Although many species communicate acoustically, the vast majority of animals use a genetically innate repertoire of sounds to exchange information. But some species, including humans, are capable of imitating sounds and adding it to their own repertoire, a process known as vocal learning. It is thought that the acquisition of this ability may have been a first step in the evolution of human language.

Although this trait is extremely rare, it is not unique to humans and has been discovered in 6 groups of animals: 3 groups of birds and 3 groups of mammals. Now, thanks to new research, we know that killer whales are capable of cross-species vocal learning. When socialized with bottlenose dolphins in captivity, the team discovered that they transitioned from their typical vocalizations and emitted more dolphin-like noises. According to the researchers, this suggests that cetaceans (dolphins, whales and porpoises) may use this trait to facilitate social interactions. The work has been published in The Journal of the Acoustical Society of America.

Killer whales, or orcas, emit three main types of vocalization: clicks, pulsed calls and whistles, with pulsed calls being the dominant form of communication. These are known to vary across social groups in terms of duration and pitch, but killer whales living together tend to produce similar calls that are distinct to that particular group, which is known as a dialect. Researchers had their suspicions that killer whales learn this dialect, but there was no experimental proof. Since dolphins produce similar vocalizations to orcas, and the two are sometimes housed together in captivity, the researchers took this unique opportunity to investigate whether killer whales could learn vocalizations from their cross-species social partners.

For the study, the researchers analyzed recordings of vocalizations produced by 10 captive orcas; three of these lived with bottlenose dolphins for several years, whereas the rest were housed with their own species. They then compared these recordings with the vocalizations produced by the dolphins.

They found that 95% of the 1551 vocalizations made by the seven orcas that were living with members of their own species were the typical pulsed calls that dominate their repertoire. The orcas that were living with dolphins, however, emitted far more whistles and clicks, just like their cross-species social partners. Intriguingly, they found that one of the killer whales even learned how to produce an artificial chirp sequence that a human trainer had taught the dolphins before they were introduced to each other.

According to the researchers, this demonstration of cross-species vocal learning suggests that orcas have substantial vocal plasticity and are highly motivated to match the vocalizations of their social associates. This is important because the fate of orcas in groups disrupted by change, such as oil spills, will be partly dependent on their ability to socialize with new populations and thus their vocal plasticity.

[Via Acoustical Society of America, The Journal of the Acoustical Society of America and Science]