Some unusual social calls of the Nathusius' pipistrelle's (Pipistrellus nathusii) are trills and warbled qCF calls. These kind of calls are almost non-spoken about in literature about this species. The type D social calls of the Nathusius' pipistrelle can be categorized into different parts, of whom part A, B, C, D and E have been described in literature (Russ and Racey 2007; Hargreaves et al. 2017; Jahelková 2011; Middleton 2022).
However, I renamed part E as described in Jahelková (2011) and Hargreaves (et al. 2017) to part D0, since the majority of these kind of FM sweeps are in front of a part D motif. Another motif consisting of FM sweeps, but more often used as a stand-alone motif, gained the name part E.
Jahelkova (2011) also described another unusual social call, the W-type social call. To cite her description: "In May and June, a continuous social vocalization of quite unusual structure and composition was recorded apart from these standard calls. Most of these calls were designed in a long “wavy line” pattern with the peak frequency of 14–36 kHz, and were accompanied by standard or modified echolocation calls.".
I also had my own encounter with these continuous wavy line calls. They generally appear to be higher in frequency than the trills and wavy lines that we will discuss next in this blog post. Those are often between 10-20 kHz and are emitted once or twice. Perhaps some of them do belong to the wavy line calls as described by Jahelkova and the other calls that are higher in frequency might be missed due to the distance of the recording device, but perhaps they might be a different kind of unusual social call.
I introduced the part F motif to categorize the trills, wavy-lines and almost line-like calls of the Nathusius' pipistrelle that seem to be used non-continuous. There is overlap in these kind of calls, hence why I think they all belong to the group "F". In this blog post, I will take you through my thought process on how I came to this conclusion.
At first, I called them slow trills and fast trills. Below are shown snippits of slow trills and calls that show similarity to them. The (previously called) slow trills can be complemented by (the first half of) a part D. I also believe that audio files 913306, 911808 and the right snippit of 934232 show 'non-joined components' variations of the slow trill - them being different from a regular part A. Note the presence of harmonics as well. I will categorize these trills as a part F motif.
Date of recording: 2024-05-26 Recorded by: Niels Jansen Audio file: 911808
Date of recording: 2024-05-28 Recorded by: Anice Hut Audio file: 911811
Date of recording: 2024-06-14 Recorded by: Lisa Vermaning Audio file: 913306
Date of recording: 2024-07-01 Recorded by: Jasper Geukemeijer Audio file: 917979
Date of recording: 2024-09-13 Recorded by: Kaz Veldtrom Audio file: 934232
Date of recording: 2024-09-15 Recorded by: Douwe van der Wijk Audio file: 935110
Date of recording: 2024-09-09 Recorded by: Kaia Pieters Audio file: 933070
Date of recording: 2024-08-19 Recorded by: Declan Frerichs Audio file: 929731
The (previously called) fast trills on the other hand, might possibly originate from a part A, being a 'joined components' variant. This theory is supported by multiple recordings in whom the fast trills and part A calls emitted by the same individual bat show a lot of similarity.
Date of recording: 2024-06-19 Recorded by: Levi Laluan Audio file: 914575
A typical part A-B-C sequence:
Date of recording: 2024-08-16 Recorded by: Kaia Pieters Audio file: 947668
A fast trill on the left and a part A on the right:
Date of recording: 2024-08-19 Recorded by: Declan Frerichs Audio files: 929731
The reason I called this category fast trills, even though some parts of the trills of the previous examples may appear similar in size to the slow trills, is because some examples within this category appeared to be 'extra fine' in structure: consisting out of a lot of small components. My hypothesis was that these were potentially originated from the start of a typical part A as well.
The calls of the audio file 920400 and 920326 are emitted by the same bat within 2 seconds.
Date of recording: 2024-06-28 Recorded by: Hubert Matuszewski Audio file: 917429
Date of recording: 2024-07-11 Recorded by: Job Hoven Audio file: 920400
Date of recording: 2024-07-11 Recorded by: Sam Harbers Audio file: 920326
A fast trill on the left (with an echo present) and a part A of the same bat on the right:
Date of recordings: 2024-08-24 Recorded by: Kaz Veldtrom Audio files: 929680
Multiple fast trills on the left and a call, that already looks more like a part A, of the same bat on the right:
However, I had to reevaluate the category of these calls after seeing these two calls, both I would have called "fast trills", next to each other:
Date of recording: 2024-08-19 Recorded by: Declan Frerichs Audio files: 929731
There appears to be intermediate states between the trills and the ones that appear more like a line, leaving some calls in a grey area while categorizing them:
Currently I am thinking that it would be better to devide the calls by their structure. One being true trills and the other being a line-character. The trills I previously called "slow trills" would be categorized into being part F1 (true trills), the trills I called "fast trills" that are not a line in character would be categorized into being part F2 (originates from a part A) and the "fast trills" that are a line character would be categorized into being part F3 (mordents).
The following three snippits are from the same recording. The first snippit contains a mordent (F3) on the left and a true trill (F1) on the right. The second snippit also contains a true trill. The third snippit might contain another category of unusual Nathusius' pipistrelle social calls: wavy-line calls.
The suspected wavy-line call appears between 23,700s and 23,850s:
Date of recording: 2024-08-19 Recorded by: Declan Frerichs Audio files: 929731
Noteworthy might be that the mordents of the audio files 920400 and 920326 were recorded at the same location as the true trills of audio files 911811 and 913306, but in July instead of May and June. And at the same location, this wavy-line call was recorded during mating season (August):
Date of recording: 2024-08-17 Recorded by: Gert-Jan Hendriks Audio file: 928168
Wavy-line calls are difficult to distinguish. From the structure of the calls they don't appear as true trills. Their frequency goes up and down more randomized. I will categorize them as part F4 for now.
The two wavy-line calls of the following recording were used as a motif in the following sequences of calls: the first being the sequence "wavy-line + part B" and the second sequence being "wavy-line + cheep + part B". A call consisting out of a part B + C and a call being only a part A are also present in the recording.
Date of recording: 2021-05-10 Recorded by: Sarah Mahie Audio file: 911931
Another great example of a wavy-line call (between 1,240s and 1,330s), also used as a motif between other type D social call motifs:
Date of recording: 2024-09-20 Audio file: 1001463
In this audio file, there appears to be two wavy-line calls that are followed by the call sequence "Part B + C + B". Part E motifs are also present in the recording.
Date of recording: 2024-07-02 Recorded by: Chris Johan Diepenmaat Audio file: 918721
Trying to categorize the following recordings based on the suggested categories, seems to be the most doable for now. Below are some examples where I try to categorize different social calls. I do believe that these trills and lines are on a spectrum, hence why I keep them clustered in the part F motif.
Why could categorizing be important? The language of bats is complex. Currently it is not known if these unusual social calls of the Nathusius' pipistrelle are used for advertising or if they are used in an agonistic manner. Perhaps the true trills have a different message than the mordents. When we start to understand their function, we can get more insight in the behaviour of the bats that emit the calls. For example, does this species mate in spring? New discoveries might be waiting to be made.
Up: A part F3 + a part D.
Below: Three part F3's and some modified echolocation calls.
A part F2 on the left and a part A (that was followed by a part B and C) on the right:
A part F1 (part E above):
A part F3:
Date of recording: 2024-09-05 Recorded by: Sander Boersma Audio file: 932327
A part F2:
A part F1:
Two part F4's, one at the start (between 3,150s and 3,250s) and one at the end of the snippit (between 3,900s and 4,000s):
In what category would you place the following trills, the ones that are emitted after the more typical type D social calls?
The only way to be able to understand these calls better, is to document and analyse more calls. Every recording can be precious. Yours too!
Who would like to participate in unraveling the language of bats?
All recordings are licensed under the following Creative Commons Attribution-NonCommercial-NoDerivs 4.0 license and in courtesy of Sarah Mahie.
All sonograms are screenshots of the recordings imported in the ultrasound analysis software BatExplorer 2.2 (Elekon, Switzerland).
Bilbiography:
- A. Schmidt (1985). Zum Jugendetwicklung und phänologischem Verhalten der Rauhhautfledermaus, Pipistrellus nathusii (Keyserling u. Blasius, 1839) im Süden des Bezirkes Franfurt/O. Nyctalus 2: 101–118.
- Daniel Hargreaves, Helena Jahelkova, Oliver Lindecke and Guido Reiter (2017). Bat Species of the Year 2015: Nathusius’ pipistrelle (Pipistrellus nathusii). Facts compiled for BatLife Europe.
- Erik Broer (2024). Zeldzaam: derde kraamkolonie ruige dwergvleermuis ooit in Nederland gevonden. Natuurmonumenten; Bureau Viridis; Zoogdiervereniging. Retrieved from: https://www.zoogdiervereniging.nl/actueel/nieuws/zeldzaam-derde-kraamkolonie-ruige-dwergvleermuis-ooit-nederland-gevonden
- G. Heise (1984). Zur Fortpflanzungensbiologie der Rauhhautfledermaus (Pipistrellus nathusii). Nyctcdus 2: 258–260.
- Helena Jahelková (2011). Unusual social calls of Nathusius' pipistrelle (Vespertilionidae, Chiroptera) recorded outside the mating season. Institute of Vertebrate Biology, Czech Academy of Sciences. Folia Zoologica, 60(1): 25-30. https://doi.org/10.25225/fozo.v60.i1.a4.2011
- Jon Russ and Paul Racey (2007). Species-specificity and individual variation in the song of male Nathusius’ pipistrelles (Pipistrellus nathusii). Behavioral Ecology and Sociobiology, 61(5): 669-677. DOI:10.1007/s00265-006-0295-9
- Jon Russ (2021). Bat Calls of Britain and Europe: a Guide to Species Identification. Pelagic Publishing.
- Neil Middleton, Andrew Froud and Keith French (2022). Social Calls of the Bats of Britain and Ireland (second edition). Pelagic Publishing.
- Riccardo Pravettoni (2015). Nathusius' Pipistrelle distribution and migration. Living Planet: Connected Planet, Rapid Response Assessment. UNEP/GRID-Arendal.
- Theo Douma, Daniël Tuitert & André De Baerdemaeker (2019). Een tweede kraamkolonie van ruige dwergvleermuizen Pipistrellus nathusii voor Nederland. VLEN-Nieuwsbrief 80(1): 8-11. https://www.zoogdiervereniging.nl/sites/default/files/2022-09/vlen_nieuwsbrief_80.pdf
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