On January 26, 2020, biologists with the Olympic Cougar Project captured a female cougar near Shelton, Washington. The cougar’s male cub was still with her—he was a little over a year in age, and young cougars might stay with their mothers for about eighteen months—so the researchers captured him, too. Both cougars were measured and given special GPS collars to track their movements, and then released; the young male, per the protocol, was designated M161.
M161 hung around with his mother for a few more months before striking off on his own the following May. He meandered about the southern peninsular landscape matrix, slipping among woodlands in Mason County, before, early in the morning on the 14th of July, he swam across Puget Sound to Squaxin Island. Why he decided to do this is unknown. He may have been in someone’s backyard and chased off by a dog. Or maybe Squaxin Island didn’t really look that far away from the shore. “We have some working hypotheses,” says Mark Elbroch, a biologist with Panthera and one of the leaders of the collaring effort.
If a cougar can swim half a mile or more, what sort of territories does that open up to them in Puget Sound that researchers might not have considered before?
What is known is that the shortest distance between where M161 started swimming and where he finally stopped is 1.1 kilometers, or a little more than half a mile. (“Really, though, given the tides and currents and everything,” Elbroch says, “it’s doubtful he swam in a straight line.”)
For Elbroch and the Olympic Cougar Project researchers, M161’s swim was a real eye-opener. One of the project’s main interests is dispersal corridors and, as Elbroch says, a landscape’s functional connectivity. What sort of spaces do the cats actually use? What features of the land make it easier or harder for them to travel? After that swim, the project’s biologists started to wonder: if a cougar can swim half a mile or more, what sort of territories does that open up to them in Puget Sound that researchers might not have considered before?
That particular question became the focus of a paper recently published in the journal Northwest Naturalist. Andrew Stratton and Read Barbee, the two lead authors, overlaid cougars’ capacity for swimming long distances against all the islands in the Salish Sea. Using M161’s 1.1-kilometer swim as a conservative estimate, they identified over 3,800 islands that a swimming cougar could reach if it were sufficiently motivated. And nudge a cougar’s theoretical swimming range up to two kilometers, and the number of accessible islands jumps to 4,583, out of 6,153 in the Salish Sea.
“Cougars swim because of either a push or a pull,” says Scott Pearson, a biologist with WDFW who was not affiliated with the work. “A young male could get injured in by an older male, and so might swim away to avoid that conflict. So that’s a push. But there could be a pull, too, to other islands. Deer can swim a long way, too, and cougars might follow them.”