Burst-pulse Sounds Research Articles

Sounds in common: Time-frequency as the classification parameters for pulsed sounds produced by Delphinus delphis

Sounds produced by dolphins can be grouped into tonal (whistles) and pulsed sounds (e.g., echolocation clicks and burst sounds). Clicks are broadband pulses temporarily spaced to allow echo processing between the sound source and the object. Echolocation is related mainly to prey detection and environmental recognition. Echolocation click trains tend to present a decreasing inter-click interval due to a continuous changing of the target's location when the animal approaches to capture the prey. In addition to foraging and feeding contexts, burst pulsed sounds have been associated with short social communication. Although echolocation clicks are relatively well documented, there is no consensus regarding the broad variety of the burst pulsed signals. The present study analyzed time-frequency characteristics by conducting a clustering and discrimination analysis to classify pulsed sounds. A total of 64 click trains were analyzed from short-beaked common dolphins recorded in the slope region of the western South Atlantic Ocean. Three analyses (time; frequency; and combined time-frequency parameters) were compared through k-means clustering and posterior cluster validation using Random forest analysis. The k-means clustering resulted in four clusters for all groups of analysis. The time parameters were the most accurate among the comparisons, with the first two-dimensional axis corresponding to 87 % (Dim1 = 70.2 % and Dim2 = 17.2 %). The random forest analysis showed that the time-frequency dataset was the best classification of pulsed sounds in D. delphis (Accuracy = 84.6 %; confidence interval CI = 65.1 %-95.6 %; p < 0.01). This result considers the animal an acoustical identity, emphasizing the importance of certain parameters that influence this identity and thus reflecting the energy-cost optimization for sound production.

The Acoustic Repertoire of Bottlenose Dolphins (Tursiops truncatus) in the Cres-Lošinj Archipelago (Croatia): Site Dependent Diel and Seasonal Changes

Describing the acoustic repertoire of cetaceans is necessary to understand the functionality of their sounds and the effect anthropogenic pressures have on animals living in a marine environment. This study provides a description of the acoustic repertoire of bottlenose dolphins (Tursiops truncatus) in the Cres-Lošinj archipelago based on continuous 24-h recordings collected from two monitoring stations, both inside and outside the Natura 2000 Site of Community Importance, during an 8-day period in March/April 2020 and a 13-day period in July/August 2020. A total of 1008 h were visually and aurally analyzed to identify vocalizations and investigate diel and seasonal patterns in their parameters. Furthermore, sound pressure levels were calculated for the low (63 Hz–2 kHz) and high (2 kHz–20 kHz) frequency range. Bottlenose dolphins in the Cres-Lošinj archipelago were found to produce whistles, chirps, low frequency narrow-band sounds, burst pulse sounds, and echolocation clicks showing that dolphins are present at both monitoring stations, during both diel and seasonal periods, in a comparable manner. This paper also provides evidence that whistles, chirps, and low frequency narrow-band sounds change their parameters in relation to the background noise in the area, that varies according to diel and seasonal patterns. This suggests a vocal plasticity in the species and a coping strategy to avoid masking of relevant acoustic signals for the local population in the Cres-Lošinj archipelago.

Acoustic Repertoires Related to Surface Behaviours of the Irrawaddy Dolphins (Orcaella brevirostris) in Brunei Bay, Malaysia

Behavioural observation and acoustic recordings of Irrawaddy dolphins (Orcaella brevirostris) were performed simultaneously in Brunei Bay, Malaysia. Surface behavioural observations were classified into four categories: travelling, foraging, socialising, and milling. A total of 8.43 hours of acoustic recordings were used to retrieve four different types of sounds: whistles, burst-pulsed sounds, click trains, and biphonal sounds. The recorded whistles were frequency-modulated sounds with durations ranging from 0.06 to 3.86 s and a mean minimum frequency of 6.5±2.5 kHz. The burst-pulsed frequency ranged from &gt;48 kHz in at least four variations. Click trains were made up of broadband clicks with variable inter-click intervals and frequencies &gt;48 kHz. The first biphonic sounds for Irrawaddy dolphins have been revealed in this study. Whistle rates were extremely high in milling. Compared to travelling and foraging, socialising had a significantly higher rate of click trains. Across all surface behaviours, there was no significant difference in burst-pulsed rates. This study laid the groundwork for ongoing monitoring of Irrawaddy dolphins and expanding conservation efforts for this species in Malaysia.

Vocal universals and geographic variations in the acoustic repertoire of the common bottlenose dolphin

Acoustical geographic variation is common in widely distributed species and it is already described for several taxa, at various scales. In cetaceans, intraspecific variation in acoustic repertoires has been linked to ecological factors, geographical barriers, and social processes. For the common bottlenose dolphin (Tursiops truncatus), studies on acoustic variability are scarce, focus on a single signal type—whistles and on the influence of environmental variables. Here, we analyze the acoustic emissions of nine bottlenose dolphin populations across the Atlantic Ocean and the Mediterranean Sea, and identify common signal types and acoustic variants to assess repertoires’ (dis)similarity. Overall, these dolphins present a rich acoustic repertoire, with 24 distinct signal sub-types including: whistles, burst-pulsed sounds, brays and bangs. Acoustic divergence was observed only in social signals, suggesting the relevance of cultural transmission in geographic variation. The repertoire dissimilarity values were remarkably low (from 0.08 to 0.4) and do not reflect the geographic distances among populations. Our findings suggest that acoustic ecology may play an important role in the occurrence of intraspecific variability, as proposed by the ‘environmental adaptation hypothesis’. Further work may clarify the boundaries between neighboring populations, and shed light into vocal learning and cultural transmission in bottlenose dolphin societies.

Long‐term passive acoustics to assess spatial and temporal vocalization patterns of Atlantic common bottlenose dolphins (Tursiops truncatus) in the May River estuary, South Carolina

AbstractPassive acoustics has been used extensively to study bottlenose dolphins; yet very few studies have examined the spatial, temporal, and environmental influences on vocalization types (echolocation, burst pulse sounds, and whistles), and few are long‐term and provide high temporal resolution over multiple years. We used data from 2013 to 2018 to establish baseline acoustic patterns for bottlenose dolphins in the May River estuary, South Carolina. We deployed acoustic recorders at six stations during 2013–2014 and three stations during 2015–2018, with locations spanning the entire estuary (headwaters to the mouth). We discovered that acoustic detection of dolphins varied not only spatially, but also yearly, monthly, and tidally. Higher numbers of echolocation bouts, burst pulse sounds, and whistles were detected at the mouth as compared to the headwaters. At the mouth, vocalization detections were greatest in fall and winter for multiple years, and echolocation detection was greatest during falling and low tides. This study provides an example of another tool, long‐term passive acoustics monitoring, to better understand spatial and temporal distribution of dolphins in a typical salt marsh estuary, that can be applied to other ecosystems throughout the southeastern United States and globally.

Acoustic behaviour of bottlenose dolphins under human care while performing synchronous aerial jumps

Synchronous behaviours occur when two or more animals display the same behaviour at the same time. However, the mechanisms underlying this synchrony are not well understood. In this study, we carried out an experiment to determine whether or not Bottlenose dolphins use acoustic cues when performing a known synchronised exercise. For this, we recorded three dolphins while they performed requested aerial jumps both individually or synchronously in pairs, with a hydrophone array and a 360° underwater video camera allowing the identification of the subject emitting vocalisations. Results indicated that in pairs, dolphins synchronised their jumps 100% of the time. Whether they jumped alone or in pairs, they produced click trains before and after 92% of jumps. No whistles or burst-pulsed sounds were emitted by the animals during the exercise. The acoustic localisation process allowed the successful identification of the vocalising subject in 19.8% of all cases (N = 141). Our study showed that in all (n = 28) but one successful localisations, the click trains were produced by the same individual. It is worth noting that this individual was the oldest female of the group. This paper provides evidence suggesting that during synchronous behaviours, dolphins use acoustic cues, and more particularly click trains, to coordinate their movements; possibly by eavesdropping on the clicks or echoes produced by one individual leading the navigation.

Burst-pulsed sounds of rough-toothed dolphins (Steno bredanensis) in Southeastern Brazil

Recordings of Steno bredanensis were done in Southeastern Brazilian coast during eleven days between 2013 and 2017. The system consisted of a C54-XRS hydrophone (−165 dB re: 1 V/μPa, 0.009 to 100 kHz) and a Fostex FR-2 digital recorder with a 192 kHz sample rate. Recordings were inspected for burst-pulsed sounds in Adobe audition 1.5 software in a 512 Hann window, 50% overlap. When they were found, the sound was cut to a new file of 2-s window, and a butterworth high-pass filter was used when necessary. A burst-pulse sound was considered for analysis when its pulses were correctly and clearly identified in the Sound Ruler software, which was used to obtain the acoustic parameters (512 Hann window, 50% overlap). Thirty-one burst pulsed sounds were analyzed. The mean number of pulses per burst-pulse was 52 ± 44 (varying between 6 and 224), mean inter-pulse interval was 5.1 ± 1.9 ms (varying between 2.4 and 8.4 ms), mean burst-pulse duration was 0.27 ± 0.23 s (varying between 0.04 and 1.1s), and mean peak frequency was 26.1 ± 11.3 kHz (varying between 7.0 and 64.7 kHz). Although preliminary, these results show a first characterization of the burst-pulsed sounds of this species.

Contexts of emission of non-signature whistles in bottlenose dolphins (Tursiops truncatus) under human care

Bottlenose dolphins are social cetaceans that strongly rely on acoustic communication and signaling. The diversity of sounds emitted by the species has been structurally classified into whistles, clicks and burst-pulsed sounds. Although click sounds and individually-specific signature whistles have been largely studied, not much is known about non-signature whistles. Most studies that link behavior and whistle production conduct aerial behavioral observations and link the production of whistles to the general category of social interactions. The aim of this study was to determine if there was a correlation between the non-signature whistle production and the underwater behaviors of a group of bottlenose dolphins (Tursiops truncatus) under human care, during their free time in the absence of trainers. To do this we made audio-video recordings 15 min before and after 10 training sessions of eight dolphins in Boudewijn Seapark (Belgium). For the behavioral analysis we conducted focal follows on each individual based on six behavioral categories. For the acoustical analysis, carried out at the group level, we used the SIGID method to identify non-signature whistles (N = 661) and we classified them in six categories according to their frequency modulation. The occurrences of the six categories of whistles were highly collinear. Most importantly, non-signature whistle production was positively correlated with the time individuals spent slow swimming alone, and was negatively correlated with the time spent in affiliative body contact. This is the first analysis that links the production of non-signature whistles with particular underwater behaviors in this species.

The higher, the closer, the better? Influence of sampling frequency and distance on the acoustic properties of short‐beaked common dolphins burst pulses in the Mediterranean Sea

Abstract When implementing conservation strategies involving passive acoustic monitoring, an accurate description of signal properties is crucial, especially when studying threatened and elusive vocalizing species. Misrepresentation of detected sounds can result in information loss or misclassification of species, thus compromising the management process. Distortion of the time–frequency features depends on the characteristics of acoustic propagation through sea water, sensitivity and sampling frequency of the acquisition system and distance between cetacean source and the receiving sensor (hydrophone). This study examined how the sampling frequency and the distance from the source affect the properties of burst pulsed sounds emitted by short‐beaked common dolphins in the Mediterranean Sea and how the signal is modified in relation to the recording scenarios. Burst pulses were collected at 300 000 samples/s, and down‐sampled at 192 000, 96 000, 48 000 and 44 100. Fifteen acoustic parameters were automatically measured. The median values were measured and compared among the signals sampled at different rates. Finally, a transmission loss model was applied to explore the variation of the power spectrum density during click propagation through seawater. The results showed that, even if higher sampling rates are a more accurate match with the original signal, some parameters (number of clicks, inter‐click‐interval and maximum peak) measured at 96 000 and 192 000 Hz did not display significant differences compared with 300 000 Hz, except for the frequency parameters. The transmission loss model also showed that the highest frequency components strongly attenuate within 800 m from the source. These results suggest that high recording distances and lower sampling rates do not allow an accurate analysis of burst pulsed signals. However, taking into account data storage limitations, recording at the highest frequency is not always required for an accurate description of signals and the outcomes of this study improve the accuracy of passive acoustic monitoring systems, thus enhancing the potential for conservation of short‐beaked common dolphins.

Mapping cetacean sounds using a passive acoustic monitoring system towed by an autonomous Wave Glider in the Southwestern Atlantic Ocean

Passive acoustic monitoring techniques provide a useful alternative to visual surveys for monitoring of marine mammals since they are less affected by adverse weather conditions. An autonomous unmanned Wave Glider, equipped with a towed hydrophone and recording system was used to collect acoustic data in the Brazilian offshore waters of the Southwestern Atlantic Ocean between 6 and 25 February 2016. Nearly continuous data were obtained during this period (light and dark hours) for the 750 km traveled. There were 165,130 high-frequency detections in 31 encounters, including 1789 whistles, 389 burst-pulse sounds, and 162,952 echolocation clicks. A total of 705 low-frequency tonal signals were recorded in 5 encounters. Although high-frequency detections occurred at all hours of the day, the majority occurred during dark hours. Low-frequency detections were not evenly spread through all hours of the day, with the majority of them occurring during dark hours. High-frequency and low-frequency detections represented 26% and 3% of the recording hours, respectively. Duration, the number of emissions, and ocean depth varied among acoustic encounters. Encounters composed by high-frequency sounds were separated into seven different groups, probably different species. One of the encounters presented whistles that were previously recorded in the Rio de Janeiro Coast for Steno bredanensis (Rough-toothed dolphins). All of the low-frequency encounters were composed of a type of Balaenoptera brydei (Bryde's whales) call. This type of data collection is un-precedented for the Southwestern Atlantic Ocean and highlighted the use of the sampled area by delphinids on different days and different times of the day, including the dark hours.

Antarctic type C killer whale (Orcinus orca) call repertoire from McMurdo Sound, Ross Sea

Killer whales (Orcinus orca) are found in all oceans of the world. In Antarctic waters, five ecotypes have been described, each displaying distinct differences in morphological features, foraging behaviours, habitat and diet preferences, and genetic structure. Acoustic recordings of Type C killer whales were collected between December 2012 and January 2013 in McMurdo Sound, Ross Sea, Antarctica. Spectrograms of acoustic data were examined for characteristic patterns of Type C vocalizations and a call type catalogue was produced. We measured acoustic parameters of each call type for both whistle and burst-pulse sounds and we then compared call features of Type C animals to those of other killer whales described in the Southern Hemisphere. Analysis of calls revealed that Type C killer whales produce a large number of biphonations and complex calls with multiple frequency-modulated and pulsed components. The limited accessibility of Antarctic regions year-round makes passive acoustic monitoring (PAM) a very effective tool to derive information on ecotype-specific distribution and seasonal occurrence. This study provides new information on the call repertoire of Type C killer whales, investigates the potential use of PAM to study Antarctic ecotypes, and also examines utilising call repertoire as a reliable diagnostic tool for identifying sympatric ecotypes in Antarctic waters.

Characteristics of Guiana dolphins (Sotalia guianensis) burst-pulse sounds emitted during different surface activity rates in Rio de Janeiro’s coast

Burst-pulses are still the least studied signals in delphinid acoustic repertoire. In this study, acoustic data were gathered in two Rio de Janeiro coastal bays where groups of Guiana dolphins can be found regularly. The acoustic equipment consisted of a C54XRS hydrophone (-155.8 dBV, 0.006 Hz a 203 kHz) and a Fostex digital recorder (192 kHz sampling rate). During each recording, the surface activity rate of the group was classified as being high or low. Burst-pulses were analyzed using SoundRuler software. Fifty signals were randomly selected and the values for duration (low = 143.9 ± 145.4; high = 82.2 ± 74.8), interpulse interval (low = 2.81 ± 1.92; high = 1.34 ± 1.35), number of pulses (low = 52.6 ± 55.7; high = 71.6 ± 64.5), peak frequency (low = 37.4 ± 2.5; high = 38.5 ± 3.2), and minimum frequency (low = 15.4 ± 6.5; high = 6.7 ± 5.3) were measured. Additionally, a Mann-Whitney U test compared all acoustic parameters of burst-pulses emitted during both surface activity rates. Significant differences between activity rates were found for interpulse interval (p<0.01) and minimum frequency (p<0.01). This scenario could indicate that some burst-pulse parameters are related to group arousal and behavior.Burst-pulses are still the least studied signals in delphinid acoustic repertoire. In this study, acoustic data were gathered in two Rio de Janeiro coastal bays where groups of Guiana dolphins can be found regularly. The acoustic equipment consisted of a C54XRS hydrophone (-155.8 dBV, 0.006 Hz a 203 kHz) and a Fostex digital recorder (192 kHz sampling rate). During each recording, the surface activity rate of the group was classified as being high or low. Burst-pulses were analyzed using SoundRuler software. Fifty signals were randomly selected and the values for duration (low = 143.9 ± 145.4; high = 82.2 ± 74.8), interpulse interval (low = 2.81 ± 1.92; high = 1.34 ± 1.35), number of pulses (low = 52.6 ± 55.7; high = 71.6 ± 64.5), peak frequency (low = 37.4 ± 2.5; high = 38.5 ± 3.2), and minimum frequency (low = 15.4 ± 6.5; high = 6.7 ± 5.3) were measured. Additionally, a Mann-Whitney U test compared all acoustic parameters of burst-pulses emitted during both surface activity rates. Significant difference...

High-Frequency Modulated Signals Recorded Off the Antarctic Peninsula Area: Are Killer Whales Emitting Them?

High-frequency modulated signals with a stereotyped down-swept contour were recorded in the northwestern Antarctic Peninsula using an autonomous recorder and a towed hydrophone array. Signals have a mean start frequency at 21.6 kHz, end frequency at 15.7 kHz, −10 dB bandwidth of 5.9 kHz, and duration of 65.2 ms. Bouts of signals were generally recorded with a median inter-signal interval of 2.1 s. HFM signals partially modulated in the non-ultrasonic range similar to the ones described in this paper have already been reported for killer whales in the North Pacific, Western South Atlantic and Western Australian coast. The HFM signals were recorded in the presence of other odontocete sounds such as whistles, echolocation clicks and burst-pulsed sounds. The similarities of these sounds with vocalizations described for killer whales in the Western Australian coast lead us to strongly believe that the described HFM signals were produced by Antarctic killer whales. This paper described for the first time HFM signals in Antarctica and discussed evidence suggesting that Antarctic type A killer whales are the most probable candidates to produce such signals. However, a visual confirmation is still needed and the function of the HFM signals remains unknown.

Review of Underwater and In-Air Sounds Emitted by Australian and Antarctic Marine Mammals

The study of marine soundscapes is a growing field of research. Recording hardware is becoming more accessible; there are a number of off-the-shelf autonomous recorders that can be deployed for months at a time; software analysis tools exist as shareware; raw or preprocessed recordings are freely and publicly available. However, what is missing are catalogues of commonly recorded sounds. Sounds related to geophysical events (e.g. earthquakes) and weather (e.g. wind and precipitation), to human activities (e.g. ships) and to marine animals (e.g. crustaceans, fish and marine mammals) commonly occur. Marine mammals are distributed throughout Australia’s oceans and significantly contribute to the underwater soundscape. However, due to a lack of concurrent visual and passive acoustic observations, it is often not known which species produces which sounds. To aid in the analysis of Australian and Antarctic marine soundscape recordings, a literature review of the sounds made by marine mammals was undertaken. Frequency, duration and source level measurements are summarised and tabulated. In addition to the literature review, new marine mammal data are presented and include recordings from Australia of Omura’s whales (Balaenoptera omurai), dwarf sperm whales (Kogia sima), common dolphins (Delphinus delphis), short-finned pilot whales (Globicephala macrorhynchus), long-finned pilot whales (G. melas), Fraser’s dolphins (Lagenodelphis hosei), false killer whales (Pseudorca crassidens), striped dolphins (Stenella coeruleoalba) and spinner dolphins (S. longirostris), as well as the whistles and burst-pulse sounds of Australian pygmy killer whales (Feresa attenuata). To date, this is the most comprehensive acoustic summary for marine mammal species in Australian waters.

Vocalizations Produced by Bottlenose Dolphins (Tursiops truncatus) during Mouth Actions in Aggressive and Non-aggressive Contexts

Dolphins exchange information with conspecifics using different types of vocalizations that are often associated with specific behaviors. The present study used simultaneous acoustic and video recordings of captive bottlenose dolphins (Tursiops truncatus) in Honduras to describe potential correlations between the type of mouthing behavior (open mouth, mouthing, bite) and associated vocalizations (whistle, whistle-squawk, chirp, moan, burst-pulse ‘A’, burst-pulse ‘B’, clicks). Literature on sound-behavior relationships among odontocetes with the noted infrequent systematic analyses of mouth actions highlights the need for this investigation. The influence of aggression on vocalization use was also addressed. From this observational study a series of general expectations on the interaction of sound, mouth action, and aggressive context are presented. Mouth actions are associated with vocalizations more often than not, and results suggest an overall flexible association of vocalizations during mouth actions, with the production of various sounds altered during aggressive contexts. There is an apparent distinction of frequency-modulated sounds with mouthing, suggesting that frequency parameters are an important characteristic of information exchange during mouth actions, and further that mouth actions are individually distinct behaviors. A dichotomy of burst pulse sounds in association with aggressive and non-aggressive contexts also introduces the need to analyze pulsed sounds according to inter-pulse interval. This paper proposes that there may be an interactive function to the use of vocalizations during mouth actions that is not yet understood.

Modulation of whistle production related to training sessions in bottlenose dolphins (Tursiops truncatus) under human care.

Bottlenose dolphins are highly social cetaceans with an extensive sound production including clicks, burst-pulsed sounds, and whistles. Some whistles, known as signature whistles, are individually specific. These acoustic signatures are commonly described as being emitted in contexts of stress during forced isolation and as group cohesion calls. Interactions between humans and captive dolphins is largely based on positive reinforcement conditioning within several training/feeding sessions per day. Vocal behavior of dolphins during these interactions might vary. To investigate this, we recorded 10 bottlenose dolphins of Parc Asterix dolphinarium (France) before, during and after 10 training sessions for a total duration of 7 hr and 32 min. We detected 3,272 whistles with 2,884 presenting a quality good enough to be categorized. We created a catalog of whistle types by visual categorization verified by five naive judges (Fleiss' Kappa Test). We then applied the SIGID method to identify the signatures whistles present in our recordings. We found 279 whistles belonging to one of the four identified signature whistle types. The remaining 2,605 were classified as non-signature whistles. The non-signature whistles emission rate was higher during and after the training sessions than before. Emission rate of three signature whistles types significantly increased afterwards as compared to before the training sessions. We suggest that dolphins use their signature whistles when they return to their intraspecific social interactions succeeding scheduled and human-organized training sessions. More observations are needed to make conclusions about the function of signature whistles in relation to training sessions. Zoo Biol. 35:495-504, 2016. © 2016 Wiley Periodicals, Inc.

Context specificity of Atlantic spotted dolphin acoustic signals in the Canary Islands

The behavioural context provides opportunities for studying the use and characteristics of acoustic signals. We analysed the context-specific use of acoustic signals in a population of Atlantic spotted dolphins around the Canary archipelago. We calculated the whistle diversity, the mean value of whistle stereotypy and the repetition rate of both tonal and burst-pulsed sounds. Eleven parameters of frequency, signal duration and modulation were measured from each whistle. Results showed that whistle diversity and whistle and chirp repetition rates were negatively correlated with group size, but only whistle diversity and the mean number of stereotypy were related to behavioural activity. Whistles were more complexly modulated during high behavioural activity than when engaged in moderate movements. Furthermore, during socialising and feeding, the highest mean value of stereotypy was displayed, and the parameters of non-stereotyped whistles had lower variability. Our results suggest the use of a complex communication system to improve the efficiency of communication through context-specific signal combinations, the usage of different signals and their modulation pattern. Our study produces evidence to support the hypothesis that acoustic plasticity and differences in call characteristics may be indicative of behavioural and social acoustic environment.

Vocalisations of Killer Whales (Orcinus orca) in the Bremer Canyon, Western Australia.

To date, there has been no dedicated study in Australian waters on the acoustics of killer whales. Hence no information has been published on the sounds produced by killer whales from this region. Here we present the first acoustical analysis of recordings collected off the Western Australian coast. Underwater sounds produced by Australian killer whales were recorded during the months of February and March 2014 and 2015 in the Bremer Canyon in Western Australia. Vocalisations recorded included echolocation clicks, burst-pulse sounds and whistles. A total of 28 hours and 29 minutes were recorded and analysed, with 2376 killer whale calls (whistles and burst-pulse sounds) detected. Recordings of poor quality or signal-to-noise ratio were excluded from analysis, resulting in 142 whistles and burst-pulse vocalisations suitable for analysis and categorisation. These were grouped based on their spectrographic features into nine Bremer Canyon (BC) “call types”. The frequency of the fundamental contours of all call types ranged from 600 Hz to 29 kHz. Calls ranged from 0.05 to 11.3 seconds in duration. Biosonar clicks were also recorded, but not studied further. Surface behaviours noted during acoustic recordings were categorised as either travelling or social behaviour. A detailed description of the acoustic characteristics is necessary for species acoustic identification and for the development of passive acoustic tools for population monitoring, including assessments of population status, habitat usage, migration patterns, behaviour and acoustic ecology. This study provides the first quantitative assessment and report on the acoustic features of killer whales vocalisations in Australian waters, and presents an opportunity to further investigate this little-known population.

The acoustic repertoire of wild common bottlenose dolphins (Tursiops truncatus) in Walvis Bay, Namibia

Describing the repertoire of sounds produced by wild cetaceans is necessary for understanding their function, for acoustic population monitoring and for measuring the potential influence of anthropogenic impact. Geographic variation in the types and parameters of sounds makes regional assessment of vocal behaviour necessary. We describe the acoustic repertoire of a small population of common bottlenose dolphins (Tursiops truncatus) inhabiting Walvis Bay, Namibia from recordings made over 59 encounters (72 h) between 2009 and 2012. The characteristics of burst pulse (BP) sounds, low-frequency narrow-band (LFN) sounds, brays, whistles and chirps are described. The BP sounds identified were generated at 150–1050 pulses per second, and most were short, lasting less than 1 s in duration. Bottlenose dolphins from Walvis Bay produce the lowest frequency LFN sounds described for the species. Whistles ranged in frequency from 1.58 to 23.24 kHz, and the mean acoustic parameters were within the range of those described from other geographic regions. Chirps were identified infrequently and usually as single occurrences. Although several sound types were often produced in close temporal succession, we found little evidence of stereotyped bray production, even during recordings of animals feeding. Our results demonstrate geographic variation in both the characteristics and sound types used by bottlenose dolphins and highlight the importance of regional data collection as a pre-curser to passive acoustic monitoring programmes.

Clicks, whistles and pulses: Passive and active signal use in dolphin communication

The search for signals out of noise is a problem not only with radio signals from the sky but in the study of animal communication. Dolphins use multiple modalities to communicate including body postures, touch, vision, and most elaborately sound. Like SETI radio signal searches, dolphin sound analysis includes the detection, recognition, analysis, and interpretation of signals. Dolphins use both passive listening and active production to communicate. Dolphins use three main types of acoustic signals: frequency modulated whistles (narrowband with harmonics), echolocation (broadband clicks) and burst pulsed sounds (packets of closely spaced broadband clicks). Dolphin sound analysis has focused on frequency-modulated whistles, yet the most commonly used signals are burst-pulsed sounds which, due to their graded and overlapping nature and bimodal inter-click interval (ICI) rates are hard to categorize. We will look at: 1) the mechanism of sound production and categories of sound types, 2) sound analysis techniques and information content, and 3) examples of lessons learned in the study of dolphin acoustics. The goal of this paper is to provide perspective on how animal communication studies might provide insight to both passive and active SETI in the larger context of searching for life signatures.