Missing something? Importance of measurement criteria of acoustic parameters in the analysis of bats recordings

Abstract

Ultrasound detectors are becoming an increasingly used tool in bat research. Still, the lack of standardization of measurement criteria in the analysis of recordings is problematic when attempting identifications. For instance, the analytical procedures depend on the technique for obtaining the spectral content of an echolocation pulse (eg. zero-crossing, Fourier analysis) –which is directly related to the detection device and software-, and they should be as consistent as possible among studies’ and observers’ to allow comparisons. Using full-spectrum recordings of a Myotis species, we measured the minimum frequency and maximum frequency on the spectrogram, as well as considering four thresholds on the power spectrum: at -55 and -50 decibels from 0 decibels, and at 18 and 6 decibels below peak frequency. Focusing on the minimum frequency, we found statistically significant differences of measurements obtained on the spectrogram vs. power spectrum, with higher mean values in the latter as product of pulse truncation, as well as statistically significant differences between two trained observers. The measurements relative to the peak frequency were less variable. Without proper considerations, these issues may represent confounding factors and derive data unsuitable for cross-studies comparisons and potential misidentifications. We make recommendations about measurement criteria and emphasize the importance of replication and more rigorous reports.