San Francisco’s coyotes are going after an unexpected source of prey, new study shows
This story was posted with permission from the author, Amanda Bartlett. It was originally published January 21, 2025 on SFGate, and here is a link to that article.
A coyote is seen atop a sand dune along Crissy Field in San Francisco, with the Golden Gate Bridge in the distance. Photo by Robert Ho
On a brisk Saturday morning in late September, Tali Caspi stood behind an information booth she had just set up on the sandy shoreline of Crissy Field near the East Beach parking lot. It was draped with a black tablecloth and accentuated by a single cardboard sign.
“My PhD is on SF coyotes,” it read. “Ask me anything!”
Caspi wasn’t sure what to expect. But she certainly didn’t think she’d spend the next three hours talking “nonstop” with over 100 San Franciscans who lined up to speak with her about the presence of the urban apex predators in their city and the purported risk they posed to their children and pets.
It had been just over a month since a spate of coyote attacks on dogs had been reported not far from where the growing crowd of locals had gathered. Earlier that summer, a coyote bit a 5-year-old girl who was attending day camp just a few miles away in Golden Gate Park.
Signs posted on the field at St. Mary’s Park in Bernal Heights warn residents of a coyote den in the immediate area. Charles Russo/SFGATE
Some of the residents were frightened. Many of them were angry. And all of them had questions. Was the coyote population skyrocketing? Were they developing a taste for their canine peers? And why didn’t the city relocate the carnivores — or get rid of them entirely?
“It was intense,” Caspi remembered during a recent conversation with SFGATE. “I think people are struggling to understand the ecology of what’s going on, and the individuality of these animals.”
For the past five years, the UC Davis PhD student has been working on a study exploring what the native California species is actually eating, published in the scientific journal Ecosphere on Tuesday. Throughout her research, she’s heard her fair share of misconceptions about the maligned canine, but for the first time, she has the data to debunk them.
What’s on the menu
The study, completed between September 2019 and April 2022, utilizes 707 pieces of scat left behind by over a hundred coyotes across the city. Armed with Google Maps and a fanny pack, Caspi spent countless mornings seeking out and collecting the crucial evidence for her research in manicured golf courses, busy neighborhoods and quiet cemeteries. Back at the lab, Caspi and her team at UC Davis’ Mammalian Ecology and Conservation unit ran the scat through a DNA metabarcoding process and were stunned by what they found.
A coyote is seen on the field at St. Mary’s Park in San Francisco early in the morning, on Friday, Sept. 20, 2024. Charles Russo/SFGATE
The highest overall contributor to coyote diets in San Francisco was anthropogenic, or human-origin, food, which was identified in 78% of the samples collected. The data was most frequently traced back to coyotes dwelling in parts of the city with more manmade land cover, like asphalt and brick. Caspi cited three hotspots in particular — Coit Tower, St. Francis Wood and Bernal Hill — all of which have smaller ratios of green space to dense urban landscape.
“I don’t think people realize the sheer extent of human food that is consumed,” she said. “It surprised me.”
A chart showing the diets of coyotes throughout San Francisco. Tali Caspi/Figure 2a of "Impervious surface cover and number of restaurants shape diet variation in an urban carnivore"/Ecosphere
The breakdown of human food consumed by coyotes included 509 detections of chicken and 250 detections of pig, followed by 32 detections of cattle and 15 detections of salmon and other fish. The findings come with the caveat that Caspi is unable to distinguish the original source of the food — if a sample of chicken is coming from a wayward McNugget tossed out of a car window, scraps left in an unsecured trash can, or a whole rotisserie feast intentionally left out for the wild animals, which she once witnessed firsthand.
“There’s no way to know for certain,” she said. “But it’s a novel behavior, and the reason why we’re focusing on it is because anthropogenic food consumption can presumably exacerbate conflict and have other physiological consequences for the animals.”
The second most commonly eaten food group in San Francisco’s coyotes was small mammals, which were found in 73.8% of the collected samples and include invasive pest species such as black rats, Norway rats and house mice, Interestingly, Caspi was able to link higher rates of consumption of these pest species to territories with more restaurants, specifically the 1-kilometer areas surrounding Coit Tower and North Beach as well as Corona Heights and the bordering Castro, Haight and Mission District neighborhoods. She argued that it demonstrates the “enormous power” people have to manipulate their surroundings in ways that shape individual animals’ foraging behaviors. On one hand, businesses and residences in the area could be more diligent about how they dispose of waste, but on the other, they could look at the ecological service as a benefit.
“If people don’t want coyotes in certain areas, then we need to make sure that we don’t have attractants there for them to use,” she said. “Because they are using them. And they are using them massively.”
A coyote hunts for gophers in the grass of Crissy Field, on Tuesday, Oct. 1, 2024. Inge_Curtis/Daniel Solorzano-Jones/NPS
The rest of the coyote diet breakdown included a 23.6% occurrence of birds, primarily pigeons and ducks, a 22.8% occurrence of medium-sized mammals such as raccoons and skunks, and less than a 1% occurrence of herptiles like slender salamanders and bullfrogs. In the marine mammal category, Caspi found traces of a lone sea lion and a fin whale that washed up on Fort Funston in 2021. But also eye-opening to her were the individual preferences that varied from animal to animal, as was the case with one coyote that had a particular affinity for skunks.
“We can only hypothesize why,” she said with a chuckle. “Maybe it truly did not have a good sense of smell, or some other kind of olfactory dysfunction. But it’s not so crazy to think about. Let’s say you and I are going to an ice cream shop — we’re going to pick different flavors because we have different preferences. Why would we assume that other animals don’t as well?”
The same theory extends to the coyote that went after the small dogs in the Presidio last year. Notably, Caspi’s study is unable to turn up results for domestic canines because the marker she uses to sequence DNA is the same across all canid species. In terms of other pets, she found just 32 detections of domestic cats, which made up 4.5% of all samples, and two domestic guinea pigs, which she thinks may have been let loose in Golden Gate Park.
It’s true that several components may factor into the dietary decisions San Francisco’s coyotes are making, including the hunting and foraging strategies they learn from their parents, as well as the success rate of their own experiences with new sources of prey. While Caspi’s study shows family groups tend to have similar diets, the individual favoring dogs in the Presidio territory was part of a group that ate a greater percentage of small mammals like voles and pocket gophers. This lends evidence to her belief that the choices of one individual do not reflect the entire population.
A coyote is seen on the field at St. Mary’s Park in San Francisco early in the morning, on Friday, Sept. 20, 2024. Photo by Charles Russo
“It wasn’t that all of a sudden all of the coyotes in San Francisco were attacking small dogs. There was one,” she said. “I don’t know why or how it adopted that strategy, but I think the role of research is to try to figure out how these individual differences develop so we can target them before they cause havoc.”
Coyotes in the city
With a population of over 870,000 people, San Francisco is one of the most densely populated cities in the U.S., and also famously has more dogs than children. Sightings of coyotes are not uncommon, and the city regularly enforces closures around denning areas when pupping season is underway. Confrontations with pets can happen, but many of the hundreds of calls made to San Francisco Animal Care and Control are unsubstantiated reports, spokesperson Deb Campbell told SFGATE in September. She referred to one instance last summer when reports of a coyote with a Pomeranian in its mouth in Bernal Heights turned out to be a mom carrying her pups.
The last few months have been “fairly quiet” in terms of human-coyote disturbances, Campbell told SFGATE on Monday, with the late fall and winter season tending to be less active for the agency, but staff are still receiving reports of coyotes rifling through garbage and of people feeding the animals.
Signs posted at the entrance of Baker Beach in San Francisco. NPS GOGA Public Affairs
A myth Caspi hears all too often that could be driving the calls is that San Francisco’s coyote population, which currently sits at around 100 according to Animal Care and Control’s estimates, is rapidly increasing. Not only is that biologically impossible, she said, but it’s also more reflective of human perception than anything else. “There’s been an explosion of coverage, and that makes people more aware,” she said.
Caspi also attributes the pandemic to a change in human behavior as people began to spend more time outdoors and in the city’s parks.
“Just because a lot more people are paying attention and seeing coyotes doesn’t mean there are more coyotes,” she said. “They could be seeing the same individuals.”
As people and coyotes continue to overlap, Caspi also often hears the question of whether the animals belong in the city or if they should be pushed out. It’s an important reminder that they predate European settlement in this part of California and were “here first,” she said. Though coyotes were locally extirpated in the 1920s as a result of killing competitions, bounties and poisoning, new laws were passed that banned state and federal agencies from incentivizing such practices, and they began to make their way back to the city in 2002.
The opportunistic creatures quickly reacclimated and are here to stay. Not only is it illegal to relocate coyotes, per California law, but it’s also ineffective: The animals will try to return to their home territory and either create conflict with other coyotes or die on the journey. If that happens, coyotes can respond to changes in their populations by producing larger litters, Caspi said.
A coyote in the Bernal Heights neighborhood of San Francisco. Jouko van der Kruijssen/Getty Images/Image Source
Yet, she feels San Franciscans are resistant to viewing their city as a broader ecosystem where all of the organisms within it have important roles to play. Coyotes help control nuisance species like rodents, reduce disease transmission, boost bird populations by reducing the numbers of other predators, and provide other services like distributing seeds for a wide variety of plants. The best thing people can do, Caspi said, is accept the reality of their presence and learn how to coexist with them.
She also pointed out that Crissy Field, in particular, is part of National Park Service land and the Golden Gate National Recreation Area, which lists “preserve local biodiversity” among its priorities for wildlife management.
“You wouldn’t have somebody go to [Yellowstone] and get their dog gored by a bison and be like ‘What the heck?’” she said. “My bias is how wonderful that we have these natural places and access to biodiversity in our city. How amazing that San Francisco is a city where all of its residents live within a couple blocks of a public park. But that talking point doesn’t always work as well.”
An urban jungle
Aside from one other 2022 study published on the diets of urban coyotes in New York City, Caspi’s paper is the only one of its kind to utilize DNA metabarcoding to understand what coyotes are eating at population, family group and individual levels. As part of her ongoing research, she plans to compare the diets of coyotes in San Francisco to those in non-urban environments by using stable isotope analysis to detect diet composition from coyote whiskers based on their distinct chemical signatures. She’s also studying how stress levels and thyroid hormones respond to coyote diets. Both are expected to be published in her dissertation when she graduates later this year.
FILE - Coyote at Bernal Heights in San Francisco, Feb. 14, 2016. Frank Schulenburg via Wikicommons CC 4.0
“I think there’s a lot to learn from this species and how much they’ve done to adjust,” she said. “The reality is they live here and we can’t change that. I hope it encourages people, in some ways, to find something to admire about these animals.”
When Caspi set up her information booth last September, something peculiar caught her eye just beyond the swarm of people asking her questions. A man was running by with his AirPods in, while his small off-leash dog trailed along behind him. They passed one of the signs warning of coyotes in the area and disappeared into the fog.
“I also hope people realize that a lot of conflict is preventable,” she said. “And they have the tools to stop it.”
ASSISTANT LOCAL EDITOR
Amanda Bartlett is an award-winning assistant local editor for SFGATE covering culture, history, science and breaking news. Prior to joining the newsroom in 2019, she worked for the Roxie Theater, Noise Pop and Frameline Film Festival. Outside of writing, she has presented repertory movies with Cinema SF and the California Film Institute, and appeared on the Midnight Mass and Western Neighborhoods Project podcasts. She lives in Oakland with her rabbit, Cheeto. Send her an email at amanda.bartlett@sfgate.com.