Imagine, if you will, that you have a daughter and a son. You feed and care for the pair as they grow and mature. They rarely leave the house and you have little time for yourself. Eventually your daughter will grow up and feed herself.
Your son, on the other hand? He only leaves to hang out with other girls and have sex. He goes home after his amorous adventures, and while he sometimes gets his own food, he pretty much hoards it and you’re still forced to take care of him day in and day out.
If this sounds exhausting, it is. Welcome to the life of orca mothers from the south.
These endangered whales are mainly found off the coast of British Columbia and Washington State. Only 73 are still alive.
It is not known why this population is struggling, but there are suggestions that it could be to blame reduced food sources, boats or even pollutants in the water that can reduce reproductive success.
Now a new study has found something else that could be a contributing factor: the neediness of male offspring.
According to the study published today in Current Biology — who used data from 1982 to 2021 on 40 females — this need to constantly provide comes at a high cost to the mothers, especially when it comes to reproduction.
Michael Weiss of the Center for Research in Animal Behavior at the University of Exeter, and the study’s lead author, used an example of a 21-year-old female killer whale who hasn’t had a calf in the past year (they can’t have a calf until they don’t do that). breastfeeding longer).
“Our best estimate for that female is that she has about a one in five chance of giving birth to a calf each year, a 20 percent chance in any given year,” Weiss said.
“Same woman, same situation, but [she] has a single son she cares for: that drops to less than a one in ten chance. So 10 percent chance. So you’re basically about halving or even slightly more than halving the chance in any given year of successfully having a calf by raising one son.”
‘They need more food’
Weiss noted that previous studies have taken a closer look at the orcas’ behavior and found that, unlike female offspring where the mothers stop sharing food, they continue to share with the males into adulthood.
“This makes sense, given that males are larger and require more food,” Weiss said. “Because they are bigger, they may be less agile and have a harder time catching their own food. There are also some good evolutionary reasons why you might want to support your son or daughter.”
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Several species are known to sacrifice their future reproductive success to increase their offspring’s chances of survival, which is known as parental investment. But this is the first time maternal investment in this particular group of killer whales has been studied.
Weiss said he was amazed at how much maternal investment there was.
“You know, this wasn’t some subtle thing of, oh, you know, over a lifetime you could miss an average of one extra offspring. This is if, our best guess is more than a 50 percent drop in your reproductive output, because you’re taking care of a son.
The data showed that there was negligible change if the mothers had daughters.
‘It shows how much we don’t know’
Weiss said that as these orcas evolved, this kind of behavior — when there may have been more food around — may not have hurt their reproduction as much. More abundant food means mothers can have enough to both keep them alive and reproduce. But now that may not be the case.
“I think this kind of research shows how much we don’t know about killer whales that live in the South. We are trying to understand why they are so endangered’, says Fanny Couture, a marine ecologist and PhD student at the university. of British Columbia’s Institute for the Ocean and Fisheries, who was not involved in this study.
Couture recently published a study showing that these killer whales have not been getting enough food since 2018. She said these new findings indicate there may be other factors threatening this population.
“It is the first example of long-term investment by parents in [these’] friendly. So it shows how many other factors we have to consider when talking about residents of the South,” she said.
Weiss noted that killer whales living in the South have been studied for decades and exact counts are provided annually. But there are other populations that are doing better – such as the orcas that live in the north and Bigg’s (temporary) orcas – that he would also like to study.
“We’re very interested in the future to see if we can take some of that data and see if the same effects happen in those other populations,” he said. “And specifically for me, I’m interested to see if there’s the same kind of effect in the first place. And if there is, that effect is reduced because these populations have less food stress.”
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