Female Atlantic right whales lower their voices to a whisper when communicating with their young in order to prevent "eavesdropping" by predators, researchers said Wednesday.
Several species of adult whales rarely get hunted by predators in the wild owing to their size, but preying on their young is common.
A team of scientists used microphones attached by suction cups to look at the voice patterns of right whales -- an endangered species with only around 500 known specimens remaining.
They found that pairs of mother and calves reduced the number of loud, long-distance calls, compared to juvenile or pregnant whales.
The maternal pairings also increased the percentage of very quiet sounds they used to communicate.
Whereas a typical right whale call could be heard from roughly a kilometre away, the modified speech would only be audible at a range of 100 metres or so.
"These lower amplitude signals may minimise the risk of detection while still allowing mother-calf communication," said the authors of the study, published in the journal Royal Society Open Letters.
It would also "minimise the risk of eavesdropping by predators."
Whale hunters such as orcas are thought to rely on sounds issued by their prey to locate them, given that the light is often poor at sea.