Killer whales are among the few species on Earth that manage to live many years after going through menopause, and this offers scientists some insight into the benefits of this reproductive strategy.
In a new study published in the journal Current Biology, researchers reported that the female orcas that get past their child-bearing years often proceed to become leaders of their pod with valuable survival skills.
For the study, Darren Croft from the University of Exeter in the UK, together with colleagues, watched more than 700 hours of video showing orca family pods and found that post-menopausal females were between 32 and 57 percent more likely to lead the groups compared with non-menopausal adult females or adult males.
The researchers also observed that post-menopausal killer whales were more likely to be the group leader when the marine animals' staple food, the Chinook salmon, has a shortage of supply. The researchers said that the reason post-menopausal killer whales were more likely to lead the group could be attributed to accumulated experience.
In the case of hunting for prey, for instance, these females likely know where and when to look for their prey. Shortage of salmon is a primary factor that leads to mortality in the population of this species, so there appears to be a benefit when the older females know when and where to hunt for salmon.
Humans, killer whales and another type of whale are the only three known species that thrive long after they stop producing. Orcas, in particular, breed between 12 and 40 years old, but they can survive into their 90s.
Earlier studies have shown that the menopausal females greatly raise the survival odds of children and grandchildren, albeit how these old females help with their relatives' survival was a mystery. One of the leading theories is that these females accumulate wisdom with age and store crucial details about the environment that they share with their kin to aid them during environmental hardships.
The new study strengthened this idea because the results have shown that the wisdom of older whales boosts the survival of their relatives through the transfer of their ecological knowledge.
"Our results show that post-reproductive females may boost the fitness of kin through the transfer of ecological knowledge. The value gained from the wisdom of elders can help explain why female resident killer whales and humans continue to live long after they have stopped reproducing," the researchers wrote in their study.
Photo: Kat Kellner | Flickr
