Individuality embedded in the isolation calls of captive beluga whales (Delphinapterus leucas)

Abstract

IntroductionSpecies with fission-fusion social systems tend to exchange individualized contact calls to maintain group cohesion. Signature whistles by bottlenose dolphins are unique compared to the contact calls of other non-human animals in that they include identity information independent of voice cues. Further, dolphins copy the signatures of conspecifics and use them to label specific individuals. Increasing our knowledge of the contact calls of other cetaceans that have a fluid social structure may thus help us better understand the evolutionary and adaptive significance of all forms of individually distinctive calls. It was recently reported that one type of broadband pulsed sounds (PS1), rather than whistles, may function as individualized contact calls in captive belugas. The objective of this study was to assess the function and individual distinctiveness of PS1 calls in an isolation context. Recordings were made from five captive belugas, including both sexes and various ages.ResultsPS1 was the predominant call type (38 % in total) out of five broader sound categories. One sub-adult and three adults had individually distinctive and stereotyped pulse repetition pattern in PS1; one calf showed no clear stereotyped pulse repetition pattern. While visual inspection of the PS1 power spectra uncovered no apparent individual specificity, statistical analyses revealed that both temporal and spectral parameters had inter-individual differences and that there was greater inter-individual than intra-individual variability. Discriminant function analysis based on five temporal and spectral parameters classified PS1 calls into individuals with an overall correct classification rate of 80.5 %, and the most informative parameter was the average Inter-pulse interval, followed by peak frequency.ConclusionThese results suggest that belugas use individually distinctive contact calls in an isolation context. If belugas encode signature information in PS1 calls, as seen in bottlenose dolphins, the pulse repetition pattern may be the carrier, as it is individually stereotyped and appears to require vocal development. This idea is supported by the finding that the average inter-pulse interval is the most powerful discriminator in discriminant analysis. Playback experiments will elucidate which parameters are perceived as individual characteristics, and whether one of the parameters functions as a signature.Electronic supplementary materialThe online version of this article (doi:10.1186/s40851-015-0028-x) contains supplementary material, which is available to authorized users.

Relationships of cochlear coiling shape and hearing frequencies in cetaceans, and the occurrence of infrasonic hearing in Miocene Mysticeti

“…It is generally accepted that most animals are able to hear the frequencies they produce. The odontocetes Delphinapterus leucas (beluga whale) and Tursiops truncatus (common bottlenose dolphin) are good examples to support this approach, as known vocalization limits are almost equal to known hearing limits (e.g., Johnson, 1966;Awbrey et al, 1988;Herzing, 2000;Karlsen et al, 2002;Blomqvist and Amundin, 2004;Castellote et al, 2014;Mishima et al, 2015). Hearing data were used whenever possible, and vocalization data when no hearing data were available.…”

Vocalizations of captive beluga whales, Delphinapterus leucas: Additional evidence for contact signature “mixed” calls in belugas

“…, Mishima et al . ). In the Vancouver Aquarium in Canada, these signals were produced by belugas in situations requiring the maintenance of contact between individuals, such as isolation, birth, the death of a calf, the presence of divers in the pool, husbandry procedures, as well as reunions of belugas after separation (Vergara and Barrett‐Lennard , Vergara et al .…”

“…), PS1 calls had fixed individual‐specific pulse‐repetition patterns with a PRR of about 104–190 pulses/s and a duration of about 0.68–0.80 s (Mishima et al . ).…”

“…, Mishima et al . ), or mixed pulsed‐tonal variants of Type A calls (Vergara and Barrett‐Lennard , Vergara et al . ).…”

“…, Mishima et al . ) demonstrated that the proportion of contact calls in belugas vocalizations can vary widely—from more than 90% during the birth and death of a calf (Vergara et al . ) to total absence in some isolation sessions (Mishima et al .…”