Have you ever seen a group of birds flying overhead and wondered where they're going?

你是否曾經看過一群鳥從頭頂飛過，而想知道他們要飛向何方？

Why can birds fly hundreds or thousands of miles to a feeding ground, while I get lost on the way to the store?

為什麼鳥兒可以飛數百或數千英里，到達它們想要去的覓食地，而我卻會在前往商店的途中迷路？

How do they know which way is north or south?

他們怎麼知道哪個方向才是北方或是南方？

I looked into this question and found some surprising answers.

我研究了這個問題，並找到了一些令人驚訝的答案。

Let's look at the interesting ways that birds navigate.

讓我們來看看鳥類奇特的導航方式。

Many birds fly between areas with lots of food.

許多鳥類在食物豐富的地區之間飛行。

Parrots fly a few hundred miles.

鸚鵡飛了幾百英里。

Canada geese fly 2 to 3 thousand miles in their annual migration.

加拿大鵝每年的遷徙要飛行 2 至 3 千英里。

And Arctic Terns take the prize for most ridiculously long migration by flying a 12,000 mile migration from the Arctic to the Antarctic circle.

北極燕鷗從北極圈到南極圈總共飛行 12000 英里，使牠贏得了最不可思議之長距離遷徙的冠軍。

But we're not here to talk about migration.

但今天我們不是來討論遷徙的。

We're here to talk about how they maintain the sense of direction as they travel.

我們是要討論，牠們如何在飛行時還能保持方向感。

Dead Reckoning. First off, and most simple, is the White Crowned Sparrow.

先說「航位推算法」，最簡單的也最具代表性的鳥類就是白冠帶鵐。

They use dead reckoning.

牠們就是使用航位推算法。

That means they know which direction to travel, and they know how long to travel that direction.

這意味著牠們知道要飛行的方向，也知道朝這個方向要飛行多久。

But they don't know what their destination is.

但牠們不知道的目的地是何處。

Some researchers did an experiment.

一些研究人員做了一個實驗。

They captured White-crowned Sparrows migrating due south between Washington and Southern California.

他們捕獲了正在從華盛頓州往南遷到南加州的白冠帶鵐。

They loaded them onto airplanes and flew them across the country to New Jersey.

研究人員把牠們裝上飛機，橫越美國飛到新澤西州。

The birds continued migrating.

然後讓鳥兒繼續牠們的遷徙之旅。

Juvenile sparrows that had never migrated before just continued flying south as if nothing happened.

從未遷徙過的幼鳥只是繼續往南方飛去，好像什麼事也沒發生過似的。

So we are pretty sure that they have a built-in set of migration instructions.

所以我們非常確定，牠們體內有一套機制會發出遷徙指令。

Fly south for roughly so long, you'll end up where you need to be with all the other White-crowned sparrows.

告訴牠們向南飛大約多久，就會到達目的地與所有其他的白冠帶鵐會合。

An interesting effect was noticed in that experiment.

在這個實驗中他們發現了一件有趣的事。

While juvenile white-crowned sparrows did not react to their plane flight, adults almost universally noticed that something happened.

雖然幼鳥對於搭乘飛機這一段旅途沒啥反應，但是老鳥卻幾乎普遍地意識到有事情發生了。

So adults either headed southwest, correctly compensating for their cross-country detour and aiming toward Southern California.

所以老鳥們不是將路線重新修正後繼續往南飛，朝南加州飛去，

Or they went due west, which aimed them back toward their original migration path.

不然就是飛向西方。飛回到牠們原始預定要飛的航路上。

So what did the adult sparrows use to determine that they were in the wrong place?

那麼，老鳥到底是怎麼知道牠們到了錯誤的地方呢？

Scientists have looked at several different possible answers.

科學家歸納了幾種可能的答案。

Sun compass. Birds can look at the sun and figure out which direction to go.

太陽導航。鳥類會依太陽的方位計算出牠們要飛往的方向。

This is more difficult than it sounds, because obviously the sun changes position throughout the day.

這看似簡單其實不然，因為一天之中，太陽的方位是一直在變化的。

So for this to work, birds need both the ability to see the sun and an internal clock so they know exactly what time it is and therefore where the sun should be.

為了能夠發揮這項功能，鳥類必須具備看到太陽的能力，以及有一個體內生理時鐘，如此他們才能確切地知道，在什麼時間太陽會在哪個位置。

Researchers trained European Starlings to get food from a feeder in a particular compass direction.

研究人員訓練歐洲八哥，從特定方位的餵食器獲取食物。

Then, using a mirror, they flipped the apparent position of the sun.

然後，他們利用鏡子將太陽的位置反射在另一邊。

The bird responded by checking the feeder in the opposite direction of what it was trained.

這隻鳥的反應是，牠會去找反方向的餵食器，而不是平日被訓練取食的餵食器。

Further experiments like this found that birds are able to compensate for time of day, latitude, and season.

類似的實驗進一步發現，鳥類能夠依緯度、季節和一日中不同的時間點來修正牠的方向感。

So, looking good that birds have a sun compass.

所以，似乎不錯—鳥類有太陽導航的本能。

Star compass. Not only do birds use obvious information like the sun, they are able to use the position of stars to navigate!

星座導航。鳥類不僅能利用大自然中明顯的訊息，像是太陽；牠們還可以利用星星的位置來導航！

Researchers put birds in a planetarium and projected a starry sky for the birds to look at.

研究人員將鳥類放入天文館，並投射出星空，讓鳥類可以看到。

But the stars in their projection were rotated, meaning that the northern constellations were in the East.

但他們投射出的星星的方位是旋轉後的，這意味著實際位於北方的星座卻顯示在東方。

The birds may have been confused, but they adapted quickly and oriented in the new "correct" direction and moved toward the new "south" for their migration.

這些鳥兒的方向感可能已經被搞混了，但是牠們很快地就適應了，並導向新的「正確」方向，然後朝向新的「南方」遷徙。

Birds didn't seem to use the North Star, but did use constellations.

鳥兒似乎沒在利用北極星，但確實利用了星座。

The use of constellations means that they could use this ability even in the southern hemisphere, where they can't see the north star.

利用星座意味著，牠們甚至可以在南半球—那裡看不到北極星—發揮這種能力。

Unfamiliar constellations were useless to the birds, which means that they learn constellations as they migrate and use them to navigate on future migrations.

不熟悉的星座對鳥類而言是毫無用處的，這意味著牠們一面遷徙，一面在認識星座，未來的遷徙就可以利用星座來導航。

Magnetic compass. We use magnetic compasses like this one all the time, and so do birds.

磁場導航。我們一直在使用這種磁羅盤，而鳥類也是如此。

Magnetic compasses respond to the Earth's magnetic field.

磁羅盤會依地球磁場而變化。

Researchers put birds in weak artificial magnetic fields and the birds reacted as it changed direction and intensity.

研究人員將鳥類置於微弱的人造磁場中，在改變磁場方向和強度時，鳥兒也會有相對的反應。

We're not sure exactly how birds sense the Earth's magnetic field at this time.

我們目前還不清楚，鳥類究竟是如何感知地球磁場的。

There's evidence to support the sense as located in their beak, ears or eyes.

有證據支持一種說法，就是這牠們的感知，是來自於喙，耳朵或眼睛。

Personally, I like the idea of them seeing magnetic fields with special eye cells, because it would be such a cool sense to have.

就我個人而言，我喜歡牠們用特殊眼細胞來感知磁場的說法，因為這種能力超酷的。

But for now, we don't know for sure.

但到目前為止，我們還不知道真正的原因。

Scientists have discovered other methods used by birds.

科學家們還發現了鳥類所使用其他的導航方法。

Landmarks are important.

地標是很重要的。

Birds use rivers, mountains, and forests to find their way along a migration route.

鳥類會利用河流，山脈和叢林，在牠們遷徙的路線上來定位。

Some birds appear to use smell landmarks, sniffing their way across a map of familiar smells.

有些鳥似乎使用嗅覺地標，循著熟悉的氣味前進。

They also use polarized light that passes through clouds if they can't see the sun or stars due to weather.

如果因天氣原因無法看到太陽或星星，牠們也會利用可穿透雲層的偏光。

There may be even more senses that we don't know about.

可能還有更多我們不知道的感知方式。

Thanks for taking the time to learn about bird navigation.

感謝您抽出寶貴的時間來了解鳥類導航。

I hope you enjoyed your time here.

希望您喜歡今天的影片。

If you did, navigate to the subscribe button below so you don't miss future videos.

如果你喜歡，請按下面的訂閱按鈕，這樣您就不會錯過以後的影片。

Thanks and have a great day!

謝謝，祝你有美好的一天！