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Listening for Noctule Calls

With your detector tuned at 25kHz you should be able to detect both noctule and serotine bats. Both should sound quite clear at this frequency but you need to do a little more investigation to tell them apart. In most situations they can be separated (but not all) and this is why we have a space on the form for ‘Unsure’ passes.

The noctule bat typically uses a two-part call often referred to as a ‘chip chop’ sound. Each pulse is fairly long compared to other bats and this gives it a very rich flavour.

These bats are big and fly fast but the repetition rate of the calls is slow, on average about 4-5 pulses per second, but sometimes even less as they fly high above the trees.

Play the sound at the top to hear a noctule heard through a heterodyne detector tuned to 25kHz.

The bat is flying high with its typical loud two part call - high and then low.

If you hear this classic two part ‘chip-chop’ call when you are tuned to 25kHz tune down towards 20kHz and see if the sound gets deeper. Try to find the peak frequency – i.e. where the sound is at its deepest

The ‘chop’ part of the call is the deeper and longer of the two sounds and is easier to tune into to find the peak frequency. If you find that the deepest frequency is at 21kHz or below you can be fairly sure this is a noctule bat.

Identifying Typical Noctule Calls:

• Call often has two parts and sounds like ‘chip-chop’ (but not always alternating).
• Repetition rate slow at 4/second (sometimes down to 2/second)
• Rhythm - regular punctuated with erratic bursts
• Tonal quality - deep, rich ‘chop’ sound & slightly higher ‘chip’
• Pitch/peak frequency – deepest at 21kHz or below

 

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