Both humpback whales and southern right whales communicate through a variety of vocalizations. Studies published in 2017 and 2019 show that these whales can also 'whisper', and that mother and calf pairs frequently do so in order to avoid detection.
In April of 2017, researchers published a study in Functional Ecology that touched on communication between humpback mothers and calves. The study showed that humpback mothers and calves communicated more during dives than when resting, and the communications were very quiet.
These vocalizations are difficult to hear beyond 100 meters, intentionally reducing the risk of discovery by predators or by male humpback whales that wished to mate and would separate the mother from her calf.
Humpback whales have a wide range of vocalizations, ranging from very loud to nearly a 'whisper'. They can produce vocalizations intended for a far-reaching audience, for an immediate group of multiple individuals, or for a more private communication between a mother and calf seeking to avoid other cetaceans.
In July of 2019, researchers at Aarhus University in Denmark published a study in the Journal of Experimental Biology that showed their findings on communication between mother and calf pairs of southern right whales.
They tagged 9 mother and calf pairs in Flinders Bay – a breeding and calving ground for the whales in Australia. Through these sound tags they recorded roughly 63 hours of communication and sounds from the whales.
The recordings showed that the mothers and calves called very rarely while they were diving, and the calls that were made were extremely quiet. It was impossible to hear these calls beyond a few hundred meters, making it very difficult for predators like orcas and sharks to locate the vulnerable calves. The whales also stayed very close to the shore in the waves. While more turbulent, the sound from the waves helps to mask the calls that the whales make to each other.
Most research on whale communication has focused on the loud calls, songs and other vocalizations that different species make when communicating. These new studies indicate that their communication is more complex and specialized than previously thought. Mothers take extra care to both communicate quietly, and impress the importance of this upon their calves who follow suit.