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A Seal’s Spray Adds a Chapter to the Science of Spitting

ScienceA Seal’s Spray Adds a Chapter to the Science of Spitting

On Jan. 3, 2022, Clare Jacobs, a bird-watcher, was delighted to spot a rare white-tailed eagle, or Haliaeetus albicilla, at a nature reserve on the Isle of Wight in southern England. These birds, also known as sea eagles or ernes, vanished from the region some 250 years ago, but more than two dozen birds have been released on the island since 2019.

Mrs. Jacobs trained her camera on the eagle when she noticed something moving in the water below it: a grey seal. The large mammal popped out of the waves and opened its mouth. “It made me jump,” Mrs. Jacobs said.

Then the seal spit a stream of water at the raptor. Although Mrs. Jacobs didn’t realize it immediately, this was highly unusual. Seals had never been seen spitting before, and reports of interactions between these two apex predators are essentially nonexistent.

Mrs. Jacobs’s photos made their way to her daughter, Megan Jacobs, who studies fossils as a doctoral student at the University of Portsmouth, and David Martill, a lecturer at the school. Together, they published the observation last month in the journal of the Isle of Wight Natural History and Archaeological Society.

Both animals feed on fish, though eagles also go for water birds and carrion, and the study authors reason that the seal most likely spat at the eagle to deter a potential competitor. It seems the seal was telling it to “sod off,” Megan Jacobs said.

Sean Twiss, a professor at Durham University who’s spent 30 years studying grey seals, has never seen one spitting. He thinks it’s possible that the seal aimed to deter the eagle, or that it was just being playful. Seals often feed at depth and don’t usually forage in such shallow water bodies such as this harbor, he said, so he couldn’t be sure what the motivation was for the water spout.

The finding makes grey seals one of the few species known to spit. Some of the most famous members of this coterie include cobras, which can shoot venom from their fangs into the eyes of would-be predators, with impressive accuracy. The ability has evolved three separate times among cobra lineages, says Maarten Jalink, a researcher at University Medical Center in Utrecht, Netherlands, who has researched the phenomenon.

Perhaps the most impressive spitters are archerfish, said Stefan Schuster, who studies the fish at the University of Bayreuth in Germany. These little creatures, native to mangrove swamps in Asia and the Western Pacific, knock insects and arthropods off leaves using jets of water, which they produce by pressing their tongues against the tops of their mouths and rapidly squeezing. They then quickly eat the fallen prey. This spitting ability requires exquisite stabilization of the body attained by activating the fins, Dr. Schuster said.

It also requires incredible vision. The top halves of archerfish eyes are sensitive to colors above water and the lower halves to submarine hues, explained Cait Newport, a researcher at Oxford University. “Their brains are capable of accounting for the refraction caused by having eyes underwater but spitting at objects above water,” she added. Other fish, such as the Picasso triggerfish, have spit at her in aquariums, and also use this behavior to find food underneath sediments and to move things around underwater.

Some spiders also spit, hawking globs of gluey webs to subdue prey at a distance.

Many mammals have been known to expectorate, such as camels, alpacas and their relatives. Such emissions, which include saliva and often stomach contents, are produced as a defense mechanism against perceived threats. But spitting can also be a more reasoned way of transferring water from one place to another. In one study published in 2020, for example, Bornean orangutans retrieved food from a hollow tube by spitting water into it. Some monkeys are also known to expel seeds considerable distances from their mouths while eating, probably to more efficiently feed.

Dr. Twiss says these kinds of singular observations are often not published — which was almost the case in this instance. And that’s a shame, he said, because rare sightings can teach us much about the natural world and alert others to new behaviors to study.

The sighting is also the indirect result of the grey seal’s range expansion after a curtailment of hunting and the reintroduction of white-tailed eagles after centuries of absence. More discoveries await as these and other species’ populations grow and reclaim old territory.

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