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Study: Killer whales are really mama's boys

Suzanna Caldwell
Photo courtesy of DFO

Turns out that male killer whales, despite their ferocious name, are really mama’s boys

A study published Thursday in Science Magazine found that mothers matter, especially when it comes to survival among young male killer whales. Using 36 years of data on killer whales in the Pacific Northwest and a calculation insurance companies rely upon to calculate life insurance premiums, researchers from the University of Exeter found that whales with long-lived mothers tended to survive longer themselves. So much so that male killer whales have a 14-fold increase in the risk of death in the year following their mother’s death, according to researcher Emma Foster.

Foster said that increase in death is not seen in daughters -- and may explain why female whales live so long past their reproductive years.

Females outlive males

So why stick around past whale menopause? It comes down to spreading genes.

“While it is believed that the menopause evolved in humans partly to allow women to focus on providing support for their grandchildren, our research shows that female killer whales act as lifelong carers for their own offspring, particularly their adult sons,” Foster wrote in an email.

Female killer whales can live anywhere from 50 to 90 years in the wild, while males have a much, much shorter lifespan -- only about 35 years, according to marine mammal biologist Craig Matkin of Homer.

That life span dips sharply when mothers are out of the picture. Matkin has studied killer whales in the Gulf of Alaska for more than 20 years. He said he's seen a few cases of male orphans surviving long after their mother's deaths, but it's rare.

“It's not a death sentence,” he said.  “But it's much more likely they'll die.”

While the females are known to help their children gather food and offer protection, Matkin said the reasons they assist with male survival may be more complex.

“If a male loses its mother, he loses status,” Matkin said. “It's how that translates in that society where you're pushed out or less able to survive.”

Females dominant

Females are more dominant in killer whale society. The mammals have complex social structures and offspring live with their mothers for their entire lives. Having too many sons can ostracize a mother, Matkin said, the opposite of many western human cultures that strive for male children.

Foster said keeping the males alive longer helps spread the genes of the mother while placing more burden within mother's pod, since males will breed with whales from other pods.

Foster said menopause, among all animals, is “bizarre” and “one of nature's great mysteries.” The study is part of a larger study that aims to look at the mechanisms causing this prolonged female post-reproductive lifespan, she said. With this data, Foster hopes to do more research on exactly how killer whales help their male children survive.

“(This study) is an exciting breakthrough in our understanding of the evolution of the menopause,” she said.

Contact Suzanna Caldwell at suzanna(at)alaskadispatch.com