He's seen it in a pair of birds dozing side by side in the zoo and in a single pet bird sleeping by a mirror.

他在动物园里的一对并排打盹的鸟和一只在镜子旁睡觉的宠物鸟身上看到过。

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Keeping a single checklist may not be sufficient - twitchers often keep checklist for particular seasons or locations to keep track of just where they've seen the many birds on their life list.

对于他们，只记一份清单是不够的——“猎奇党”鸟人常常为不同的季节和不同的地点都单独列出一份清单，以便记录他们在哪儿看到的鸟最多。

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And,like birds they have a single opening with which they produce eggs, have sex and expel waste.

VOA: special.2009.07.07

Experiments suggest this is going on within single molecules in birds' eyes, and John Morton of University College London explained that the way birds sense it could be stranger still.

BBC: Perfume chemist

It says that the freeze could be the single biggest killer of birds since the Arctic snap of the early 1960s and has asked the public to help feed them.

BBC: Cold fuel payment increase urged

How is it that a three-year old knows how to play Angry Birds without needing a single adult to teach them?

FORBES: How Gamification Kills Classroom Training