Underwater Vocalizations Research Articles

Presence of ribbon seal vocalizations are related to sea ice extent in the Nemuro Strait, the Okhotsk Sea

Vocalizations of ice-breeding ribbon seals Histriophoca fasciata were recorded using underwater passive acoustic methods from November 2012 to March 2014 off the Nemuro Strait, Japan. Seal presence in the strait was examined in relation to the sea ice extent in the Okhotsk Sea. Ribbon seal downsweeps were only detected when sea ice was present in the strait (February and March), with more detections in March leading up to the spring breeding season. Since ribbon seals require ice for breeding, underwater communication for breeding could be needed during the sea ice presence in this strait. Northeasterly winds were another indirect driver of ribbon seal occurrence, since winds from this direction likely transport sea ice from the central Okhotsk Sea into the Nemuro Strait. Downsweep detections decreased in the middle of the day, which is consistent with observations that seals hauled out on the ice during this time, and thus were producing fewer underwater vocalizations. Our results suggest that a decrease in the sea ice extent in the Okhotsk Sea may change the distribution of ribbon seals and impact their breeding behaviour since the Nemuro Strait region of the Okhotsk Sea is likely the southern limit of their breeding range.

Sequential calls and associated behavior in captive bearded seals (Erignathus barbatus)

Bearded seals produce complex underwater sounds suggested to function as territorial and/or courtship signals. However, little is known about behavioral context of the vocalization, mainly because direct observation is difficult in the wild. In this study, we recorded underwater sounds and behaviors of three captive bearded seals (an adult male and two adult females) in Otaru aquarium, Japan, between March 2012 and April 2016, in order to identify the caller and to record association between vocalization and behaviors. The male continuously vocalized from December until April with a peak in March, equivalent to breeding season in the wild. In contrast, the females vocalized only 1-2 weeks in March or April. The male and the females produced 3 and 5 call types, respectively, sharing 2 call types. The 3 call types of the male occurred in a regularly ordered sequence that was stable during this study. The females responded to the male sequential calls by nuzzling against the throat of vocalizing male during the breeding season, when the females also actively vocalized. Our results suggest that underwater vocalization of bearded seals might be used as a courtship signal between male and female possibly to advertise their reproductive status.

Geographically specific underwater vocalizations of ribbon seals (Histriophoca fasciata) in the Okhotsk Sea suggest a discrete population

Geographically specific underwater vocalizations of ribbon seals (<i>Histriophoca fasciata</i>) in the Okhotsk Sea suggest a discrete population

Underwater vocalizations and associated behavior in captive ringed seals (Pusa hispida)

In pinniped species, especially those that mate in the water, acoustic communication is suggested to play an important role in various aspects of behavior. However, little is known about the behavioral context or function of vocalization, principally because direct observation is difficult in the wild. In the present study, we analyzed the seasonality, sexual differences, and behavioral contexts of the vocalizations of captive ringed seals to explore the function of such communication. The behavior of and underwater sounds made by three ringed seals (an adult male, an adult female, and a subadult female) living in Otaru Aquarium, Japan, were recorded for 19 days between August 2011 and April 2012. Six call types (long snort, knock, yelp, bark, click, and woof) were identified in the recordings. The 12 observed social behaviors could be categorized into three categories (male courtship, aggression, and submission). All call types except clicks were vocalized during social behavior. Vocalizations of all types increased during the breeding season. The long snorts were only produced by the adult male toward an adult female during his courtship behavior. All three individuals emitted knocks, yelps, and bark sounds. Of these three call types, knocks were associated with aggressive behavior or the male’s courtship behavior. In contrast, alternate series of yelps and barks were vocalized by the recipients of aggressive behaviors, suggesting their function as submissive signals. This study could be applied to the monitoring of wild ringed seals with passive acoustic recordings to assess not only their distribution but also their behavior.

Potential Masking of the Baltic Grey Seal Vocalisations by Underwater Shipping Noise in the Lithuanian Area of the Baltic Sea

Acoustical surveys were completed in the Lithuanian Sea Museum and the Lithuanian area of the Baltic Sea during the period of 2012–2013. Underwater vocalisations of the Baltic grey seals were recorded and collated with underwater shipping noise recorded in the shallow area of the Lithuanian area of the Baltic Sea with the aim to evaluate possible masking of social vocalisations of animals. The following paper focuses not on the complex biomedical auditory or brain stem response research, but on the acoustical measurements and evaluation of possible masking of social vocalisations of grey seals by shipping noise. The results of the survey show masking potential of grey seal communication calls at significant distance in the presence of local shipping noise where the detection distance of calls between conspecifics can be significantly reduced. DOI: http://dx.doi.org/10.5755/j01.erem.70.4.6913

Acoustic characterization and vocal behavior of North Atlantic right whale surface active groups

Focal acoustic surveys were conducted to assess the vocal behavior of North Atlantic right whales in the shallow waters of the southeast critical habitat. Underwater vocalizations were archived using autonomous buoys in close proximity to surface active groups (SAGs) providing sound production data vital for regional passive acoustic monitoring and conservation. Classification trees were used to examine the distinguishing characteristics of calls and quantify their variability within the surface active groups vocal repertoire. Calling rates were higher than those reported in the Bay of Fundy, which may be a factor of habitat demographics. Sound production rate and call type usage were correlated with group cohesion, revealing a consistent call distribution pattern across SAGs of varying sizes and composition. The within-bout clustering probability of low and high frequency calls suggest that temporal affinities between vocalization classes may be indicators of shared social functions. The results demonstrate that concurrent temporal and spectral analysis is powerful for investigating and presenting the interrelationships of calls with social behavior and group composition.

Vocalization characteristics of North Atlantic right whale surface active groups in the calving habitat, southeastern United States.

Passive acoustic surveys were conducted to assess the vocal behavior of North Atlantic right whales (Eubalaena glacialis) in the designated critical calving habitat along the shallow coastal waters of southeastern United States. Underwater vocalizations were recorded using autonomous buoys deployed in close proximity to surface active groups (SAGs). Nine main vocalization types were identified with manual inspection of spectrograms, and standard acoustic descriptors were extracted. Classification trees were used to examine the distinguishing characteristics of calls and quantify their variability within the SAG vocal repertoire. The results show that descriptors of frequency, bandwidth, and spectral disorder are the most important parameters for partitioning the SAG repertoire, contrary to duration-related measures. The reported source levels and vocalization statistics provide sound production data vital to inform regional passive acoustic monitoring and conservation for this endangered species.

Motorboat noise can potentially mask the whistle sound of estuarine dolphins (Sotalia guianensis)

Masking the sounds uttered by cetaceans is an important issue in underwater noise pollution produced by vessels. This research aimed to determine whether noises produced by the engines of tourism boats can mask whistles emitted by estuarine dolphins (Sotalia guianensis). Data collection was conducted at Baía dos Golfinhos (English: Dolphin Bay) (Rio Grande do Norte, Brazil), an area mainly used for foraging by these animals. We recorded underwater vocalizations of the animals and the sound generated by motorboats in the Bay using equipment capable of capturing sounds with frequencies up to 40 kHz. Sound amplitude was compared at 6, 10, 16 and 30 kHz. We also observed the boats activity in the area. The results showed that the noise produced by motorboats can reach frequencies of up to 40 kHz (average: petrol = 17.1 kHz, ± 8.4; diesel = 13.1 kHz, ± 4.9) and is similar to the whistles uttered by the estuarine dolphin (up to 35 kHz; average: 19 kHz, ± 6.2). The sound amplitude also reached similar values at the frequencies of 6, 10, 16 and 30 kHz for petrol engines, and 6 kHz for diesel motorboats (whistles were higher at 10 and 16 kHz). Thus, engine noise is a potential source of disturbance to the whistles uttered by these cetaceans. Even the presence of one tourism boat can potentially interfere with the communication between individuals and, as a consequence, on the performance of natural behaviours. Thus, our results can help to explain previous studies on estuarine dolphins that found behavioural disturbances in the presence of tourism boats. In addition, such findings are in accordance with a number of studies on other cetacean species that recorded negative impacts caused by motorboats. As a precautionary measure, a number of areas constantly used by the estuarine dolphins, such as the Baía dos Golfinhos, should be closed to motorboat traffic. This would minimize the negative impact caused by human activities on the welfare and conservation of the estuarine dolphins.

Spatio-temporal distribution of ice seals in the Chukchi Sea using underwater vocalizations: Special focus on male bearded seals

Underwater vocalizations of ringed, ribbon and bearded seals were recorded over a wide region of the northeastern Chukchi Sea between July 2007 and October 2011. Ringed seals were identified by their barks and yelps, ribbon seals by their sweeps and puffing sounds and bearded seals by their trills, ascents and moans. Ringed seal vocalizations were detected in all months of the year, whereas vocalizations from ribbon seals occurred only in October and November. To determine the seasonal variation in the frequency of occurrence of male bearded seal vocalizations throughout a year 20-min recordings were analyzed to determine call counts between 02:00 and 06:00 every 3 days. Bearded seal acoustic detections increased progressively from August to March, peaked between April and June but were essentially absent in July. Outside of the mating period (April - June) the frequency of occurrence of vocalizations varied on a diel cycle and was higher during periods of darkness. To determine the influence of diel cycle, the duration of vocalizations and the proportion of each vocal type throughout the mating season 10-min recordings on a 17-20% duty cycle were analysed between April and June every 10 days. Results are currently under review and will be presented.

Anatomy to Acoustics: The Mechanism of Humpback Whale Sound Production

Humpback whales emit complex songs comprised of successive sound units with a fundamental frequency and harmonics. It is unknown how these calls are produced, given that the respiratory tract is closed (i.e., no egress of air from the nose or mouth) during underwater vocalizations. Unlike open system of terrestrial mammals, the whale vocal tract is subject to flow cessation as pressure builds. Prior studies on cetacean laryngeal anatomy (Reidenberg and Laitman, 2007) showed a communication for airflow between the trachea and an expandable ventral diverticulum called the laryngeal sac. We propose a theoretical model of humpback whale sound production based on the source‐filter theory that accounts for a closed system constrained by the dimensions of the trachea, the nasopharynx, and the laryngeal sac. We used recordings of humpback whales from the Indian Ocean (provided by Cetamada Association, Madagascar). Results show a relationship between time (duration) and spectral features (fundamental frequencies) of these calls. As this is a closed system, duration is dependent upon laryngeal sac pliability, while frequency is determined by vocal tract length. Our investigation is a first step towards defining individual acoustic signatures. Future studies will assess whether predicted durations and frequencies, based upon known vocal tract measures, fall within the range of actual recorded sounds.

The relationship between the behavioral activity and the underwater vocalization of the beluga whale (Delphinapterus leucas)

The underwater vocalizations of the beluga whale summering in Onega Bay (64°24′N, 35°49′E) were recorded in June–July of 2008. The vocalizations were classified into five major whistle types, four types of pulsed tones, click series, and noise vocalizations. To determine the relationship between the behavioral activity and the underwater vocalizations, a total of fifty-one 2 minute-long samples of the audio records were analyzed in the next six behavioral contexts: directional movements, quiet swimming, resting, social interactions, individual hunting behavior, and the exploration of hydrophones by beluga whales. The overall vocalization rate and the percentage of the main types of signals depend on the behavior of the belugas. We suggest that one of the whistle types (the “stereotype whistle”) is used by belugas for long-distance communications, while other whistle types (with the exception of “squeaks”) and three types of pulsed tones (with the exception of “vowels”) are used for short distance communication. The percentage of “squeaks” and “vowels” was equally high in all the behavioral situations. Thus, we assume that “squeaks” are contact signals. “Vowels” have a specific physical structure and probably play a role in identification signals. A high rate of the click series was observed in the process of social interactions.

Aerial Vocalizations by Wild and Rehabilitating Mediterranean Monk Seals (Monachus monachus) in Greece

It is important that all aspects of the life history and behavior of Mediterranean monk seals (Monachus monachus) are documented to ensure effective management and conservation of this critically endangered species. Little is known about either airborne or underwater vocalizations for this species. Field research and rehabilitation of Mediterranean monk seal pups by MOm (MOm/Hellenic Society for the Study and Protection of the Monk Seal) provided opportunistic video recordings of the airborne sounds of this species. This study is the first to report acoustic features of airborne vocalizations from eight wild adult females and six of their pups, short-term recordings of a sick pup, and longer-term recordings of three rehabilitating pups. Although sample sizes are small, every effort was made to garner the most acoustic information from these recordings. The aims of this study were to document the acoustic properties and types of aerial vocalizations from wild and rehabilitating Mediterranean monk seals and to compare the acoustic features of their sound repertoire to the airborne vocalization characteristics of other monachids. Audio-tracks were spectrographically analyzed using six frequency and five time variables with Spectrogram software. Through examination of realtime spectrograms and audibly distinguishable characteristics, this study classified four airborne vocalization types (bark, snort, scream, and chirp) for adult females. Three aerial vocalization types (bark, gaggle, and squawk) were documented from pups. The bark was the most common vocalization type from wild and rehabilitating pups. Wild adult female Mediterranean monk seal vocalizations ranged in frequency from 438 to 3,050 Hz and consisted of 1 to 6 components within a series with a total duration from 42 to 8,171 ms. Airborne vocalization types of rehabilitating pups ranged in frequency from 269 to 1,584 Hz and consisted of 1 to 11 components within a series with a total duration from 88 to 12,006 ms. Using Pearson’s correlation analyses, many of the frequency and time variables were highly correlated. Principle Component Analysis (PCA), using nine variables, produced a 3-factor model that explained 98.8% of the variability in the acoustic features of the whole repertoire. A more parsimonious, 3-factor PCA model, using only six variables, still explained a high percentage of variability (81.5%). These results indicated that collecting only two frequency measurements (beginning frequency and first harmonic interval) and four time measurements (number of components within a series, total duration, component duration, and the component interval) is sufficient to distinguish among species-specific vocalizations. Results of this acoustical analysis are from a small number of Mediterranean monk seals, and further acoustic research is warranted to record adult males, and to increase the sample sizes of vocalizations from wild adult females and pups. In addition, more recordings of ill, stressed, and captive monk seals are needed. Lastly, vocalizations of wild Mediterranean monk seals should be studied at the other two main population sites (i.e., Archipelago of Madeira and Cabo Blanco region), at other times of the year, and outside of the breeding season to provide a better understanding of the overall vocal behavior of this species. The preliminary analyses presented herein hold promise that with sufficient data on acoustic features of airborne vocalizations researchers could acoustically monitor wild Mediterranean monk seals and determine their sex, pup age, and perhaps their health.

The behavioral context of common dolphin (Delphinus sp.) vocalizations

AbstractCorrelations between surface behavior and concurrent underwater vocalizations were modeled for common dolphins (Delphinus spp.) in the Southern California Bight (SCB) over multiple field seasons. Clicks, pulsed calls, and whistles were examined, with a total of 50 call features identified. Call features were used to classify behavior using random forest decision trees, with rates of correct classification reaching 80.6% for fast travel, 84.6% for moderate travel, 59.8% for slow travel, and 58% for foraging behavior. Common dolphins spent most of their time traveling. The highest number of clicks, pulsed calls, and complex whistles were produced during fast travel. In contrast, during foraging there were few pulsed calls and whistles produced, and the whistles were simple with narrow bandwidths and few harmonics. Behavior and vocalization patterns suggest nocturnal foraging in offshore waters as the primary feeding strategy. Group size and spacing were strongly correlated with behavior and rates of calling, with higher call rates in dispersed traveling groups and lower call rates in loosely aggregated foraging groups. These results demonstrate that surface behavior can be classified using vocalization data, which builds the framework for behavioral studies of common dolphins using passive acoustic monitoring techniques.

Classification of behavior using vocalizations of Pacific white-sided dolphins (Lagenorhynchus obliquidens)

Surface behavior and concurrent underwater vocalizations were recorded for Pacific white-sided dolphins in the Southern California Bight (SCB) over multiple field seasons spanning 3 years. Clicks, click trains, and pulsed calls were counted and classified based on acoustic measurements, leading to the identification of 19 key call features used for analysis. Kruskal-Wallis tests indicated that call features differ significantly across behavioral categories. Previous work had discovered two distinctive click Types (A and B), which may correspond to known subpopulations of Pacific white-side dolphins in the Southern California Bight; this study revealed that animals producing these different click types also differ in both their behavior and vocalization patterns. Click Type A groups were predominantly observed slow traveling and milling, with little daytime foraging, while click Type B groups were observed traveling and foraging. These behavioral differences may be characteristic of niche partitioning by overlapping populations; coupled with differences in vocalization patterns, they may signify that these subpopulations are cryptic species. Finally, random forest decision trees were used to classify behavior based on vocalization data, with rates of correct classification up to 86%, demonstrating the potential for the use of vocalization patterns to predict behavior.

Long-range underwater vocalizations of the crabeater seal (Lobodon carcinophaga)

This study provides a comprehensive description of the acoustic characteristics of the predominant long-range underwater vocalizations of the crabeater seal, Lobodon carcinophaga, derived from stationary and continuous long-term recordings obtained in the Southern Ocean in 2007. Visual screening of data recorded between 1 October and 15 December 2007 indicates that the principal period of vocal activity of the crabeater seal is the latter part of October and all of November, coinciding with the breeding season of this species. Two call types were identified during this period: the low moan call, which has been described in previous studies and the high moan call, a call type newly described here. Out of 17 052 manually extracted crabeater seal calls, high-quality recordings of 152 low moans and 86 high moans with a signal-to-noise ratio exceeding 15 dB were selected and call-specific acoustic features were determined. While the mean duration of the two call types was comparable ( approximately 2.5 s), the high moan occurred at notably higher frequencies (1000-4900 Hz) than the low moan (260-2500 Hz). This study provides baseline information necessary to develop automated detection algorithms to facilitate systematic screening of extended data sets for crabeater seal vocalizations.

Acoustic Analysis of Underwater Vocalizations from Crabeater Seals (&lt;I&gt;Lobodon carcinophagus&lt;/I&gt;): Not So Monotonous

Underwater vocalizations of pack-ice crabeater seals (Lobodon carcinophagus) were recorded by J. A. Thomas off the western side of the Antarctic Peninsula during the austral breeding season in November 1978. Data were collected by dropping an ANS 57 sonobuoy from the side of a ship to a depth of 15.3 m and recorded on a Nagra III reelto-reel recorder (system frequency response linear from 20 Hz to 20 kHz ± 2 dB). The acoustic properties of 315 underwater vocalizations were analyzed using Spectrogram real time software. As previous investigators documented, all crabeater seal sounds during the breeding season were of one type, a long groan. D. Cothran recorded a solitary crabeater seal of unknown age and sex foraging during the nonbreeding season in February 2007 in the same general area of the Antarctic Peninsula using a Sony TRV-900 digital underwater video camcorder. Twenty seconds of underwater acoustic data were spectrographically analyzed, and 18 vocalizations were identified and classified into four previously unreported sound types: (1) short groan, (2) whistle, (3) screech, and (4) grunt. For the first time, the acoustic characteristics of the common long groan and four previously undescribed underwater vocalizations by crabeater seals were examined spectrographically with parameters of frequency and time reported herein. The long groan showed little frequency or temporal variation and was repeated by other distant crabeater seals at about 20.0-s intervals. No long groans were recorded during the short February videotape. The four previously undocumented vocalizations were produced while a single crabeater seal foraged in shallow water. Hierarchical cluster analysis showed that the long groan was acoustically dissimilar to the four new vocalizations; however, only 18 sounds were available for analysis. Still, this videotape documents that this species does produce more than one sound type. Further research should be conducted to adequately document the underwater acoustic repertoire of the crabeater seal, especially outside the breeding season.

Age-related differences in the acoustic characteristics of male leopard seals, Hydrurga leptonyx

During the breeding season, the underwater vocalizations and calling rates of adult male leopard seals are highly stereotyped. In contrast, sub-adult males have more variable acoustic behavior. Although adult males produce only five stereotyped broadcast calls as part of their long-range underwater breeding displays the sub-adults have a greater repertoire including the adult-like broadcast calls, as well as variants of these. Whether this extended repertoire has a social function is unknown due to the paucity of behavioral data for this species. The broadcast calls of the sub-adults are less stereotyped in their acoustic characteristics and they have a more variable calling rate. These age-related differences have major implications for geographic variation studies, where the acoustic behavior of different populations are compared, as well as for acoustic surveying studies, where numbers of calls are used to indicate numbers of individuals present. Sampling regimes which unknowingly include recordings from sub-adult animals will artificially exaggerate differences between populations and numbers of calling animals. The acoustic behavior of sub-adult and adult male leopard seals were significantly different and although this study does not show evidence that these differences reflect vocal learning in the male leopard seal it does suggest that contextual learning may be present.

Underwater vocalizations of male harbor seals (Phoca vitulina) during the mating season at Brookfield Zoo

Underwater vocalizations of harbor seals were recorded between April and October of 2006 in many settings, including male only, two females prior to the breeding season, and all seals as a group before, during, and after the breeding season. Recordings were made using a Dell XPS M140 laptop, with a linear frequency response up to 96 kHz, and Goldwave sound recording software. All recordings were analyzed using Spectrogram 14.0 software. Three call types were identified: short roars, long roars, and growls. A total of 736 roars were identified and 256 randomly sampled roars were analyzed. A total of 109 growls were identified and analyzed. The frequency range of the call types was 209 to 3406 Hz, based on dominant minimum and dominant maximum frequency measurements, and duration ranged from 0.8 to 10.5 s. The male produced stereotypical roars in late June. As there was only one male in the group, it is suggested that the function of this roar is to announce breeding condition or to attract a female for mating, not for competition among males.

Structural and temporal emission patterns of variable pulsed calls in free-ranging killer whales (Orcinus orca)

Resident killer whales off Vancouver Island, British Columbia, produce variable burst pulsedcalls most commonly during close-range interactions such as socialising or social-travelling. Earlier studies indicated that variable calls are graded and can be arranged into a scale from low-frequency calls to high-frequency ones. These graded calls are often emitted in sequences, were call-classes of similar frequency follow one another more often than different classes. However, a detailed analysis of sequences was lacking to date. Therefore, our understanding of the function of variable calls during interactions among killer whales is rather limited. Simultaneous recordings of underwater vocalizations and behavioural observations from resident killer whales were collected off Vancouver Island, British Columbia during1996-2001. Socialising activities were divided into four categories: male-female, male-male, female-juvenile and juvenile-juvenile. Variable call sequences were analysed with RTS and SIGNAL acoustic-software. We found no positive correlation between group-size and number of used calls or the duration of sequences, indicating that only one or a few animals were involved in the production of each sequence. Furthermore, sequences were present in all four behaviour categories and the composition of the group had no influence on the duration of calls and used call-classes. One particular call class (V4) could be further separated into structurally distinct sub-classes. These sub-classes often formed rather stereotyped sequences. The results of our study indicate that sequences of variable calls emit broad motivational information that is not age or sex-related. Sequences of distinct sub-classes might encode more subtle information on emotional states during socialising. Therefore, variable calls might posses different functions, depending on the nature of the interaction. Thus, variable calls might be of great importance for close-range communication in wild killer whales.

ASPECTS OF UNDERWATER SOUND COMMUNICATION IN FLORIDA MANATEES (TRICHECHUS MANATUS LATIROSTRIS)

We recorded underwater vocalizations of captive and wild Florida manatees (Trichechus manatus latirostris) to assess variability in acoustic structure of their sounds and to test hypotheses regarding the importance of specific acoustic traits in individual distinctiveness and in certain behavioral contexts. Manatees use vocalizations to maintain contact when in groups. The highest rates of vocalizing occur during antiphonal calling between females and calves. Vocalizations are complex, single-note calls with multiple harmonics, frequency modulations, nonharmonically related overtones, and other nonlinear elements. We measured 6 acoustic variables and found that individuals varied significantly in fundamental frequency, emphasized band, frequency range, and call contour (the overall pattern of complexity in frequency modulation). These traits did not vary within individuals on different dates or when manatees were alarmed and fleeing. Individual fundamental frequencies ranged from 1.75 to 3.90 kHz, and were negatively correlated with body size. Little sound energy occurred above 18 kHz in 502 call notes of 6 captive manatees sampled with a recording oscilloscope. Presence of harmonics and call duration differed by date and manatees emitted longer calls when fleeing disturbance. Call duration varied from 118 to 643 ms (geometric mean = 271 ms, 95% confidence limits = 264, 279 ms) in a sample of 479 vocalizations we recorded from 14 individuals. The maximum call duration recorded over the entire study was 900 ms. Females and calves responded only to each others' vocalizations when rejoining a group after brief separations, strongly suggesting individual recognition by sound. Structural complexity in the calls of manatees is similar to that in other sirenians, and may reflect their auditory capabilities and the unique physical properties of sound in shallow water.