Animals know that different sounds mean different things. And they know the sound patterns they need to focus on and the ones they can safely ignore.
All animals are tuned to their environment, but they can’t stay finely tuned to everything all the time. This is why they pay more attention to certain patterns than others. They have evolved ‘awareness hacks’.
All prey animals’ eyes pick up motion and they will focus on it until they have identified the cause – you don’t survive long as prey if you ignore things moving nearby. But what is the equivalent pattern in the soundscape?
The next time you are walking over a woodland floor, try to notice how often you can hear your feet break something.
There are thousands of things that can trigger a noise in a wild environment, but few that trigger the same noise twice in short succession. The wind snaps twigs and branches regularly, but it very rarely creates the same sound twice in rapid succession. If an animal hears a snap or crack sound on its own it will switch to ‘alert’ behaviour. But it probably will not react more urgently than that – it would be a waste of energy to flee every time something snaps in the forest.
But, if an animal hears a similar sharp sound twice in short succession, this normally triggers a different response. Prey animals switch to ‘flight behaviour’ and predators will often investigate or leave the area.
The Fox Demonstrates
I filmed the video above on a cold winter morning, in the twilight before the sun rose. It is still quite dark, which is why the picture quality is poor. But it is good enough to study the effect of a sound pattern on the fox (helped by the small light on my camera reflecting back from the ‘tapetum lucidum‘ at the back of the fox’s eyes.)
The fox is happy foraging and does not notice my presence – I am downwind and well-hidden behind a fallen tree. To demonstrate the sound patterns above, I click my fingers once – at the 27 second mark. Notice how the fox clearly hears this and turns towards me, but he is still unable to see me clearly or smell me at all. At this point the only thing that has changed in its world is a single sharp sound – and that’s not enough to react strongly, it could easily have been the wind. The fox returns to foraging behaviour.
But, at the 41 second mark, I click my fingers twice and now the fox responds differently. It still can’t see or smell me, but it can sense that something animate is in the area, from the double sharp sound. The wind doesn’t make that sound pattern. It could choose to investigate, but on this occasion it leaves the scene.
One or Two Sounds Amongst Friends
Animals are also sensitive to the difference between a single sound and two or more sounds from among their own species. If a pigeon hears another pigeon take off, that single sound will not trigger alarm. But if it hears two pigeons take off within a couple of seconds of each other, that triggers a different response – the pigeon will instantly sense danger and take off.
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