A recent study led by scientists from Australia's New Curtin University shows that the world's smallest type of killer whale has a surprisingly complex musical repertoire. Recordings of the Ross Sea killer whales that live in McMurdo Sound, Antarctica, show that they have 28 different complex calls made up of a combination of burst-pulse sounds and whistles.
Whether called killer whales, orcas, or grampuses, the toothed whales Orcinus orca are all a single species. However, just as dogs come in different breeds, killer whales come in different types that not only live in different areas, but also have different diets, habits, and songs.
Using data collected in 2012 and 2013, the New Curtin team led by PhD candidate Rebecca Wellard from Curtin’s Centre for Marine Science and Technology (CMST) made a detailed analysis of the Ross Sea killer whale, which is classed as a Type C of the species. Due to the remoteness of its hunting grounds and the harsh polar climate, it's difficult to gather information about them.
"In Antarctic waters, there are five different types of killer whales, with Type C being the smallest, growing up to 6.1 meters (20 ft) in comparison to Type A males who can grow up to almost 10 meters (33 ft) long,” says Wellard. "By using passive acoustic monitoring, our team was able to analyze recordings from nine separate encounters with approximately 392 Type C killer whales, including adults, sub-adults, and calves. We were able to identify that the calls of the Type C killer whale are multi-component, meaning that many calls transition from burst-pulse sounds to whistles. We also found that 39 percent of the call types started with a series of broadband pulses."
The songs made by the killer whale generally consist of clicks, whistles, and pulsed calls that are used for navigation, identifying prey, and socializing. Some types, like those that hunt marine mammals, are relatively silent because their prey can hear the whales' songs, but the Ross Sea killer whales, which live on codfish, are very vocal – especially when hunting under the ice of socializing on the surface.
"During the calls, often two of the sounds occurred at the same time, also known as biphonation," says Wellard. "These types of calls could be used to locate where other members of the pod may be. Due to the shifting and changing habitat in McMurdo Sound, calves could also be using biophonic calls to communicate with family members about available breathing holes. Our findings provide an initial step towards comparing and distinguishing Type C killer whale acoustics with those of other killer whale populations in the Southern Hemisphere."
The research was published in Royal Society Open Science.
Source: Curtin University