A new study has found that orca mothers still feed their adult children. That bond may come with costs, researchers say.
David K. Ellifrit/Center for Whale Research/NMFS research permit #21238
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David K. Ellifrit/Center for Whale Research/NMFS research permit #21238
A new study has found that orca mothers still feed their adult children. That bond may come with costs, researchers say.
David K. Ellifrit/Center for Whale Research/NMFS research permit #21238
Twenty years ago in the waters off the coast of Washington State and British Columbia, an adult female orca (called K16 by those who know her well) gave birth to a son, K35.
“These two have a very close social relationship,” said Michael Weiss, director of research at the Center for Whale Research in Friday Harbor, Washington.
It’s hard for Weiss to think of a time when she didn’t catch a pair hanging out in the same group, and from time to time close to each other.
“[They’re] it’s just a pair of whales that are basically best friends with each other,” he said.
Weiss observed that the mom and son pair spend a lot of time close together, touching and floating on the surface – and sharing a salmon.
Orcas are big, and so are their appetites. They are also less manoeuvrable, because it is more difficult to catch prey. This means that a male like K35 needs help getting enough food.
So his mother would often lie down, says Weiss, “catching a salmon and bring it to the surface and bite off half of the fish and leave half for her son. So she shares a huge meal.”
And here’s where things get shocking – since K35 was born two decades ago, his mother has never had another calf. Compare with other women in the population.
“Some of the whales started giving birth at the same time,” says Weiss, “and they had daughters.”
Not just K16 either. In the paper this week in the newspaper Current Biology, Weiss and his colleagues looked across four decades of life history records of southern populations of whales in the Pacific Northwest. The tendency was evident;
“Orca mothers pay an enormous cost to care for their young,” says Weiss. The cost is that they have fewer children. “And they do this throughout their children’s lives, and never cease to make the expense of keeping their children alive.”
For when the mother dies, the son generally perishes within a year or two. “Clearly we think that’s because they saw a huge reduction in the amount of food consumed,” explains Weiss.
Weiss can’t think of another animal that does this endless investment when it has the option to multiply multiple times. Why, then, would this orca sacrifice only her children? Weiss argues that the potential payoff is huge.
“K35 is now one of our largest male populations,” says Weiss. “He grew up big and healthy and looks good.”
In this way he is ready to become a father.
“Really, I wouldn’t be surprised if some of the next calves that pop out are in her population,” Weiss said.
It so happened that his mother became a grandmother several times over. His genes would be the limit in a pack of calves. And because they are born in other pods, it will not be difficult to raise them.
“It’s amazing work,” says Eva Jourdain, director of the Norwegian Orca Survey. Jourdain, who was not involved in the study, hopes that similar research will be conducted in Norway.
“Immediate comparisons can be made across populations,” says Jourdain. “And then finally we can begin to better understand how important it is for the preservation of those species.”
It is noteworthy that this decision of mothers to invest only in their children has a dark side. Killer whales like K16 and K35 are in trouble in the Southern Resident. Over the years, the population has dwindled to just 73 animals. And what these orcas really need now is to be more reproductive women.
“That’s how you keep the population of lazy animals from going away,” says Weiss. “So investing in children for people like ours, which is so stressed, is really not ideal.”
Weiss worries that this maternal strategy, which has served this people well in the past, could raise the risk of extinction, that the kind of life-long bonds she saw between K16 and her son could bind these creatures to an uncertain fate.
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