Menopause is very rare among animals. Here’s why orcas go through it.

In our human-centric view, the ability to shoot ink or change colors may seem odd, but you know what’s really odd? Menopause.

“It's incredibly rare trait in the natural world,” says Charli Grimes, an animal behaviorist at the University of Exeter in the United Kingdom. Only six animals—humans and five toothed-whale species—live past their reproductive years.

Orcas, or killer whales are one of those animals, and they have been studied extensively to learn why living past menopause is beneficial to their species. Research has shown a new power of menopause, which has often been portrayed in pop culture as a negative.

Grimes and her colleagues have identified a new way that these older females help the group: By protecting their sons from getting injured in fights with other orcas.

(Why are these orcas killing sharks and removing their livers?)

They did this by examining tooth-rake marks, scars from an opponent’s teeth going up the surface of the skin.

This protection, however, is for sons only. Daughters and grandchildren need not apply.

“That was really striking,” Grimes says, “to see that these females are just targeting the social support toward their male offspring.”

The study, published in the journal Current Biology, focused on southern resident killer whales, an endangered population in the Pacific northwestern U.S. It was done by researchers from Exeter, the University of York, and the Center for Whale Research in Washington.

Killer whales are apex predators and since this population are exclusively fish eaters, they wouldn’t be scarred by prey species.

“We can say with certainty that these rakes come from within the population,” Grimes says. The rakes come from fighting, or possibly play that turns rough—but without seeing the interaction it’s hard to say for certain.

(Vengeance—or playtime? Why orcas are coordinating attacks against sailboats.)

“That's something we really want to explore further, using drones to observe this behavior directly,” Grimes says.

The Center for Whale Research has been collecting information on this group of orcas for 47 years, and has almost 7,000 photos of the 103 members of the population. The researchers know each orca so well they can identify them by the sight of their dorsal fins and the white pattern behind it, called a saddle patch.

For this study, the scientists looked at the rake density—the number of pixels visible in photographs that were raked—of individual orcas. They found that males with post-reproductive mothers in the group showed fewer rake marks than males whose mother was still in her reproductive phase.

There were no differences between the scars on males with a reproductive-age mother and no mother in the group.

“That was a surprise,” says Deborah Giles, science and research director with the nonprofit Wild Orca, who was not involved in the study. “I would have expected it to be a mother, period.”

Reproductive moms may be “busy taking care of their current young,” Giles says, while older females “have more time and more interest.”

Brad Hanson, a wildlife biologist at the National Oceanic and Atmospheric Administration who wasn’t involved with the study, says that on one hand, he wouldn’t have thought that tooth rakes would affect the overall fitness of killer whales when compared to other species that are more heavily scarred.

On the other hand, he knows how much damage a skin wound can do. In 2016 a whale darted with a satellite tag from a program Hanson started over a decade earlier died from fungal infection introduced via the tag.

“It was devastating to say the least,” he says, and “clearly demonstrated the vulnerability these animals face from skin wounds.”

All the better to have mom’s help.

This study adds to our “knowledge about the complexity and strategies employed in killer whale societies and presents yet another reason why menopausal females are important,” Hanson says.

This study also found that there was no difference in scarring among young females regardless of the reproductive status of their mother—meaning that there was no special protection afforded to them.

Previous research on the same population has shown the same phenomenon is true in the other roles that post-reproductive females play in the matriarchal society of orcas.

For one, these females lead their groups to important foraging grounds, a role especially prominent in times when salmon, the group’s main prey, is hard to find. These mothers will bite salmon in half and give the other half to their son, continuing to feed them well into adult life while daughters tend to become more independent when they sexually mature.

(Here are other ways post-menopausal whales help their pod survive.)

Daughters and sons both stay with the group for their whole lives, but males can mate with multiple females outside of it. This means that caring for his offspring ultimately falls to that other group—a benefit to any orca family looking to cut costs. It also gives a mother more opportunities to pass on her genes through her sons than her daughters.

“Males have the greater reproductive potential than females, and females prefer mating with older, larger males,” Giles says. “If [post-menopausal females] can keep their males well-fed and out of conflict then the males have a better opportunity to forage get big and old.”

This paper offers “more support for this idea that females preferentially care for their adult sons in order to increase their fitness and pass on their genes,” Giles says.

How about their extended families? While post-reproductive female orcas may help their grand-offspring through ecological knowledge, like where to find food, this study shows injuries were not lower for them if a post-reproductive grandmother was around.

Interestingly, it seems these post-menopausal mothers don’t get physical to protect their sons from aggression—previous research has shown that they are the least scarred in the whole group.

They may be using their knowledge of social dynamics to navigate conflict or “signaling to help [their sons] navigate or avoid a risky behavior,” Grimes says. Among hunter-gatherers, for example, females tend to mediate social conflict vocally and with physical gestures.

So when does menopause begin for orcas? Similar to human women—who generally enter menopause between ages 40 and 50—menopause for orcas begins at about age 40, Grimes says.

So we humans may be outliers—but we’re in some pretty impressive company.