Within-pod variation in the sound production of a pod of killer whales, Orcinus orca

Pod-specific calling behaviour of resident killer whales has been shown to include: discrete call types not shared among pods, different production rates of shared call types, and differences in the detailed structure of shared call types. To investigate the mechanisms leading to pod-specific calling, we compared the repertoire and structure of calls produced by three different matrilineal units within the same pod, and described call features encoding matrilineal-unit distinctiveness. The three matrilineal units had different production rates of shared calls, including one call type used almost exclusively by one matrilineal unit. Cross-validated discriminant function analyses revealed matrilineal-unit distinctive structure in five of the six shared call types examined, with duration of the terminal component being the most distinctive feature for all call types containing a terminal component. Calls generally consist of low- and high-frequency components that may follow different time-frequency contours. In our sample, a particular high-frequency contour was consistently paired with a particular low-frequency contour, both contours had roughly equal overall variability, and each contained independent matrilineal-unit distinctive information. The only call type that did not differ structurally between matrilineal units is reportedly used more in interpod meetings than in intrapod contexts. The differences in calling behaviour between matrilineal units were similar in form to previously described differences between pods, although more subtle. These results suggest that pod-specific calling behaviour in resident killer whales arises primarily as a consequence of accumulated drift or divergence between highly cohesive matrilineal units as they gradually separate into different pods. Copyright 2000 The Association for the Study of Animal Behaviour.     

The influence of social affiliation on individual vocal signatures of northern resident killer whales (Orcinus orca)

Northern resident killer whales (Orcinus orca) live in highly stable groups and use group-specific vocal signals, but individual variation in calls has not been described previously. A towed beam-forming array was used to ascribe stereotyped pulsed calls with two independently modulated frequency contours to visually identified individual killer whales in Johnstone Strait, British Columbia. Overall, call similarity determined using neural networks differed significantly between different affiliation levels for both frequency components of all the call types analysed. This method distinguished calls from individuals within the same matriline better than different calls produced by a single individual and better than by chance. The calls of individuals from different matrilines were more distinctive than those within the same matriline, confirming previous studies based on group recordings. These results show that frequency contours of stereotyped calls differ among the individuals that are constantly associated with each other and use group-specific vocalizations, though across-group differences were substantially more pronounced.     

Stereotyped acoustic signals of the killer whale <Emphasis Type="Italic">Orcinus orca</Emphasis> (Cetacea: Delphinidae) from the Northwestern Pacific

In this paper the classification of the discrete calls of killer whales recorded in the Northwest Pacific is presented. It was shown that most of the calls can be divided into 20 discrete types easily distinguished by ear. The frequency parameters of the sounds made the maximum contribution into discrimination between call types, while their temporal parameters turned out to be less significant. The repertoires of stereotyped calls of killer whales from Chukot, Kamchatka, and the Commander and Kurile Islands were similar, due to the presence of shared types of calls. The greater the distance between the above-mentioned regions the fewer calls were shared by the resident killer whales. High vocal activity and the phenotypic features of the surveyed killer whales implied their attribution to the resident ecological type.     

Dialect change in resident killer whales: implications for vocal learning and cultural transmission

Variation in vocal signals among populations and social groups of animals provides opportunities for the study of the mechanisms of behavioural change and their importance in generating and maintaining behavioural variation. We analysed two call types made by two matrilineal social groups of resident killer whales, Orcinus orca, over 12-13 years. We used a neural network-based index of acoustic similarity to identify mechanisms of call differentiation. A test for structural modification of the calls detected significant changes in one call type in both groups, but not in the other. For the modified call type, the rate of divergence between the two groups was significantly lower than the rate of modification within either group showing that calls were modified in a similar fashion in the two groups. An analysis of structural parameters detected no strong directionality in the change. The pattern of call modification could have been caused by maturational changes to the calls or, if killer whale dialects are learned behavioural traits, cultural drift in the structure of the calls together with horizontal transmission of modifications between the two groups. Such vocal matching between members of different matrilines would suggest that vocal learning is not limited to vertical transmission from mother to offspring, which has important implications for models of gene-culture coevolution. Copyright 2000 The Association for the Study of Animal Behaviour.     

Responses of Kamchatkan fish‐eating killer whales to playbacks of conspecific calls

Killer whales produce repertoires of stereotyped call types that are primarily transmitted vertically through social learning, leading to dialects between sympatric pods. The potential function of these call repertoires remains untested. In this study, we compared the reaction of Kamchatkan fish‐eating killer whales to the playbacks of calls from the same and different pods. After the playback of recordings from a different pod, in three cases whales changed the direction of their movement toward the boat, and in three cases no changes in direction were observed. After the playback of recordings from the same pod (either from the same or a different unit within the pod), in seven cases whales changed the direction of their movement toward the boat, and in only one case no change in direction was observed. Whales remained silent after all six playbacks of recordings from a different pod, even when they changed direction toward the boat. After the playback of recordings from the same pod, however, in all eight cases whales started calling in response. Our playback study shows that killer whales may react to playbacks of conspecific sounds and that reactions are dependent on the type of playback stimuli.     

Diversity in sound pressure levels and estimated active space of resident killer whale vocalizations

Signal source intensity and detection range, which integrates source intensity with propagation loss, background noise and receiver hearing abilities, are important characteristics of communication signals. Apparent source levels were calculated for 819 pulsed calls and 24 whistles produced by free-ranging resident killer whales by triangulating the angles-of-arrival of sounds on two beamforming arrays towed in series. Levels in the 1–20 kHz band ranged from 131 to 168 dB re 1 μPa at 1 m, with differences in the means of different sound classes (whistles: 140.2±4.1 dB; variable calls: 146.6±6.6 dB; stereotyped calls: 152.6±5.9 dB), and among stereotyped call types. Repertoire diversity carried through to estimates of active space, with “long-range” stereotyped calls all containing overlapping, independently-modulated high-frequency components (mean estimated active space of 10–16 km in sea state zero) and “short-range” sounds (5–9 km) included all stereotyped calls without a high-frequency component, whistles, and variable calls. Short-range sounds are reported to be more common during social and resting behaviors, while long-range stereotyped calls predominate in dispersed travel and foraging behaviors. These results suggest that variability in sound pressure levels may reflect diverse social and ecological functions of the acoustic repertoire of killer whales.     

FRIENDS OF WILDLIFE SOUND AT NSA

ABSTRACT

The problem of categorization arises in any classification system because classes should be discrete while the characteristics of most natural objects and aspects of nature are more or less gradual. In systematics, this problem usually is solved by creating several levels of categories, such as class, order, family, genus and species. In the existing killer whale discrete call classification, only two levels occur—call type and call subtype. In this paper we describe structural categories at a broader level than call type in the discrete sounds of killer whales and compare these categories between and within vocal clans in a community of resident killer whales from Southeast Kamchatka, Russian Far East, and also with killer whales outside this community. We found four main classes of discrete calls in the repertoire of resident killer whales from Southeast Kamchatka. The calls of Southeast Kamchatka transient killer whales and Sakhalin killer whales do not fall into these classes. This suggests that the resident killer whale community from Southeast Kamchatka has some rules defining the structure of calls which are typical for this community. Consequently, all resident killer whales from Southeast Kamchatka can be said to share the same vocal tradition.     

The communicative content of the common marmoset phee call during antiphonal calling

Vocalizations are a dominant means of communication for numerous species, including nonhuman primates. These acoustic signals are encoded with a rich array of information available to signal receivers that can be used to guide species‐typical behaviors. In this study, we examined the communicative content of common marmoset phee calls, the species‐typical long distance contact call, during antiphonal calling. This call type has a relatively stereotyped acoustic structure, consisting of a series of long tonal pulses. Analyses revealed that calls could be reliably classified based on the individual identity and social group of the caller. Our analyses did not, however, correctly classify phee calls recorded under different social contexts, although differences were evident along individual acoustic parameters. Further tests of antiphonal calling interactions showed that spontaneously produced phee calls differ from antiphonal phee calls in their peak and end frequency, which may be functionally significant. Overall, this study shows that the marmoset phee call has a rich communicative content encoded in its acoustic structure available to conspecifics during antiphonal calling exchanges. Am. J. Primatol. 72:974–980, 2010. © 2010 Wiley‐Liss, Inc.     

The relationship between the acoustic behaviour and surface activity of killer whales (<Emphasis Type="Italic">Orcinus orca</Emphasis>) that feed on herring (<Emphasis Type="Italic">Clupea harengus</Emphasis>)

We describe the acoustic behaviour of piscivorous killer whales in Norwegian and Icelandic waters. Whales were assigned to one of three activities (feeding, travelling or other), and sound recordings were made in their proximity with a single hydrophone and a digital audiotape (DAT) recorder. A quantitative analysis of the production of pulsed calls, whistles and echolocation clicks in the three activities revealed that there was a significant effect of activity on the production of these sound types. Both killer whales in Icelandic and Norwegian waters produced high rates of clicks and calls during feeding and low rates of click, calls and whistles during travelling. The differences can be used as acoustical markers and provides new possibilities for acoustic monitoring of killer whales in these areas. Based on the similarity between their prey choice, hunting strategies, phenotype and acoustic behaviour, we suggest that the killer whales in Icelandic and Norwegian waters belong to the same ecotype: Scandinavian herring-eating killer whales.     

Horizontal transmission of vocal traditions in killer whale (<Emphasis Type="Italic">Orcinus orca</Emphasis>) dialects

Unlike most other mammals, killer whales are capable of vocal learning and learn the dialect of their natal pod from their mothers. The classical model of killer whale dialect development suggests that the repertoire of calls is learned only “vertically” from mother to offspring, and calls evolve gradually with time by random drift caused by the accumulation of copying errors. However, some observations suggest that not only “vertical” (from mother to offspring) vocal learning can occur in killer whales, but also “horizontal” (between adult animals). In this study we analyzed the distribution of different call types and similarity of calls from the same type in different pods of killer whales from Kamchatka waters to estimate the probability of existence of interpod horizontal transmission of vocal traditions in killer whales. We found that the degree of similarity of K1 calls and K5 calls in different pods can differ. This situation contradicts the classical hypothesis and is possible in two cases: if different call types change with various speed in different pods, or if horizontal transmission of call features takes place. The distribution of K4 and K10 call types across pods also suggests the existence of horizontal transmission: K4 calls occur in the dialects of five of ten pods, and K10 calls, in six of ten pods, but only one pod has both K4 and K10 calls. Our results suggest that the real picture of the distribution of call features and call types in killer whale dialects contradicts the classical hypothesis of killer whale dialect evolution through the accumulation of copying errors.     

THE EFFECT OF VESSEL NOISE ON THE VOCAL BEHAVIOR OF BELUGAS IN THE ST. LAWRENCE RIVER ESTUARY,CANADA

During June-July 1991, we monitored the vocal behavior of belugas before, during, and after exposure to noise from a small motorboat and a ferry to determine if there were any consistent patterns in their vocal behavior when exposed to these two familiar, but different sources of potential disturbance. Vocal responses were observed in all trials and were more persistent when whales were exposed to the ferry than to the small boat. These included (1) a progressive reduction in calling rate from 3.4–10.5 calls/whale/min to 0.0 or <1.0 calls/whale/min while vessels were approaching; (2) brief increases in the emission of falling tonal calls and the theree pulsed-tone call types; (3) at distances <1 km, an increase in the repetition of specific calls, and (4) a shift in frequency bands used by vocalizing animals from a mean frequency of 3.6 kHz prior to exposure to noise to frequencies of 5.2-8.8 kHz when vessels were close to the whales.     

Is Alarm Calling Risky? Marmots Avoid Calling from Risky Places

Alarm calling is common in many species. A prevalent assumption is that calling puts the vocalizing individual at increased risk of predation. If calling is indeed costly, we need special explanations for its evolution and maintenance. In some, but not all species, callers vocalize away from safety and thus may be exposed to an increased risk of predation. However, for species that emit bouts with one or a few calls, it is often difficult to identify the caller and find the precise location where a call was produced. We analyzed the spatial dynamics of yellow-bellied marmot (Marmota flaviventris) alarm calling using an acoustic localization system to determine the location from which calls were emitted. Marmots almost always called from positions close to the safety of their burrows, and, if they produced more than one alarm call, tended to end their calling bouts closer to safety than they started them. These results suggest that for this species, potential increased predation risk from alarm calling is greatly mitigated and indeed calling may have limited predation costs.     

Synchronized interdigitated calling in the Kuvangu running frog, Kassina kuvangensis

Male Kuvangu frogs show repetitive calling of pulsed advertisement calls in which up to seven calls are repeated in short succession. Recordings of pairwise interactions between males showed that calls were highly synchronized, with individual calls interdigitating with each other. Males frequently switched between the leader and follower role with neither male dominating the interaction. Interactive playback experiments using synthetic calls revealed that males slightly but significantly increased the number of calls per call group with increases in stimulus call number. Males also significantly increased call rate with the number of calls in the playback stimulus. Furthermore, when presented with shortened intercall intervals, males increased their own intercall intervals, thus ‘skipping’ a call and avoiding overlap with the playback. The low degree of call matching suggests that repetitive calling, apart from maintaining a male's attractiveness to females relative to rival males, may mediate male-male competition. In addition, synchronized interdigitated calling may serve to reduce predation, while maintaining species-specific temporal features of advertisement calls important to females. Kuvangu running frogs may have reduced the costs associated with synchrony and alternation by using a signal timing scheme that allows them to do both simultaneously.Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.       

Usage of monophonic and biphonic calls by free-ranging resident killer whales (Orcinus orca) in Kamchatka, Russian Far East

Killer whale discrete calls include types containing an overlapping high-frequency component (biphonic calls) and types without an overlapping high-frequency component (monophonic calls). In the resident killer whales of the Northeast Pacific, biphonic discrete calls exhibit higher source levels than monophonic calls, which suggests different active space and consequently different functions for monophonic and biphonic call types. In this study we investigate the potential communicative functions of monophonic and biphonic discrete calls produced by killer whales from Kamchatka (Northwest Pacific). We analyze how the usage of these calls depends on the number of pods present in the area and type of activity. Our results show that the usage of monophonic and biphonic calls in Kamchatkan killer whales depends on the number of pods in the area and is less dependent on the type of activity. Biphonic calls are more common when more than one pod is present in the area and could therefore function as markers of pod and matriline affiliation, serving mainly as cohesion signals. Monophonic calls dominated the vocalizations when a single pod was present, while in the presence of more than one pod both categories were used in equal proportions.     

Dependence of killer whale (Orcinus orca) acoustic signals on the type of activity and social context

We investigated the influence of the type of activity and the social context on the proportion of four different structural categories of stereotyped calls in the acoustic communication of Kamchatkan killer whales. Using generalized linear models, we described the dependence of each sound category on the type of activity, the number of killer whale pods and the presence of mixed-pod groups. We found that the proportion of different sound categories depended on the number of pods and the presence of mixed-pod groups, while the type of activity did not affect the proportion of sounds of different categories. Based on the observed differences we suggest that biphonic and high-frequency monophonic calls are mainly used as family and pod markers, and help to track the position of family members at long ranges, and low-frequency monophonic calls are used as close-range intra-group signals to maintain contact between pod members in the conditions of limited underwater visibility.     

Troop-specific responses to long calls of isolated tamarins (Saguinus mystax)

Recently captured moustached tamarins (Saguinus mystax) were briefly separated from other members of their troop. Most separated animals emitted long calls that were, in general, similar in acoustic structure to those of sympatric tamarin species while retaining species distinctiveness. Individual differences also appeared in call structure. The long calls of a separated animal were responded to almost entirely by members of the animal's own troop rather than by other troops, and reciprocal calling occurred among troop members significantly more often than expected by chance. Although there was no evidence of troop-specific call structure or dialect, there were troop-specific responses to the calls of separated tamarins. This response implies the existence of a stable and integrated troop structure that allows troop members to learn and to respond to the individual specific features of each troop member's calls.     

Near-synchronous calling in the hip-pocket frog Assa darlingtoni

Sustained perfect synchrony of signal production by animals is unrealistic, but even near-synchronous signalling is extremely rare. Near-synchronous signalling has been documented in some orthopteran insects and fireflies, and one kind of frog. This study provides observations and analyses of sustained bouts of impressive near-synchronous calling by a terrestrial breeding frog from Australia, the hip-pocket frog (Assa darlingtoni). Males called in scattered clusters of several individuals from the rainforest floor of northern New South Wales. In eight of nine pairs of semi-isolated males, there was sustained near-synchronous calling in bouts consisting of 16–20 calls and lasting 5–10 min. There was extensive overlap of the pulsed calls, and calls of a lagging male began overlapping that of a leading male after 2–5 pulses of a leader’s call note. In five pairs, one male’s calls were usually in the leading position; in three pairs, leadership frequently switched between males. In the latter interactions, males frequently skipped a call and produced its next call or calls in the leading position. This tactic has been interpreted as sexual competition between neighbours in orthopterans, but further research is required to rule out possible alternative hypotheses.     

Individual recognition during bouts of antiphonal calling in common marmosets

Many vocalizations are encoded with a diversity of acoustic information about the signal producer. Amongst this information content are social categories related to the identity of the caller that are important for determining if and how a signal receiver may interact with that individual. Here, we employed a novel playback method in common marmosets (Callithrix jacchus) to test individual recognition during bouts of antiphonal calling. These experiments utilized custom, interactive playback software that effectively engaged subjects in antiphonal calling using vocalizations produced by a single individual and presented 'probe' vocalization stimuli representing a different individual at specific points within bouts of calling. The aim here was to test whether marmosets would recognize that the probe stimulus was a phee call produced by a different individual. Data indicated that marmosets were able to detect the change in caller identity; subjects produced significantly fewer antiphonal call responses to probe than control stimuli and, in some conditions, exhibited a shorter latency to produce the vocal response. These data suggest that marmosets recognize the identity of the individual during bouts of antiphonal calling. Furthermore, these results provide a methodological foundation for implementing the probe playback procedure to examine a broader range of social categorization during vocal interactions.     

SOCIETY FOR EXPERIMENTAL BIOLOGY CONFERENCE,UNIVERSITY OF ST. ANDREWS,APRIL 1995

We describe the interactive nature of vocalizations emitted by African elephant (Loxodonta africana) family groups while visiting waterholes. Despite being in close visual contact with each other, individuals called interactively within a series of overlapping or antiphonal vocal bouts that increased significantly while departing from the waterhole. After initiating departure from the waterhole, elephants in this study increased their calling rate and their production of overlapping vocal bouts. The majority of calls either overlapped or occurred within 1.5 seconds of another call as part of an antiphonal bout, rather than as isolated calls. The departure of larger herds was accompanied by a greater number of calling bouts. The increase in interactive antiphonal bouts during departure might serve to facilitate group coordination and cohesion, as well as possibly reinforce social bonds. The longer repeated bouts could also facilitate eavesdropping by distant elephants by boosting signal detection since the repetition of these longer calls may yield an increase in the signal-to-noise ratio (SNR) that reduces the noise floor for better longer distance communication.