Interpreting the Extraordinary Surface Behaviour of Humpback Whales

The collision between the water surface and the animal’s body produces sounds that can be heard over varying distances. This is why the scientific community agrees that these sounds are part of a particularly broad repertoire of noises used for communication between individuals. Whales can communicate both verbally (thanks to their wide vocal spectrum) and non-verbally (thanks to their behaviour and the sounds they can produce), a bit like humans and many other animals.

While verbal sounds have been studied extensively, those produced by the whales’ surface activity are still enigmatic. However, the behavioural repertoire of humpbacks plays an important role in understanding social interactions between individuals. Amongst other things, these sounds might allow dispersed groups to stay in contact and locate each other, as well as individuals within the same group to communicate.

According to one hypothesis, tail slapping might also be an antagonistic behaviour adopted during interactions between competing groups. For example, when several males compete for the favours of a female, tail swipes may even be used to strike their rivals.

However, females and calves have also been observed slapping the water surface with their tails while no males were in the vicinity. This behaviour could therefore also be a kind of game for young animals imitating their elders or simply having fun in the choppy waters.

One last very surprising – and yet highly probable – hypothesis exists to justify these antics: it could be a feeding technique! Indeed, the thunderous noises produced by the whale’s tail are believed to frighten nearby prey. Tiny crustaceans may therefore congregate in tighter groups, making it easier for their predator to engulf large, calorie-rich mouthfuls of prey.

The first hypothesis is that this position would allow the mother to rest while monitoring her calf from the corner of her eye. It is also possible that the mother is more easily able to feed her calf while she is positioned vertically in the water. This position would place the adult’s mammary glands in the perfect position to eject milk into the calf’s mouth. Lastly, this unusual posture could also be a thermoregulation technique. A wet caudal fin sticking up above the water surface on a breezy day might help the whale stay cool, a bit like the sweat on our skin during a heatwave.

Given that these three explanations are not mutually exclusive, it would not be surprising if the female humpback benefits from all three techniques simultaneously when standing vertically in the water.

A clearer understanding in the future

It is difficult to ascertain the functions of these various behaviours with confidence. Their functions vary depending on the groups involved, the animals’ age and sex, the distance between them, the context of the interactions and their environment. However, these studies contribute to a more detailed understanding of the social behaviour of these spectacular giants.