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There's an old saying that if you think you're in danger, you might ought to sleep with one eye open.
老話講的好，如果你發覺自己處于危險之中，你會只睜著一只眼睡覺。
Well it turns out that many kinds of birds do just that.
事實上許多鳥類確實如此。
A group of scientists at Indiana State University studied mallard ducks to learn more about this trait.
印第安納州立大學的科學家們通過研究野鴨對它們的這一習性有了更深入的了解。
They filmed a row of ducks while they were sleeping.
他們在鴨子們睡覺時進行拍攝。
Sure enough they found that a good part of the time the ducks at the ends of the row kept the eye facing away from the group open,while the eye toward the other ducks closed in sleep.
果不其然，他們發現隊伍兩端的鴨子朝外的那只眼睛長時間睜著，而朝向其它鴨子的那只眼睛閉著睡覺。
The ducks within the row were more likely to close both of their eyes to sleep.
而隊列中間的鴨子們睡覺時則雙眼緊閉。
The ducks at the ends of the line were actually controlling which side of the brain stayed awake,and which dozed.
隊列兩端的鴨子實際上在控制哪邊的大腦保持清醒與休息。
They were engaging in what scientists call single-hemisphere sleep.
這是處于科學家們所稱的單邊睡眠狀態。
The eye controlled by the sleeping side of the brain closed, while the active side kept its eye open and onthe lookout.
被睡眠狀態大腦控制的眼睛閉上，而被運轉狀態大腦控制的眼睛睜開進行警戒。
You can see how this is good for the group and for the lookout duck as well.
這種習性對整個群體及放哨鴨子而言非常有幫助。
The group gets the protection from having someone pulling guard duty, while the guard duck is at least able to getsome rest.
鴨群通過一些鴨子放哨獲得保護，而同時放哨的鴨子得到了一些休息。
