When dolphins played with a snake

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When dolphins played with a snake

Why did Bolivian river dolphins swim with a large predatory snake in their mouths? “There are so many questions,” said a researcher

A photo of Bolivian dolphins playing with a Beni anaconda in August 2021. OMAR M. ENTIAUSPE NETO et al via NYT

In August 2021, a research team was documenting biodiversity near the Tijamuchi River in Bolivia when they saw animals that are usually difficult to observe: Bolivian river dolphins.

Just seeing them with their heads above the river was extraordinary, said Steffen Reichle, a biologist at the Noel Kempff Mercado Natural History Museum in Santa Cruz de la Sierra, Bolivia, and a member of the team. The researchers knew something was wrong and started taking pictures.

It was only after scrolling through the footage captured by the team that the researchers realized the dolphins were waving an anaconda as they swam.

The researchers described what they saw in the review Ecology last month. While dolphins in captivity and in the wild are known to be playful, the surprising behavior of Bolivian cetaceans appears to be a new frontier for frolicking among aquatic mammals, and some scientists are still unsure what to make of what the team has observed.

Mr Reichle said Bolivian river dolphins usually swim below the surface and sightings often only grab a fin or tail. But some of the six animals they saw kept their heads above murky water for an unusually long time.

At one point, two male dolphins apparently swam in sync, a snake held by the animals mouth. Anacondas are semi-aquatic and can hold their breath for quite some time. But because the snake was handled for at least seven minutes, much of it submerged, it likely perished.

“I don’t think the snake had a very good time,” Reichle said.

Due to the duration of this interaction, the team suspects play – not predation. The native Beni anacondas of Bolivia are apex predators. Other than a single case of cannibalism, researchers have not documented the snakes being eaten. In this case, the team did not see where the snake ended up.

With the liveliness of the dolphins, “playing seems like a pretty good response,” said Omar Entiauspe-Neto, one of the paper’s authors and a taxonomist at the Universidade Federal do Rio Grande do Sul in Brazil.

Some of the dolphins gathered were juveniles, which could suggest another dimension of the interaction: The adults may have taught the youngsters about anacondas or showed them a hunting technique.

But Sonja Wild, a behavioral ecologist at the Max Planck Institute for Animal Behavior in Germany, who was not part of the study, was skeptical that the interaction was deliberately informative. It’s more plausible that the juveniles were watching because they were curious, she said.

And because anacondas are strong, Ms Wild wondered if the snake was injured or dead before the dolphins got to it. Of all the things you could take away, “it seems a little extraordinary,” she said.

“This is the first time I’ve heard of dolphins playing with a big snake,” added Ms Wild, who has observed bottlenose dolphins using seashells as tools.

Something else in the photos stood out: the erect penises of the male dolphins.

“It could have been sexually stimulating for them,” said Diana Reiss, a marine mammal scientist and cognitive psychologist at Hunter College in New York, who was not involved in the study. “It could have been something to rub on.”

The excited males could have had sex with each other before the snake became entangled.

Researchers who study dolphins are well aware of the animals’ sexual tendencies, such as rubbing their genitals on toys or inserting their penises into objects, both animate and inanimate. They often use their penises for tactile interactions, Professor Reiss said. She even observed male bottlenose dolphins trying to enter the blowhole of a rescued pilot whale in an aquarium. It is possible, she added, that the males attempted to insert their penises into the snake.

“There are so many questions,” Mr. Entiauspe-Neto said.

Much more is known about ocean dolphins than about river dolphins, in part because it’s harder to see what’s going on when the river water is muddy. Although limited in nature, “these observations are still valuable,” Prof Reiss said. “It gives us another insight into the lives of these animals, especially in the wild.”

Whatever happened in that animal encounter is not the stuff of children’s storybooks.

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