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Ask any gradeschooler to imitate an owl1 and you'll probably get one of two responses: the giant, staring eyes or that amazingly swivel-prone neck. As it turns out, these two characteristic features are related; they are part of an overall system owls2 have for catching3 prey4.
To understand the connection, remember that owls are nocturnal birds: they hunt for food at twilight5 and even in the dark. Food for an owl may be something as large as a rabbit or as small and hard to see as a field mouse. Not only is this kind of meal difficult to spot, it also has a tendency to bolt away quickly at the slightest sound.
The owl overcomes these difficulties by having evolved a visual system that works even at great distances and in low light. This is partly the result of having large eyes that are set on a relatively6 flat face, thus increasing binocular vision. However, those big eyes don't move much in their sockets7, and the owl's total visual field is therefore reduced. At any given time, it only sees about one third as much as birds with eyes on either side of their heads.
That means the only thing to do is to be able to turn those staring eyes in any direction, without the noise that would be caused by actually getting up and moving. And now you can see how the staring eyes and swiveling neck work together: the owl's super-flexible spine8 allows it to remain silent while it scans 180 degrees on either side. Yes indeed -- from a forward-facing position, an owl can look entirely9 backwards10.
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1 owl | |
n.猫头鹰,枭 | |
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2 owls | |
n.猫头鹰( owl的名词复数 ) | |
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3 catching | |
adj.易传染的,有魅力的,迷人的,接住 | |
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4 prey | |
n.被掠食者,牺牲者,掠食;v.捕食,掠夺,折磨 | |
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5 twilight | |
n.暮光,黄昏;暮年,晚期,衰落时期 | |
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6 relatively | |
adv.比较...地,相对地 | |
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7 sockets | |
n.套接字,使应用程序能够读写与收发通讯协定(protocol)与资料的程序( Socket的名词复数 );孔( socket的名词复数 );(电器上的)插口;托座;凹穴 | |
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8 spine | |
n.脊柱,脊椎;(动植物的)刺;书脊 | |
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9 entirely | |
ad.全部地,完整地;完全地,彻底地 | |
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10 backwards | |
adv.往回地,向原处,倒,相反,前后倒置地 | |
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