Bat ID using a full spectrum detector
A full spectrum bat detector produces a recording of the bat call, recording from the lowest of sounds, up to and including ultrasound, up to 126kHz or 192kHz. This can be displayed as a static or rolling spectrogram on screen.
A spectrogram is a visual picture of sound that shows frequency, time, and volume all on one graph. It maps out how high or low a tone is and how loud it is as time passes.
How to Read a Spectrogram
- Horizontal Axis (X-axis): Shows time moving from left to right.
- Vertical Axis (Y-axis): Shows frequency (pitch or tone), with low sounds at the bottom and high sounds at the top.
- Colours (3rd Dimension): Show amplitude (volume or loudness). Brighter or warmer colours mean louder sounds, while dark or cool colours mean quiet or no sound
Types of bat call spectrogram
For the common UK bats there are 4 basic shapes of call you might see onscreen:
Below is a simplified version of full spectrum bat ID, for more detailed knowledge we strongly recommend – Bat Calls of Britain and Europe: A Guide to Species Identification by Jon Russ.
Hockey Stick
These calls look like the shape of a upright hockey stick with the blade facing towards the right. So each calls start at a high frequency, and reduces frequency rapidly, to a peak in volume at the towards the end of the call.
Common Pipistrelle – pipistrellus pipistrellus
If the bottom of the blade of the hockey stick is around 46kHz (within 3kHz), then this is likely to be a Common Pipistrelle – pipistrellus pipistrellus.
Put simply, if the bottom of the hockey stick call is in the 40’s its probably a common.
Soprano Pipistrelle – pipistrellus pygmaeus
These sound very similar to Common Pipistrelle but just at a slightly higher frequency. So if the bottom of the blade of the hockey stick is around 55kHz (within 5kHz), then this is likely to be a Soprano Pipistrelle – pipistrellus pygmaeus.
In summary if bottom of the hockey stick call is in the 50’s its probably a soprano.
Serotine – cnephaeus serotinus (formerly eptesicus serotinus)
Sounding very different to a Pipistrelle, these call are at a much lower frequency onscreen. If the hockey stick shape is slightly more sloping and stretched out, and the bottom of the blade of the hockey stick is around 22kHz (within 3kHz), then this is likely to be a serotine – cnephaeus serotinus.
So if a stretched out hockey stick call is in the low 20’s its probably a serotine.
Low flat call
Noctule – nyctalus noctula
Slow, very loud calls, perhaps sounding like whip cracks on heterodyne detectors.
The noctule produces two tyres of calls at the bottom of the screen, they could be either:
- A flat line at around 19khz (within 2 or3 kHz) when flying high
- A curved call ending at around 24 kHz (withing a few kHz)
In summary if the call is flatter and in high teens or low 20’s its likely a noctule.
Vertical stripes
A Myotis species
If you see long near vertical strips, perhaps close together, you can say with confidence it is one of the 6 UK Myotis species. The myotis calls are so similar it is next to impossible to tell these species apart:
Daubenton’s bat (Myotis daubentonii), Natterer’s bat (Myotis nattereri), Whiskered bat (Myotis mystacinus), Brandt’s bat (Myotis brandtii), Bechstein’s bat (Myotis bechsteinii) and Alcathoe bat (Myotis alcathoe)
One slight clue is if the bat is low over water, with a paler tummy, its likely to be a Daubenton’s.
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Bat Detectorists 