Humpback whale mothers and their newborn calves ‘whisper’ to each other during the first months of the calves’ life to avoid being overheard by killer whales, researchers have learnt.
The first few months are crucial to the calves’ survival when migrating to their feeding grounds but little else is known about the early life stages of whales in the wild.
The migration could be as long as 5,000 miles, through rough seas and with strong winds, and can be very demanding on a young calf.
The researchers from Murdoch University and University of Aarhus in Denmark were studying the first months of a humpback’s life. They attached temporary tags onto the mothers and their calves in Exmouth Gulf, off Western Australia.
Professor Lars Bejder, from Murdoch University, said that one thing the study highlighted was the importance of Exmouth Gulf for humpback whales.
“In Exmouth Gulf, we have seen that calves are suckling more than 20 per cent of the time.
“The high suckling rates from mothers to calves ensure that the calves have sufficient energy to migrate to Antarctica,” he said.
“These calves only suckle when the mothers are resting and so it is important that humpback whale mothers and calves are disturbed as little as possible during this important time period.”
Using the special tags, the researchers were able to record faint sounds of eight calves and two mothers.
The recordings revealed that newborn humpbacks communicate with their mothers using soft grunts and squeaks — a far cry from the loud, haunting song of the male humpback whale.
“We also heard a lot of rubbing sounds, like two balloons being rubbed together, which we think was the calf nudging its mother when it wants to nurse,” said Dr Simone Videsen, of the University of Aarhus.
She believes such quiet communication helps reduce the risk of being overheard by killer whales nearby:
“Killer whales hunt young humpback calves outside Exmouth Gulf, so by calling softly to its mother the calf is less likely to be heard by killer whales, and avoid attracting male humpbacks who want to mate with the nursing females,” she said.
The researchers believe that mother-calf pairs were likely to be sensitive to increases in ship noise. Because mother and calf communicate in whispers, shipping noise could easily mask these quiet calls.
The findings will help conserve the humpback’s habitat and — crucially — ensure these nursery waters are kept as quiet as possible.
Read more about the humpback whale study here. Story credit: Murdoch University newsroom.
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