You’ve probably seen the recent video taken by a State Parks employee of a coyote swimming across Raccoon Straight in San Francisco Bay toward Tiburon. Coyotes are known to be speedy hunters, running up to 43 mph, but did you know they’re also excellent swimmers? In fact, that’s how State Parks staff believes the coyote population began at Angel Island State Park.

State Parks Interpreter II Casey Dexter-Lee has been living on Angel Island, the largest natural island in San Francisco Bay at 1.2 square miles, for 24 years and had never seen a coyote until recently. The first sighting of a coyote on the island occurred in 2017. Initially, Parks staff dismissed reports of sightings because coyotes historically didn’t live on the island. But subsequent observations and photos confirmed their presence. 

How did coyotes get on Angel Island?It’s believed that a single coyote swam to Angel Island, likely from the Tiburon mainland, across the Raccoon Straight in 2017. Parks staff could hear the coyote calling to others on the mainland. Shortly after, it’s believed another coyote made the swim to the island, and the first litter of pups was reported around 2019. According to Senior Environmental Scientist Brett Furnas with the California Department of Fish and Wildlife (CDFW), the genetics suggest that the current population of coyotes (between 14 and 17) on Angel Island can be traced back to this now-deceased mother or grandmother who made that initial solitary swim.

Coyotes Impact on the EcosystemState Parks Environmental Scientist Bill Miller with the Bay Area District says coyotes have now become Angel Island’s new top mammalian predator, filling a niche previously occupied by raccoons. Before coyotes arrived, the local deer population on the island was overpopulated, starving and causing damage to native plants. Deer population rose to the 300s in the 1980s. Previous solutions included relocation, contraceptives and supplemental feeding. The deer population seemed to stabilize to around 80 to 100 at the last count in 2014. With coyotes now preying on deer and fawns, the deer population appears to have dropped by half since the arrival of coyotes 8 years ago. 

However, coyotes don’t only eat deer. They eat invasive species such as black rats and house mice, as well as fallen fruit from trees like the Catalina cherry and Canary Island date palm. They’ve also reduced the island’s raccoon population.

The Future of Coyotes on Angel IslandIn 2024, scientists with State Parks, CDFW and UC Davis launched a five-year study on Angel Island’s coyotes to understand their genetics, diet and population changes. This isolated population offers a unique opportunity to study the effects of a predator on a closed environment. 

If you do come across a coyote on the island, be sure not to feed it because it will disrupt the ecosystem. While coyotes are not normally dangerous to humans, you can raise your hands above your head to appear larger to shoo coyotes away. 

And if you’re lucky, you may spot a coyote swimming the next time you’re on a ferry crossing the bay.