Abstract
Much can be learned by investigating the click trains of odontocetes, including estimating the number of vocalizing animals and comparing the acoustic behavior of different individuals. Analyzing such information gathered from groups of echolocating animals in a natural environment is complicated by two main factors: overlapping echolocation produced by multiple animals at the same time, and varying levels of background noise. Starkhammar et al. [(2011a). Biol. Lett. 7(6), 836-839] described an algorithm that measures and compares the frequency spectra of individual clicks to identify groups of clicks produced by different individuals. This study presents an update to this click group separation algorithm that improves performance by comparing multiple click characteristics. There is a focus on reducing error when high background noise levels cause false click detection and recordings are of a limited frequency bandwidth, making the method applicable to a wide range of existing datasets. This method was successfully tested on recordings of free-swimming foraging dolphins with both low and high natural background noise levels. The algorithm can be adjusted via user-set parameters for application to recordings with varying sampling parameters and to species of varying click characteristics, allowing for estimates of the number of echolocating animals in free-swimming groups.
Highlights
Toothed whales and dolphins use two broad categories of vocalizations: whistles and clicks (Janik, 2009; Tyack, 2019)
Much can be learned by investigating the click trains of odontocetes, including estimating the number of vocalizing animals and comparing the acoustic behavior of different individuals
All echolocation clicks are short duration (
Summary
Toothed whales and dolphins (odontocetes) use two broad categories of vocalizations: whistles and clicks (Janik, 2009; Tyack, 2019). Whistles are narrowband and frequency-modulated vocalizations used for social communication in most odontocete species (Morisaka, 2012; Tyack, 2019). These tonal vocalizations have been best studied in bottlenose dolphins (Tursiops spp.), which have typical whistle durations of 0.06–5.4 s and fundamental frequencies up to 41 kHz (Hiley et al, 2017; Kaplan and Reiss, 2017; Jones et al, 2020). Echolocation clicks have been best studied in bottlenose dolphins (Tursiops spp.), which have typical click train durations of 0.1 to 5.0 s (Lilly and Miller, 1961; Finneran et al, 2014; Jones et al, 2020; Starkhammar et al, 2011a; Starkhammar et al, 2019)
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