Postmenopausal orcas protect their male offspring from attacks by other orcas

Female killer whales can live up to 90 years, but the last 20 are no longer fertile.. But why do they spend such a long period of their lives without reproducing?. According to a study, they do it to take care of their sons and protect them from attacks by other orcas.

Previous work had shown that, even after giving birth to their last calf, mothers care for their families by sharing the fish they catch, but now a new study has found that these mothers also support their children socially by protecting them from fights.

The details of the research have been published this Thursday in the journal 'Current Biology'. “The aim of the project was to understand how these post-reproductive females help their young and our results show that menopause is adaptive in killer whales,” explained first author Charli Grimes, an animal behavior scientist at the University of Exeter.

For the study, the researchers studied a group of killer whales living off the Pacific Northwest coast.. These orcas live in matriarchal social units consisting of a mother, her calves, and her daughters' calves.

Using data from the Center for Whale Research's annual photographic census of the orca population, the researchers looked for scars on the skin of each orca recorded.

Killer whales have no natural predators other than humans, so it is highly likely that a tooth mark capable of piercing an orca's skin was inflicted by another orca.

The study found that if the mother of a given male was still alive and was no longer reproducing, that male had fewer teeth marks than his conspecifics without a mother or conspecifics with a mother that was still reproducing.

“It was surprising to see how targeted the social support was,” says lead author Darren Croft, an animal behavior scientist at the University of Exeter.

“If you have a post-breeding mother who is not your mother within the social group, there is no benefit. It's not that these females perform a general policing function but that these mothers focus their support on their children.”

Researchers still can't say for sure what kind of social conflicts tooth marks cause or how older females protect their offspring against them.

What they did observe is that postmenopausal females have the lowest incidence of tooth marks in the entire social unit, suggesting that they do not physically intervene in a conflict.

If older female killer whales play a role similar to that of older women in human societies, they could be acting as mediators, preventing conflicts from happening in the first place.

To dig deeper into this topic, the researchers plan to conduct an additional study using drone images to observe the behavior of the whales from above.

“It is possible that with age their social knowledge increases. Over time, they might have a better understanding of other social groups,” Grimes said.

“Given these close mother-child associations, it could also be that she is present in a conflict situation so that she can signal her children to avoid risky behavior in which they might be engaging.”

“We have hypotheses, but we need to test them by seeing what happens underwater when these different groups interact,” says Croft.