The Wisdom of Elders in Orca Pods
Orcas are one of only two species other than humans in which females live for many more years following the onset of menopause. Evolutionarily speaking, it doesn’t really make sense for animals to continue to live once the ability for reproduction has ceased, yet female humans, orcas and short finned pilot whales will often live for 30-40 more years after they have stopped reproducing. One theory that serves to explain this phenomenon in orcas is that older animals pass on their knowledge of the seas to their younger pod members, using their wisdom to ease the hardship of survival to their fellow orcas.
Now scientists from the University of Exeter, the University of York and the Center for Whale Research have put this theory to the test. Researchers compiled over 35 year’s worth of observational data of one population of southern resident orcas in the Pacific Northwest. It is important to note that the diet of these orcas is mostly made up of fish, with chum salmon making up around 90 percent of their diet. It emerged that post-menopausal females would typically lead the group and swim at the front during the collective movement of the pod. They found that this behaviour was even more prominent during times of low salmon abundance, suggesting that these elder females take on an even bigger role when times are tough for the orcas.
“One way post-reproductive females may boost the survival of their kin is through the transfer of ecological knowledge,” says Lauren Brent of the University of Exeter. “The value gained from the wisdom of elders can help explain why female killer whales and humans continue to live long after they have stopped reproducing.”
During periods of low salmon availability, the leading elder female orcas were almost always flanked by their own sons when hunting.
A pod of killer whales swims in tight formation. (David Ellifrit, Center for Whale Research)
“Killer whale mothers direct more help toward sons than daughters, because sons offer greater potential benefits for her to pass on her genes,” explains Daniel Franks of the University of York. “Sons have higher reproductive potential and they mate outside the group, thus their offspring are born into another group and do not compete for resources.”
This research offers a great insight into the lives of orcas and how elder females can effect pod dynamics. More generally it can tell us why menopause might exist amongst humans.
“In humans, it has been suggested that menopause is simply an artifact of modern medicine and improved living conditions,” says Darren Croft of the University of Exeter. “However, there is mounting evidence suggesting that menopause in humans is adaptive.”