Vibrations in the ground are a poorly understood but probably widespread means of communication between animals.
It seems unlikely that these animals could have detected seismic① “pre-shocks” that were missed by the sensitive vibration-detecting equipment that clutters the world’s earthquake laboratories. But it is possible. And the fact that many animal species behave strangely before other natural events such as storms， and that they have the ability to detect others of their species at distances which the familiar human senses could not manage， is well established.
Such observations have led some to suggest that these animals have a kind of extra-sensory perception. What is more likely， though， is that they have an extra sense─a form of perception that people lack. The best guess is that they can feel and understand vibrations that are transmitted through the ground.
Almost all the research done into animal signalling has been on sight， hearing and smell， because these are senses that people possess. Humans have no sense organs designed specifically to detect terrestrial② vibrations. But， this anthropocentric③ approach has meant that interactions via vibrations of the ground (a means of communication known as seismic signalling) have been almost entirely over-looked. Such signals are far more common than biologists had realised─and that they could explain a lot of otherwise inexplicable④ features of animal behaviour.
Until now， the only large mammal known to produce seismic signals was the elephant seal， a species whose notoriously aggressive bulls slug it out on beaches around the world for possession of harems⑤ of females. But the scientist who is one of the speakers at the symposium， suspects that a number of large terestrial mammals， including rhinos⑥， lions and elephants also use vibration as a means of communication. At any rate they produce loud noises that are transmitted through both the ground and the air─and that can travel farther in the first than in the second. Elephants can transmit signals through the ground this way for distances of as much as 50km when they trumpet， make mock charges or stomp their feet.
A seismic sense could help to explain certain types of elephant behaviour. One is an apparent ability to detect thunderstorms well beyond the range that the sound of a storm can carry. Another is the foot-lifting that many elephants display prior to the arrival of another herd. Rather than scanning the horizon with their ears， elephants tend to freeze their posture and raise and lower a single foot. This probably helps them to work out from which direction the vibrations are travelling—rather as a person might stick a finger first in one ear and then in the other to work out the direction that a sound is coming from.
In the past decade many insects， spiders， scorpions， amphibians， reptiles and rodents， as well as large mammals， have been shown to use vibrations for purposes as diverse as territorial defence， mate location and prey detection. Lions， for example， have vibration detectors in their paws and probably use them in the same way as scorpions use their vibration detectors─to locate meals.
In order to try to work out how prairie⑦ mole crickets， a highly territorial species of burrowing⑧ insect， manage to space themselves out underground. But the crickets were actually more interested in her own footfalls than in the airborne⑨ music of their fellow crickets. This suggests that it is the seismic component of the song that the insects are picking up and using to distribute themselves.
This really has implications for such things as earthquake prediction is， of course， highly speculative⑩. This is a salutary reminder that the limitations of human senses can cause even competent scientists to overlook obvious lines of enquiry. Absence of evidence， it should always be remembered， is not evidence of absence.
① seismicadj. 地震的；因地震而引起的
② terrestrialadj. 地球的；陆地的
③ anthropocentricadj. 以人类为宇宙中心的；以人类观点解释宇宙万物的
④ inexplicableadj. 无法说明的；难以理解的，莫名其妙的
⑤ haremn. 妻妾；女眷们
⑥ rhinon. 犀牛(=rhinoceros)
⑦ prairien. 大草原；牧场\[C\]
⑧ burrowv. 在……挖洞(或通道)
⑨ airborneadj. 空中传播的，风媒的
⑩ speculativeadj. 思索的；推测的
动物特别的感知能力
地面的振动虽不为人类所了解，但却可能是动物间最广泛的沟通方式。
连全世界的地震实验室里摆放着的精密的震动监测仪都无法测出的地震前震，似乎也不会被动物所察觉。但是，这却是可能的。而且，许多动物在其他自然现象如暴风雨发生之前会有奇怪的表现，以及它们能够探查到远在人类所有的感知能力范围以外的同类，这种能力都是早已被确认了的。
这些观察结果使一些人相信，这些动物拥有某种特别的感知能力，一种人类所缺乏的感知能力。最可接受的猜想是，它们可以感受和理解通过地表传递的振动。
几乎所有对动物间信息传递的研究都集中于视觉、听觉和嗅觉，因为这些感官知觉是人类所拥有的。人类没有专门用于探查地面振动的感觉器官。但是，这种以人类为中心的研究方法意味着，通过地表的振动进行交流(一种被称作为地震信号的沟通方式)这一现象几乎被完完全全忽视了。这种信号的存在范围比生物学家现已意识到的要广泛许多——而且，就此可以解释许多过去令人费解的动物行为。
直到现在，人们所知的能够发出地震信号的大型哺乳类动物只有海象。其极富攻击性的雄性在全世界的海滩上为了争夺妻妾而相互争斗的特性是广为人知的。但包括犀牛、狮子和大象在内的众多大型陆栖哺乳动物也利用地面的振动作为交流的方式。至少有一点是肯定的，它们发出的响声既通过地表也通过空气传播，而前者的传播速度要比后者更快。当大象吼叫、摆出攻击的架势或者跺脚的时候，它们能将信号通过地面传送到远至50公里的地方。
震动感知能力可以帮助解释大象的某些行为。其一是，即使远在声音传播的距离之外，大象也显然有能力测知暴风雨的来临。另一现象是，在另一群大象到来之前，许多大象都会做出提脚的行动。它们不是用耳朵搜索地平线，而是保持静止，然后提起和放下一只脚。这种行为可能帮助它们确定振动来自哪个方向，就像一个人先用手指堵住一只耳朵、然后再堵住另一只来确定声音的方向一样。
在过去的十多年里，科学家发现许多昆虫、蜘蛛、蝎子、两栖动物、爬行类动物和啮齿类动物，以及大型的哺乳动物，都会利用振动来保卫领地，寻找配偶及发现猎物等。比如狮子在它们的爪子上就有感受振动的器官，其作用就像蝎子感受振动的器官一样，用以发现食物。
为了搞明白牧场蟋蟀这种领地特征明显的穴居昆虫是如何在地下划分领地。它们的叫声被录下来播放以使它们有反应。但是，它们对脚步声似乎比空中传来的同类的叫声更感兴趣。这说明，这些昆虫是依靠所接收的叫声中振动信号部分来划分领地的。
这些结论提醒我们，人类感知能力的局限会导致即使是能干的科学家也会因此而忽视那些显而易见的研究方向。