Older, "post-menopausal" orca mothers protect their adult sons from fights, according to new research.

The study examined tooth rake marks on the animals' bodies - inflicted in confrontations with other orcas.

It revealed that, when an adult male's post-menopausal mum is with him, he is much less likely to be harmed.

But, while four or five-tonne males benefit from this maternal protection, female offspring do not receive the same attention.

Lead researcher Charli Grimes from the University of Exeter told BBC News that the protection from these older mothers was very targeted: "Mum is definitely, in some way, trying to protect her sons."