After menopause, female whales serve as group leaders

Chuck Bednar for redOrbit.com – @BednarChuck

Once they undergo menopause and their reproductive cycles come to an end, older female killer whales help lead the rest of their pod and direct them to the best food sources, according to a new study published on Thursday in the journal Current Biology.

The research could solve the mystery as to why female whales (and people, for that matter) live so long after their childbearing days are done, explained National Geographic. It is because they have experience and information to pass on that can be essential for their group’s survival.

Female orcas stop having calves when they are around 40 years old, but can live up to the age of 90, the website said. In comparison, male killer whales typically only live to be about 50. Thus, it is up to the older females to show their pods things like where to go when food is hard to find.

Girl power – female whales more likely to be group leaders

As whale biologist Rob Williams, who was not involved in the study, explained, “Pioneers of killer whale ecology have long felt that matriarchs serve as repositories of traditional ecological knowledge that can help these whales survive through years of low prey abundance. This study tests that theory and offers a compelling hint that whales… follow the matriarch to find food.”

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Darren Croft, a behavioral ecologist at the University of Exeter, and his colleagues looked at southern resident killer whales that live in the Seattle, Washington area. These whales travel in groups of about 80 and live primarily on salmon, and Croft and his team examined data dating back to 1976 to see if menopausal whales took on leadership roles during pod movements in and out of their primary foraging areas.

They found that females were more likely to serve as group leaders than males were, and that females over the age of 35 tended to do so more often than younger females. This proved to be especially true in years when salmon were less available, Nat Geo said. When combined with the results of a similar 2012 study, the findings indicate that menopausal mothers played a key role in ensuring the survival of their offspring.

Croft told the website that the structure of the pods go a long way to explain why this happens. As females grow older, they become increasingly related to the other whales in their group, and have had more times to have babies than a younger female that arrived more recently. Thus, by sticking around and helping out, they keep more of their relatives alive, which proves to be “advantageous in an evolutionary sense,” according to Nat Geo.

Similar to humans

Lauren Brent, an associate research fellow in animal behavior at the University of Exeter and one of the scientists behind the new study, told NBC News that similar factors were most likely also in play in humans before culture evolved and writing provided a different way to pass knowledge down to future generations.

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“The families of humans and resident killer whales are structured in a very kin-focused way,” she said. “As humans did not develop writing for almost the entirety of our evolution, information was necessarily stored in the minds of individuals. The oldest and most experienced people were those who were most likely to know where and when to find food, especially during dangerous conditions such as drought.”

However, Eric Ward of the US National Marine Fisheries Service in Seattle is skeptical of the study’s conclusions. In an email, he told Nat Geo that he investigated a similar hypothesis some five or six years ago, and found that there was “really not much benefit of older post-reproductive females.”

Instead, he said that menopause in orcas is just one result of growing older, adding, “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.”

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Source: http://www.redorbit.com/news/science/1113348275/after-menopause-female-whales-serve-as-group-leaders-030715/