Categorizing click trains to increase taxonomic precision in echolocation click loggers

Abstract

Passive acoustic monitoring is an efficient way to study acoustically active animals but species identification remains a major challenge. C-PODs are popular logging devices that automatically detect odontocete echolocation clicks. However, the accompanying analysis software does not distinguish between delphinid species. Click train features logged by C-PODs were compared to frequency spectra from adjacently deployed continuous recorders. A generalized additive model was then used to categorize C-POD click trains into three groups: broadband click trains, produced by bottlenose dolphin (Tursiops truncatus) or common dolphin (Delphinus delphis), frequency-banded click trains, produced by Risso's (Grampus griseus) or white beaked dolphins (Lagenorhynchus albirostris), and unknown click trains. Incorrect categorization rates for broadband and frequency banded clicks were 0.02 (SD 0.01), but only 30% of the click trains met the categorization threshold. To increase the proportion of categorized click trains, model predictions were pooled within acoustic encounters and a likelihood ratio threshold was used to categorize encounters. This increased the proportion of the click trains meeting either the broadband or frequency banded categorization threshold to 98%. Predicted species distribution at the 30 study sites matched well to visual sighting records from the region.

Habitat use of a coastal delphinid population investigated using passive acoustic monitoring

“…2.2 | Data quality 2.2.1 | Acoustic data processing C-POD data from 2013 to 2015 were processed with the accompanying KERNO classifier version 2.042 (www.chelonia.co.uk) for the were subsequently processed with the categorization system described in Palmer et al (2017). This system categorizes each acoustic encounter into one of the following three categories: 'broadband' , 'frequency banded' or 'unknown'.…”

“…Each acoustic encounter consisted of all high-or moderate-quality 'other cetacean' click trains starting within 20 min of the end of another click train. Acoustic encounters were subsequently processed with the categorization system described in Palmer et al (2017). This system categorizes each acoustic encounter into one of the following three categories: 'broadband' , 'frequency banded' or 'unknown'.…”

“…To incorporate classifier uncertainty into the analysis, we used the probability that broadband clicks were detected (P(Broadband)) as the response variable in the acoustic occupancy models (Palmer et al, 2017;Supporting Information). Broadband click detection probability was defined as the probability that broadband clicks were actually present, given the category produced by the classification system.…”

“…An acoustic classification system (Palmer, Brookes, & Rendell, 2017) was applied to C-POD detections in order to group detections into one of three classes: broadband, frequency banded or unknown. An acoustic classification system (Palmer, Brookes, & Rendell, 2017) was applied to C-POD detections in order to group detections into one of three classes: broadband, frequency banded or unknown.…”

“…In this research, a heuristic approach was taken to misclassification wherein species uncertainty is built into the model response. An acoustic classification system (Palmer, Brookes, & Rendell, 2017) was applied to C-POD detections in order to group detections into one of three classes: broadband, frequency banded or unknown. The broadband category represents click trains matching bottlenose dolphin and common dolphin (Delphinus spp.)…”