Killer whale mothers provide social support to their sons long after they have their last calf, a new study has found.
University of Exeter scientists found that males are protected from other orcas by their “post-menopausal mothers “, who also share the fish they catch.
In a paper for the journal Current Biology, the behaviour of a group of orcas that live in matriarchal social units off the Pacific Northwest coasts was studied.
The scientists found that while male orcas will outbreed with whales from other pods, both males and females stay in their unit of birth, with their mother, for life.
Drawing on data from the Center for Whale Research's annual photographic census of the orca population, the researchers looked for evidence of scarring on each catalogued whale's skin.
Killer whales have no natural predators other than humans, so a tooth mark that is able to puncture an orca's skin is usually inflicted by another orca.
The study found that, if a given male's mother was still alive and no longer reproducing, that male would have fewer tooth marks than his motherless peers or his peers with a mother who was still reproducing.
"It was striking to see how directed the social support was," Darren Croft, University of Exeter animal-behaviour scientist noted.
"If you have a post-reproductive mother who's not your mother within the social group, there's no benefit. It's not that these females are performing a general policing role. These post-reproductive mothers are targeting the support they are giving to their sons,” he said.
Female killer whales live up to 90 years in the wild, and most live an average of 22 years after menopause.
The study noted that they have the lowest incidence of tooth marks in the social unit, suggesting they may be acting as mediators, rather than getting directly involved in conflict with other orcas.
The full study is published in Current Biology here
