Humpback whales are famous for their songs, but young calves aren't singing tunes. Rather, they babble very quietly to mom with squeaks and grunts. They keep these sounds quiet, and the scientists listening in think they know why.
According to NPR:
"There are lots of killer whales in the area which are predating on these calves," says Videsen, "and they can use these sounds between mother and calf as like homing cues."
So why do the calves say anything at all? The researchers found that baby whales mostly whisper when they're swimming, rather than when they're resting or nursing, so it may be that these intimate sounds help mothers keep track of their young in murky waters.
The researchers discovered the quiet sounds after attaching special recording devices that suction to the baby's skin. They stay put for about a day before falling off and being retrieved by the scientists. The recordings gained from these devices are the first recordings made with a device attached directly to the calf, and can help reveal much more about the relatively elusive lives of these massive, intelligent mammals.
Have a listen to the sounds of a young calf in this recording: