Monday, September 03, 2012

Can crocodiles predict earthquakes?

Things have been a little quiet on the Croc Blog of late, so to shake things up here's a curious news item from the Philippines. Apparently seconds before the strong magnitude 7.7 earthquake tremor in East Samar recently, Lolong reacted violently while resting in his enclosure. The news agency suggests that Lolong was able to predict the earthquake, although with seconds to spare I doubt he'll be making that role official. But what's going on? Can crocodiles really predict earthquakes?

Well there is a more reasonable explanation. Lolong was simply responding to low frequency vibrations transmitted through the ground immediately prior to the earthquake. These are termed P waves, or compressional waves, and it's often difficult for humans to detect these. Crocodiles, however, are experts at detecting changes in pressure and vibrations, so it's very likely that Lolong was feeling the P waves produced at the beginning of the tremor. S waves, or shear waves, tend to follow P waves and are the ones that do the damage, and the ones that we are most aware of.

Why did Lolong react to the P waves? We know that crocodiles are highly sensitive to pressure waves, senses that are used not only to detect potential prey but also for social communication. Thunder and vibrations transmitted through the ground frequently trigger a territorial response from large male crocodiles (and a fear, distress response from small, subordinate crocodiles), and an earthquake's P wave would only heighten that response. There wouldn't be many crocodiles capable of giving Lolong a serious territorial challenge, but the P wave of an impending earthquake would very likely feel like one.

Did giant croc 'Lolong' predict 7.6 quake? | ABS-CBN News

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Paul said...

No. They can't ... at least not in any way that would actually be useful to humans ... we could follow this post with 'can crocs cure cancer?' ...

Adam Britton said...

I think you may have missed the whole point of the post, Paul. I'm using the news article suggesting that Lolong predicted the earthquake to illustrate how and why crocodiles can detect subtle vibrations.

Also, we've already shown that crocodiles have potent antimicrobial and antiviral properties in their blood, so crocs can potentially cure (or be used to find the cure to) disease. Cancer? Who knows, but if you never ask you never discover.

Paul said...

Yep, okay Adam, I accept that. A poorly written comment from me - I should actually know better.

It was the emotive header, not the actual post that made my knee jerk.

But hey, it's your blog and I am interested in your research - so you know, I'll shut the hell up now.

Adam Britton said...

Heck no, don't shut up. Discussion is the best part of any blog. But you must have realised by now that I love emotive titles to blog posts because they get your attention and ask interesting questions. Besides, it was the original news story that suggested that Lolong may have predicted the earthquake. That's too irresistible not to use.

Neerav Singh said...

Hey Adam!

When i used to work at Crocodile Bank near Chennai, there were these two African slender snouted crocs (Crocodylus cataphractus) in an enclosure right in front of my house. Every evening i will hear loud calls from them. I also used to hear a plane passing by at the same time. I kind of know that the calls were in someway linked to the sound of the plane. But would be great if you could throw some light on this assumed theory of mine.


Adam Britton said...

Hi Neerav,

Low frequency sounds produced by machines, vehicles, and naturally by thunder for example can all set crocodiles off. It's entirely possible that the plane engine triggered bellowing in the cataphractus. Studies have been done which identify the frequency band that triggers calling and bellowing (in alligators), which of course closely approximates the frequencies that other alligators produce during social interactions. Thunder can be fascinating in the way it triggers calling responses, with adult males responding with territorial signals (bellows and jawclaps) and juveniles responding with distress signals and shelter-seeking behaviour to the same rumble, implying that the sound is being interpreted as the product of a large dominant crocodile.