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Some cougars in the Pacific Northwest may routinely brave frigid saltwater to reach islands. Based on an analysis of island cougar sightings, these cats may be swimming up to 2 kilometres to reach new territory, food and mates.

Many large felines are adept swimmers, though cougars (Puma concolor) – also referred to as pumas and mountain lions – tend to avoid the water. Still, there have been of the cats taking a dip. It is even more remarkable, says of the nonprofit organisation Panthera, that the cats in the Pacific Northwest would be willing to face icy waters, boats and occasional orcas.

The discovery was made thanks to data collected as part of Panthera’s , a collaboration with six local tribes. The project’s goal is to better understand the movement of cougars around the Salish Sea, a network of islands and ocean channels between British Columbia, Canada and Washington state in the US.

“We had no idea that we were about to investigate swimming,” says Elbroch.

The researchers were surprised when, in July 2020, a young male cougar called “Nolan” – wearing a collar that transmits location information to satellites – made an impressive 1.1-kilometre swim from the eastern edge of Washington’s Olympic peninsula to nearby Squaxin Island. Even if Nolan’s journey represents the maximum swimming range of cougars, the team estimated that as many as 3808 of the Salish Sea’s 6153 islands could be accessible to cougars.

“When we first saw that he swam to Squaxin Island, our whole team was thrilled,” says Elbroch. “We were like, ‘Oh my gosh – this is amazing.’”

When the researchers searched for confirmed sightings of cougars on islands in the region, they found evidence of island-hopping cougars on four islands that were only accessible via a 2 kilometre-long swim or longer. With that over-water range, cougars might be capable of swimming to more than 4500 islands between Washington and Canada.

“We shouldn’t always see water as a barrier to movement,” says at the Washington Department of Fish & Wildlife, who wasn’t involved in the study. Beausoleil, who has observed cougars swimming in fresh and saltwater in the state, says he isn’t surprised by the findings given earlier reports, but says the work is “still interesting and important to note”.

Elbroch thinks the main reason Olympic peninsula cougars are willing to take the plunge is because of their geographic predicament: the cats are penned in by natural and human-made barriers, like major highways and vast bodies of water. These isolated cougars can’t regularly interbreed with populations off the peninsula, so they have than mainland felines, increasing their vulnerability to disease. Swimming may be the only way for young cats to find food, mates and territory, says Elbroch.

Within two weeks of his swim to Squaxin Island, Nolan was shot and killed by an unknown person. Elbroch hopes Nolan’s swim will provide researchers with a more complete picture of how cougars are moving in the area, which is critical for guiding habitat connection projects like wildlife overpasses. Such links could boost the cats’ genetic diversity and limit fatal interactions with people, potentially reducing the chance that other cougars meet Nolan’s fate.