The matriarchal structure of orca society is well known, with females potentially living up to 90 years and playing a crucial role in passing on knowledge to the younger animals. Previous research into why these females live so long after they stop reproducing – an average of 22 years – has suggested it’s to play an ‘elder’ role in the society, passing on culture, language and more to the youngest pod members.
Now, new insights suggest that post-menopausal southern resident killer whales (Orcinus orca) play a pivotal role in keeping the pod's young male calves out of brawls.
“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.
The researchers analyzed nearly 7,000 images of the orcas, which live off the US Pacific coast, and found that the males with a post-menopausal mother or grandmother watching over them had significantly fewer tooth rake marks, the 'battle scars' inflicted by other orcas during fights.
“Tooth rake marks are indicators of physical social interactions in killer whales and are typically obtained through fighting or rough play,” Grimes said. “These males had 35% fewer tooth marks than other males.”
Males without a mother had 45% more tooth rake marks.
While the scientists aren’t certain how the females intervene in juvenile conflicts – it could potentially be through their complex vocalizing – intervention is unlikely to be physical as the senior orcas had no higher rates of scarring than their younger counterparts.
Also, mums that were still breeding didn’t display this style of protective helicopter parenting, suggesting it’s a specific behavior belonging to the post-menopausal orca life stage.
“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,” Grimes said.
As for daughters? Not a concern. The researchers note that because males will ‘outbreed’ with several females of other pods, there’s an evolutionary need to ensure genes are passed on. And because of greater competition between young males, an elder bodyguard is useful. The injuries from tooth rakes can result in infection or worse.
“It’s possible that the older females use their experience to help their sons navigate social encounters with other whales,” said Darren Croft, a professor at the University of Exeter. “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,” he added.
The study was published in the journal Current Biology.
Source: University of Exeter