Killer whale mothers struggle to regain body fat with more offspring

A year and a half of pregnancy, two years of breastfeeding, then hunting and sharing food with their adult children who never leave.

Orca mothers work hard.

Biologist and author Sharon Kay said, “There is a long, long cost of caring for offspring because they spend so much time with them throughout their lives.” New research in journal scientific report This shows the physical effects of that motherhood.

The study looked at body fat – a key marker associated with survival in these marine mammals – and how quickly mothers regain it after pregnancy. Turns out, this is how many births there will be now – this is how many children there will be later.

Experts say these findings help shed light on the social pressures these animals face, even as human pressure persists in their environments.

pixel-perfect patch

The study focused on northern resident killer whales, whose range extends from Alaska to the coastal waters of British Columbia to northern Washington. they too Listed as threatened Under Canada’s Threatened Species Act.

“When they give birth and start lactating, their fat levels actually drop drastically,” said study co-author Amy Rowley, a biologist at the Raincoast Conservation Foundation. This decline lasts for about three years, but some mothers struggle to get back to their pre-pregnancy state.

To find out why, the team needed to measure body fat, but different from other terrestrial animalsIt is not possible to capture and measure a wild orca. So they used a drone, flying 30 meters above the animals and taking pictures.

“The body condition of these killer whales is mostly related to obesity at the back of their heads because that’s where they lose fat first,” said Kay, who led the research as a graduate student at Victoria University.

Those images will be reconstructed pixel by pixel to measure changes in the white spots over the eyes.

“If the eye patch is tilted more outward, that’s a fat, healthy whale,” Rowley said. “Versus if they’re kind of parallel or facing slightly inward, that’s a sign that the whale doesn’t have a lot of fat and is potentially in poor condition.”

number of surviving children

Studying 66 adult women, researchers found that the strongest factor influencing body fat levels was the number of surviving offspring. (Up to half of all killer whale calves do not survive beyond the first year.)

“It’s not just the rearing and reproduction of these offspring that takes a toll on mothers, but it’s also the lifelong care of actually finding fish and sharing that food,” Kay said.

Hannah Myers, a marine ecologist at the University of Alaska Fairbanks, said this work adds another piece to the puzzle of these socially complex animals.

“It’s really exciting to see some of these questions that you could never answer without this type of long-term monitoring program and some of the new technologies that have come online,” Myers said.

“This has yielded some very surprising results, some of which are actually quite consistent with what we might have predicted about how killer whales work,” said Michael Weiss, research director at the Center for Whale Research.

Interestingly, the new study of northern resident killer whales did not find evidence of what he and his team found in the more endangered, southern resident killer whales: that sons love their mothers more than daughters. But Weiss explains that they weren’t looking for the same things.

“Whereas our previous research looked at the kinds of end results – how do they reproduce? – this research is looking at the middle step, which is how does their body condition change?” Weiss told CBC News from the San Juan Islands in Washington.

One theory to explain that discrepancy, Rowley suggests, might be that daughters stick around – meaning their offspring become another mouth to feed – increasing the pressure on the mother, who is now a working grandmother. Weiss explains that in southern populations, fertility rates are lower so there may be fewer mouths in general.

human and social pressure

Experts say it is important to understand this effect on body condition, as it is one of many stressors that orcas face.

“This study really highlights how big a deal maternal investment is for any animal,” Myers said. He said human influences add to what they have to deal with.

These include chemical contaminants in their environment, noise pollution from shipping traffic, and changes in the location of their prey due to climate change. Ultimately, this could mean further decline in body fat – which could be a harbinger of death.

“They have a lot to maintain, and so as we go and create more stress through these anthropogenic conditions … they become even more stressed,” Kay said.