A new study has revealed that young humpback whales keep their voice down when communicating with their mothers.
Ecologists from Denmark and Australia made this discovery after tagging two mother humpback whales and eight calves in Exmouth Gulf off western Australia. The reason for this subtle form of communication is to avoid detection by killer whales.
Humpback whales spend the summer in Antarctic or Arctic, where prey is abundant. In the winter, they migrate to the tropics to mate and breed. While in the tropics (like Exmouth Gulf), the calves have to consume as much as they can, so as to increase their chance of surviving the upcoming migration, a journey that would be very strenuous and demanding on the young calves.
Data from the tags (which remain attached to the whales only for up to 48 hours before detaching) revealed that mothers and calves spend much time nursing and resting, and that the newborn humpbacks communicate with their mothers using intimate grunts and squeaks.
This communication usually took place when the whales were swimming, suggesting that they helped the mother and calf to stay 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 lead author Dr Simone Videsen of Aarhus University.
“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 added.
The study was published in a recent issue of Functional Ecology.