Bats jamming to get their dinner

When bats swoop in darkness to catch their dinner, they emit high-pitched sound waves and then listen to the echoes that come back. They use this echolocation technique to find food AND also to avoid crashing into things.  Now scientists have discovered that they also use the sounds for more nefarious purposes: they can JAM the echolocation of other bats. Jade Lauren Cawthray works with the Wildlife Trust; she's also a bat enthusiast and takes groups on night-time bat walks. She's been taking a look at this new study and Ginny Smith spoke to her to find out more...

Ginny -  Jade, can you tell us a little bit about how echolocation works to start with?

Jade -  Yeah.  So, with echolocation, a bat literally does this very, very big shout and the soundwaves travel through the air and then bounce off the environment and they come back to the bat, giving an idea of the shape and the textures of its environment.  So, objects that are really close to the bat, the sound will come back to the bat nice and quickly.  So, it knows it's not very far away, say, a moth for example.  But if there was a tree much further away, the soundwave would take a longer amount of time to come back to the bat so it knows it's much farther.  So, they get an idea of distance and the shape of their environment.

Ginny -  So, you say the bats are shouting, but when I go out at night, I can't hear a load of noise coming from the sky.  Why is that?

Jade -  So, bats do shout and they shout very, very loud.  They shout at about 110 decibels which is equivalent to a jet flying low overhead.  So, it's a really, really loud noise.  But the shout is actually a different frequency.  A frequency above that which we as humans can hear.  So, we can hear up to about 20 kilohertz but the bats, their echolocation can be anything from 20 to 200 kilohertz.  So, it's just a frequency above what we can hear.

Ginny -  So, it's just too high pitched for our ears.

Jade -  Yes.

Ginny -  But you've got an example of some bat noise that we can actually hear that I think you've brought with us.

Jade -  Yeah.

Ginny -  Do you want to play that for us?

Jade -  (bat noise).  So here, what you can hear is a slowed down version of bat echolocation and you'll hear these little shout points and they're getting faster and faster.  And they get faster and faster as the bat gets closer to an insect.  So, as it gets closer and the insect is moving around, it needs to be able to pinpoint where the insect is more accurately.  So, it does more and more shouts to get more and more information of the location of the insect.

Ginny -  But now, some researchers have found out that bats are doing something completely different with their echolocation.

Jade -  Yeah.  So, this piece of research that has been released this week, it's quite exciting because it's the first time something like this has been recorded.  Basically, what they found is in Mexican free-tailed bats, the bats are actually interfering with each other's echolocation.  So, one bat will make an echolocation call, trying to capture an insect, but another bat will come along and send a different type of sound, a different type of call that actually interferes with the soundwaves of the first bat.  What this means is that the first bat isn't able to judge the distance of the insect as accurately and actually misses the prey.

Ginny -  I think we've got a recording of that one as well.

Jade -  (bat noise).  So, you can hear that like we had before and then in a second, you can hear like a whistly up and down noise.  This is a kind of jamming tone that they're doing.  They're making this very different call around about the time that the first bat is increasing the speed of its echolocation.  So, as it's starting to hone in on that insect, the other bat starts to send a different frequency which stops it capturing the insect.

Ginny -  It sounds quite different so it's not just that that bat is also echolocating to find that insect.  Are they really trying to prevent their fellow bats from getting food?  I thought bats are quite a social species.

Jade -  Yeah, so the report suggests, they look very carefully at this.  They wanted to know, was it that the second bat was trying to disturb the first bat by sending the sound towards the bat or were they trying to capture the insect and sending the noise at the insect.  And they seem to be sending it at the insect to interfere with those soundwaves.  So, they're definitely trying to prevent the other bat from getting the food.  The Mexican free-tailed bats are quite famous particularly in the States because they roost in numbers of a million or more individuals.  And so, what could be happening here is that because there are so many individuals, the number of insects available per individual is much lower.  So, there's actually more competition between them for food.