大象用脚倾听

Elephants may be listening with their feet as well as with their ears, say researchers who are studying how well super-low frequency elephant song moves through the ground.

　　大象在用耳的同时，还能用脚倾听——研究大象超低频鸣叫地面传播的研究人员如是说。

　　For about 20 years it's been known that African elephants sing out and respond to calls so low that they are beyond human hearing. Until now, however, no one was sure if the rumbling calls were also moving through the Earth as seismic waves, possibly helping elephants communicate when there is too much noise above ground.

　　二十多年前科学家们就曾研究发现，非洲象会使用各种低频声音进行交谈，这些低频声音甚至连人的耳朵也无法捕捉到。然而，在此之前谁也不曾料到这种“交谈”会像地震波一样通过地表传播。当地面噪音过大时，大象们很有可能就是用这种方式进行交流。

　　"They are trying to prove the concept is possible," said elephant researcher Katy Payne of the Cornell University Bioacoustics Research Program, referring to a team of Stanford University researchers who have published a paper on seismic elephant infrasound calls in the current issue of Geophysical Research Letters.

　　《地球物理研究通讯》最近期发表了斯坦福大学的一组研究人员关于大象的地震波次声传播的一篇论文。康奈尔大学生物声学研究项目的大象研究人员Katy Payne正根据这篇论文进行实验，她说：“我们在试图证明这个设想是可行的”。

　　"We have several experiments going on right now to try to determine whether elephants perceive seismic cues via bone through their toenails and foot bones to their middle ear bones, or through vibration-detecting cells in the bottom of the foot," said Stanford's Caitlin O'Connell-Rodwell, now studying the matter in Namibia.

　　正在纳米比亚进行研究工作的斯坦福大学研究人员Caitlin O'Connell-Rodwell说：“我们目前正在进行数个实验，用以断定大象是否能通过趾甲、脚骨、中耳骨或者脚底的震动探测细胞来察觉到地震信号。”

　　What is clear from the Stanford team's earlier work with trained African elephants is that under ideal conditions, elephant infrasound calls can make seismic waves that can travel almost a mile and a half （two kilometers）.

　　在通过驯服的非洲象进行的较早的研究中，斯坦福大学研究小组已清楚：理想条件下，大象的次声吼叫能使震波传播两公里左右。

　　The seismic signals are identical to the elephant calls in the air, says O'Connell-Rodwell.

　　地震信号和大象在空气中的鸣叫是相同的，O'Connell-Rodwell说。

　　But are the elephants really picking up distant seismic calls through their feet?

　　但大象们真的通过脚接收了远端的地震信号吗？

　　"It seems evident from their behavior," said O'Connell-Rodwell.

　　“从它们的动作来看，这是很明显的，”O'Connell-Rodwell说。

　　Telltale behaviors that an elephant is listening to a call include standing very still and adjusting their ears, explained Payne.

　　Payne解释泄密的动作是：大象在倾听时，总是静静伫立，并且调整他们的耳朵。

　　But since infrasound in the air is known to travel much further then a mile and a half （two kilometers）, it's hard to be sure if elephants ever notice the seismic side of their calls or use them as a back up "line" on noisy days.

　　但因为次声在空气中传播的距离要远大于两公里，所以很难断定大象是否留意到了地震波的信息，还是只是在地表嘈杂的日子把它作为一条备份“专线”。

　　To sort that out, the Stanford team is now sending elephant calls through the ground only and watching the reactions of wild elephants to see if it catches their attention.

　　为了区分清楚，斯坦福的研究小组现在正通过只给大象发送地震波，然后通过观察野生动物的反映来判断他们是否留意到地震波传递的信息。

　　"We are now conducting seismic playback experiments in Etosha National Park, Namibia, that will tell us for sure if they detect the signals," said O'Connell-Rodwell.

　　O'Connell-Rodwell说：“我们目前在纳米比亚的Etosha国家公园进行地震波回放实验，很快就能确定它们是否察觉了信号。”

　　As for whether the ground can also get too noisy for seismic elephant songs, O'Connell-Rodwell says it's possible. Generators, vehicles and airplanes all can make a lot of seismic noise and can easily drown out elephant calls entirely.

　　谈到地表是否会因为别的震波而影响了大象的声音传播，O'Connell-Rodwell说这是可能的。发电机、车辆、飞机都能制造大量的地震波，而且轻易就把大象的声音完全盖过。