I found out recently that mice sing. Not just little squeaks that we can hear, but little notes that occur at the edge of our hearing – ultrasonic for those of us over 30. Slowed down they sound like whale songs. The common deer mice do it, so I set out to find out if I have any singing mice in my yard. I set up my recorder set to record at 96 kHz sampling rate, which means it will record up to 48 kHz. I set it out in my backyard at about 11 pm, and let it run, assuming it would run out of batteries or space on the SD card long before dawn.
When I collected it in the morning, I found about 2 hours of recording. After sifting through the helicopter flyover, the distant trains, a doggie telegraph straight out of 101 Dalmatians, there it was. A plaintive little series of notes, right at 20 kHz. Slowed down to about a 10th of its normal speed, it sounds like this:
I also picked up a couple of bat recordings, but they sounded quite different. I’ll be including more bat recordings in future posts, so you will know what I mean.
So I had a mouse, near as I could tell, but what mouse? I set out some live traps to see if I could catch anything in the area and try to identify it. I didn’t catch anything, but the closest packrat kept gathering my traps and adding them to the pile of cactus he or she calls home. I don’t think packrats are supposed to vocalize in the ultrasound, but maybe this rat didn’t read the book, so I set up my Ultramic, which can record sounds up to 100 kHz, and pointed it right at the packrat den. I let it record for about a half-hour, from around 10 pm to 10:30. I filtered out the stuff below 10 kHz – the usual dogs barking, trains, cars, neighbors talking. There were a lot of sounds between 20 kHz and 55 kHz, so I slowed it down and was amazed. No packrat or mouse sounds, but the rat seems to have it’s own band! These crickets, or whatever they were, kept up this rhythm throughout the entire recording. A bat jammed with them for a microsecond, too (listen for it).
Now I was intrigued, so I set up my microphone in the front yard – hopefully blocking the trains. I let the recorder run for about 20 minutes, and after filtering out 2 helicopter flyovers, dogs barking, etc., I was left with the sounds of two more crickets, but these were in the sonic range. This recording also includes a bat at 35 kHz. If you download the recording and slow it down, you can hear it.
Recording notes: Mouse recorded with Zoom H4n. Crickets and bush crickets recorded with Ultramic 200k (Dodotronics, Inc) and an Acer Iconia W500. Recording subject to high and low-pass filtering to remove hiss.
Thanks to Vicky Powys of www.caperteebirder.com for advice on recording and analyzing ultrasounds.