A new study shows that because mule deer numbers are declining, cattle are the No. 1 item on the menu for wolves in northern California. According to researchers at the University of California-Davis, samples collected from wolf packs during the summers of 2022 and 2023 found 72 percent of wolf scat contained cattle DNA.

“Whether it’s through scavenging or whether it's through depredation, it’s a huge component of the wolves’ diet,” said lead author Tina Saitone, a professor of Cooperative Extension in the UC Davis Agricultural and Resource Economics Department. “Their conservation success is because of livestock producers in the state.”

Researchers found cattle DNA in 86 percent of samples in 2022 and 55 percent in 2023. Scientists say California’s dwindling mule deer population gives wolves few wild ungulate prey options. They also say keeping wolves away from livestock is a daunting task.

“Conservatively, we’re talking about a million acres in our study area and 10,000 cow-calf pairs,” said Saitone. “It’s not as simple as putting up an electric fence on a two-acre pasture or putting cattle in the barn at night.”

One wolf pack killed more than 110 cattle over a seven-month span in 2025 across two California counties 125 to 160 miles northeast of Sacramento. Those depredations cost ranchers and the state millions of dollars, causing the California Department of Fish and Wildlife to euthanize four wolves.

A second UC Davis study showed wolves are a major stressor for cattle. Researchers compared cattle in areas shared by wolves with those in non-wolf areas. They found those close to wolves have stress levels 58 percent higher.

"What this really confirms is that death or depredation is not the only impact here," said Saitone. "Living among wolves for cattle is a chronically stressful experience, and that could ultimately have production-related impacts in both the short and the long term."

Next, researchers want to understand whether elevated stress levels translate into lower conception rates – a concern long raised by ranchers that has not yet been established through direct biological evidence. When breeding cows fail to conceive, it can directly affect a rancher’s bottom line.

"That's their whole purpose,” said Saitone. “These are mother cows that are supposed to be generating calves as a marketable product.”

Read the UC Davis news release here.

About Hunt 2 Conserve

Hunt 2 Conserve is a 501(c)4 nonprofit organization affiliated with the Rocky Mountain Elk Foundation. Its mission is to advance a legacy of hunting and conservation by educating, activating and developing stewards and defenders of these fundamentally American ideals. For more information, go to hunt2conserve.org.

(Photo credit: Tina Saitone/Kenneth Tate/Don Preisler/UC Davis)