New Research Expands the Potential Range of Mountain Lions in the Salish Sea
Written by Elizabeth Claire Alberts
Originally published by Mongabay
A mountain lion crossing a river in Montana (Photo: Gerard Lacz)
Scientists have documented cougars swimming long distances across the Salish Sea, which challenges former conceptions of cougar ranges and habitat connectivity.
The research suggests that cougars could access thousands of islands in the Pacific Northwest by swimming up to about 2 kilometers (1.2 miles) across the sea.
Other experts have documented cougars swimming across rivers, strengthening the idea that cougars spend more time in the water than previously thought.
It’s often been said that big cats don’t like water — but this mythological thinking isn’t entirely accurate. New research provides evidence that some male cougars (Puma concolor), or pumas, not only swim, but travel long distances in the chilly sea, dodging boats and orcas.
The study focused on a GPS-collared cougar known as M161, or Nolan, who slipped into the Salish Sea in the early hours of July 16, 2020, at the edge of Washington state’s Olympic Peninsula. He began to swim, not stopping until he’d reached Squaxin Island, a journey of about a kilometer, or two-thirds of a mile.
Nolan isn’t the only cougar known to swim; many others have done the same. For instance, Mark Elbroch, study co-author and director of the puma program at Panthera, the global wild cat conservation NGO, says he once tracked a long-distance swimming cougar in Chilean Patagonia that swam several times to a lake island inhabited by sheep, in 2010.
But few scientific studies have documented this phenomenon, and reports of swimming cougars have mostly been limited to non-academic literature and anecdotal evidence, Elbroch says.
“I’m sure they’ve been swimming for years and years and years,” he tells Mongabay, “and we’re just finally catching up.”
Elbroch says documenting evidence of swimming cougars is necessary for the conservation of this species, since it challenges conceptions about their range and habitat connectivity.
“It has implications for conservation managers because suddenly, you view a map very differently,” Elbroch says. “The whole point of our work here on the [Olympic] Peninsula is wildlife connectivity and we have been painting very strict boundaries on where we thought cats could go.”
Based on Nolan’s journey, the authors estimate that island-hopping cougars can access 3,808 out of 6,153 islands between the southern section of Puget Sound and Larcom Island in British Columbia on shorter swims, and that they are capable of reaching 4,583 islands on longer swims of about 2 km (1.2 mi).
Glen Kalisz, a habitat connectivity biologist at Washington state’s Department of Transportation and Fish and Wildlife Program, who was not involved in the study, says cougars are becoming genetically isolated on the Olympic Peninsula and in the Willapa Hills due to a number of busy highways, including Interstate-5 (I-5), which makes it nearly impossible for the animals to disperse to other areas.
“The ability of cougars to island hop gives them another skill to help find and occupy habitat that we used to think was out of the question, but I-5 runs north/south across the entirety of Washington, and even with strategic swimming most cougars (all animals) will eventually have to cross it if they intend to access the broad habitat offered in the Cascade Mountain Range,” Kalisz tells Mongabay in an email.
“What I personally feel when thinking about this study is that cougars are trying everything they can to disperse, going so far as to brave cold, dangerous marine waters,” Kalisz adds, “and that we should be trying everything we can to provide safe passage across I-5 via wildlife crossing structures to ensure their efforts aren’t in vain!”
Experts say genetic diversity is key to species survival. However, the cougar population on the Olympic Peninsula currently has one of the lowest levels of genetic diversity and highest cases of inbreeding.
Siobhan Darlington, a scientist at the Southern BC Cougar Project, who was also not involved in this research, says she wasn’t surprised by the study’s findings since she’s already aware that cougars swim across rivers. She says that in her own research, she found that cougars usually cross rivers that are less than 0.5 km (0.3 mi) wide, but not wider than about 1 km. One GPS-collared cougar was found to cross 11 rivers within a year. (These findings have yet to be published, Darlington says.)
“They are pretty good swimmers though [but] just don’t have much endurance for running or swimming long distances,” Darlington tells Mongabay in an email. “Large bodies of water are barriers to connectivity, and we have observed a few individuals that are dispersing to new territories encounter a large lake or reservoir, follow the coastline for a few days, and turn around and go a different direction because they can’t cross. Their ability to swim longer distances is probably different between freshwater and salt water because of buoyancy making it easier to swim in salt water.”
She says there’s great value in the new study for its quantification of cougar habitat connectivity based on swimming ability.
“Understanding the barriers to dispersing cougars on the landscape is important for ensuring connectivity for the population,” she says, “whether those barriers are natural or human-made.”
As for Nolan, things got more challenging for him after arriving on Squaxin Island. Fourteen days after he swam to the island’s shore, someone legally shot and killed him.
Elbroch, who went to collect Nolan’s body on the island, says that if Nolan had managed to take two more swims he would have ended up at a national wildlife refuge, joining a new population of cougars.
“The habitat exists for them to hop between islands,” Elbroch says. “But we also need to work on the human element, the tolerance for allowing these cats to pass through. We now know they can swim [to] the islands off the coast of the Pacific Northwest, but in the end it is dictated by whether we allow them to do so.”