noise at low frequencies

Hi,

I am a new user of audiomonth and new to bioacustics as well, so my question might be naive but I still hope somebody can help me. I want to use the audiomonth to monitor owls. The species of interest (Eagle Owl) calls in the range of 300-600 Hz. When doing some tests over the last days, I can clearly hear the calls on the audio, but when looking at the spectrograms the calls are hard or even impossible to detect among the noise signals. This is not the case for higher frequency calls by other species though as the noise is limited to below 600 Hz. As I will have thousands of hours of recording later, I was hoping to see the calls on the spectrograms, rather than needing to listen to everything. Is there any possibility to reduce the noise signature other than reducing the gain? Would it help to have microphone foam around the entire audiomoth?

Thanks

Arne