Investigating individual distinctiveness in the calls of wild belugas   

Beluga whales produce a multitude of sounds for a variety of functions. To date, calls used for group cohesion and for mother-calf contact, known as ‘contact calls’, are the best understood ^{4,6,8,11,13,14}. 

The fact that contact calls sound nothing like the typical chirps and whistles that are common in  the beluga vocal repertoire, but instead sound like chainsaws or creaky rusty doors, makes it reasonably easy to identify them reliably, and therefore to study them.  

Most studies of beluga contact calls to date have indicated that they are used predominantly in situations of isolation where there is a need for the animals to regain or maintain contact with their group ^4,8,11,13, and for mother-calf contact ^1,12.  

Beluga contact calls are typically produced in series and consist of long duration broadband rapid pulse trains with strong acoustic energy up to 150 kHz. When these calls have an additional stereotyped component (often a whistle) that overlaps the broadband pulse train, they are referred to as complex contact calls, and when the pulse trains have no overlapping component they are referred to as simple contact calls ¹⁴.

Why are some contact calls complex? What is the function of the stereotyped component that characterizes complex contact calls? Could it serve to identify the individual caller? Our study conducted in Cunningham Inlet, in the Canadian High Arctic, attempted to answer this question ¹⁴.  

Researching contact calls in a wild population

We examined the vocalizations produced during 14 natural temporary entrapment events, when belugas swam into a river pool and became separated from the free-ranging herd at low tide, until the water was high enough again for the whales to swim out. These events provided an ideal context in which to study contact calls, as it became very clear that when the whales were temporarily entrapped in the river pool, they produced contact calls much more often than usual.

Only 10% of the vocalizations produced by the free ranging herd were contact calls, while more than half (61%) of the calls produced by entrapped whales were contact calls. 

We inspected, via spectrograms, all the complex contact calls from our recordings and grouped them into types, based on their stereotyped visually salient overlapping component (remember that complex contact calls are mixed calls). We classified 87 distinct types or categories.  Although all 87 types shared the same pulse train structure, they differed in their overlapping components. 

Importantly, this classification was verified by naïve human judges, a commonly used technique to classify animal vocalizations. In our study, a total of 55 naïve judges verified our initial classification, resulting in an overwhelming agreement with each other and with our classification.

The exciting findings

Interestingly, we found a strong relationship between the number of whales and the number of complex contact call types recorded in an entrapment. We also found that the number of contact call types never exceeded the number of entrapped whales, so that the only entrapment that had a single whale, had a single contact call type.

This could mean one of two things; that each individual produced its own distinct contact call type, or, if the entrapments contained groups of associated individuals (the larger the entrapment, the larger the potential number of such associations), that each contact call type was potentially shared by a few close associates. 

These findings offer preliminary evidence that beluga contact calls may be true vocal signatures, or individually distinct calls used to broadcast identity. 

Vocal signatures are like sonic ‘name tags’! 

This is an exciting finding, because although individuals of all vocal species, including humans, have their own voice characteristics that help tell them apart, vocal signatures are much more rare, and denote individual differences that are more accentuated than the subtle differences in voice characteristics.  

Furthermore, we know from research on other species that while voice prints can be innate, true vocal signatures often need to be learned ², much like human toddlers must learn to pronounce their own names.  This fits our research on beluga whales very well, as we know that beluga calves learn these contact calls from their mother, and it takes them one to two years to perfect them ^1,12.  

One of the few cetacean species for which true vocal signatures have been documented is the bottlenose dolphin; they produce signature whistles that act as “names” and play an important role in helping individuals keep track of one another in their fission-fusion societies, in which the size and composition of social groups changes periodically and often drastically ^3,10.  

Beluga whales also have that kind of fission fusion society that would favour the evolution of vocal signatures. Their societies involve close and fluid long-term associations with both kin and non-kin, cooperation, and strong cultural traditions in the context of communities that include large numbers of individuals of all sexes and ages 7. 

Males form friendships and alliances that can last years ⁵, unrelated females travel together, presumably helping to raise each other’s young, and juveniles of multiple ages and different maternal lineages gather together in bands to play and socialize ⁷. 

Identity calls may help belugas mediate these complex and fluid social relationships and help them recognize and keep track of relatives and friends in an aquatic environment where vision would not be as effective.  However, to be completely certain that complex contact calls are true vocal signatures, we are still missing the most important part of the puzzle: identifying the individual callers! Can we put a face (or rather, a dorsal ridge!) to a call?  

We are currently analyzing recordings from non-invasive Digital Recording Tags (DTAGS), which attach to the whales via suction cups, deployed on St. Lawrence Estuary belugas by DFO and GREMM colleagues. We are matching the contact-calls produced by individuals carrying these temporary DTAGS with photo-IDs of those individuals (using GREMM’s extensive photographic catalogue of this endangered population).  We hope that this analysis will illuminate whether beluga contact-calls are strictly individual or shared with close relatives or friends.  

If beluga contact calls are individual (akin to bottlenose dolphin signature whistles), or even shared at the matrilineal level, then one would predict that a community, believed to be an assemblage of several matrilineal units, would have a set of contact-calls specific to that community.  It is for this reason that our ongoing project conducted by PhD student Jaclyn Aubin is studying contact call production in three putative female communities of the St. Lawrence population (known as South Shore, Upstream, and Saguenay) to determine if the communities share a set of contact calls specific to that community.  

Recognising individuals, groups, and even communities acoustically has important conservation implications for declining populations. 

If we confirm that contact calls are indeed vocal signatures, then it follows that we could use acoustic monitoring alone to understand habitat use and ranging patterns of individual beluga whales and their close associates. Similarly, distinguishing female communities by their calls will allow acoustic monitoring of such communities and inform population management decisions. 

Understanding beluga sounds helps us better protect them.

This webarticle is adapted from an essay written as part of our “Window on Belugas” project, a collaboration between the Group for Research and Education on Marine Mammals (GREMM), the Marine Mammal Observation Network (MMON), and Raincoast. 

References

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3. King, S. L., Sayigh, L. S., Wells, R. S., Fellner, W., & Janik, V. M. (2013). Vocal copying of individually distinctive signature whistles in bottlenose dolphins. Proceedings. Biological Sciences, 280(1757), 20130053. https://doi.org/10.1098/rspb.2013.0053

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5. Michaud, R. 2005. Sociality and ecology of the odontocetes. Pages 303–326 in K. E. Ruckstuhl and P. Neuhaus, eds. Sexual segregation in vertebrates: Ecology of the two sexes. Cambridge University Press, Cambridge, U.K.

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7. O’Corry-Crowe, G., Suydam, R., Quakenbush, L., Smith, T. G., Lydersen, C., Kovacs, K. M., … Ferrer, T. (2020). Group structure and kinship in beluga whale societies. Scientific Reports, 10(1), 1–21. https://doi.org/10.1038/s41598-020-67314-w

8. Panova, E., Agafonov, A., Belikov, R., & Melnikova, F. (2017). Vocalizations of captive beluga whales, Delphinapterus leucas: Additional evidence for contact signature “mixed” calls in belugas. Marine Mammal Science, 33(3), 889–903. https://doi.org/10.1111/mms.12393

9. Sayigh, L S, Tyack, P. L., Wells, R. S., Solow, A. R., Scott, M. D., & Irvine, A. B. (1998). Individual recognition in wild bottlenose dolphins: a field test using playback experiments. Animal Behaviour, 57, 41–50. https://doi.org/10.1006/anbe.1998.0961

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11. Van Parijs, S. M., Lydersen, C., & Kovacs, K. M. (2003). Sounds produced by individual white whales, Delphinapterus leucas, from Svalbard during capture. The Journal of the Acoustical Society of America, 113(May 2002), 57–60. https://doi.org/10.1121/1.1528931

12. Vergara, V., & Barrett-Lennard, L. G. (2008). Vocal development in a Beluga calf (Delphinapterus leucas). Aquatic Mammals, 34(1). https://doi.org/10.1578/AM.34.1.2008.123

13. Vergara, V., Michaud, R., & Barrett-Lennard, L. G. (2010). What can Captive Whales tell us About their Wild Counterparts? Identification, Usage, and Ontogeny of Contact Calls in Belugas (Delphinapterus leucas). International Journal of Comparative Psychology, 23, 278–309. https://escholarship.org/uc/item/4gt03961

14. Vergara, Valeria, & Mikus, M.-A. (2018). Contact call diversity in natural beluga entrapments in an Arctic estuary: Preliminary evidence of vocal signatures in wild belugas. Marine Mammal Science. https://doi.org/10.1111/mms.12538

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