A lone coyote that swam more than a mile across the San Francisco Bay to Alcatraz Island is being monitored by scientists and could be moved if its presence threatens birds on the infamous Californian island.
The canine, called Floyd, appears to be thriving on The Rock - renowned for its abandoned prison - and getting by on an avian diet.
Whether Floyd can stay on Alcatraz depends entirely on how it behaves, says Aidan Moore, a local tour guide who shared footage of the coyote's journey.
Complicating matters, he adds, is that there are no fresh water sources, which could make the animal's welfare dependent on human intervention.
Video footage of Floyd - believed to be a male - hopping onto Alcatraz's rocks was captured by a tourist and shared with Moore.
The gaunt coyote appeared to be shivering from the bay water which is about 10C (50F). But he has plumped up since, says Moore, who is originally from the Cotswolds, in England.
On Saturday, the Golden Gate National Recreation Area (GGNRA) observed and photographed the coyote. The GGNRA confirmed to the BBC that the animal is believed to be the same coyote seen swimming to and coming ashore on the island nearly two weeks earlier.
This coyote is the first documented coyote presence on Alcatraz since the island was transferred to the National Park Service in 1972, the GGNRA said.
Park biologists and staff are actively monitoring the coyote to better understand how it is surviving on the 22-acre (89,030m) island and to assess any potential impacts to the seabird breeding colony, the GGNRA said.
The coyote's presence, it added, does not affect public access to the island, which remains open to visitors.
Alcatraz island - nicknamed the Rock because it was regarded as an impregnable fortress - is home to the shuttered federal penitentiary that housed some of the most dangerous criminals in the US.
It also served as the backdrop of the 1996 action thriller The Rock starring Sean Connery and Nicolas Cage and the 1979 drama Escape from Alcatraz with Clint Eastwood.
Coyotes, the wolf-like creatures that are native to North America, are not uncommon in the San Francisco Bay.
According to Moore, nearby Angel Island has at least 16 coyotes that are thriving there because there's fresh water and bigger prey, such as deer, that they can hunt.
But not so on Alcatraz, part of Golden Gate National Recreation Area, and a registered sanctuary for seabirds, whose sensitive nesting time runs from February through September.
Floyd has to be able to catch enough birds to sustain his dietary needs, Moore says, and suspects that catching them is like shooting fish in a barrel given the thousands of birds there.
Floyd might also be staying hydrated with rain puddles and by water from the gardens on the island, said Janet Kessler, a self-taught naturalist who has been documenting coyote behaviour in San Francisco for about 20 years.
Kessler told the BBC that she suspects Floyd made the journey because he might have felt interspecies territorial pressure in the city and needed to find a new area to call home.
He can't go anywhere. When he gets to a territory, they're going to drive him out of that territory, because that's what coyotes do, Kessler said. That's actually what limits our population. That's their natural population control is their territoriality.
Coyotes could be leaving the mainland because the Bay Area is becoming too crowded, Brett Furnas, a wildlife ecologist with the California Department of Fish and Wildlife, told the Los Angeles Times.
The species was driven out of the city but re-emerged about 25 years ago, he said, since which sightings have increased.
While coyotes are adaptable and natural survivalists, tour guide Moore is worried about Floyd's future and is pushing for human intervention. But finding him might be a challenge as coyotes are masters of disguise, he says.
And the coyote seems to be hiding in areas that are not accessible to the public.
Moore and his colleagues have been trying to spot him on their walks, but instead have only found evidence he is leaving behind, like half-eaten birds. Some of his droppings have been collected and are undergoing DNA testing to get a better sense of Floyd's origins, he says.
Whether he will stay or go appears to be dependent on his behaviour too, and the tourists visiting the island.
Project Coyote, a North American organization focusing on science-based education around the animals and coexistence, is concerned that the barrage of visitors to Alcatraz could pose safety risks for both the animal and tourists.
Most conflicts with coyotes stem from humans either intentionally or unintentionally feeding them, says Project Coyote founder Camilla Fox.
Coyotes are incredibly resourceful and able to coexist with coyotes even in the most densely populated urban environments, Fox told the BBC. So if not harassed, we believe this coyote could survive on the island- though it could be a lonely existence without a mate.
We hope whatever decision is made by the National Park Service, this coyote will have an opportunity to thrive and flourish.
Kessler, the naturalist, believes this coyote might leave the island at some point because it's too small of a territory.
This is new to everybody. We're all going to be watching and seeing what this coyote does, Kessler said. I would assume, at some point, if he wants to go back, he'll swim.
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