HOW DO BIRDS KNOW WHERE TO MIGRATE?
鳥類如何知道遷徙到哪裡？
It's long been one of nature's greatest mysteries: how do birds know where to gofor the winter? If most humans tried to migrate south without a map or a GPS, we'd probably end up in Nova Scotia.
長期以來，這一直是自然界最大的謎團之一：鳥怎麼知道冬天該去哪裡？如果大多數人試圖在沒有地圖或GPS系統的情況下向南遷徙，我們最終可能會走到加拿大新斯科舍。
Scientists have been trying to solvethis mystery for a long time. Even Aristotle, renowned smart person, was baffled. Mental Floss thought birds just changed species for the winter, which is a handy way of explaining why the garden warbler population gets replaced by a bunch of blackcaps when the weather starts to change. So, maybe he wasn't actually as smart as we all thought he was.
長期以來，科學家們一直試圖解開這個謎。甚至有名聰明的人亞里斯多德也感到困惑。而Mental Floss認為鳥類只是在冬季改變了物種，這簡單粗暴地解釋了為什麼當天氣開始變化時，花園內鶯群會被一群黑頭所取代。所以，也許他沒有我們想像的那麼聰明。
Some species of bird are known to migrate ridiculously longdistances — the arctic tern travels from Greenland to Antarctica, which is roughly 44,000 miles. And you thought it was tough walking from the back of the parking lot all the way to the front door of Target.
一些鳥類的遷徙距離很長——北極燕鷗從格陵蘭島到南極洲，大約有44000英裡。而你會覺得從停車場後面走到塔基特超市的前門都很困難。
So how do they do it? The answer is, well…we still don't really know. We do have some clues, though. Birds undergobehavioral changes that appear to be triggered by photoreceptors in their brains. As the days get shorter, they eat more and become restless, and this happens even if they're kept in a cage. But still: how do they actually know where to go? A 1978 study found that captive birds that couldn't see the sky still experienced migratory restlessness, and preferred to fly in the same direction as non-captive birds of the same species. Researchers concluded that they were using "external orienting cues, probably of the earth's magnetic field."
他們是怎麼做到的？答案是，嗯……我們還是不知道。不過，我們確實有一些線索。鳥類的行為變化似乎是由它們大腦中的感光器觸發的。隨著白天變短，它們吃得更多，變得不安，即使它們被關在籠子裡，這種情況也會發生。但是：他們怎麼知道該去哪裡？1978年的一項研究發現，看不見天空的圈養鳥類仍然經歷著遷徙不安，它們更喜歡與同一物種的非圈養鳥類朝同一方向飛行。研究人員得出結論，他們使用的是「外部定向信號，可能是地球磁場的信號。」
Just how they're able to sensethat magnetic field is still the subject of research, though. National Geographic explains that some species have special molecules in their eyes that can sense planet Earth's magnetic field. Those molecules are linked to the parts of the animals' brains that process visual input, which means they can literally see the Earth's magnetic field. Other birds seem to have different ways of knowing where to go. Pigeons may use their sense of smell to guide them, and some other species just learn their migration patterns from the previous generation.
然而，他們如何能夠感知磁場仍然是研究的主題。《國家地理》解釋說，有些物種的眼睛中有特殊的分子，可以感知地球磁場。這些分子與動物大腦中處理視覺輸入的部分相連，這意味著它們可以從字面上看到地球磁場。其他鳥類似乎有不同的方法知道去哪裡。鴿子可能會用它們的嗅覺來引導它們，而其他一些物種只是從上一代學到它們的遷徙模式。
The methods different birds use to get to the right place also appears to beinfluenced by genetics. In 2008, researchers decided to confuse the heck out of a bunch of poor birds by crossbreeding species with different migratory patterns and then laughing while their offspring blundered around in the sky trying to figure out where they were supposed to go. The result was a bunch of birds who tried to take the middle road between each parent's migratory path.
不同鳥類到達正確位置的方法似乎也受到遺傳的影響。2008年，研究人員決定將一群可憐的鳥類與不同遷徙模式的鳥雜交，使它們混為一體，然後在它們的後代在天空中蹣跚而行，試圖弄清它們應該去哪裡的時候大笑起來。結果是，一群鳥試圖走在父母遷徙路線之間的中間道路。
So at the end of the day, we're a little closer to understanding how birds do that amazing thing they do every winter, even though we still have to work outsome of the details. At least we've pretty much ruled out the whole changing species thing. Sorry, Aristotle.
所以在一天結束的時候，我們更接近於理解鳥類是如何在冬天做這些令人驚奇的事情的，儘管我們仍然需要解決一些細節問題。至少我們已經基本上排除了整個物種變化的可能性。抱歉！亞里斯多德。
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