When Aidan Moore heard a guest had spotted a coyote on Alcatraz Island, he figured they were mistaken.
Then the visitor showed video proof to the 43-year-old, who drives a tram and helps people board tour boats on the island off San Francisco.
The footage, taken Jan. 11, shows the coyote paddling to the southern shore and then climbing up onto some rocks, hunched and shivering. It does not show where the coyote came from or reveal its fate — whether it was washed back into the frigid water or trotted off into the island’s interior.
The video, originally reported by SFGate, is the first documented instance of a coyote swimming to Alcatraz, scientists say. It came months after a coyote was filmed swimming in the San Francisco Bay a couple of miles to the north, near Angel Island, where a lone coyote first traveled in 2017 before possibly being joined by another, resulting in a pack that now numbers at least 14.
In a storyline that may be recognizable to some human inhabitants, the coyotes are likely leaving the mainland in search of new territory because the Bay Area is becoming too crowded, said Brett Furnas, a wildlife ecologist with the California Department of Fish and Wildlife.
Coyote sightings have increased in San Francisco since the species, which was once wiped out in the city, reemerged roughly 25 years ago, he said. Evidence suggests that happened when some coyotes walked across the Golden Gate Bridge from Marin County, where Furnas noticed the coyote population growing while researching deer about 10 years ago.
The ecologist, who is studying the Angel Island pack, plans to launch a broader inquiry into how often coyotes swim across the bay and what happens when they do. “Anytime you have an island,” he said, “it’s like a natural laboratory.”
Moore reported the coyote sighting over the radio, prompting what he said was an ultimately fruitless search by rangers with the National Park Service, which manages Alcatraz as part of the Golden Gate National Recreation Area. For the past week, the island has been shut down to visitors for repairs to its dock pilings, he added.
Coyotes are common in just about every part of the Golden Gate National Recreation Area and play an important role in managing rodents across the sprawling network of parks, but the video marks the first time biologists have seen them on Alcatraz, according to Park Service spokesperson Julian Espinoza.
“The swim to Alcatraz is difficult even for a person in peak physical shape,” Espinoza wrote in an email. “We were as surprised as anyone to see that video of the coyote swimming ashore.”
The Park Service has received no other reports of coyotes on the island since the sighting and isn’t sure what happened to the animal, he said Tuesday.
The coyote most likely arrived on Alcatraz from San Francisco, which is the closest potential point of origin, Furnas said. If so, it would have been a remarkable feat — a swim of about 1½ miles across cold, choppy waters with strong tides.
But it also could have come from Marin County or even Angel Island and been buffeted about by the currents, Furnas said. If there are additional sightings, he hopes that scientists will take a genetic sample from its scat or another source, which they could analyze to learn more about its ancestry.
Christine Wilkinson, research associate with the California Academy of Sciences, speculates the coyote may have come from a pack that lives in San Francisco’s Coit Tower area, which has very little green space. Dispersal season, when coyotes go looking for their own territory, typically lasts from fall to early winter, but it’s not unheard of in January, Wilkinson wrote in an email. It’s also coyote mating season, which may have further pushed the coyote to fan out, she wrote.
Dispersing coyotes are constrained by Interstate 280 to the south, where coyotes are struck and killed every year, she added.
Although this animal appeared weak when it arrived onshore, coyotes are incredibly resilient, Wilkinson noted. It has ready food sources including rodents, birds and their eggs. In fact, Alcatraz is a noted sanctuary for nesting shorebirds, in part because it lacks mammalian predators such as coyotes, bobcats and foxes.
Still, the predatory hawks that used to feed on those birds haven’t returned this year, Moore said, attributing their absence to avian flu. So even if the coyote does remain on the island and start hunting, he thinks it’s unlikely to affect the local bird population too much. “My hope is that he gets better and is able to feed himself.”
He wonders whether the coyote may establish a pack like the one that swam to Angel Island, which was either pregnant when it made the trip or called across the bay until a mate joined it.
Scientists pointed out that Alcatraz is much smaller than Angel Island — 22 acres versus 740 — and said it’s unclear whether a coyote pack would take root in such a tiny territory. Even if it did, it’s unlikely that it would be a stable population, Furnas said. The genetics of the Angel Island coyotes, for instance, show a lot of inbreeding, and there’s always a risk that, due to either a lack of genetic diversity or a random event, the small population could go extinct.
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