Baby whales know how to whisper to their mums to avoid detection by predators, says new research.
Scientists have found that, despite humpbacks being renowned for their beautiful, loud songs, babies use quiet grunts and squeaks to communicate with their mothers to avoid being tracked down by the likes of killer whales.
The study tagged eight humpback calves and two mothers with the suction cup devices that recorded both their sounds and movements for up to 48 hours before detaching and floating to the surface.
According to Sky News, Dr Simone Videsen, from the University of Aarhus in Denmark, who led the research in Exmouth Gulf, Western Australia, said: "We ... 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.
"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."
The tags showed that quiet calls usually occurred when whales were swimming, suggesting they help the babies not to get lost in murky water.
Humpbacks famously spend their summer in the Antarctic or Arctic, where food sources are plentiful, before migrating to the tropics to breed in the winter.
The migration is tough and demanding for young calves.
According to the Telegraph, Dr Videsen added: "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."