Killer whales protect adult males but not females, new study reveals

The new research indicates that postmenopausal female killer whales protect their sons – but not their daughters – from fights with other whales.
Loukia Papadopoulos
Representational image of a killer whale.jpg
Representational image of a killer whale.

Dave Hutchison Photography/iStock 

New research is indicating that postmenopausal female killer whales protect their sons – but not their daughters – from fights with other whales, highlighting a clear bias in genders.

This is according to a press release by the University of Exeter published on Thursday.

Scientists looked at the scarring left when one whale scrapes their teeth across the skin of another and found males had fewer marks if their mother was present and had stopped breeding.

The study was conducted by the universities of Exeter and York and the Center for Whale Research.

“We were fascinated to find this specific benefit for males with their post-reproductive mother,” said lead author Charli Grimes from the Centre for Research in Animal Behaviour at the University of Exeter.

“These males had 35% fewer tooth marks than other males.

“For males whose mother was still breeding, we found no evidence that her presence reduced tooth rake injuries.

Why the change after menopause?

“We can’t say for sure why this changes after menopause, but one possibility is that ceasing breeding frees up time and energy for mothers to protect their sons.

“Tooth rake marks are indicators of physical social interactions in killer whales and are typically obtained through fighting or rough play.”

The body of work indicates that female killer whales have evolved to pass on their genes by helping their children and grandchildren.

They, however, protect their sons more than their daughters because “males can breed with multiple females, so they have more potential to pass on their mother’s genes,” Grimes said.

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

Navigating social encounters

Southern resident killer whales, the types of whales studied in this work, have no natural predators apart from humans, so tooth marks on their skin can only be inflicted by other killer whales.

Professor Darren Croft, also from the University of Exeter, said: “We can’t say for sure. It’s possible that the older females use their experience to help their sons navigate social encounters with other whales."

“They will have previous experience of individuals in other pods and knowledge of their behavior, and could therefore lead their sons away from potentially dangerous interactions."

“The mothers might also intervene when a fight looks likely.”

Professor Croft added: “The similarities with humans are intriguing. Just as in humans, it seems that older female whales play a vital role in their societies – using their knowledge and experience to provide benefits including finding food and resolving conflict.”

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

“They perform protective behavior, 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."