Killer whales use seaweed to groom one another

Tool use in the animal kingdom is not confined to primates, birds or elephants. A team of researchers has brought to light a previously unrecorded behaviour in Southern Resident killer whales: the social use of manufactured tools made from giant kelp.

A behaviour observed from the air

Since 2018, the Center for Whale Research, based at Friday Harbor (Washington), has been carrying out aerial observations of this killer whale population of the Pacific Northwest. Using high-resolution video captured by drone, the team has documented an activity that had gone unnoticed despite five decades of observation in the field.

The animals observed take hold of kelp stipes (in particular Nereocystis luetkeana), which they deliberately break in order to take the end sections. They then press these against the body of another whale and roll them repeatedly between the two, in what resembles a session of mutual grooming.

Tool-assisted social interactions

The behaviour is neither rare nor isolated. It has been recorded in killer whales of all ages, both sexes and every social subgroup.

• The whales use these tools in the presence of close companions, often relatives.
• Frequency of use is higher in individuals with patches of moulting or dead skin.
• The grooming takes place during extended social interactions, suggesting a role in group cohesion.

A grooming tool with several functions?

The team led by Michael Weiss has identified a dual use: hygienic and social. That the behaviour is directed preferentially towards close genetic relatives or partners of similar age hints at a cultural dimension within the group.

What makes the finding more striking still is its frequency: the behaviour is observed almost daily, and yet it had never been described before.

A distinct population with singular practices

The whales concerned: the Southern Residents are genetically, ecologically and culturally distinct from the other populations of the species Orcinus orca. With fewer than 80 individuals counted, they are considered critically endangered.

The researchers stress that this ability to make and use a tool for social ends had never been reported in a marine mammal, opening a new avenue in the study of animal culture.

Tools, and still few answers

The question remains open: is this behaviour particular to this group, or does it exist elsewhere, inconspicuous but widespread? Answering it will require systematic observation of other populations, in other settings, with the same aerial methods.

As Weiss points out, this discovery illustrates both the power of new observation methods and the extent of our ignorance about these cetaceans. Despite half a century of effort, many areas of their behaviour remain to be discovered.

Source of this article: https://www.cell.com/current-biology/fulltext/S0960-9822(25)00450-6