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Listening for Serotine Calls

The serotine also makes a fairly long and slow call but it is never a two part call. It is often described as a ‘tock’ sound heard through the heterodyne and is not as rich as the noctule ‘chop’.

Play the sound track of a serotine bat on the right at the top. Again the detector is tuned to 25kHz.

You can hear that the rhythm is very irregular, sometimes faster and sometimes slower and it has quite a musical effect.

If you hear a bat you think might be a serotine try to find the peak frequency by tuning into the deepest pitch. It might be at 25kHz or often slightly higher up around 30kHz.

Identifying Typical Serotine Calls:

• Never a two part call, single call sounds like ‘tock’
• Repetition rate - slightly faster than noctule 5-6/sec
• Rhythm – erratic and sometimes ‘funky’
• Tonal quality – not as rich as the noctule
• Pitch/peak frequency – deepest at 25-32kHz

Unsure Passes for Noctule and Serotine Bats

In certain situations, particularly when flying close to obstacles, the differences between noctule and serotine bats become much less obvious.

If the bats are flying within woodland, by a hedge, or around a tree or lamp-post it can be very difficult to tell noctules apart from serotines as their calls change and the characteristics can become overlapping. Noctule bats will drop the deep long ‘chop’ part of the call and use a series of loud calls that sound similar to the serotine.

Either walk a little way away to try to identify or note down as unsure.

If you hear a bat and you don’t know what it is at all then do not mark it down as unsure unless you think it may be a noctule or serotine.


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