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Separating Noctule and Serotine bats in the Field

If you hear a bat you think might be a noctule or serotine there are steps you can take to try to identify the species.

1. Pause. Walking creates a lot of noise at 25kHz so it is best to stop.

2. Listen to whether you can hear a two part call or a single type of call.

3. Focus on the repetition rate and the rhythm and see if it is slow and regular or funky.

4. If it is two part call tune slowly down towards 20kHz and see if the sound gets deeper.

5. If sound does get deeper find the peak (deepest) – if it is below 21kHz it is likely to be a noctule

6. If the sound gets higher as you tune to 20 go back up to 25 or above and try to find the peak frequency. For a serotine it will be 25 or above.

7. Look for visual clues

 

 

 

 

 

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Leisler’s Bats

Leisler’s bats are closely related to noctules and make a similar type of ‘chip-chop’ sound. They are slightly smaller but also have long pointy wings and fly out in the open.Their call is very similar to noctules although it is faster and they make the deeper ‘chop’ parts less frequently. The main difference is that the peak frequency of the ‘chop’ part, where the deepest pitch is found, is usually above 24kHz whereas noctules are 21kHz or below.

If the bat is making a two part call but when you tune the detector the deepest pitch is between the ranges of 22 and 24 kHz it could be a noctule or Leisler’s.

If you cannot tell if it is a noctule or Leisler’s bat mark as ‘unsure’.If it is definitely a Leisler’s bat with a clear two-part call during which the peak of the deepest ‘chop’ part is above 24kHz, do not record on the survey form, but make a note elsewhere.

It is difficult to be confident in separating these species and does take some practice in the field!

 

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