These full-grown sea lions won’t stop feeding, and scientists don’t know why

Alexandra Childs never got used to seeing fully grown Galapagos Islands sea lions happily suckling from their mother’s breasts.

“Whenever you came across it, you doubled it,” said Childs, a PhD candidate in behavioral and marine biology at the University of Bielefeld in Germany. as it happens Host Nil Koksal.

“You went back to the computer, like, ‘I have to check the age again. Am I sure that’s what’s happening?’ It blew our minds.”

childs leyThe authors of a new study documenting the prevalence of so-called “superscalar” sea lions in the Galapagos, published last month in the journal American naturalist.

researcher fuAnd about 11 percent of the population remained dependent on their mother’s milk until adulthood. The children said it would be like humans continuing to breastfeed into their teens and 20s.

“Why? We have no idea,” Childs said. “We can’t understand why mothers would continue to allow this, because it’s a lot of energy to devote to an offspring that is able to hunt for itself.”

milking carts

The study looks at 20 years of data from the population of Galapagos sea lions, whose scientific name is Zalophus wollebecki.

Childs said sea lions can live about 23 years. most of Zalophus wollebecki weaning They hatch from their mothers between 1.5 and 4.5 years of age, just before they reach sexual maturity, which is exactly what researchers would have expected.

This is not the case for superscalers.

“These guys are crossing that line,” Childs said.

The oldest person he saw drinking milk, he said, was 16 years old – though this appears to be an anomaly, not the norm.

“So it’s (like) someone over 60 who is still breastfeeding,” Childs said.

He said, some of them made a group activity out of it, forming The New York Times dubbed “Multigenerational Feeding Trains.”

“We saw all three of them lined up, the mother feeding on the older female, and the baby feeding on the mother,” Childs told CBC. “So we had grandma, mom, and baby.”

Other sea lions do this too – but not as much

Andrew Trites, director of the Marine Mammal Research Unit at the University of British Columbia, says this type of behavior has also been seen in several other species of sea lions and some seals, but not to this extent.

“It’s much more extreme in the Galapagos,” Trites, who was not involved in the research, told CBC. “It’s a really interesting study.”

Sea lions typically do this when they don’t have enough high-quality food to survive, Trites said, and the mother wants to ensure her offspring’s chances of survival and reproduction.

“It takes a lot of energy to grow, to become really big, and puppies need a lot of energy,” he said, adding, “One way a mother can ensure that the puppies will grow big enough to become breeders in the future is to continue to feed them milk.”

But Galapagos study says superscaling This occurred more frequently during weather patterns that caused low sea surface temperatures, which is associated with high food resources. In contrast, this occurred less during weather patterns associated with higher temperatures.

“We actually found that it happens more often during good conditions, so when there’s a lot of food around,” Childs said.

While unexpected, Childs says this may be because it isn’t too much pressure on the mother to provide extra milk when she already has plenty to eat.

worn outHowever, he is not convinced. There are many factors that affect the food supply, he said.

To rule out nutrient deficiencies as a cause, he says you have to pay attention not only to the quantity of food, but also the quality. For example, he says Steller sea lions have seen population declines when their diet consisted primarily of low-fat fish.

“The quantities can be a little misleading,” he said. “If you’re a lean mammal, it’s all about fat. You need a lot of fat in your diet. And eating lean food won’t do it for you.”

The study itself cautions that conclusions cannot be drawn from weather patterns alone.

Childs says there are some other possible explanations for the Galapagos sea lions’ tendency to superscalp.

Superscaling may have an immunological benefit that scientists don’t know about at all, he said.

Or, she said, it could be something more than a social behavior.

“It is possible that it is a means of expressing the long-term bond between mother and offspring,” he said.

More research will be needed to say for sure.

“Sadly, my time on the island came to an end,” he said. “But we hope we’ll have some fresh, fresh-faced, brave people to go out there and collect data for us.”