Orca mothers make ‘lifelong sacrifice’ for sons

Orca Mothers in the North Pacific make a “lifelong sacrifice” for their boys, according to research.

The chances of a female killer whale having more offspring were drastically cut when she had a son.

Feeding sons appears to drain a mother’s energy to the point where she can’t create as many offspring as she’d want.

“Mothers sacrifice their own food and their own vitality,” explained University of Exeter professor Darren Croft.

When it comes to their families, Orca Mothers never really let go. But although female offspring grow up to be self-sufficient, male offspring continue to rely on their moms for everything, including a fair part of the food their mothers catch.

That’s a “fresh perspective into the intricate social lives and family lives of these remarkable animals,” as Prof. Croft put it.

This study, which has been going on for decades and was recently published in Current Biology, is part of an ongoing effort to learn more about killer whale families.

The Center for Whale Research (CWR) made it feasible by studying the Southern Residents, a subspecies of killer whale, for over 40 years.

Biologists have been able to disentangle important social behaviour and family relationships that directly affect the survival of the animals thanks to the CWR’s systematic censusing of the Southern Resident population since 1976.

Scientists looked at the lives of 40 female orcas between 1982 and 2021 and found that the likelihood of a mother successfully nursing another calf to one year of age was reduced by half for each surviving son.

Sons, according to Dr. Michael Weiss of the University of Exeter and the Center for Whale Research, have a better chance of survival if their mother is there.

“We investigated to see if there is a cost associated with this assistance and found that there is. As a result, female killer whales incur a heavy reproductive cost in order to ensure the survival of their sons.”

Families of killer whales Orca Mothers

Dr. Ken Balcomb began the continuous research of the endangered killer whale population that inhabits the coastal waters between Vancouver and Seattle. At first, he planned to look into the dangers they faced.

Follow-up research eventually uncovered details on killer whale existence that had previously been hidden. Biologists have collaborated with the CWR to uncover insights like the pivotal function played by killer whale grandmothers and the reason females of this species, like humans, stop reproducing at a certain point in their lives.

Scientists have known for a long time, based on their extensive research, that moms and sons “hang out” together far into the male’s adulthood.

In contrast to their female offspring, who will go on to hunt independently as adults, “they’ll even feed their sons salmon they capture,” Prof. Croft said.

The fact that the largest, oldest males go on to father many children has led academics to speculate that this may be a form of evolutionary “bet-hedging.”

“If a mother can get their son to become that huge male in the population, then he is the one who will father [much of the following generation],” Prof. Croft said.

While it may seem counterintuitive that such strong and smart animals will always need their mothers, it appears that males just don’t have to grow independent as long as their mother is around.

Prof. Croft joked, “If my mother made my meal every night, perhaps I just wouldn’t learn to cook my own dinner.”

But, in a roundabout way, it seems to be in a mother’s best interest.

Scientists say they need to know everything there is to know about these killer whales because there are only 73 of them remaining and protecting them is a priority.

• According to Professor Croft, “these southern resident killer whales are teetering on a knife edge and are at risk of extinction.” Therefore, anything that prevents women from reproducing is bad news for this group.