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Grandmother killer whales boost survival rates of their grandchildren
10 December 2019, 00:00
Young killer whales with grandmothers are more likely to stay alive than those without, a study has shown.
Scientists have long been baffled by the fact that killer whales, or orcas, along with three other species of toothed whales and humans, are the only groups known to experience the menopause.
In an attempt to understand why females of these species stop reproduction well before they die, researchers studied a group of killer whales and found that post-reproductive grandmothers were most important to youngsters during difficult periods where the supply of salmon to eat is particularly low.
The study suggests that, with more time on their hands no longer nurturing their own children, post-menopausal grandmothers can help their grandchildren instead.
If a grandmother dies, in the years following her death, her grandchildren are much more likely to die, scientists claim.
Female killer whales stop reproducing in their 30s to 40s, but just like humans they can live for many decades following menopause, while their sons and daughters typically stick with them for life.
With humans, some evidence suggests that grandmothers aid in the survival of their children and grandchildren, a hypothesis called the "grandmother effect".
These new findings suggest the same effect occurs in orcas.
Co-author of the study, Professor Darren Croft from the University of Exeter, said: "Our new findings show that just as in humans, grandmothers that have gone through menopause are better able to help their grand offspring and these benefits to the family group can help explain why menopause has evolved in killer whales just as it has in humans."
“It’s really important work,” adds Janet Mann, an animal behaviorist at Georgetown University in Washington, D.C, “We’re just scratching the surface of what these grandmothers are doing.”
Orcas tend to live in close-knit family groups of up 40 individuals.
The research was carried out by scientists at the University of York and University of Exeter - alongside the Centre for Whale Research in the US, and Fisheries and Oceans Canada.