FILE: A gull at Leo Carrillo State Park in California. (Antonio Busiello/Getty Images)

Scott Shaffer saw the bird for the first time in the spring of 2018, protecting her eggs next to a rock pile on the rugged Farallon Islands about 26 miles west of San Francisco. It was a good sign for the San Jose State University biology professor, who knew that a nest meant she would reliably return to the same spot. That was ideal for his research monitoring the western gull population on the cluster of islets, home to one of the largest breeding colonies of the species in California. But first, he had to catch her.

Shaffer managed to place the gull in a pillowcase before taking her back to the lab, where he affixed a GPS tracker no larger than the size of a matchbox to the base of her tail. He marked a single dot on her forehead using a Sharpie to make her more easily recognizable. Then, he let her go for about a week before finding her again to retrieve the tag and download the valuable data it held on her declining species' diet, foraging behaviors and habitat use. But when he checked Google Earth to observe her comings and goings, he noticed something strange: She had gone completely off the map.

"I thought, ‘Where the hell did this bird go?'" Shaffer said.

The gull at its nest on the Farallon Islands. (SA Shaffer)

He scrolled and zoomed in, tracing her 80-mile journey that appeared to start at the San Francisco Recology site near Candlestick Point. She went over the Bay Bridge, down Interstate 880 and onto Highway 580 before reaching a composting center in the Central Valley near Modesto. What threw him was her speed, which averaged 60 mph - clearly too fast for her to be flying herself. He soon confirmed she had backup, having hitched a wild ride on an 18-wheel garbage truck and staying overnight before flying back to her colony in the Farallones.

But this was no Pixar movie plot. Shaffer suspected the bird most likely became trapped under the layer of wire mesh lining the top of the truck while foraging for scraps. Yet, even more remarkable was the fact that she repeated the voyage the following day: going to San Francisco Recology to hitchhike down to the same composting facility, this time taking the San Mateo-Hayward Bridge while her mate watched over the nest in her absence.

The findings, published recently in the scientific journal BioOne, mark the first time a western gull has ever been observed embarking on such an adventure. "I have not seen that behavior in any other species that I've studied," Shaffer said.

Gulls on the go

A map shows the gull's journey. (Courtesy of SA Shaffer)

The new discovery is just one piece of the puzzle in the broader research local experts are conducting on western gulls, colloquially known as seagulls, including how they seek out food and when and why they travel. Shaffer has been working with a team of researchers including Megan Cimino, a biological oceanographer and researcher at UC Santa Cruz. Cimino decided the hitchhiking gull was "so unusual" that the bird warranted her own paper but said her behavior is demonstrative of just how flexible western gulls can be as a species. They forage at sea and on land to eat a wide variety of food sources, from fish and krill to garlic fries left behind at Oracle Park and chicken scavenged from Fourth of July barbecues. A separate paper Cimino and Shaffer published in 2022 aimed to determine why the gulls spent some years at sea and some on land, and they've tracked as many as 30 individuals per year looking for answers. They found that in the years the gulls spent more time on land, less prey was in the ocean and fewer whales were around.

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"You're probably wondering, ‘What does a whale have to do with any of this?'" Cimino said. "But for birds that aren't capable of diving, there needs to be prey at the surface of the water. When whales like humpbacks breach and lunge feed, they can help make that food more accessible for them."

In another study published last year, Cimino and Shaffer found that some western gulls also had a penchant for hitching rides on boats, though only for brief stints while looking for food nearby - they didn't travel nearly as far as the gull in the garbage truck. The findings raise new questions for the researchers, who are trying to learn more about the relationship between avian species and marine mammals.

A gull stands next to a discarded surgical gown in a trash pit at Recology on April 2, 2021, in San Francisco. (Justin Sullivan/Getty Images)

"We started to think, if gulls forage in association with whales, and they often get hit by boats, maybe gulls can help us understand if there's a high probability of ship strikes in a given area," Cimino said. "They could be a new ecosystem tool to help us understand what's going on."

A ‘big presence'

Shaffer's interest in studying western gulls goes back to the 1990s, when he used to work as a zookeeper at SeaWorld while earning his bachelor's degree at San Diego State University. The species was considered a "constant problem" at the park, he said - the western gulls relentlessly stole food from the guests and the birds he was caring for - but he began to appreciate them for their "big presence" and intelligence.

"They recognize faces," he said, pausing for a moment. "Well, they recognize my face."

Scott Shaffer holds the gull. (Emma Kelsey)

These days, when Shaffer is leading the seabird monitoring program on the Farallones, he uses a rotation of Halloween masks, ranging from a bold Blue Man Group number to a loud Kiss guise, to hide his features. He also has to wear a new change of clothes every time he goes out to their nests to avoid recognition. Nevertheless, he's regularly pecked and barfed on, but he doesn't mind. He just uses it in his research.

"They hit you in the head with their feet," he said. "They s-t all over you. And usually, my hands get pretty cut up by the end of the season. They're a challenge compared to other species, and that's what I like about them. I'm always curious to see what I can learn."

Similar to coyotes, the birds are native to California and have found a way to adapt to increasing urbanization by finding food there. They also have an uncanny ability to navigate vast distances and return to reliable dining options. One gull Shaffer tracked with his students on Alcatraz would regularly fly to a dumpster behind a deli in the Tenderloin, to the Palace of Fine Arts to bathe and then back to the island.

"Once they find food, they have their hotspots and seem to go back," he said.

Recycling collection trucks are parked in a Recology maintenance yard on Seventh Street in San Francisco on Thursday, Aug. 30, 2018. (Getty Images/S.F. Chronicle)

A city-dwelling diet can pose its fair share of risks to gulls, like vehicle collisions, exposure to microplastics or pathogens from bacteria. Though the garbage truck-riding gull's journey seemed to be an accidental one, it's still not clear why the bird returned. Cimino and Shaffer believe it could be a sign of more widespread behavior in the species as a response to climate change and limited prey resources in the ocean.

"I would emphasize that this is an unusual occurrence and you never know what animals are going to do," Cimino said. "But I think it shows why studying gulls is important. They're birds that are considered to be a nuisance if you're having a picnic on the beach but can tell us a lot about the health of our environment right offshore from San Francisco."

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