Microphone quiet

Make sure they are stored in dry conditions, preferably outside of the housing to avoid condensation. Then when they are deployed check that the acoustic vent is in good condition. If you hold it to the light you can check for holes.

Hi Ann and Alex,

I always have an extra set of the vents handy and inspect my cases as Alex suggests. Unfortunately, ants and rodents sometimes get at the cases and damage the vents while they are deployed, if that pairs with some heavy rains, the units will be vulnerable. The one I reported for this initial post was in that situation with the cases having some chew marks and the vent punctured. The hole for the microphone is the weak spot by necessity I assume because sound has to be received by the microphone. I haven't figured out what sorts of sites will be less rodent and ant prone compared to others in the environment they are deployed in but I do try to avoid areas where I can see clear ant activity. Just my experiences. Thanks.

Yes, the vents are a compromise between robustness and acoustic transparency. Justin Kitzes's team at the University of Pittsburgh deploy AudioMoth for recording birds in plastic freezer bags and get good results - https://github.com/rhine3/audiomoth-guide/blob/master/guide.md. Similarly, Rainforst Connection have previously used waterproof dive bags. Both are much thicker than the acoustic vents so incur some signal loss, but in many applications that doesn't seem to matter.