Species-specific beaked whale echolocation signals

Abstract

Beaked whale echolocation signals are mostly frequency-modulated (FM) upsweep pulses and appear to be species specific. Evolutionary processes of niche separation may have driven differentiation of beaked whale signals used for spatial orientation and foraging. FM pulses of eight species of beaked whales were identified, as well as five distinct pulse types of unknown species, but presumed to be from beaked whales. Current evidence suggests these five distinct but unidentified FM pulse types are also species-specific and are each produced by a separate species. There may be a relationship between adult body length and center frequency with smaller whales producing higher frequency signals. This could be due to anatomical and physiological restraints or it could be an evolutionary adaption for detection of smaller prey for smaller whales with higher resolution using higher frequencies. The disadvantage of higher frequencies is a shorter detection range. Whales echolocating with the highest frequencies, or broadband, likely lower source level signals also use a higher repetition rate, which might compensate for the shorter detection range. Habitat modeling with acoustic detections should give further insights into how niches and prey may have shaped species-specific FM pulse types.

Using passive acoustic monitoring to document the distribution of beaked whale species in the western North Atlantic Ocean

“…To detect and classify beaked whale echolocation signals, we used a multi-step approach based on the methods described in Baumann-Pickering et al (2013). We performed all signal processing using the custom software program Triton (Wiggins and Hildebrand 2007) and custom-written MATLAB (Mathworks, Inc., Natick, Massachusetts) routines.…”

“…In the case of duty-cycled recordings, we defined a detection event as all potential beaked whale clicks occurring within a single data file corresponding to the 2-5 min "on" period of the recording cycle. For each detection event, an experienced analyst (author JES) reviewed summary figures displaying histograms of peak frequency and ICI, a concatenated spectrogram of all clicks in the event, and a plot of mean click spectra overlaid on spectral templates of known beaked whale echolocation signal types (as per Baumann-Pickering et al 2013). After examining these figures and browsing waveforms and spectrograms of individual clicks, the analyst assigned one or more species classifications to each detection event, or marked the event as a false detection.…”

Cetacean acoustic detections from free-floating vertical hydrophone arrays in the southern California Current

“…The analyst classified clicks into these general categories based on peak frequency, the signal's waveform, evidence of an upsweep in a Wigner plot, interclick interval (ICI), the vertical bearing angle, and, for sperm whales, the timbre and rhythm of the clicks (listening to playbacks). Beaked whale clicks were sub-categorized based characteristics outlined by Baumann-Pickering et al (2013). Not all beaked whale click types have been identified to species, and we used the nomenclature outlined by Bauman-Pickering for click types that could not be identified to species (including her BW40, BW43, and BW70 designations).…”

Shifts in frequency-modulated pulses recorded during an encounter with Blainville's beaked whales (Mesoplodon densirostris)

“…Beaked whales (family: Ziphiidae) produce a variety of acoustic signals, including whistles (Dawson et al, 1998), burst pulses Rankin and Barlow 2007), and echolocation signals [clicks and frequency-modulated (FM) pulses] (Baumann- Pickering et al, 2013Pickering et al, , 2014Johnson et al, 2004Johnson et al, , 2006Johnson et al, , 2008. While all call types have been detected by one or more species, the full vocal repertoire is known for few, if any, species.…”

“…While all call types have been detected by one or more species, the full vocal repertoire is known for few, if any, species. FM pulses produced by a beaked whale have potentially evolved over time to create a niche separation due to physical and/or habitat restrictions (Baumann-Pickering et al, 2013). These FM pulses have a natural variation in their characteristics (peak frequency, center frequency, À10 dB bandwidth, duration, and inter-pulse-interval; see Baumann-Pickering et al, 2013).…”