BATS AND THEIR TWITCHY EAR MUSCLES

Bats have a small, but nonetheless significant presence in metal, from the Overkill bat first drawn by D. D. Verni to Ozzy's infamous bat eating incident. Outside of metal, they're best known for their bloodsucking proclivities.

When I was little and spent a while in Spain, I saw the bats swoop down at dusk every evening and drink from the swimming pools. In fact, one family in that Spanish village had even drained their pool and filled it with toads and snakes, but that's a whole other story, so back to the bats.

I hadn't thought about bats for a while, but I picked up "Second Nature" by Jonathan Balcombe, and it reminded me that bats are really interesting, because they're so common - if you took all the mammals living on Earth today, one in every four would be a bat - but also because they're so unique and different. Bats are the only mammals that can fly (flying squirrels and other little airborn rodents don't count, because they just glide). Not only that, but they live in an entirely different sensory universe from ours.

They can switch their hearing on and off on command. Why do they do that? Well, it's because some of them use echolocation to find their way around, and the way echolocation works is that the bat listens for echoes of its own vocalizations to pinpoint where things are. The echoes are very faint, so the bat has to shout very loud - in fact, it makes a pulse of sound that can be over 140 dB, loud enough to cause human ears physical pain. So the bat's solution to this problem is to use muscles in its ears that can twitch 120 times a second to switch its own hearing on and off - when it makes its call, it switches its hearing off, and when it listens for the echoes, it switches it back on.
Our ears are sadly not this advanced. If mine were, I would use my twitchy ear muscles to switch my hearing off every time there's a horrible poser-metal band opening at some show.

Spotted bat

But bats are not just living in a different sonic world, they also live at a different speed. They give a whole new meaning to the expression "live fast, die young." Bats can make time discriminations in their perception of echoes down to 10 billionths of a second! They can also see ultraviolet light. So there you have it - bats perceive space, light, time and sound differently.

They're also little reservoirs for disease - all the nasty ones like rabies, SARS, and ebola, but they've evolved some sort of symbiosis with these viruses so they can carry them without actually getting sick. A useful skill for vampire bats, since they go around drinking blood that could potentially be infected with any number of nasty things.

Food for thought!

Simmon's, J.A. "Formation of perceptual objects from the timing of neural responses: Target-range images in bat sonar." The Mind-Brain Continuum: Sensory Processes. 1996.