Female orcas who've gone through menopause appear to serve as "wise women," guiding their entire pod to food and ensuring its survival using their accumulated wisdom and experience, researchers say.
Menopause is rare, and outside of humans the only other species known to outlive their reproductive lives in such a major way are orcas and short-finned pilot whales, they point out.
The menopausal orcas have been found to act as a kind of library of information, directing their groups or pods to where food can be found when fish are scarce.
"This is the first study showing these post-menopausal orca females act as repositories for important knowledge," says Darren Croft of the University of Exeter in the United Kingdom. They serve as essential storehouses of vital survival information, he says.
The findings go a long way toward explaining the reason female orcas can live as long as 90 years, long past the point when they typically stop breeding at age 40, the researchers say. In contrast, males normally only survive to the age of 50.
For their study Croft and his colleagues analyzed hundreds of hours of video footage of family pods of orcas living in coastal Pacific waters off Washington and British Columbia.
The video included more than 100 individually recognizable orcas.
The researchers were able to determine post-menopausal females as 32 percent more likely to be group leaders than non-menopausal adult females, and 57 percent more likely to head a pod than adult males.
When the orcas' primary food staple, Chinook salmon, was scarce, post-menopausal females were even more likely to be seen leading pods, Croft says.
"It's probably accumulated experience," he says. "Anyone who fishes for migratory trout or salmon will tell you that timing is key, that the fish return in particular cycles of tides and times of the year. Post-menopausal females probably get to know where to look and when."
The early end of reproduction followed by a long post-menopausal lifespan make evolutionary sense for orcas, whose family structures in many ways are like those found in human hunter-gatherer societies, Croft argues.
Unlike in most animal species, where males quickly leave parents to become independent, most male and female orcas stay together in a family unit for all their lives.
Since females survive for many decades, and breed for just the first three or four of them, their pod is increasingly composed of their own descendants, making it more important for them to ensure the survival of the pod and survival of their own genetic legacy, Croft says.
"There's a tipping point where they stop reproducing and help their offspring instead, as do grandmothers in the human context," he says.
