'Whispering' keeps humpbacks safe from killer whales

May 12, 2017

A humpback mother and calf, photographed in Exmouth Gulf in northwest Australia.
Credit: Fredrik Christiansen

Newborn humpback whales 'whisper' to their mothers to avoid being overheard by killer whales, researchers have discovered.

Ecologists from University of Aarhus in Denmark and Murdoch University used temporary tags on humpback mothers and their calves in Exmouth Gulf, off Western Australia, to learn more about the first months of a humpback's life.

Lead author, Dr Simone Videsen of the University of Aarhus, said: “We know next to nothing about the early life stages of whales in the wild, but they are crucial for the calves' survival during the long migration to their feeding grounds.

“This migration is very demanding for young calves. They travel 5,000 miles across open water in rough seas and with strong winds.

“Knowing more about their suckling will help us understand what could disrupt this critical behaviour, so we can target conservation efforts more effectively.”

Humpbacks spend their summer in the food-rich waters of the Antarctic or Arctic, and in the winter migrate to the tropics to breed and mate. While in tropical waters such as Exmouth Gulf, calves must gain as much weight as possible to embark on their first, epic migration.

Professor Lars Bejder, from Murdoch University, said the results highlighted 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.”

The faint sounds of eight calves and two mothers were recorded using special tags developed by the University of St Andrews.

The tags attach to whales via suction cups and record sounds made and heard by whales, along with their movements, for up to 48 hours before detaching to float at the surface.

The study found that mothers and calves spend significant amounts of time nursing and resting. The recordings also revealed that newborn humpbacks communicate with their mothers using intimate grunts and squeaks – a far cry from the loud, haunting song of the male humpback whale.

The data tags showed that these quiet calls usually occurred while whales were swimming, suggesting they help mother and calf keep together in the murky waters of Exmouth Gulf.

“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 Videsen.

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.

“From our research, we have learned that mother-calf pairs are 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 this important humpback habitat and – crucially – ensure these nursery waters are kept as quiet as possible.

The study was published in Functional Ecology.

All the latest news from Murdoch University can be read here.

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Media contact: Pepita Smyth
Tel: (08) 9360 1289  |  Mobile: 0417 171 551  |  Email: p.smyth@murdoch.edu.au
Categories: General, Research, School of Veterinary and Life Sciences Research
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Comments (One response)

Suzanne May 14, 2017

Very interesting article, and great to see work being done to help conserve these beautiful animals for future generations.

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