A study of orcas in the North Pacific (Pacific Ocean) found that mothers of this species of mammal make "lifelong sacrifices" for their sons.
Raising a son greatly reduced the female killer whale's chances of reproducing in the future.
The energy they need to feed their young appears to compromise their health, leaving them less able to reproduce and raise other cubs.
"Mothers sacrifice their own food and energy," said Professor Darren Croft of the University of Exeter.
Watch a video about the behavior of killer whales:
Orcas remain closely attached to their families throughout their lives.
But while female cubs become independent as adults, males depend on their mothers - even needing some of the food they catch.
Professor Croft described it as "a new insight into the complex social and family lives of these amazing animals".
A study that has been in the works for decades published in the magazine Aktuelna biologija (Current Biology) and is part of an ongoing mission to understand the family life of killer whales.
The Center for Whale Research worked on it (Center for Whale Research), which for more than 40 years has followed the lives of the population of this type of aquatic mammal, i.e. the community it is called southerners.
Starting in 1976, the Center made a complete census of the population southern residents, which has allowed biologists to conduct multigenerational studies like this one—disentangling critical social behavior and family bonds that directly affect animal survival.
For this study, scientists tracked the lives of 40 female orcas between 1982 and 2021 and found that for every living son, the annual probability of a mother raising another year-old cub was halved.
"Our previous research showed that sons have a better chance of survival if their mother is nearby," said Dr Michael Weiss from the University of Exeter and the Center for Whale Research.
"We wanted to find out if this kind of help leaves consequences, and the answer is - yes."
"Mother killer whales pay a high price in terms of their future reproduction to keep their sons alive."
Families of killer whales
An ongoing study of this endangered killer whale community, which lives in the coastal waters between Vancouver and Seattle, was started by Dr. Ken Balcombe.
Further work provided insight into the life of killer whales, which could only be achieved through decades of study.
Biologists have worked with the Center for Whale Research to discover, for example, the vital role of orca grandmothers and why, like humans, females of the species stop reproducing during their lifetime.
Based on years of studying killer whale interactions, scientists already knew that mothers and sons spend time together well into the males' adulthood.
"They even feed their sons the salmon they catch," Professor Croft explained, while adult female offspring hunt independently.
This, the researchers believe, could be some sort of evolutionary adaptation since the largest, oldest males produce many offspring.
"If the mother can get her son to become the dominant male in the population, then he will be the ancestor (of most of the next generation)," Professor Croft explained.
It may seem paradoxical that such powerful, intelligent animals depend on their mothers for life, but it seems that males simply do not need to become independent, because their mother stays with them.
"If my mother made me dinner every night, I might not have learned to cook myself," Professor Croft joked.
"But, indirectly, it seems to be in the mother's interest."
Only 73 orcas from this community remain, so scientists say they need to understand everything that could help them make decisions about how to protect these marine mammals.
"Southerners they are playing on thin ice and are in danger of extinction," Professor Croft said.
"So anything that reduces female reproduction is cause for concern for this population."
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Bonus video:
