Two killer whales spyhopping.

A young killer whale ‘spyhops’ with a bigger partner. Killer-whale calves benefit from the presence of their grandmothers. Credit: Emma Foster

Zoology

Why female orcas make killer grandmas

Matriarch whales have a powerful effect on the lives of their grandchildren.

It’s a grandma’s job to spoil her grandchildren, but some grandmothers do much more than that. Killer-whale grandmothers help to boost the survival of their daughters’ calves, especially when food is scarce.

Daniel Franks at the University of York, UK, and his colleagues analysed more than 40 years of census data on two populations of killer whales (Orcinus orca) off the Pacific coast of the United States and Canada. The researchers quantified the survival rate of 378 calves with living or recently deceased maternal grandmothers.

Calves whose maternal grandmother had died within the past two years were 4.5 times less likely to survive than those with a living grandmother. These negative effects were more pronounced in years of food scarcity and when calves lost a grandmother that could no longer reproduce.

Grandmother killer whales play a key role in helping their kin to forage, and those without calves of their own might be more likely to share food with their grandchildren, the researchers say.