05/11/2018

A Stomp, A Roar, An Elephantquake?

11:36 minutes

Elephant walk.
Credit: Mortimer et al. 2018

An adult African elephant, the largest land animal on Earth, can weigh as much as two tons. Their activities—walking, playing, even bellowing—might shake the ground beneath them. But new research in the journal Current Biology this week finds that the signals from an elephant’s walk are capable of traveling as far as three kilometers, while a roaring bull, or male elephant, might be detectable a full six kilometers away with just seismological monitoring tools.

Biologist Beth Mortimer and seismologist Tarje Nissen-Meyer, both at the University of Oxford and co-authors of the new research, describe the signals they captured in the ground and explain how a network of seismological sensors might help us study elephants from a distance, and even protect endangered elephants from poaching. 

[Dusting off Voyager 1’s thrusters.]

A series of elephants walking past a geophone. Credit: Mortimer et al. 2018.

Bull elephant source rumbles
Bull elephant source rumbles at 200 meters, under high noise and a sandy terrain environment. The frequency (y axis) over time (x axis) where the color represents how loud each frequency is (blue = low through to red = high). Credit: Mortimer et al. 2018
six different line graphs of elephant vibrations
A rumble from a bull (A, B, C) versus each footfall in a fast walk (D, E, F) differs in recorded vertical ground velocity versus time (A, D), determined source function force versus time (B, E) and modelled propagation sampled at 200 m and 1000 m from the source (modelled with high noise on sandy terrain; C, F). Credit: from the journal Current Biology/CC-BY

Segment Guests

Beth Mortimer

Beth Mortimer is a research fellow in the Department of Biology at the University of Oxford in Oxford, United Kingdom.

Tarje Nissen-Meyer

Tarje Nissen-Meyer is an associate professor of Geophysics at the University of Oxford in Oxford, United Kingdom.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Later in the hour, we’re going to talk about the growing E coli outbreak in Romaine lettuce, and how farm food safety tests could use a bit of an update. But first, I want you to listen to a sound and guess what it is.

[SOUND PLAYING]

Yeah, it does sound like a heartbeat, but it is not. It is the seismic sound of an elephant walking. The vibrations in the Earth. Let me play it again.

[SOUND PLAYING]

Really cool, huh? That African elephant is the largest land animal still alive today, and more importantly for this story, they are the heaviest. They weigh up to two tons. So it might not surprise you to learn that we can listen to them in the shaking of the ground. And new research in the journal Current Biology this week reports that earthquake monitoring tools are capable not just of detecting elephants from distances up to 6 kilometers away, but also distinguishing what kind of behavior is being heard, whether the elephant is walking quickly or even just roaring.

And the researchers speculate, perhaps this information could help us monitor elephants at risk of poaching among other conservation efforts. Here to talk with me about that is Beth Mortimer, research fellow in the Department of Zoology at the University of Oxford in UK. Welcome, Beth.

BETH MORTIMER: Hi, thanks for having me on the show.

IRA FLATOW: And Tarje Nissen-Meyer is associate professor of geophysics, also at the University of Oxford. Welcome, Tarje.

TARJE NISSEN-MEYER: Thanks very much, also for me.

IRA FLATOW: You’re welcome. Beth, what sent you looking for elephants seismology in the first place?

BETH MORTIMER: So I’m interested in animals that use vibrations through materials for information. So some of my previous research has looked at spiders, and how they use vibration through the spider web. So I have obviously looked at the other end of the size spectrum.

But for the elephant, their spider web is basically the Savannah terrain. So I was interested in what the role that the physical environment plays, and how they can use these vibrations for information.

IRA FLATOW: Tarje, have you ever tried to measure the seismological signal of an animal before?

TARJE NISSEN-MEYER: No. Certainly not consciously. So this is certainly something that we did deliberately. Now, seismic instruments essentially measure anything you could imagine. But in this study, what we really tried to do is focus on this mammal behavior.

IRA FLATOW: How difficult is it to do this?

TARJE NISSEN-MEYER: How difficult?

IRA FLATOW: Yeah. Describe the equipment you use, and how you set it up, and how it works.

TARJE NISSEN-MEYER: So the recording of vibrations works very much like what we’re doing right now, which is talking to a microphone. So we just sort of put the ear to the ground, and then listen through the waves as it propagates through the substrate. So wherever the source comes from, it could be an earthquake, could be a volcano, an impact, a nuclear bomb, or in this case an animal. Is the art and science of seismology to disentangle this vibration in terms of where it comes from.

IRA FLATOW: All right I want to play the sound one more time, and then I want to ask both of you to sort of dissect it for me. Let’s take one more, longer listen.

[SOUND PLAYING]

Wow. It sounds to me either like a heartbeat or a motorboat under water.

BETH MORTIMER: It does. Yes. So what we did to generate this audio track was using this geophone which measures the vibrations through the ground, and basically generates exactly the same as a kind of audio track. But what I had to do for this vibration, so that we could hear it, is I had to increase the frequency.

So the actual pitch is actually a lot lower. So think like really low base that you can feel rather than hear. And then I also had to amplify this recording as well. So it’s modified from its original form. But you can imagine, it’s the same techniques that you would use to record say, our voices right now.

IRA FLATOW: And that was one single elephant we were listening to.

BETH MORTIMER: That was one elephant walking past which was recorded in the fields in Kenya.

IRA FLATOW: Now, you find that these signals can travel three or even six kilometers, what is that, up to five miles away from the elephant itself. Is this something a human could feel just standing there?

BETH MORTIMER: So humans do you have a sense of vibration, we’re not very good at using it, though. So it’s a lot better to use these types of geophones than to use our senses itself. But it doesn’t mean that humans couldn’t be taught to use these types of vibrations. In terms of the long distance scale that you’re talking about there, what we were able to do with these recordings is basically get an idea of how much force the elephant was generating, and we put these into the computer models.

So that quote of kind of six kilometers was using computer models. So under favorable conditions. So by that, I mean kind of low noise, and on a sandy terrain, these high force behavior, such as walking around, could be able to detect and be able to discriminate up to that kind of range.

IRA FLATOW: Now, Tarje, something that I’ve found really interesting and surprising is that vocalizations like that, really loud male elephant roar we always hear, they could travel further than the mass of animals walking do? Why is that?

TARJE NISSEN-MEYER: So this is something that is not entirely explained. But I guess the main answer is that these are the sort of very low-frequency rumbles couple really well to the ground. And additionally, the frequency range just propagates quite well into far distances through the substrate that we’re looking at. I would say, in general, this is not entirely surprising. Any sort of vibration that happens in any body, such as a large mammal, could, in principle, couple to the ground and therefore transmit energy. It’s just something that we end up disentangling now.

IRA FLATOW: Beth, you say in your research that this same kind of signaling might be able to help us detect when, let’s say a bunch of elephants are stampeding, say if they’re being harassed by poachers.

BETH MORTIMER: Yes. So one of the main aims with this study was to basically use the seismological techniques that are used very widely to investigate some of the Earth processes Tarje has talked about. And be able to detect and discriminate different types of vibrations that are generated by wildlife. So you mentioned the stampeding there, so elephants are obviously very well suited to this type of monitoring because of their large size.

But they’re also likely to generate the largest amount of force when they’re running. So really, this technique is going to be best suited for measuring these panic runs that elephants do not do unless they have to. It takes a lot of energy to have a full out run for an elephant. So the idea is, we could be able to use this technique to monitor these behaviors which could be a sign of distress, and perhaps we could use that to help intervene when there might be some poaching threat.

IRA FLATOW: So, yeah. You’d just hear them sort of massing and running. Tarje, you know I have an Apple Watch that I put on my night table at night, and it can detect when I’m walking across the room just by my tiny– could we not crowdsource this with, you know, electronic devices– our phones, our watches, or whatever– to make sort of crowdsource all this detection.

TARJE NISSEN-MEYER: I think it’s a very good point, and it’s certainly one that we have thought about and talked about as well. And something like that actually has been tried in terms of earthquake detection as well. So in terms of wildlife monitoring, and sort of a pragmatic approach to deploying instrumentation in the Savannah, I mean it’s a potential avenue. But I would think realistically speaking, having hundreds of phones lying around in the savannahs might not be sustainable in a long sense.

And there are lots of different types of wildlife walking around. And animals are curious too. So I think having instrumentation safely–

IRA FLATOW: Right.

TARJE NISSEN-MEYER: –deployed is really crucial.

IRA FLATOW: Beth, if you and Tarje and others can hear the elephant’s footprints and also them bellowing, could they, the elephants themselves, be signaling to each other by–

BETH MORTIMER: Yes. Indeed, so we think that, well, starting with their vocalizations, you mentioned the bellowing there, and we’ve talked about these rumbles. These are certainly kind of signals that the elephants are sending out in specific social situations. So they will have a specific type of vocalization for a greeting, for example, or for an alarm signal. So they’re certainly communicating with each other using these vocalizations.

And obviously, part of that will go through the air, and part of it goes through the ground, and obviously, we’re interested in that part that goes through the ground. Really understanding how their physical environment plays a role in that. But yes, they’re certainly communicating.

IRA FLATOW: Could you test that? Could you actually do your own little footprints and see if they respond?

BETH MORTIMER: Absolutely. There have been some excellent studies before that have used seismic recordings, who use these ground-based recording, and played them back to the elephants. And we know that the elephants respond to these vibrations. And they can even discriminate in terms of who has sent that particular vocalization, so whether it was a known elephant or an elephant that they didn’t know. And obviously, this is something that needs a lot more study in terms of understanding the sensitivity of the elephants, and really starting to look at how that might change under different noise conditions for example.

IRA FLATOW: I have to prevent myself from humming I talked to the elephant song from–

[LAUGHTER]

Remember that one? What about other animals besides the elephants? Can we use seismic detect and talk to them possibly?

BETH MORTIMER: So this technique is going to be best suited for animals that generate a large amount of force. So large land mammals, it’s possible that we can pick them up. The research that needs to be done is obviously looking at how not only whether we can detect them, but whether we can discriminate between say antelope versus zebra or looking at different behaviors. So that is certainly the next research project. It needs a lot more data to look at that.

IRA FLATOW: Tarje, id you ever think, as a geophysicist, you’d be involved in tracking elephants?

TARJE NISSEN-MEYER: No. I mean I’ve certainly had an interest in animals of all sorts of sizes ever since being a child, like many others. But I guess growing into the field of seismology, you sort of realize that vibrations just happen everywhere on the planet, and of course, it shouldn’t prevent us from studying any sort of vibration, rather than just earthquakes. So it’s a natural trajectory, I think, that we’re taking.

[LAUGHTER]

IRA FLATOW: That’s interesting. Beth Mortimer, research fellow in zoology, and Tarje Nissen-Meyer, associate professor of geophysics. Both at the University of Oxford in the UK. Thank you for taking time to be with us today.

BETH MORTIMER: Thank you.

TARJE NISSEN-MEYER: Thank you.

IRA FLATOW: You’re welcome.

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