Is there a calibration curve available somewhere for the Audiomoth with the MEMS microphone ?
This calibration curve should give the sensitivity versus frequency for at least one direction. Is this sensitivity flat versus frequency up to 100 kHz ? Without an answer to this question, it is very difficult to evaluate the potential usefulness of this product to records bats for example.
Yep @Edwin Houwertjes is correct. AudioMoth 1.0.0 and 1.1.0 use the SPM0408LE5H - datasheet here. AudioMoth 1.2.0 uses the SPU0410LR5H - datasheet here.
Oh, it seems there could be a small error in the picture I posted. The actual part name is SPU0410LR5H-QB, the versions 1.0.0 and 1.1.0 use the SPM0408LE5H-TB like the uMoth. These elements don't have info in the datasheet above 10kHz, but have a look at the popular FG elements, these also have no specs in the ultrasound range but are very well known for their ultrasonic response. The SPM0408LE5H-TB has a built in amplifier, the pinout for SPM0408LE5H-TB and SPU0410LR5H-QB is also different so it is no drop-in replacement. The SPU0410LR5H-QB seems to work a little bit better on the higher ultrasound frequencies.
I suspect the element used on the 1.2.0 pcb is this element. It seems this is only element of which I have seen a frequency response curve up to 80Khz in a datasheet. You can see the response is not entirely flat and the higher sensitivity will probably show in your recordings. The type of mounting (PCB thickness and hole diameter) will alter the curve slightly. It would be nice to know if this is actually the type of element that is used on the 1.2.0. version.