Recording Bat Calls
While it is interesting and exciting to be out in the dark listening and watching bats, its great to be able to share your experience with someone who was not there. Perhaps you are unsure about the species you were hearing, especially if you could not see them well. Maybe the calls they made weren't typical of the species. Recording the sounds for later playback or analysis can bring a new dimension to your interest, and give you greater insight into the amazing capabilities of bat sonar. It can also be used (with a considerable degree of caution) to HELP identify or discriminate between different species.
Some alternative techniques
1: Direct recording of bat call
Perhaps the best way of recording bat calls is to record the original bat sound. Avisoft BioAcoustics, Wildlife Acoustics and others make ultrasound recording equipment that records to an internal SD type card, or links directly to a computer or tablet, enabling the actual sound from the bat to be recorded. This professional standard equipment is expensive (£2000 upwards) and you would need to consider the practicality of its use in the field.
A more economical alternative is the Dodotronic Ultramic which also records direct to a computer or tablet via USB.
Less expensive approaches are based on recording the output from your bat detector.
2: recording from bat detector direct to computer.
A good solution because it allows immediate analysis in the field. The audio (headphone) output from your bat detector is connected through a wire to your tablet or laptop computer, either through a "line in" or "ext mic" connector, or if necessary through an external USB sound card. You need to ensure the sampling rate is sufficient - many modern USB sound adaptors offer 96kHz, but 48kHz is also fine.
3: recording from bat detector to sound recorder for later transfer to a computer.
Any bat detector with a signal output can be connected to a sound recorder to record signals. Heterodyne detectors are not ideally suited to this kind of work as they lose the most important part, the frequency of the original signal; however time expansion detectors and frequency division detectors change the signal in a very precise and predictable way that supports detailed analysis.
3a: Using a time expansion detector
Using a time expansion detector allows very good quality recording and faithful analysis of the signal. A professional quality set up would typically include a Petterson Time expansion detector, such as the D240x (£950). To go along with this you would need a recorder; A ZOOM or ROLAND like this will cost around £150-250. You would then need a sound analysis package, and the software recommended for the D240x is the BatSound package, priced at £280. (All available from NHBS.) Digital recorders have the advantage of allowing you to transfer the recorded and encoded signal directly to your computer.