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Science and technology
科學技術
How dung beetles navigate
蜣螂如何導航
Stars in their eyes
眼里有星辰
An insect that steers by the Milky Way
觀天識途的昆蟲
THE number of animals that navigate by the stars is small.
靠觀察星辰行走的動物不多。
Only some birds, a few seals and, of course, humans have the ability.
僅僅有某些鳥類、海豹，當然人也有這個本事。
It had been assumed that other creatures that might do this would need reasonably well-developed brains.
過去人們設想其他具備這種能力的生物很可能擁有發達的大腦。
That notion has now been proved wrong as the celestial-navigation club welcomes its latest member: the humble dung beetle.
現在這種見解被推翻了，因為天文導航俱樂部迎來了自己最新的成員—不起眼的蜣螂。
Life in the world of dung beetles is fiercely competitive.
蜣螂在這個世界上過著你爭我奪的生活。
After rolling up a ball of highly nutritious dung, the beetle must race off with it or risk having the ball stolen by other beetles.
蜣螂必須把自己團好的極富營養的糞球搬走，否則勞動成果會被其他的蜣螂偷走。
Strength is important, but so too is the route taken.
力量很重要，運輸路線也不能輕視。
The ideal tactic on the open plains where many dung beetles live is to move in a straight line.
很多生活在廣闊平原上的蜣螂采用走直路的理想策略。
This is easy enough during the day, but at night—when the beetles are most active—it is more challenging.
這在白天不難辦到，然而晚上才是蜣螂最活躍的時間，此時走直路對它們來說就是挑戰了。
Previous work has shown that dung beetles can make use of the moon to help them navigate, yet some still set a straight course on moonless nights.
以前人們發現蜣螂利用月亮導航，如果晚上沒有月亮，也有蜣螂走直路。
To find out how, a team working in South Africa led by Eric Warrant and Marie Dacke, of Lund University in Sweden, designed an intriguing experiment.
為了找到蜣螂夜里能走直路的原因，Eric Warrant和Marie Dacke領導的瑞典隆德大學工作團在南非設計了一個有意思的試驗。
They made caps for 19 dung beetles.
他們給19只蜣螂做了帽子。
Ten wore caps made of cardboard to prevent them seeing the sky and, as a control, nine wore caps made of transparent plastic.
10只蜣螂戴著薄紙板做的帽子，這樣他們就看不到天空了。作為對比，其他9只蜣螂戴上了透明塑料制成的帽子。
The beetles and their dung balls were then released in the centre of a circular arena made of flattened sand and enclosed by a featureless circular wall.
這些蜣螂和它們的糞球都被放在了一個平鋪著沙子圓形場地的中央，場地的圍墻也沒有什么特別之處。
As the beetles rolled away under a moonless night sky they were filmed by infra-red cameras.
在沒有月亮的晚上，紅外線攝影機記錄蜣螂搬運糞球的活動。
The team found that the beetles prevented from seeing the sky by their caps had path lengths that averaged 476.7cm, much longer than the average of 143.4cm travelled by the beetles wearing clear hats.
試驗人員發現被帽子遮擋了天空的蜣螂平均行走476.7cm，遠遠超出戴著透明帽子的蜣螂的平均路程143.4cm。
As the beetles might have used other overhead landmarks, like trees,
因為蜣螂可能使用位于高處的其他地標。
a second arena was built with a high black wall and a small, dry moat around it.
第二個場地是黑色高墻圍起來的，
This time the beetles—minus their hats—were timed to see how long it took them to roll their balls from the centre to the point where they could be heard falling into the moat.
附近有一條干涸的壕溝—這次蜣螂沒有戴帽子—實驗人員要看看他們從場地中央滾糞球到跌入壕溝能用時多久。
Under a full moon the beetles took an average of 21.4 seconds to reach the moat.
滿月之夜蜣螂抵達壕溝平均耗時21.4秒。
On a moonless, starry night, their speed was somewhat reduced, but not significantly so.
在繁星滿天的無月之夜，它們的速度有所下降，但降得不多。
However, under overcast conditions, when neither moonlight nor the stars were visible, the beetles took an average of 117.4 seconds.
如果晚上陰天，看不到星星和月亮，蜣螂抵達目的地要平均耗時117.4秒。
Curious as to what it was in the sky that the beetles were using to navigate, the team moved their arena inside the Johannesburg planetarium and reran their experiments.
因為試驗人員急于了解蜣螂到底利用天上的什么物體導航，他們到約翰內斯堡天文館做室內實驗。
As they report in Current Biology, the beetles presented with a full starlit sky, including the Milky Way or just the Milky Way, took statistically the same amount of time to exit the arena.
他們在《當代生物學》雜志上統計了蜣螂在繁星滿天的夜空下走出場地用的時間在統計學上是相同的，
Under a sky full of dim stars they were only a little slower.
天上的星光不亮，它們要稍微慢一點。
This, speculates Dr Warrant, is because they were still able to spot the cluster that forms the Milky Way.
通過試驗Warrant,博士推測，這是因為蜣螂還能認出銀河系形成的星團。
When allowed to see only the 18 brightest stars or immersed in total darkness, the beetles took more than twice as long to exit the arena.
如果暗夜里只有18顆最亮的星星，蜣螂離開場地的時間要高出兩倍以上。
The team now wonders how many other animals might be able to use the glowing strip of light created by the Milky Way to guide them.
這個團隊的工作人員現在想知道到底有多少動物可以利用銀河系形成的發光帶活動。
