killer whale mums provide more support to sons than daughters
Raising sons is so exhausting for female killer whales they often can't nurture any more offspring, reveals a new study.
Researchers found that each living son cut a mother’s annual likelihood of having a calf that survives for at least a year by around 50 per cent.
And the effect continued as sons grew older – suggesting they're a lifelong burden on their mothers.
The practice previously benefited the whales, but now researchers say such extended nurturing of sons into adulthood threatens the very existence of the "critically endangered" species.
It was previously known that killer whale mums provide more support to sons than daughters, especially after daughters reach adulthood.
But the new study, conducted by researchers from the universities of Exeter, York and Cambridge along with the Centre for Whale Research in the United States, shows that such support comes at a huge cost to the mothers.
Dr Michael Weiss, of the University of Exeter, said: “The magnitude of the cost that females take on to care for their weaned sons was really surprising.
“While there’s some uncertainty, our best estimate is that each additional surviving son cuts a female’s chances of having a new calf in a given year by more than 50 per cent. This is a huge cost to taking care of sons!”
Dr Weiss says the findings, published in the journal Current Biology, suggest that there are significant benefits to keeping adult sons alive and well.
He said: “Females gain evolutionary benefits when their sons are able to successfully reproduce, and our results indicate that these benefits are enough to outweigh a large direct cost."
SWSCwhales - by Stephen Beech