Bat calls at low frequencies

Hi all,

I've recently been using Audiomoth for nocturnal bird migration sampling in Spain and I was surprised to catch bat calls at unusual very low frequencies (5kHz or lower) with a sampling rate of 44kHz or less. Attach to this message you can find some examples. Having in mind bats usually call >20kHz (except for the bigger Noctules -10-20kHz- and the European Free-tailed Bat-usually around 10kHz-), those bat calls should not be there. They sound like they were sampled using a frequency division detector and some of them are probably Soprano Pipistrelle, which I have every night flying around home and sing 10x higher in freq. (usually 50-55kHz). Other Audiomoth users I know have also experienced this.

I've tried to find a possible explanation for this. Perhaps Audiomoth "mixes" configuration parameters and those calls are actually sampled at a higher rate but displayed as if they were sampled in a lower rate?

Have any of you come across this matter? Many thanks in advance,

Robert Manzano