Bat Friday

Tonight was my first bat walk with Plecotus (the bat group of the Walloon nature association Natagora) and the local association CCN Vogelzang in the Vogelzang reserve, South-West Brussels.

I won’t show you any pictures because night photography and compact cameras are not really good friends ๐Ÿ˜€ …but this is a very beautiful place surrounding a small river, with pastureland, meadows, hedges and old farms. It’s also the last sanctuary for the Little Owl (Athene noctua) in Brussels.
Armed with a Batbox heterodyne detector like this one, we wandered through the reserve, trying to hear and maybe see some bats.

Seeing them proved to be difficult, because there was little light, and bats tend to avoid flashlights. However, with the detector, it’s quite easy to know if there are some bats around. Here they seemed to be concentrated around ponds, along the river and also doing round-trips along the hedges. Most bats appeared to be hunting alone (if the bats are too close, they have to shift their ultrasound frequencies so they won’t disturb each other..and you can hear it with the detector).

The sound was louder at 45 kHz, so it’s probably the Common Pipistrelle (Pipistrellus pipistrellus), which is the most common bat in Brussels (and in urban environments in general) and the smallest (3,5 cm long, weighing as much as a sugar lump!). Here you go :

At 0:09, you hear a characteristic ‘bzzz’ sound…called a feeding buzz. When the bat moves closer to an insect, the echo takes less time to come back. If the bat wants to locate the insect precisely, it needs to produce very fast ultrasounds. The two schemes from Jon Russ book, “The Bats of Britain & Ireland” illustrate this very well. The left one shows “normal” ultrasounds emitted by a Pipistrelle, the right one shows a “feeding buzz”.

We also heard a 20 khz, lower ultrasound which could be the Common Noctule (Nyctalus noctula), much larger than the pipistrelle (8,5 cm).

A nice and interesting evening! I can’t wait for the two other training days on bats which are coming ๐Ÿ™‚


  1. Very nice post! I’d really like to write a bat post but as you say they’re extrememly difficult to photograph, and not just with a compact. I have pipistrelles flying round my house in the summer but it’s always too dark to photograph them at such high speed. BTW is the purpose of the ‘normal’ sound to get an approxiimate fix on the prey before upping the frequency to the feeding buzz?

  2. Hi Finn, thanks for your kind comment! The “normal” ultrasounds are used to determine the distance and direction of the prey, the “feeding buzz” is used as the bat moves closer to get a precise idea of the insect size and shape, in order not to miss it!
    Pipistrelle is, I believe, the species that is the least disturbed by the urban environment, so you can see it around street lights for example…but still, it has an erratic and fast flight, so it’s hard to take any good picture!

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