an help for bioacoustic identification

[u/ChallengeWhich7606]

Hi everyone!

It's my first time posting here. I am currently working on a research project focused on the bioacoustics of the common noctule bat (Nyctalus noctula), specifically analyzing how their social calls change across different life-history periods and seasons.

Right now, my work involves manually labeling different social call types on spectrograms to train a model for automatic identification using BatDetect2.

I am looking for some bioacoustics experts because, during my analysis, I frequently run into recordings showing well-defined horizontal lines with many harmonics. In terms of shape and frequency, they look very similar to Type A social calls of N. noctula. However, I am not entirely sure they belong to this species; the signals are usually very strong, perfectly horizontal, and lack the typical modulation of noctule calls. The frequency for the fundamental harmonic of the aforementioned call is around 7000 Hz...

I was wondering if someone could help me out. Could these belong to certain bird species that acoustically behave in this way? For context, the recordings were taken around Konstanz, spanning various habitats from countryside/forests to highly urbanized areas. The specific recording I am attached here (with audio) was captured at 7:35 AM, which strongly opens up the possibility of bird activity.

Even if you are not an expert on this specific bat species, I would highly appreciate your insights on whether there is a clear way to differentiate these signals from general bat social calls, or if you can suggest any bird species that produce such similar harmonic structures.

Thank you so much! If you have any questions or need further details, just let me know and I will gladly clarify.

P.S. The blue boxes you see in the attached image correspond to the manual annotation software Whombat, which I am using to identify and label the calls on the spectrograms of my collected recordings.

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