SAN FRANCISCO (AP) — A lone coyote stunned biologists and others when it paddled its way to remote Alcatraz Island earlier this year, a former federal prison in the San Francisco Bay surrounded by swift, choppy waters notorious for thwarting prisoners' escapes.

At the time, biologists guessed the coyote swam from San Francisco, which is a little over 1 mile (1.6 kilometers) from the fortress. But it turns out the male coyote actually made an even longer swim from nearby Angel Island, 2 miles (3.2 kilometers) away.

“Our working assumption was that the coyote made the swim from San Francisco because it is a significantly shorter distance. We couldn’t help being impressed by his accomplishment in making it to Alcatraz,” National Park Service wildlife ecologist Bill Merkle said in a news release Monday titled “Alcatraz Coyote Wasn’t a City Boy After All.”

“Coyotes are known to be resilient and adaptable, and he certainly demonstrated those qualities,” he said.

Camilla Fox, founder and executive director of nonprofit Project Coyote, said the coyote likely departed its home base in search of a mate or new territory to defend. She said coyotes, like wolves, do swim, although it's incredibly rare for humans to spot one doing so.

“We have never, ever heard such a story of a coyote making such a long journey in a pretty challenging ocean current,” she said.

Video from early January shows the coyote paddling in the chilly San Francisco Bay and then struggling to get onto the rocky island. It was followed by a Jan. 24 visitor sighting and photographs by Rebecca Husson, who was in town for a cousin's wedding.

She and her family were surprised to spot the coyote on their morning tour of Alcatraz Island.

“He looked like a drowned rat when he ended up on the island, and when we saw him he looked healthy and so beautiful. He looked like he had been eating well,” she told The Associated Press on Tuesday.

Biologists found fresh coyote tracks and scat, which they sent to the University of California, Davis, for DNA analysis. Officials were stunned to learn the swimmer was part of the coyote population on Angel Island.

The park service was prepared to capture and relocate the coyote because of Alcatraz's role as a seabird nesting habitat. But he has never again been spotted or caught on recording devices and there is no evidence the coyote is still on the island.

Alcatraz Island became a federal prison in the 1930s, designed to house the worst criminals, but it closed in the 1960s because its remoteness made it too costly to operate.

Still, 36 men attempted 14 separate escapes from Alcatraz. Nearly all were caught or didn't survive the cold, swift current. In 1973, the island reopened as a park.

Angel Island is a state park that once served as a processing and detention center where Chinese and other unwanted immigrants were kept for a couple of days to months, even as long as two years.

It wasn't easy for coyotes to colonize Angel Island, but they persevered, Fox of Project Coyote said. She asks that visitors to the island and other open spaces be mindful not to disturb coyote families and their dens given that it is currently pup season.