Are your adult children not leaving home?
Orcas suffer from this too 1:01
(CNN) --
It's no secret that parenthood can be demanding and sacrifices are often made for the sake of offspring.
But for female orcas, the role can be especially difficult.
New research suggests that female orcas may be giving up having more offspring for their sons, even as adults.
The research, published Wednesday in the journal Current Biology, focused on a group of killer whales known as the "southern resident" population, off the coast of Washington state and British Columbia.
The Whale Research Center, which participated in the study, has been observing the group since 1976.
Two killer whales chase white sharks off the coast of South Africa
This is an unusual species, as males and females remain with their mothers for their entire lives.
However, the "cost" of caring for the mother is higher in the case of sons.
Michael N. Weiss, director of research at the center and a postdoctoral research associate at the University of Exeter, said in a press release: "We have known for over a decade that adult male killer whales depend on their mothers to stay alive, but it's never been clear whether mothers pay a price for it."
advertising
The data revealed "a strong negative correlation between the number of surviving weanlings of females and their annual probability of producing a viable calf," according to a news release.
And the result remained the same regardless of the age of the son.
"The magnitude of the cost that females take on to care for their weaned children was truly staggering," Weiss said.
"Although there is some uncertainty, our best estimate is that each additional surviving pup reduces the chances of a female having a new calf in any given year by more than 50%. This is a huge cost to care for [adult] pups. ".
According to experts, female whales reduce the probability of having more calves to care for their adult children.
Credit: Whale Research Center
Share the food
The researchers don't know why female killer whales are less likely to reproduce in these cases, but they suspect that sharing food with their adult offspring may mean the mothers have to survive on less.
Sam Ellis, a researcher in animal behavior at the University of Exeter and a co-author on the paper, told CNN on Thursday that the nature of the mother's care largely revolves around her diet of Chinook salmon.
"Really the key to this form of care is sharing food," he explained.
"We think a lot of caregiving is physically providing food for your adult children," she said, though they also lead them to the source of nutrition.
"Having a daughter doesn't affect her chances of reproducing, but having a son of any age has a negative impact on the mother's chances of reproduction," Ellis said.
Scientists record killer whales for the first time hunting and killing an adult blue whale
According to the team, this finding is very rare.
"It's further evidence of how special (and perhaps unique) the mother-infant bond is in killer whales," Weiss said.
Ellis added: "There are many examples [in mammals] of maternal care and maternal investment in young pups. But in all the examples that have been studied so far, once the pup reaches maturity, that investment seems to stop."
"We know that children whose mothers die have a really high probability of dying the following year," he said, adding that while female orcas can live to be 80, males are "very lucky to make it to 40."
Southern residents are critically endangered, so the study could have important implications, according to the researchers.
Ellis noted that the team wants to further study the long-term effects the findings could have on orca populations.
Luke Rendell, a professor of biology at the University of St. Andrews in Scotland, told CNN that the study, in which he was not involved, was "fascinating."
"It opens a new window... [to] how the evolutionary dance between the interests of individuals and genes constantly interacts with ecology and sociality."
"Many will smile at the jokes about children in need, but also, I hope, will ponder whether the parallels run deeper in this long-lived and highly social mammal. Such insights are only possible through dedicated, long-term studies, often underappreciated by the funders of the investigation".
Killer whale