Underwater Vocalizations Research Articles

Variation of harp seal (Pagophilus groenlandicus) underwater vocalizations among three breeding locations

AbstractWe compared the underwater vocalizations of harp seals Pagophilus groenlandicus Erxleben, 1777 recorded during the breeding season at three locations: Jan Mayen Island (north of Iceland); Gulf of St Lawrence; and the ‘Front’ ice east of Labrador. The three herds shared 17 call types. The Jan Mayen herd had one call type not found in the Gulf or Front. One of the Gulf and Front call types was not found at Jan Mayen. Based on ANOVA post hoc pairwise comparisons between locations, the three herds exhibited a similar number of within‐call type differences in duration, number of elements, start pitch and end pitch. There were no differences in proportional usage of call types between the Gulf and Front herds but both differed in a similar manner from those of the Jan Mayen herd. These findings support tagging studies that indicate that the Gulf and Front herds may be interbreeding and both are reproductively isolated from the Jan Mayen herd. We found no evidence of acoustic adaptation to the site‐specific ice and environmental conditions associated with the three study locations.

Biting in the Salamander Siren intermedia intermedia: Courtship Component or Agonistic Behavior?

In salamanders, biting serves three potential purposes: subduing prey (e.g., Reilly and Lauder, 1990), repelling competitors and predators (e.g., Jaeger, 1981; Brodie et al., 1989), and stimulating the opposite sex during courtship (Arnold, 1977). In Siren intermedia, nonpredatory biting was first reported by Gehlbach and Walker (1970), who observed it while recording underwater vocalizations. Bitten individuals often fled

Variations in the vocal repertoire of the manatee in the Caribbean (Trichechus manatus manatus)

While different life history parameters for the manatee have been well studied in Florida, little is known about these aspects of manatee biology in the Caribbean. As part of a multifaceted study in Antillean manatee life history, the geographical and individual variability in vocal repertoires of Antillean manatees from Puerto Rico and the Dominican Republic were examined and compared to the repertoire of the Florida manatee. Differences in structural sound characteristics (frequency, duration, and relative power of each harmonic), usage (number of call types), and the associated behavior were studied from recordings of wild and captive animals. Over 100 h of recording were obtained from six different natural localities in Puerto Rico and one natural locality in Florida. Captive manatees were recorded in the Dominican Republic (1), in Puerto Rico (2), and Florida (13), in addition to recording seven semicaptive individuals in Florida. The recording of underwater vocalizations has been suggested as a useful tool for the study of marine mammals distribution. In the turbid waters of rivers, bays, and lagoons where manatees congregate in the Caribbean, these acoustic data might be useful for estimating population distribution and habitat use.

Repertoire and Geographic Variation in Underwater Vocalisations of Weddell Seals (Leptonychotes weddellii, Pinnipedia : Phocidae) at the Vestfold Hills, Antarctica

The underwater vocalisations of Weddell seals (Leptonychotes weddellii) near Davis, Antarctica, were many and varied. A total of 11029 vocalisations recorded throughout and immediately after the breeding season were analysed. Vocalisations were classified by cluster analysis techniques, based on differences in frequency, duration, call shape, waveform and number of elements. Thirteen broad call categories (many with subdivisions) were identified. Twelve call types (belonging to nine categories) made up 91· 9% of the vocalisations and were present at all seven study sites within the Vestfold Hills, and a single site at the Larsemann Hills approximately 150 km away. A further eight call types (five categories) made up another 6·7% of the vocalisations. These were not detected at every recording site. An additional 29 call types (11 categories) were infrequent and probably reflect the diversity of individual seals. This study strengthens the case for macrogeographic variation in underwater Weddell seal vocalisations around Antarctica. Microgeographic differences, between sites within 150 km, were weak and not consistent between sites or years. Some adult females move to different breeding sites within the Vestfold Hills area between years. This would probably preclude the establishment of site-specific (microgeographic) repertoire differences.

BEHAVIORAL SIGNIFICANCE OF UNDERWATER VOCALIZATIONS OF CAPTIVE LEOPARD SEALS, HYDURGA LEPTONYX

AbstractTwo groups of underwater vocalizations were identified in a three‐year study of two captive leopard seals, Hydurga leptonyx (one female and one male at Taronga Zoo, Sydney). This was supplemented by recordings over three months from a male at Marineland, New Zealand. The sexual state of the seals at Taronga was deduced from serum hormonal concentrations: the female was considered to be in estrus at specific times during the breeding season. The seal at Marineland, New Zealand was assumed to be sexually mature on the basis of size and age. Of 12 different underwater sound types recorded, six were produced by the seals at Taronga Zoo during agonistic interactions (local calls) and were heard through most of the year. The other six sound types were produced by lone seals. These broadcast calls were produced by the female only when sexually receptive, and by the mature male during December and January, months believed to be the breeding season of wild leopard seals. We propose that underwater acoustic behavior is important in the mating system of this species, and that broadcast calls are used by mature females to advertise their sexual receptivity, and possibly by mature males in search of mates.

Proportional Weekly Use of Underwater Call Types by Weddell Seals, Leptonychotes Weddellii (Pinnipedia: Phocidae), During the Breeding Season at the Vestfold Hills

Underwater vocalisations by Weddell seals, Leptonychotes weddellii, were recorded during the 1992 breeding season, at the Vestfold Hills, Antarctica. Only 3 of the 12 major call types recorded at all sites had statistically significant variations in utilisation throughout the season. No consistent trends were evident. The underwater calls of Weddell seals increased;in number during the breeding season, hut the proportional weekly usage of each of the major call types did not change. The absence of vocalisation changes suggests that the breeding behaviours of Weddell seals are not synchronous and that the underwater behavioural patterns either do not change during the breeding season or could not be detected because of the asynchrony.

Pod-specific call repertoires and compound calls of killer whales, Orcinus orca Linnaeus, 1758, in the waters of northern Norway

Underwater vocalizations of 9 photoidentified pods of killer whales (Orcinus orca) were recorded in northern Norway from 1986 to 1992. In total, 34 call types and 20 subtypes were identified from the recordings. The pods had repertoire sizes ranging from 3 to 16 call types (average 9.0 call types). Pod-specific calls were found in 6 of the 9 pods. All pods had a unique repertoire combination. This study thus supports the hypothesis that vocal traditions are characteristic of killer whales. Some calls were combined, forming a total of 21 different syntactically organized compound calls. The function of this was not known, but it was suggested that adding size and flexibility to a small and rigid vocal repertoire may be advantageous.

Underwater acoustic displays and individual variation in male harbour seals, Phoca vitulina

Abstract. Vocalizing by natural-living harbour seals has been considered to be rare, limited primarily to aerial threats. A few studies on captive harbour seals, however, indicated that this species produced a wider variety of aerial vocalizations than was previously thought. The objective of this study was to determine whether adult male harbour seals in the wild vocalized under water during the breeding season and whether there was any variation in vocalizations between individuals. Underwater vocalizations of 10 males were tape-recorded at Point Lobos State Reserve, California during the spring and summer of 1991. Females did not vocalize except on land when they threatened other seals. Observational data was taken to identify the vocalizing seal and to determine whether other seals in the vicinity showed any reactions to the vocalizations. Five vocalization types were identified and analysed: grunt, groan, creak, bubbly growl and roar. There were significant differences between males with regard to the frequency measurements of the roars as well as to their entire acoustic displays but there was little intra-individual variation. It is suggested that underwater vocalizations are used in male-male competition and/or as reproductive advertisement displays to attract females.

Microgeographic variation and songs in the underwater vocalisation repertoire of the Weddell seal (Leptonychotes weddellii) from the Vestfold Hills, Antarctica

Recordings of underwater vocalisations of the Weddell seal (Leptonychotes weddellii) were made in fjords of the Vestfold Hills near Davis Station, Antarctica. The repertoire was examined for the presence of microgeographic variation. Recordings covered the period from the end of mating to the beginning of the moult in the 1989/1990 breeding season. The repertoire was classified into 44 vocalisation types using a classification method based on objective parameters. Unique vocalisations were identified at each site, with 48% exclusive to Long Fjord and 41% to Tryne Fjord. A small percentage (11%) of the repertoire was common to both fjords reflecting the limited, observed interchange of individuals between these populations due to their strong breeding site fidelity. Seven male songs are described in the present study and possibly function to maintain underwater territories.

Geographical variation of harp seal underwater vocalizations

Underwater vocalizations of harp seals (Phoca groenlandica) were recorded during the breeding season in the Gulf of St. Lawrence and north of Jan Mayen Island. Each herd had one unique call type and shared (often in different proportions) an additional 17 call types. Of these 17, 13 common call types had sample sizes large enough to permit statistical analysis of five duration, repetition, and pitch features. Only one of these call types exhibited no interherd differences; the others exhibited 1 – 5 different features. The average and maximum numbers of elements per call were higher in the Gulf than the Jan Mayen herd. Within each herd there were no differences in the call types and numbers of call elements over a 19-year period. An implication of these findings and other separate tagging studies is that the two herds are reproductively isolated.

Use of signature whistles during separations and reunions by wild bottlenose dolphin mothers and infants

We examine the contexts and patterns of “signature” whistle production by wild bottlenose dolphin mother-infant pairs (Tursiops spp.) to gain insight into the functional significance of whistles. Results are based on focal observations and simultaneous recordings of underwater vocalizations. Whistles occur primarily when mother-infant pairs are separated, and the probability of whistles increases with distance of separation. The timing of whistles during separations varies, but whistles tend to be produced in repetitive series and are generally concentrated toward the later stages of the separation, i.e., during the process of reunion. Although we focused on infants, mothers do not appear to whistle during separations as frequently as infants. Infant whistles may function to facilitate reunions by conveying information to the mother concerning the infant's motivation to reunite and/or its location. Infant whistles could induce a cooperative response from the mother including approach, slowing to allow the infant to catch up or whistling. Highly individualized signature whistles may be particularly useful in a fission-fusion society in which individuals (mothers and infants as well as adults) join and leave temporary parties in a fluid manner, yet maintain consistent, long-term associations with particular individuals.

Underwater vocalizations of ice breeding grey seals

Grey seals (Halichoerus grypus) breed both on land and on the ice. In January 1991, 36 h of underwater recordings were made from Amet Island, located in ice-covered waters in the southern Gulf of St. Lawrence. All vocalizations were examined for spectral and temporal structure and then classified into 1 of 7 call types. The majority of calls consisted of guttural "rups" and "rupes" (frequency = 100–3000 Hz), and low-frequency growls (100–500 Hz). Other less common vocalizations were low-frequency clicks (3000 Hz), as well as loud knocks, similar to knocking vocalizations recorded in walrus, and which had not been described previously for grey seals. The total number of vocalizations and the number of specific call types showed seasonal variations. The rate of vocalizations increased with the intensity of social activity and with the number of agonistic behaviors during the progression of the breeding season. Comparisons between night and day showed some changes in the vocal repertoire. Low-frequency clicks were recorded more often during darkness (17.1% of calls) than in daylight (1.9%), and when ice cover was more extensive.

Responses of humpback whales to sonar sounds

Controlled sound playback experiments were used to assess effects of a low‐frequency sonar system on humpback whales, Megaptera novaeangliae, in Hawaiian waters. Focal pods were presented with sounds of a 3.3‐kHz sonar pulse, a sonar frequency sweep from 3.1 to 3.6 kHz, or a control (blank) tape. Behavior, movement, and underwater vocalizations were monitored and compared with baseline periods. While the two types of sonar signals differed in their effects on the whales, both elicited avoidance behaviors. Humpbacks responded to the pulse by increasing their distance from the sound source. The strength of this effect varied directly with time. Responses to the frequency sweep primarily consisted of increased swimming speeds and track linearity. The latter was a direct function of increasing sound intensity. Overall, the sounds did not strongly or consistently affect the whales’ dive cycles or vocalizations. Observed avoidance reactions may have resulted from possible resemblance between the sonar signals and natural sounds in humpbacks’ environment that are associated with biological threats or warnings.

Vocal traditions among resident killer whales (Orcinus orca) in coastal waters of British Columbia

Underwater vocalizations were recorded during repeated encounters with 16 pods, or stable kin groups, of resident killer whales (Orcinus orca) off the coast of British Columbia. Pods were identified from unique natural markings on individuals. Vocal exchanges within pods were dominated by repetitious, discrete calls. Pods each produced 7–17 (mean 10.7) types of discrete calls. Individuals appear to acquire their pod's call repertoire by learning, and repertoires can persist with little change for over 25 years. Call repertoires differed significantly among pods in the resident population. The 16 pods formed four distinct acoustic associations, or clans, each having a unique repertoire of discrete calls, or vocal tradition. Pods within a clan shared several call types, but no sharing took place among clans. Shared calls often contained structural variations specific to each pod or group of pods in the clan. These variants and other differences in acoustic behaviour formed a system of related pod-specific dialects within the vocal tradition of each clan. Pods from different clans often travelled together, but observed patterns of social associations were often independent of acoustic relationships. It is proposed that each clan comprises related pods that have descended from a common ancestral group. New pods formed from this ancestral group through growth and matrilineal division of the lineage. The formation of new pods was accompanied by divergence of the call repertoire of the founding group. Such divergence resulted from the accumulation of errors in call learning across generations, call innovation, and call extinction. Pod-specific repertoires probably serve to enhance the efficiency of vocal communication within the group and act as behavioural indicators of pod affiliation. The striking differences among the vocal traditions of different clans suggest that each is an independent matriline.

Winter Distribution of Bearded Seals (Erignathus barbatus) in the Penny Strait Area, Northwest Territories, as Determined by Underwater Vocalizations

Vocalization surveys conducted in Penny Strait, Northwest Territories, indicated that before ice break-up, bearded seals (Erignathus barbatus) preferred regions of less stable ice where break-up occurred early and avoided stable, landfast ice or areas heavily used by walruses (Odobenus rosmarus). Water depth did not appear to influence distribution. Numbers of calls increased between mid-April and early June, probably because of an increase in rate of calling by individual seals. Vocalization surveys can be used to separate preferred habitats from unsuitable ones. Using a single hydrophone and our current understanding of bearded seal vocal behaviour, it is not possible to determine the absolute number of bearded seals at or near a site using vocalizations. However, it is possible to measure the relative abundance of seals for spatial and temporal comparisons.

Diving in darkness: whiskers as sense organs of the ringed seal (Phoca hispida saimensis)

Underwater vocalization and the functional structure of different vibrissae of the ringed seal (Phoca hispida saimensis) of Lake Saimaa, Eastern Finland, were studied. These seals live in darkness under the ice cover for several months during the year. It is known that blind seals are managing well in the lake. Visibility under water in some parts of the area where the seals live is only 2 m. It is suggested that echolocation is used in orientation and feeding. The Saimaa seal has click and click trial underwater vocalizations. However, both the frequency and intensity of the vocalization are low compared with, for example, those of dolphins. The structural adaptations for underwater sound localization are also not well developed.The ringed seal has, however, extremely well‐developed vibrissae. The innervation of one vibrissa is more than 10 times greater than normally found in mammals. The main structural deviations from normal mammalian vibrissae are: (1) an upper cavernous sinus, (2) a groove in the wall of the capsule at the level of the lower cavernous sinus, (3) elasticity of the connective tissue bands fixing the hair root to the capsule in the lower cavernous sinus and especially (4) the structure and innervation of the ring sinus area. Sensory elements are situated upon the glassy membrane on the surface of the outer rootsheath and in the basal cell layer of the outer rootsheath which is like a sensory epithelium. Below this epithelium a layer of liquid or gelatinous material and large amounts of glycogen are found. This sensory epithelium is especially well developed in the superciliary vibrissae. These vibrissae are protruded some millimetres when the seals are attentive. It is suggested that the vibrissae also sense sounds, which are transmitted to the sensory elements by tissue conduction through the capsule wall and via the blood sinuses. The seals may possibly detect compressional waves with the vibrissae.

Underwater vocalizations of the bearded seal (Erignathus barbatus)

The underwater vocalizations of bearded seals (Erignathus barbatus) were recorded between March and June in 1979, 1982, and 1983 at six sites in the Arctic. In total, 970 trills were measured for temporal and spectral characteristics and then classified as one of six types. Trills were narrow in bandwidth and frequency modulated. The repertoires of vocalizing bearded seals varied amongst the six recording sites. Between-site differences in temporal and spectral features, call use, and sequential organization were measured. The results suggest that bearded seals may be relatively sedentary and that geographically different vocal repertoires may be characteristic of discrete breeding stocks. A prominent daily cycle in rate of calling during April and May was found at two sites; rate of calling was higher during the early morning hours (i.e., 03:00–04:00 sun time) than at other times of the day. No distinct temporal cycle occurred during late May and early June. Rate of calling appeared to be negatively correlated with pattern of haul out. In simultaneous recordings, a few (13 of 156) bearded seal trills were recorded up to a distance of 25 km underwater.

Acoustic behaviour of resident killer whales (Orcinus orca) off Vancouver Island, British Columbia

Recordings of underwater vocalizations and behavioural observations were collected from 16 photographically identified resident pods of killer whales (Orcinus orca) off Vancouver Island, British Columbia, during 1978–1983. Vocalizations recorded during 43 days spent with three representative pods were analyzed for each of five activity states: foraging, travelling, group-resting, socializing, and beach-rubbing. The whales produced three types of sounds that were assumed to be social signals: discrete calls, variable calls, and aberrant calls. Discrete calls dominated vocalization in most contexts. An increase in production of variable and aberrant calls was observed during socializing and beach-rubbing activities. Each resident pod had a group-specific repertoire of 7–17 discrete call types (mean = 10.7) that was consistent over a number of years. The relative use of different calls varied with activity, but no call type was correlated exclusively with any behaviour or circumstance that could be identified. Discrete calls probably function as intragroup contact signals to maintain pod cohesion and coordinate activities. Structural modulations of standard call formats and variations in frequencies of call use appear to carry information on the emotional state of vocalizing individuals. Group-specific repertoires of calls may increase the effectiveness and reliability of this contact system and function as indicators of pod affiliation.

Polar bear responses to the underwater vocalizations of ringed seals

Two captive polar bears were exposed to six different marine mammal vocalizations, in an attempt to determine if polar bears would selectively respond to the underwater vocalization of their primary prey, ringed seals. Vocalizations were played to each bear for a total of eight minutes while their behavioral responses were observed. An analysis of activity indicated that the bears displayed a significantly stronger response to ringed seals' vocalizations. It is theorized that the ability to recognize the underwater vocalizations of their primary prey would increase a bear's probability of a successful capture when a ringed seal rises to breath at an ice bound breathing hole.

Variations in underwater vocalizations of Weddell seals (Leptonychotes weddelli) at the Vestfold Hills as a measure of breeding population discreteness

Weddell seal vocalizations from Davis Station showed similarities to those from McMurdo Sound and Palmer Peninsula, but none were identical. One vocalization, DD1, was unique to Davis Station. At all sites trills, or territorial defense calls, were the most common and had more types than other calls. Chugs, an aggressive sound, were common at all sites. Weddell seal calls from Davis Station showed similarities to sounds from McMurdo by sharing the use of prefixes and suffixes. Sounds from Davis Station shared the use of both ascending and descending trills and whistles with calls from Palmer Peninsula.