To Bag or Not to Bag? How AudioMoth-Based Passive Acoustic Monitoring Is Impacted by Protective Coverings.

Area of Science:

• Ecology
• Acoustics
• Bioacoustics

Background:

• Passive acoustic monitoring (PAM) relies on devices like AudioMoth recorders.
• Protecting these recorders in enclosures is necessary for field deployment.
• The impact of enclosures on acoustic data quality is not well understood.

Purpose of the Study:

• To assess how polythene bag enclosures affect the spectral characteristics of AudioMoth recordings.
• To evaluate the influence of enclosures on various acoustic metrics.
• To determine the reliability of acoustic index comparisons when using bagged recorders.

Main Methods:

• Recordings of pure sinusoidal tones (100 Hz–20 kHz) were made using AudioMoth devices in an anechoic chamber.
• Comparisons were made between bare board devices and devices enclosed in different polythene bags.
• Frequency response functions were analyzed, and filters were applied to assess the impact on 19 acoustic metrics.

Main Results:

• Bare board AudioMoth recorders exhibited consistent spectral responses with higher frequency accentuation.
• Polythene bag enclosures introduced significant, erratic, and frequency-inconsistent attenuation.
• Few acoustic metrics remained unaffected, compromising the reliability of index comparisons.

Conclusions:

• Enclosure choice critically impacts PAM data, introducing biases in acoustic metrics.
• Careful consideration of enclosure effects is vital for selecting appropriate acoustic indices in ecological studies.
• Archived recordings lacking metadata on enclosures should be interpreted with caution due to potential biases.