13/09/2012 19:03 BST | Updated 13/09/2012 19:03 BST

Killer Whales Are 'Mummy's Boys' After All, Scientists Discover

They have a fearsome reputation but in reality killer whales are mummy's boys, say scientists.

Scientists have discovered that mother killer whales have the longest menopause of any non-human species - so that they can care for their adult sons.

Female killer whales stop reproducing in their thirties or forties, but can live beyond the age of 90.

The reason for the creature's long menopause is a long-standing mystery.

Only a handful of other species, including humans, halt female reproduction part-way through their lives.

killer whales

Are whales really just 'mummy's boys'?

The team of British and Canadian scientists analysed 36 years of records from two killer whale populations in the North Pacific.

They found that the length of time a female lived after she stopped reproducing strongly influenced the survival of her offspring.

For an adult male over the age of 30, the death of his mother increased the likelihood of him also dying within a year 14-fold.

Females also stayed with their mothers, but were much less dependent. A female over 30 only had a three-fold greater chance of death after her mother died.

The research is published in this month's journal Science.

killer whales

Killer whales "struggle to survive without their mothers' help", the analysts say

Dr Dan Franks, from the Department of Biology at the University of York, said: "Our analysis shows that male killer whales are pretty much mummy's boys and struggle to survive without their mother's help. The need for mothers to care for their sons into adulthood explains why killer whales have evolved the longest post-reproductive lifespan of any non-human animal."

Killer whales live in unusual social groups, with sons and daughters remaining close to their mothers throughout their lives.

Theory predicts that to have the best chance of spreading their genes, mothers should focus their efforts on their sons.

Co-author Dr Darren Croft, from the University of Exeter, said: "Both humans and killer whales are unusual in having a long menopause. Although they share this trait, the way older females benefit from ceasing reproduction differs, reflecting the different structure of human and killer whale societies.

"While it is believed that the menopause evolved in humans partly to allow women to focus on providing support for their grandchildren, it seems that female killer whales act as life-long carers for their own offspring, particularly their adult sons. It is just incredible that these sons stick by their mothers' sides their entire lives in the original family with their grandmothers."