Swimming Cougars Take to the Sea, Astonishing Researchers in the Pacific Northwest

Cougars and their challenges have been in the news lately with the death of Los Angeles’ celebrity mountain lion, P-22. L.A.’s beloved cougar lived in a 9-square mile patch of habitat in the midst of the city, confined by freeways to a relatively small range. His was a high-profile story that perfectly illustrates a terrible predicament for cougars and many other species. As habitat fragmentation continues to create increasingly smaller and unconnected areas, many species are impacted—especially low-density, wide-ranging species like cougars.

While the Washington State’s Olympic Peninsula may be characterized by its wilderness rather than its urban sprawl, cougars there face similar constraints. The peninsula is surrounded by water in three directions, as well as the teeming Interstate Highway 5 (I-5) corridor. The authors of a new study from Panthera, the global wild cat conservation organization and partner tribal nations, note that in the Pacific Northwest, “current habitat fragmentation characteristic of the Anthropocene may threaten Cougar metapopulation connectivity important to maintaining genetic health of the species.”

Stuck on a piece of land surrounded by water sounds pretty constrictive for an animal like a male cougar, which may dominate a home range of 50 to 150 square miles. But what if cougars could swim?

Until now, anecdotal and scientific evidence for swimming cougars has been lean, leading scientists to wonder about large bodies of water serving as a barrier to cougar movement. However, the new research from Panthera reveals that cougars can swim surprisingly long distances, “challenging current thinking about the extent and connectivity of the cougar range,” according to a press release for the research.

As part of Panthera’s Olympic Cougar Project, a research initiative on the Peninsula, a mother cougar and her 1½-year-old son, known as M161, were outfitted with GPS collars to track their movement. The press release explains what happened next:

“To scientists’ astonishment, M161 spent several months on land after his collaring before swimming 1.1 km [.68 miles] from the eastern edge of the Peninsula to Puget Sound’s Squaxin Island. Based on this journey, scientists estimate that at least 3,808 of the Salish Sea’s 6,153 islands could be accessible to ‘island hopping’ cougars.”

Dr. Mark Elbroch, Puma Program Director for Panthera and co-author of the study, told Treehugger in an email that “M161 could have made another few short swims to pass undetected below I-5 in the Nisqually National Wildlife Refuge—a route we’d never considered before.”

The Olympic Peninsula is bordered to the north and east by the Salish Sea, a cold and deep body of water between Washington and British Columbia. M61’s swim was recorded in the Puget Sound, an inlet of the Salish Sea. 

“These water bodies are dotted with many islands of all sizes, creating a complex mosaic of land and sea that Cougars and other species may be able to navigate using a series of swims or ‘hops,’” write the study authors.

M61’s swim from the eastern Olympic Peninsula to Squaxin Island allowed the researchers to predict the total number of islands in the Salish Sea that may be accessible to cougars by means of swimming. They used M61’s travel as a potential upper threshold distance and used cougar sighting records from islands in the Salish Sea to confirm or refute their results. 

They estimated that 3808 of 6153 islands in the study area could be accessible to cougars with one or more 1.1-kilometer swims. They then confirmed the presence of cougars on 18 of those islands. Amazingly, four islands with confirmed cougar sightings would have required swims closer to 2 kilometers (1.24 miles). 

With that in mind, they increased the threshold distance to 2 kilometers, yielding an additional 775 islands potentially accessible by island hopping.

The findings are particularly significant because of cougars’ genetic isolation in the area, thanks to the barriers previously mentioned. The roads are especially concerning. Highways are, in effect,  turning the Olympic Peninsula into an island of its own. The I-5 corridor south of Seattle is one of the “fastest developing regions on the west coast and is increasingly severing wildlife connectivity in western Washington,” according to Panthera’s Olympic Cougar Project.

“I-5 is a daunting barrier for wildlife, with daily traffic counts along the stretch of land connecting the Olympic Peninsula to mainland Washington ranging from 50,000 in the south to 100,000 as you approach Olympia,” Dr. Elbroch told us. “Yet, this cougar reminded us of the ingenuity of nature—that cougars facing what appear to be insurmountable obstacles, may still find a way to connect with far-off populations.” 

The findings aren’t just important for cougar conservation. Cougars are keystone species, and protecting them indirectly protects numerous other species in their ecological community. A 2022 Panthera study, for example, revealed that cougars maintain relationships with an astounding 485 other species.

While the idea of cougars learning to swim to escape the challenges of the natural and built environment is a win for Team Cougar, the Pacific Northwest cougars still have a rough road ahead. Not only are there habitat constraints, but also, cougar hunting is legal in Washington state. Which appears to be the depressing fate of our intrepid M161, who was shot and killed on Squaxin Island. (Meanwhile, the USDA's Wildlife Services program killed 200 cougars in western states in 2021, the last year for which there is data.)

But as Dr. Elbroch pointed out, M161 “opened our eyes to new possibilities.” And with Panthera’s work to protect cougars, and especially to work with the state to ensure I-5 is modified to aid wildlife on the Olympic Peninsula, perhaps people will begin to rethink humankind's relationship with species like cougars—much like they did in Los Angeles. And if all else fails, at least we now know that cougars can take to the sea and swim off to new horizons.

The research, "Island Hopping Cougars in the Salish Sea," was published in Northwestern Naturalist.