Why do humpback whales get in the way of hungry killer whales?

When faced with an imminent attack, any prey has two defence options: fight or flee. For example, whale species in the genus Balenoptera (e.g. fin whales, minke whales and many others) tend to use their exceptional hydrodynamics and unparallelled speed to overwhelm predators when they are attacked.

Humpback whales – the sole representative of the Megaptera genus – tend to opt for combat. Their heavy, plump bodies do not allow them to outswim their predators, so they rely instead on their large tail and powerful pectoral fins to repel them. Measuring over five metres long and weighing at least one tonne each, their pectoral fins – the largest of their kind in the entire cetacean kingdom – give them a remarkable advantage. Flexible, manoeuvrable and equipped with numerous sharp barnacles, these genuine weapons against predators are as unique as they are effective.

According to experts, humpbacks react to killer whale predation vocalizations and intervene to defend the targeted prey even before they know which species is being threatened. This means they likely notice that the victim is not of their own species only after having travelled to the scene, though they generally continue their intervention all the same.

Over the years, scientists have formulated a number of hypotheses to try to explain the motives behind the assistance that some humpbacks provide individuals from different groups or even other species – a behaviour rarely observed in the animal kingdom.

As mentioned above, adults are believed to respond to predation calls to defend their own species. Currently, it appears that humpbacks continue to display this behaviour even if the main beneficiaries are other species, since it likely spares enough young calves to justify such a change in their habits.

A first hypothesis is that by approaching the scene of the attack, the humpbacks voluntarily signal their presence so that the killer whales understand that it is not so easy to sneak up on these cetaceans. Although getting into a direct altercation is dangerous, the increased safety that this manoeuvre would provide the calves in the long term likely outweighs the risk that adults face in the heat of the moment.

Lastly, a final hypothesis is frequently raised by the scientific community that attempts to explain this interspecific assistance as a possible form of animal altruism.

Considering their exceptional intelligence, it would not be surprising if whales voluntarily helped one another. Humpback whales are capable of elaborate thinking, decision-making, problem-solving and sophisticated communication. So why wouldn’t they have the brain power to be intentionally altruistic? Since humpbacks themselves are victims of killer whale predation, could it be possible that they are simply demonstrating a form of empathy toward other members of their species and those of different species that are also hunted by these predators? To this day, these questions remain unanswered.