A new technique for deciphering the calls of sperm whales allows the magnificent, mysterious creatures to be studied in unprecedented detail.
Researchers identified subtle variations caused by differences in the shape of individual whales’ heads. It’s the first time that sperm whale vocalizations have been linked to specific individuals.“This is the just the first step in answering a lot of questions about their vocal and social complexity,” said Shane Gero, a Dalhousie University biologist. “It’s the first time that we’re getting to the level of knowing these animals as individuals, as families — as personalities, really. It’s a whole new step.”
Vocalizations are used by every cetacean species, but only a few, such as bottlenose dolphins and humpback whales, have been studied in detail. Even those fields of research are still young, however, and it’s not always possible to extrapolate findings between species that are different both physically and socially.Sperm whales have been particularly difficult to study, as their family groups tend to be large, with a proclivity for long-distance roaming. Only snatches of communication are usually heard. It’s been enough for researchers to learn that each sperm whale family has a distinctive repertoire of sounds, but the sounds have been so mixed together that they can’t be consistently attributed to a individuals — a first step in understanding what the whales might be saying.
The latest study, currently in press at the journal Marine Mammal Science, focuses on a seven-member sperm whale family who live in waters around the Caribbean island nation of Dominique. Caribbean sperm whales have unusually small home ranges. This allowed the researchers to spend more time with them than is usually possible. Because the group was small, there were more opportunities to identify and record individual whales when they were alone.The researchers could then analyze whales’ vocalizations, which take the form of high-frequency clicks made by pushing air through structures in their skulls.
“The whales communicate by patterns of clicks. The clicks reverberate in the head. If you listen to it carefully, there are these pulses. The time between pulses reflects the time it takes for sounds to reverberate, to go from one end of the head and back. Because the heads are all different length, they have different reverberation times,” study co-author Hal Whitehead, also a Dalhousie University biologist. Until now, “just figuring out who makes which sound underwater was tough,” he said.Analysis of the whales’ vocalizations are still in their early stages, but the results are already intriguing. While the whales tended to possess the same basic repertoire of “codas” — the technical name for each distinctive series of clicks — one female had a completely different set. She happened to be a mother. The distinctive sounds could be what she used to communicate with her calf.
Apart from the mom, the researchers found that half of each individuals’ vocalizations followed one of two patterns.One pattern is formed by two consecutive, slowly-paced clicks, followed by three faster clicks. It has been found only in the Caribbean. While the pattern varies slightly between groups, this study suggests that it’s consistent within the group. According to Gero, it could function as a family identifier, letting other whales know who is around. “It says, I belong to this family, I belong to this vocal clan,” he said.
The other common pattern is composed of five regularly-spaced clicks, and has been heard in sperm whales all over the world. Preliminary research suggests that the pattern may vary slightly between each individual, said Gero. If so, the pattern could function as an individual identifier — or, from another perspective, a name.The question of whether it’s appropriate to think of sperm whales as having names is a controversial one. Some scientists think that many cetaceans should be considered persons, at least on par with non-human great apes. There’s considerable evidence to support the notion: cetacean brains are extraordinarily sophisticated, especially in areas associated with cognition and communication, and many social behaviors can be explained only as culture rather than instinct. In captivity, dolphins pass tests of self-recognition and self-awareness that were once considered markers of personhood.
Questions of consciousness and personhood are difficult to answer in another species in scientifically quantifiable ways, said Gero. But techniques like those used in this study should help.“I use the word ‘personality’ very carefully. It’s hard to quantify. But they undoubtedly have them,” said Gero. “It may take years and years to understand them, to translate their behaviors and nuances, to understand things like fear or happiness. But it’s time that the assumption was made that these animals are individuals, and have a concept of self.”
Images: Above, sperm whale mother and her calf; below, a juvenile whale the researchers nicknamed “Can Opener.”/Shane Gero.
Citation: “Individual vocal production in a sperm whale (Physeter macrocephalus) social unit.” By Tyler M. Schulz, Hal Whitehead, Shane Gero & Luke Rendell. Marine Mammal Science, in press.