With an analysis of bat recordings using Kaleidoscope Pro, one particular species seems to show low frequency calls. I get a lot of social calls from the Nyctalus noctula (the research was conducted in the Netherlands), but the lowest band seems to be rather low for bat species (around 8-9kHz where they should be +- 15kHz). Do any of you have an explanation for this? I have attached a few examples of the NYCNOC calls, they are one of the more common species, so I get a lot of similar calls. I figured it might be other sounds (like birds) parallel to the bat call that cause the low band, but as you can see in the images of the spectrogram and considering the fact that the same thing is happening in tens or hundreds of calls, I'd say that is unlikely.
Yes, there is a very strong bird call with a central frequency of 14kHz and the harmonics of this call are showing up at 28 and 42kHz. It's possible that this was saturating if the bird was very close, and the resulting square wave generates harmonics at each of these repeated frequencies.
Allright, thanks! I then still don't understand the high frequency part of the call. They are well above 20 kHz most of the time, and look like the courtship call of the species. I don't think bird calls go up to that frequency?
I think Kaleidoscope Pro is confusing the harmonics of the bird calls for bat calls.