’的美餐。
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But daily vertical movements by zooplankton in the ocean—upward by night to seek food, downward by day to escape predators—can also be considered migration.
但是海洋中浮游动物每天的垂直运动——夜里上浮以寻找食物，白天下潜以躲避捕食者——也可以被视作迁徒。
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Fear of predators doesn't just affect the penguins' daily activities, however. It also influences the birds' migration patterns, Ainley and Ballard report this week in Polar Biology.