The effect of call libraries and acoustic filters on the identification of bat echolocation

• Published in: Ecology and evolution Vol. 4; no. 17; pp. 3482 - 3493
• Main Authors: Clement, Matthew J., Murray, Kevin L., Solick, Donald I., Gruver, Jeffrey C.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.09.2014; Blackwell Publishing Ltd
• Subjects: Acoustic noise; Acoustic surveying; Acoustic surveys; Acoustics; Anabat; Analook; bat detectors; Bats; Chiroptera; Classification; cross‐validation; discriminant function analysis; Echolocation; Ecological monitoring; Endangered & extinct species; Filters; Function analysis; Habitats; Identification; Identification methods; Libraries; Model accuracy; Modelling; Myotis sodalis; Original Research; Researchers; Sensors; Software; Sound; Species; species identification; Training; Indiana; United States > US; North America; Analook; species identification; Acoustic surveys; Anabat; discriminant function analysis; cross-validation; Myotis sodalis; classification; bat detectors; Chiroptera
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.1201

Quantitative methods for species identification are commonly used in acoustic surveys for animals. While various identification models have been studied extensively, there has been little study of methods for selecting calls prior to modeling or methods for validating results after modeling. We obtained two call libraries with a combined 1556 pulse sequences from 11 North American bat species. We used four acoustic filters to automatically select and quantify bat calls from the combined library. For each filter, we trained a species identification model (a quadratic discriminant function analysis) and compared the classification ability of the models. In a separate analysis, we trained a classification model using just one call library. We then compared a conventional model assessment that used the training library against an alternative approach that used the second library. We found that filters differed in the share of known pulse sequences that were selected (68 to 96%), the share of non‐bat noises that were excluded (37 to 100%), their measurement of various pulse parameters, and their overall correct classification rate (41% to 85%). Although the top two filters did not differ significantly in overall correct classification rate (85% and 83%), rates differed significantly for some bat species. In our assessment of call libraries, overall correct classification rates were significantly lower (15% to 23% lower) when tested on the second call library instead of the training library. Well‐designed filters obviated the need for subjective and time‐consuming manual selection of pulses. Accordingly, researchers should carefully design and test filters and include adequate descriptions in publications. Our results also indicate that it may not be possible to extend inferences about model accuracy beyond the training library. If so, the accuracy of acoustic‐only surveys may be lower than commonly reported, which could affect ecological understanding or management decisions based on acoustic surveys. We demonstrate methods to isolate and select bat echolocation from sound files using computer filters. Such methods contribute to species identification by replacing ad hoc methods that are less objective and repeatable. We also demonstrate that cross‐validation of species identification models with an independent call library yields lower classification success, indicating that the accuracy of acoustic surveys may be lower than commonly reported.