A team of scientists from Hubbs-SeaWorld Research Institute (HSWRI) has found that killer whales living with bottlenose dolphins can learn to modify their vocalisations to be more like those of dolphins. Knowing that killer whales can learn, and that they are motivated to do so, sheds important light on how wild populations of whales might interact and integrate with other groups.
The study, which appears in the current issue of Journal of the Acoustical Society of America,found that three young killer whales at different marine parks changed the kinds of sounds they made so that their repertoires were more like those of dolphin companions. The whales, which had shared the same living environment with dolphins at some time in their lives, developed repertoires that were significantly different from those of whales interacting only with other killer whales. This is the first time vocal learning across species has been studied in toothed whales whose vocal repertoires differ greatly from those of dolphins.
Scientists still don’t know if and how groups of killer whales can merge after group size declines, as has been seen recently in the Pacific Northwest, where one population of killer whales is now considered endangered. Recent studies, including this one by HSWRI scientists and collaborators, are showing that killer whales might be able to learn new repertoires that could allow them to integrate with other groups.
The HSWRI study, made possible because researchers had access to animals in a controlled zoological park setting, took advantage of a unique experimental opportunity to observe killer whales in three different marine parks (two SeaWorld parks and Six Flags Discovery Kingdom) where it was possible to monitor and study vocal behavior of killer whales with and without dolphin social partners.
Different kinds of whales and dolphins have different vocal repertoires. Bottlenose dolphins in this study used whistles as their primary social signals and also produced clicks frequently. Killer whales, on the other hand, predominantly used pulsed calls, complex combinations of bursts and tones that sound like screams to the human ear. The research team found that killer whales that had lived with dolphins clicked and whistled more than their counterparts that had only lived with killer whales, and they used fewer pulsed calls. One whale learned to make novel chirps and whistles from the dolphins. The whales' ability to change their repertoires in different ways was a measure of what scientists call vocal plasticity.
Vocal plasticity is limited or non-existent in most social mammals other than humans, and it has been difficult to demonstrate even in our closest primate relatives. Previous research by students and scientists from the HSWRI Bioacoustics Program, led by Dr. Ann Bowles (the corresponding author), have already shown that killer whales can learn new types of calls when there is a change in their social association. This new study shows that killer whales, at least from birth to early adulthood, can learn not only new vocalisations but new patterns of usage if they associate with animals that have very different repertoires, such as bottlenose dolphins. This suggests that larger toothed whales may have substantial vocal plasticity. The work further suggests that social interactions are critical to learning. The whales didn't imitate arbitrary sounds that would have been within their capabilities, such as training whistle sounds.
Over a 20-year period, Dr. Bowles and her students have been collecting data on vocal communication of killer whales. For this study, University of San Diego graduate student Whitney Musser compiled data from three killer whales that, as juveniles to young adults, had lived with dolphins. They compared the vocalisations of these subjects to those of seven killer whales that had only lived with other killer whales. Because the sounds made by the two species are very different, they made comparisons based on general classes of vocalisations, such as clicks, whistles and pulsed calls. Information about Hubbs-SeaWorld Research Institute can be found at www.hswri.org.