Vocalisations

The Brown Rat uses vocalisations in a variety of situations and in a differing range of frequencies. While we are able to hear the lowest range of rat squeaks, the majority of communication falls outside our range of hearing as ultrasound. Examples of ultrasound vocalisation measured in kHz (kilohertz) include separation from the nest for a young kitten (25 to 45 kHz), shock or defeat after an aggressive situation (22 kHz), and playtime sounds (35 to 70 kHz).

The human audible range is frequencies between 20 Hz (hertz) and 20,000 Hz (20 kHz). Although we can hear some rat squeaks, our auditory range falls below that of the majority of vocalisations and we really miss out on what our rat is communicating.

To listen to my pet rats I have used a bat ultrasound detector that picks up frequencies from 18 - 120 kHz and sound analysis software that was optimised for field playback of bird song. As with many rat related needs we often look elsewhere for solutions and these solutions perform the task in hand exceptionally well.

The bat detector I am using is a CBD 305 Dual HD/FD model from http://www.ciel-electronique.de. I purchased this model directly from their eBay shop. It was better value from the eBay shop and I could also reduce costs by not needing to pay tax so I went for a more expensive model with the extra feature of frequency division (FD) mode (allows the full frequency of sound to be played at the same time). The total cost for one unit and delivery was Euro 96.60 (approximately $146 - 4th March, 2008). I am very pleased with the quality of this model and it picks up my rat's vocalisations perfectly well from a good range. If you are budget conscious then you only need the HD (heterodyne) model at Euro 59.95 (approximately $91 + delivery - tax if applicable) which allows you to select a specific frequency range. I will also use this detector to search for bats in the summer and find the additional FD feature useful.

The sound analysis software I am using is free from http://www.syrinxpc.com. The Syrinx application is summarised as 'A Windows program for spectral analysis, editing, and playback of acoustic signals'. It was developed by Dr. John Burt (Psychology Department, University of Washington) and serves well in his study of animal communication and bioacoustics. Thank you very much indeed Dr. John Burt for making this application public.

Vocalisation Analysis

Here is a recording and accompanying analysis in the form of a waveform and spectrogram image taken of my rat's ultrasound vocalisations. My rat (Sally) was about to be released from her cage and her squeaks show her anticipation of being able to scamper around freely to play. Click here to listen to the recording.

The Magenta MKIIb bat detector model kit shown in the video arrives with instructions and an essential diagram to aid in construction. The list price in February 2008 was £37.99 inc. VAT. with P&P £3.00 (UK only). I have absolutely no experience with electronics but after reading the instructions thoroughly and doing a little reading online I was able to put everything together and now have a fully functional bat detector that I shall use in the summer months around my local area. Here are pictures of the construction stages should you get the urge to try it out for yourself. Click on an image to enlarge it.

It was initially difficult to understand the diagram and instructions as I was unfamiliar with the components. The resistors were tricky as they are colour coded to reflect their ohmage. I found a very useful free resistor colour coder application online from Schematica that provided the help I needed to translate the colour bands into ohmage. In all, I made one placement error but spotted it during a circuit review and no harm was done. The circuit board was housed above the main speaker but the clearance wasn't sufficient which makes it look like the speaker was a squeezed in update from a prior model. The kit provided a sticky pad to create a break between the bottom of the circuit board and the speaker but I didn't really consider that to be a professional solution. I also received 4 casing screws that were too large for the casing holes and had to provide my own. This kit product is fun to make and I shall have a lot of fun with it for my local bats although it's not sensitive enough for rats.

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