Vocalisations may be used to help mother and calf stay together
To avoid detection by killer whales, newborn humpback whales whisper to their mothers.
Ecologists from Denmark and Australia made this discovery after they tagged two mother humpback whales and eight calves in Exmouth Gulf off western Australia in a study to find out more about the first months of their lives.
During the study – which was recently published in the Functional Ecology journal – the tags revealed newborn humpbacks communicating with their mothers using intimate grunts and squeaks. This usually took place while they were swimming, suggesting that such sounds helped the mother and calf stay together in the murky waters.
“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 lead author Dr Simone Videsen of Aarhus University.
It is thought that such communication reduced the risk of being overheard by killer whales nearby. According to Dr Videsen, “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.”
During summer, humpback whales are found in the food-rich waters of the Antarctic or Arctic; and then they migrate to the tropics in the winter to breed and mate. While they are in the tropics (like Exmouth Gulf), newborn calves need to gain as much weight as they can before embarking on their first migration.
“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,” said Dr Videsen.
The findings can help conserve this essential humpback habitat and ensure that these nursery waters are kept as quiet as possible.
“From our research, we have learnt 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,” said Dr Videsen.