The sounds of bat and owl

The sounds of bat and owl
A bat call
The call of the bat

Below is the sound of a Leisler's bat. It was recorded using a time expansion bat detector. These detectors produce a most lifelike sound. The bat call is recorded at a very high sample rate and then played back 10 times slower. Leisler's bats produce calls just at the border of human hearing - around 20kHz. Playing them back 10 times slower reduces that frequency to 2kHz easily heard even by us.

Leisler's bats are early risers and start hunting around sunset.

Leisler's bat

Soprano pipistrelle
The sound below is from a soprano pipistrelle. This is the smallest of the bats found in Northern Ireland. Its call is around 55kHz - well above human hearing. The sample below was recorded with a frequency division bat detector. This instrument detects the call of the bat and divides the received frequency by ten, bringing the call within the human hearing range, but also adding some distortion.

Soprano pipistrelle social call

Bats use ultrasound not only to locate their prey but also to communicate with each other. The higher the frequency of an ultrasound, the easier it gets absorbed by the air. So much so that a pipistrelle can't detect any insects further away than about 30 metres.

This is no good for chatting with your friends or warning them to keep their distance,. Social calls of bats are produced at a much lower frequency, so they travel further. These calls have a frequency of between 20 and 30kHz - still outside the human range of hearing

Here is the sound of a soprano pipistrelle slowed down 30 times. This makes it much easier to recognize the fine nuances of the call. The higher sounds are echo location calls, the lower notes are social calls. Notice that the social call consists of three parts, like this: pwiaou - pwiaou - pwiouuuuuu. I suspect that the social call below was produced by my friend Batrick. He is a male soprano pipistrelle living in our yard and he is advertising his presence to any female that may pass by.

Very occasionally the a soprano pipistrelle will produce a social call which consists of four rather than tree calls. Why the animal does this is anyone's guess, but it sounds like this:

Soprano pipistrelle social call and Leisler's bat echo location call

This is one of my favourites. First you hear a distant social call. followed by the echo location call of a Soprano pipistrelle. This is followed by closer social and echo location calls. The finale consists of three rather haunting calls of a Leisler's bat. This is recorded twenty times slower than normal 'bat-speed'.

The feeding buzz

Northern Irish bats feed on insects - the higher the echolocation call of the bat the smaller the insect it's trying to catch. Using echo location to locate your prey has its problems though. As the bat approaches the prey it needs constant updates of distance and direction. If the gap between ultra sound pulses is too long, the prey may be away before the bat reaches it. This is solved by increasing the rate at which the bat emits its echo location calls. As the distance between bat and prey decreases, the pulse rate of the calls increase. In a bat detector this sounds like a buzz. Below is a picture of what this looks like:

The graph on the left plots time on the horizontal axis and amplitude (loudness) on the vertical. Notice how the amplitude drops as the bat gets closer to its prey. No point wasting energy on a loud noise when a quieter one produces enough of an echo to tell you what's going on. The 'buzz' is the final closely spaced section.

Also notice the time scale at the top. The call is exactly one second long. Remember however that it is slowed down by a factor of ten, to make it audible to the human ear. This means that the actual call only lasted one tenth of a second!

I have combined a series of such buzzes into a single file, so that one can get a feeling for this technique. This is what it sounds like slowed down be a factor of 28.

Here is a time expansion file of a feeding-buzz that I only found recently. In order to hear the double sound in each call I have slowed it down by a factor of nearly 100. The sample below takes 22 seconds to play, so in real life the call lasted only 220mS.

The calls were produced by a soprano pipistrelle - our resident bat. Quite a performance!

Daubenton's bat

Here I my very first recording of a daubenton's bat (myotis daubentonii). The bat came out of nowhere, produced the call below and disappeared into nowhere as fast as it came. This was recorded from a time expansion detector and I have slowed it down 28 times.

Finally, if you have ever wondered what a soprano pipistrelle looks like in full flight whilst hunting insects, here is the first decent photograph I managed to take of just such an occasion:

You are actually looking at a single pipistrelle lit up by two flashes fired in rapid succession.

A large sample of bat calls

If what you have read above has watered your appetite and you would like to do some experimentation with bat calls yourself, why not try the link below. It leads to a page from which you can download 2 minutes of concentrated bat calls recorded with one of the best microphones available. But be warned - the file is nearly a hundred mega bytes long.

Click here to bat.

Cuckoo

Here is our local cuckoo. A bird with a very monotonous call. He will go on like this for hours on end.

Juvenile long-eared owls

The next sample is rather different. It is the sound of two juvenile long-eared owls begging for food. They will keep this duet going for an hour or more, which means that either they are not getting fed or else they are very, very hungry.

This is one of the two squeaky characters

Leo, the long eared owl chick

And here is one of the parents

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