Orcas and humans are among just a small handful of animals that undergo menopause—only six total species are known to cease menstruation, ending their ability to become pregnant. But why these creatures have evolved to live past their reproductive years is something of a mystery. One possible explanation, according to a new study of orcas, is that a pod’s aging females do not sit idly by—they play a vital role in keeping their offspring alive and safe.
Research published last week in the journal Current Biology shows that orca males with older mothers have fewer scars left by other orcas’ teeth, suggesting that after their reproductive years are over, orca moms help protect their five-ton sons from injury in fights.
The findings add to a growing body of evidence suggesting that life after menopause, though uncommon in the animal kingdom, can enable creatures to support their kin.
“The similarities with humans are intriguing,” said Darren Croft, a behavioral ecologist from the University of Exeter in England and senior author on the paper, to the Guardian’s Hannah Devlin. “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.”
If the goal of survival is to reproduce, then, evolutionarily, it doesn’t make much sense for an animal to live long past its reproductive years. But previous research has shown that post-menopausal orcas, which are often the matriarchs in their pods, play important roles like steering their families to food and boosting the survival of their grand-calves. Female orcas can live to a hoary 50 to 90 years old, meaning they can spend 20 years or more captaining their pods after they stop reproducing.
In the new study, researchers studying orcas off the Pacific coast of North America noticed that some of the animals had more damage on their dorsal fins than others. By inspecting almost 7,000 photos of orca fins dating back nearly 50 years, the scientists tried to understand how the presence of post-menopausal orcas affected the amount of fight wounds on their offspring.
Male orcas, they found, had fewer scrapes on their fins when they had an older mother nearby to protect them. Having a younger mother or no mother around was not as safe, and males in those situations showed more scarring.
Older females may take on this extra-protective role because mothers with younger offspring are “busy taking care of their current young,” says Deborah Giles, science and research director of the nonprofit Wild Orca who was not involved in the study, to National Geographic’s Liz Langley. The older orca mothers may “have more time and more interest.”
Unfortunately for daughters, the protection given to male orcas did not appear to extend to female offspring, which showed no reduction in battle scars when they had a post-reproductive mother around.
One of the most precious things about this drone image by @SR3Sealife of a group of Southern Residents, is that it holds both L pod's oldest and youngest orca. Leading is L25 Ocean Sun, with an est. age of 94yrs, and at the rear is tiny L125 Element, who is a little over 1yr. pic.twitter.com/KomRaNlVWa— Brittney Hernandez (@OrcaOceanB1983) January 29, 2022
Beyond protecting sons from injury, mother orcas also play favorites with their male children by feeding them halves of fish that they’ve caught, wrote Susan Milius for Science News in February. This preferential treatment could have evolved because male orcas can reproduce more often than females. Males also mate outside their pods—this means their mothers will not have to support the grandkids sired by their sons.
Stephanie King, a behavioral biologist at the University of Bristol in England who was not involved in the new research, tells Science’s Phie Jacobs that the study “makes an important contribution to our growing understanding of the evolution of menopause.” In a world of species that do not stick around long after reproducing, orcas are giving us clues as to why some do.