While recording whales, scientists discovered that calves "speak" in soft murmuring squeaks in order to avoid attention from hungry killer whales.
It makes perfect sense. In the watery wilds where killer whales are hungrily hunting baby humpbacks, said baby humpbacks avoid using the loud haunting songs of their adult peers. Instead, they communicate with mom by using "low level vocalisations," according to scientists who have successfully recorded the sounds.
Humpback whales are known for their epic migrations which take them from summers in the Antarctic or Arctic to winters in the tropics to breed and mate. While in the warmer climes, calves must gain as much weight as they can before hitting the open waters on their first migration, which will cover some 5,000 miles. The focus of this new research was on the early lives of calves in Western Australia's Exmouth Gulf.
"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," says lead author of the study, Simone Videsen of Aarhus University in Denmark. "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."
The team of researchers tagged eight calves and two mothers using special tags – they stick to the whales by means of suction cup and record the sounds and movements of the whales, as well as the sounds that a whale hears. The suction-cup tags remain in place for up to two days before coming off and floating to the surface.
The recordings revealed quite a lot about the whales.
Aside from learning that the calves keep their voices down, the scientists also discovered that the calves spend significant amounts of time actively nursing (whales, they're just like us!). "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," says Videsen.
But it could be the "inside voice" that is the most impactful discovery – in addition to helping the young whales avoid attention from hungry killer whales, it also helps to not draw attention to mom from suitors; baby doesn't want to share.
"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."
Discovering the whispering behavior lends another important reason to keep tabs on noise pollution when thinking about whale habitat conservation.
"From our research, we have learned that mother-calf pairs are likely to be sensitive to increases in ship noise," Videsen says, "Because mother and calf communicate in whispers, shipping noise could easily mask these quiet calls."
The study was published in Functional Ecology.