Orcas Unveiled: Deciphering the Language of the Sea

Killer whales, scientifically known as Orcinus orca, are powerful, intelligent, and beloved marine mammals found in waters across the globe. Acoustic communication is a crucial aspect of their behavior as they are highly social, living in groups of maternally related individuals known as pods. In Iceland, killer whales feed primarily on herring and are known to be very vocal, using echolocation to locate their prey and pulsed calls to communicate with their pod. Understanding their ways of communication will help us further understand killer whale behavior, social structure, ecology, and evolution.

Calls made by killer whales can vary depending on their population, social groups, or behavioral contexts and some pods even have their own distinct calls. For instance, in the North Pacific, resident killer whales (whales that feed on fish) live in closed social groups, and closely related groups often share vocalizations. On the other hand, transient killer whales (whales that feed on marine mammals such as seals) have a more widely shared repertoire due to their looser social structures. Some scientists believe that this diversity in call types is a way of sharing group identity. However, the detailed descriptions of killer whale call repertories are limited in several regions and the fine-scale differences in calls around Iceland remain largely unexplored. Anna Selbmann, a researcher at the University of Iceland, and her colleagues conducted a study and set out to change this.

Selbmann's study, published in Marine Mammal Science on July 7th, 2023, aims to investigate the variations in the call repertoires of killer whales across Iceland through the use of passive acoustic monitoring, or PAM. PAM is a recent technological advancement that provides scientists the opportunity to collect underwater acoustic data in a noninvasive, inexpensive, and effective way. This is especially useful in locations that are remote or difficult to survey, such as Iceland. The researchers used 32 years of data collected from five different locations in Iceland: Eastfjords, Vestmanneayjar, Breiðafjörður, Skjálfandi, and Reykjanes, which can be seen in the interactive map below. The researchers analyzed the recordings not only by listening to the calls but also by visually projecting them onto spectrograms. Using nearly 4,000 hours of recordings, the researchers classified 9,412 calls into a total of 91 call categories.

Four common call categories had relatively simple structures and were easily recognizable. Moreover, 56% of call categories were found at two or more locations, but only one call category was recorded in all five locations. The majority of call types were shared between two locations, Vestmannaeyjar and Breiðafjörður, popular herring feeding grounds for killer whales. Based on these findings, Selbmann and her colleagues hypothesize that individuals and groups use different acoustic calls in different social or environmental contexts. Their results also suggest that the social structure of Icelandic killer whales does not have a clear hierarchy, unlike other populations of killer whales. This variation across groups at the community level supports the idea that differences exist between groups of killer whales in Iceland.

This new research adds to our growing understanding of killer whales. By examining the variations in their vocalizations, we can gain insights into their social structures and distribution patterns. Selbmann and her colleagues recommend further studies be conducted and recognize some of their study's shortcomings, such as varying sample sizes and the timing of recordings collected in some locations.

It is still uncertain whether Iceland's killer whales have group-specific vocal repertoires due to their apparent non-hierarchical social structures. Selbamann and her team urge that research be conducted to explore this topic, so we can gain a better understanding of what drives these differences in their calls. There is still much to learn about these incredible animals, but each step researchers take is a step closer to understanding the deep, expressive, mysterious world of killer whales.