Female orcas that have gone through menopause continue to support their sons by protecting them from conflicts with other orcas, suggests a study looking at decades of monitoring data. Orcas (Orcinus orca), or killer whales, are one of a handful of species that go through menopause, but not much is known about why females stop reproducing in later life.
Previous research has found that orca mothers provide food for their sons long after they reach adulthood, despite it restricting the mothers from having more offspring.
“[Postmenopausal] females also increase survival of the offspring, particularly their males. They lead them to group foraging grounds and share food with them,” says Charli Grimes at the University of Exeter, UK.
Grimes and her colleagues decided to investigate whether older mothers may also protect their offspring from injuries.
The team analysed photographs of 130 southern resident killer whales, a population in the North Pacific Ocean that has been surveyed annually for nearly 50 years. They found that male orcas with a surviving postmenopausal mother had much fewer tooth marks on their skin than males whose mother was still reproducing or dead.
The researchers still can’t say for certain what kinds of social conflicts are leading to tooth marks or how older females are protecting their sons against them.