You may have heard a whale sing, but have you heard them whisper?
A research team has recorded humpback whale calves quietly calling to their mothers as they swim. Led by Simone Videsen from Aarhus University, the team believes these calls help stop mother-calf separation while avoiding attracting predators.
The researchers’ original aim was to study suckling behaviour in the whales, hypothesising that the calves used calls to signal when they were hungry. However, it soon became apparent that this was not the case. Not only did the calves not increase their call frequency before suckling, but they were four times more vocal during non-suckling dives than suckling dives. This data indicates that the acoustic communication between mother and calf plays a different role.
Humpback calves swim close to their mothers, gaining protection and easy access to milk. Becoming separated for a prolonged period poses a risk. Yet when swimming through murkier waters, the pair may not be able to see each other for more than a few body lengths of the mother. Since the calves’ calls were significantly quieter than those of adult whales, the team suggested that these “whispers” evolved as a way for the mother to keep track of her calf. As the calls only travel across a range of about 30m, they are unlikely to be heard by predators such as orcas.
A concern of the researchers is that loud noise pollution from human activities such as shipping may mask the calls. As the paper states, “even moderate increases in ambient noise […] may increase the risk of the calf being separated from the mother”.
Further research would be needed to support this. Not only does this paper offer a glimpse into the lives of whales, but it also may further understanding of the consequences of human activity on the natural world.
