If you travel through a country and you have an ear for dialect, you might notice odd words pop up that are particular to the location. Dialects are an occupational hazard of travel, and it turns out that killer whales from different geographical regions have them too. Ann Bowles, from the Hubbs-SeaWorld Research Institute, USA, says, ‘Some mammals have a repertoire of calls that seem specific to particular geographic areas or particular social groups.’ However, why killer whales acquire their dialect is a mystery and discovering the reason is particularly tricky because killer whales form incredibly stable family groups, making it almost impossible to study dialect acquisition. So Bowles turned her attention to six captive killer whales at SeaWorld San Diego, USA. According to Bowles, five of the animals originated from – or had a mother from – the waters surrounding Iceland, while the sixth was from the Pacific Northwest, and all had arrived in San Diego via different routes. Given the animals' different origins and life experiences, Bowles and her colleagues Jessica Crance and Alan Garver were curious to find out how much overlap there was between the animals' use of dialect (p. 1229).
According to Bowles, recording the animals' calls was particularly challenging. Fortunately, SeaWorld had installed eight hydrophones in the walls of one of the pools in the complex that the whales inhabit, so she was able to record them communicating and film them as they interacted. Then Crance identified the calls and assigned them to the individual that was closest to the hydrophone that had made the loudest recording. After months of painstaking analysis, the team clearly identified 17 call types that all of the animals with an Icelandic heritage were using. ‘There is enough overlap in their repertoires that we would consider them to have the same dialect’, says Bowles.
But then Crance noticed something change in the repertoire of the two juvenile males' dialects after 2005: they adopted some of the call patterns of the older male that shared the pools with them. Bowles admits that she was initially sceptical when Crance showed her the evidence, but as the team investigated further, they realised that the two youngsters had switched their social allegiance – they had hooked up with the older guy – and begun to learn his call patterns.
The switch happened when the mother of one of the youngsters gave birth to a new calf. Until then, her son had spent most of his time with his mother and learned her dialect. But when his mother became occupied with the new arrival, he moved on to associate more with the senior male. And Bowles laughs when she remembers that the other young male in the enclosure followed his friend, spent more time with the older male and learned his dialect too. ‘It seemed like a teenage movie’, she chuckles. And the youngsters could not have learned the novel sounds from anyone else because the older male had some unusual calls. ‘He tends to repeat elements over again, which is not typical, and our guess is that his dialect was shaped to some degree by having lived with bottlenose dolphins for a long time’, she says.
So, when the two young males began using the same idiosyncratic collection of sounds to show their new allegiance, Bowles was convinced that the youngsters had learned their mentor's dialect. And she is extremely excited by the possibility that the San Diego killer whales may be able to teach us about how human dialects evolved, saying, ‘We have an animal that is starting to look like a pretty good model.’