Advertisement

Post-menopausal killer whale mothers take on leadership roles

The research data suggests an older female's ecological knowledge is vital to the survival of orca pods.

By Brooks Hays
An overhead shot of the orca family group, featuring a two-year-old calf (second from top), and a young-of-the-year (middle). (NOAA, Vancouver Aquarium)
An overhead shot of the orca family group, featuring a two-year-old calf (second from top), and a young-of-the-year (middle). (NOAA, Vancouver Aquarium)

SEATTLE, March 5 (UPI) -- For most animals, life ends shortly after a creature's reproductive health is past the point of no return. It makes sense, reproduction is evolution's driving force.

For some species, like salmon, death follows reproduction within minutes. For a few species, like whales and humans, females can live on for several decades after their prime birthing years are past. But why?

Advertisement

Recently, a team of researchers set out to answer that question. Their hypothesis: aging orca matriarchs serve as vital sources of ecological information, especially when the going gets tough.

Scientists looked at observational data on orca behavior from whale tracking studies and compared the details with info on salmon runs. In years when salmon populations dipped -- making life as a killer whale a more perilous endeavor -- post-menopausal mothers were more likely to be leading the pack.

The data suggests an older female's ecological knowledge is vital to the survival of the pod.

"One way post-reproductive females may boost the survival of their kin is through the transfer of ecological knowledge," Lauren Brent, a researcher at the University of Exeter, in England, told Smithsonian Magazine. "The value gained from the wisdom of elders can help explain why female killer whales and humans continue to live long after they have stopped reproducing."

Advertisement

Wise old mothers were also most likely to be followed closely by their immediate offspring, with proximity preference going to the sons -- the most likely to pass on the matriarchs genes, as well as her social and biological knowledge.

The hypothesis, detailed in the latest issue of the journal Current Biology, isn't without critics.

"About five to six years ago, I was looking into some of these hypotheses with the same population, and found really not much benefit of older post-reproductive females," Eric Ward, a quantitative ecologist with the NOAA's Fisheries Service, told National Geographic.

Ward and his colleagues published a study using the same data set, finding there was little evidence that menopause was a beneficial adaptive trait. Ward says menopause is more likely a byproduct of growing old.

"I think it's very safe to say that the jury is still out as to why some females -- in populations of killer whales, humans, and other species -- live long past [when] their reproductive life spans end," he added.

Latest Headlines