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.