Grandmother killer whales help their grandchildren survive by ‘babysitting’, a study has found, in the first proof of such behaviour outside the human race.

Elder female orcas look after the offspring in particular at times when food is scarce and the mothers must go hunting, according to the report in the Proceedings of the National Academy of Sciences.

Female orcas stop reproducing in their thirties and forties but can live decades after the menopause, a rare phenomenon in the natural world. Besides humans, only four species of whale - orcas, short-finned pilot whales, belugas and narwhals - outlive their fertility.

Older female killer whales were previously known to play an important role in pods, passing on knowledge of where and what to eat.

But the University of York study showed their additional care boosts the survival rates of young orcas, with the mortality rate of one whose grandmother has died within the past two years 4.5 times higher than a peer whose relative is alive.

The effect was more pronounced in years where Chinook salmon, orca’s main food source, was in short supply.

The research was conducted to test the “grandmother hypothesis” after studies into modern hunter-gatherer human societies revealed that living grandmothers allow daughters to bear more and longer-living children.