The common pipistrelle (Pipistrellus pipistrellus) is the most common bat species in the Netherlands. One would assume that all it's calls would be well documented. But even well-known species have their surprises. This is a collection of the most eyebrow-raising recordings of common pipistrelle calls.
The following recording (first snippit) was made in an area where common pipistrelles were seen foraging in the area for at least 45 minutes. These type C social calls look very similar to other calls that were recorded next to another busy foraging area (917806). Both recordings were made in june, but at different locations. Their appearance of FM-sweeps and FM-sweeps that are followed by a (sometimes disconnected) qCF warble lower than 20 kHz in frequency is a bit unusual looking - altough they do share a lot of similarity to other type C social calls associated with juvenile bats.
Date of recording: 2024-06-08 Recorded by: Simon Boon Audio file: 911624 Location: Oudenbosch, Noord-Brabant, The Netherlands
Multiple type C social calls are present in the following recording: high frequency FM social calls and lower frequency social calls both FM-qCF- and FM-shaped. Due to the FM-sweeps, it almost appears as if a Myotis species flies by.
Date of recording: 2024-05-13 Recorded by: Eva van Well Audio file: 911804
These type C social call were emitted a whopping 240 times in the short time period of 22,5 seconds. Tessa saw three bats swarming and tapping the gabel of the house, but none of the bats entered the building. After the video was taken, the bats flew away at around 5:00 and they did not return to the location afterwards. This creates the assumtion that their roost was somewhere else. The function of these social calls are uncertain. Since the other bats were common pipistrelles, it is assumed that the social calls were emitted by a common pipistrelle as well. The function of these social calls remain a mystery.
The following recordings are not confirmed to be common pipistrelle, but I suspect them to be due to their strong similarity with type C social calls of juvenile bats. The recordings were made in a regular street of terraced houses / townhouses. However, two bat experts, Bram Aarts and Erik Korsten, think that serotine bat might also be a candidate due to the frequency distribution of the calls. None of us have certainty about the identity of the bat.
A juvenile bat had fallen out of the maternity roost and was found by the residents of the building. After a little care from a specialist, the juvenile bat was placed on the wall of the building and it climbed its way back to the roost. Around 40 individual common pipistrelles were counted leaving the roost after the juvenile made it save to his roost. Calls of the isolated juvenile (estimated to be around 2 weeks old) were recorded inside of the resident's home, before the bat was directed back to his roost.
In the vicinity of the maternity roost, the same as the previous story after the juvenile made it safely back home, an interesting trill-like call was recorded. This call is shown in the snippit on the left. At first I thought it belonged more into the type D social call category, as one would assume with a trill, but after comparing it to the type A social call of a brown long-eared bat (Plecotus auritus) that also inhibits a trill-like shape, shown in the snippit on the right, I noticed the multi-frequency properties of the common pipistrelle call that belongs to type A social calls.
The following two examples are from two different locations. Both recordings contain unusual type D social call arrangements, compromised of numerous simple FM components. They are similar to the 'rapid frequency-modulated buzz' of the soprano pipistrelle (Pipistrellus pygmaeus) shown as figure 8.6.17 in the book "Social calls of the bats of Britain and Ireland" from the authors Neil Midleton, Andrew Froud and Keith French.
In the first example, the unusual call is on the left in comparison to a regular type D social call on the right. In the second example, the unusual call is on the right in comparison to a regular type D social call on the left.
The following two examples are from two different locations. Both show reguar type D social calls with the first components joined-up.
And I think the first call in the following example is an almost fully joined-up type D social call, creating a trill. Something I haven't seen in common pipistrelles before.
Date of recordings: 2025-06-22 Recorded by: Sarah Mahie Audio files: 1008689
More calls with a trill-like nature were recorded near a maternity roost were at least 44 adult common pipistrelles reside. It appears as if these calls first make an upward opening parabola followed by a downward opening parabola. They were emitted numerous times enough to not be a coincidence. They could be the lower part of type C social calls (often emitted by juveniles), but there seems to be a true lack of the FM sweep at the beginning of the calls. A possible similar call was also recordednext to type C social calls of common pipistrelle.
Last year, some strange qCF calls around 20 kHz were recorded that were emitted in series at a maternity roost of common pipistrelle. The calls had a particular long duration, some up to 40 ms. My first impression was that these calls were from a small terrestrial mammal, so I contacted Stuart Newson for his expertise about the topic. His judgement was as follows: "I am quite confident that these calls were not produced by a rat - when I play them in 10 x expansion, they don’t sound like rat calls. They sound more like bat (social) calls – but I don’t recognise these."
Surprisingly enough, these calls were recorded at other maternity roosts of common pipistrelle at other locations as well. Non were recorded near summer roosts without maternity function. My suspicion is that these social calls might be usefull to indicate maternity roosts. Perhaps they are emitted by juvenile bats, since the isolated juvenile common pipistrelle mentioned before, also emitted qCF calls just around 20 kHz.
Date of recording: 2024-06-08 Recorded by: Anice Hut Audio file: 913072 Video footage from: Anice Hut Location: Valthermond, Drenthe, The Netherlands
Date of recording: 2025-06-14 Recorded by: Sarah Mahie Audio files: 1006424 Location: Purmerend, Noord-Holland, The Netherlands
During a survey to check for roosting bats behind wooden window shutters, a common pipistrelle was disturbed by moving the window shutter in combination with the use of a flashlight. During this moment, the bat emitted seven type C social calls in the shape of FM sweeps with a wide withband on a high frequency.
Date of recordings: 2024-09-12 Recorded by: Sarah Mahie Audio files: 933410
Type B social calls might be pretty common in the vicinity of roosts, but I appreciate how clear this recording is. It shows the broad range of vocabulary of this little bat.
Date of recording: 2024-06-07 Recorded by: Manno Kolvoort Audio file: 917123
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