Fewer tooth marks found on males where post-menopause mother present.

A new study by the University of Exeter and University of York has revealed that post-menopause female killer whales protect their sons, but not their daughters, from fights with other whales.

For the research, scientists studied tooth rake marks, which are the scars left when one whale scrapes its teeth across the skin of another. The presence of tooth rake marks is an indicator of physical social interactions in killer whales, and are usually obtained through fighting or rough play.

They found 35 per cent fewer tooth marks on males where the mother was present and had stopped breeding. For males whose mother was still breeding, there was no evidence that her presence reduced tooth rake injuries.

The scientists say that this adds weight to the increasing evidence that post-menopause females boost the life chances of their offspring, particularly males. They suggest that this could be because the absence of breeding frees up the time and energy for mothers to protect their sons.

There was no evidence that post-menopause females reduced tooth rake injuries in their daughters.

Commenting on why females focus efforts on their sons, lead author Charli Grimes from the University of Exeter, said: “Males can breed with multiple females, so they have more potential to pass on their mother’s genes. 

“Also, males breed with females outside their social group – so the burden of raising the calf falls on another pod.”

Only six species, including humans and five species of toothed whales, are known to experience menopause. 

Professor Dan Franks from the University of York, said: "Our findings offer captivating insights into the role of post-menopausal killer whale mothers. 

“They perform protective behaviour, reducing the incidence of socially inflicted injuries on their sons. 

“It's fascinating to see this post-menopausal mother-son relationship deepening our understanding of both the intricate social structures in killer whale societies and the evolution of menopause in species beyond humans.”

The study has been published in the journal Current Biology.