Yosemite National Park's Bears are Eating Less Human Food, But It's Still a Cause for Concern

A proactive effort to lessen the amount of human food that black bears in Yosemite National Park have access to has been effective, but once bears get a taste of human treats they will always continue to seek them, according to new research.

Writing in the journal Frontiers in Ecology and the Environment, lead study author Jack Hopkins, a research fellow at University of California, Santa Cruz, reports that bears' diets have changed in the years since new management strategies have gone into effect; bears are eating less human food overall, even though to number of visitors to the park has significantly increased in the last century.

"What we found was that the diets of bears changed dramatically after 1999, when the park got funding to implement a proactive management strategy to keep human food off the landscape," said Hopkins, who collaborated with UC Santa Cruz Earth sciences professor Paul Koch to determine what the bears are eating via an isotopic analysis of hair and bone samples. Hair samples were obtained from bears in the park by using wire snares to capture bits of hair, bone samples were obtained from museum specimens.

"This study shows the power of using museum specimens and archived historical material to reconstruct the ecology of a species and to answer pressing management questions," Koch said. "The remarkable thing is that the bears that eat human food are now back to the same level of dumpster diving as in 1915, despite the fact that there are now millions of visitors in Yosemite every year and presumably a lot more garbage."

The researchers found that the proportion of human food in the bears' diets has decreased 63 percent since 1999. They noted, however, that once a bear gets a taste for human food, it will seek it out. This was easier for the bears several decades ago, when regulations were lax and bears learned that they could easily rummage through human camp sites to find easy meals.

At its peak, Yosemite bears' diets contained 35 percent human food between 1975-1985. Upon the introduction of new management practices and the installation of bear-proof waste bins and food storage containers, that percentage has fallen to 13 percent, the researchers learned.

In order to keep from eliminating nuisance bears, Yosemite wildlife managers should continue their efforts to prevent bears from becoming conditioned to eat human food, the researchers contend.

"People like to see bears, and they don't like to hear about bears being killed. But the bears they often see in visitor-use areas like Yosemite Valley are the ones that are conditioned to eat human food, and those are the ones that become problems and have to be killed," Hopkins said.