Barks and grunts hold much meaning for humpbacks.
The splashes, barks and grunts of baleen whales carry much more meaning than biologists thought, according to the latest survey of the marine mammals.
The scientists behind the study say that these noises could be the ideal characteristics for conservationists to monitor to understand the growing impact of noises made by humans on the underwater environment.
The songs of baleen whales — which have characteristic mouth combs, which they use for filter feeding — have been studied extensively, as have the non-song communications of toothed whales. But non-song communication in baleen whales has received little attention.
“Most people focus on the song,” says Rebecca Dunlop at the University of Queensland in Australia. “It is simply amazing how much we were missing by not paying attention to all of the other [sounds] that the animals actually make.”
Although studies of humpback whales, Megaptera novaeangliae, in the 1980s had noted these sounds, Dunlop and her colleagues took things a step further by monitoring a population of humpbacks every year between 2002 and 2005 as they migrated from Australia’s Great Barrier Reef to the Antarctic.
The team used a combination of sightings from survey points on land, tracking software and hydrophone buoys to collect their data, which was all time stamped and then correlated to the whales’ behaviour at that moment.
Dunlop and her colleagues report in Marine Mammal Science1 that the whales seem to generate certain sounds in conjunction with specific social circumstances. Breaching, and the following splash, for instance, occurs most often in groups that contain just one adult, suggesting that it is a signal meant to alert other groups that “I’m here”.
The wop and the thwop
The team also noticed that underwater blasts of air through the whales’ blow holes were linked to encounters between a lone male and one escorting a female, suggesting that the sound is related to mate protection.
However, the most dramatic discovery was that of the ‘wop’, which seems to be a signal between a female and her calf that is apparently unique to a female humpback. Interestingly, a similar sound, dubbed the ‘thwop’, was made most often by lone males looking for females.
“Evolutionarily, it makes a lot of sense that they are being so verbal. Underwater you can’t see much of anything, but you can most certainly hear,” says Dunlop.
“This makes [humpback whales] a brilliant test bed for understanding the evolution of complex vocal communication,” says marine biologist Luke Rendell at the University of St Andrews, UK. “And in conservation terms, work like this urgently needs to get done,” he adds. It's possible that monitoring the whale's sounds could reveal how other noises in the ocean affect these animals. “Anthropogenic noise is increasing in the oceans, and while much effort is directed at understanding direct, lethal things such as military sonar, subtler behavioural changes resulting from degraded communication may over the long term be just as dangerous,” suggests Rendell.
Dunlop, R. A., Cato, D. H. & Noad, M. J. Mar. Mamm. Sci. 24, 613–629 (2008).
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Kaplan, M. Marine biologists interpret whale sounds. Nature (2008). https://doi.org/10.1038/news.2008.984