Study tracks Yosemite black bear food consumption

The Yosemite black bear is a curious, bold and predictable creature. Many of these bears, who have learned since infancy to fulfill their energy requirements through consumption of the vastly diverse and procurable human foods, pose an imminent nuisance to campers and hikers vacationing on the Yosemite grounds.

Jack Hopkins, a research fellow at the University of California, Santa Cruz (UCSC), has composed a rigorous investigation of the changing dietary patterns of the Yosemite bear population over time. He has done so hoping to highlight successful methods in deterring food based human-bear interactions.

With the help of his research, Yosemite management will continue to take successful, preventative measures in encouraging bears to return to their natural diets and to spend less time foraging in visitor areas. Through the installation of bear-resistant food-storage containers and the establishment of a “bear team,” Yosemite continues to see increased visitor compliance regarding food storage in areas that are popular spots for bears to scavenge.

“Yosemite has a rich history of bear-management practices as a result of shifting goals over the years. 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,” Hopkins said.

Hopkins, who once worked as a biologist for Yosemite National park, collaborated with Paul Koch, Dean of UCSC’s Physical Biological Sciences to conduct an isotopic analysis of bear hair samples. To do this, Hopkins set up various baited fur-traps around Yosemite’s campgrounds. In hopes of finding a dead meal to scavenge, bears that were accustomed to entering these areas would leave a patch of hair behind on these traps. Through testing for the levels of human food-derived chemical isotopes existing in the bear hair, the samples Hopkins collected allowed the team to estimate the level of human food in the bears’ diets.

In order to see how consumption patterns changed over time, Hopkins also obtained samples from deceased Yosemite black bears that reside in the park’s museum. Through obtaining data from historical bear fur and current bear fur, Hopkins was one step closer to understanding the bears’ shift in dietary composition in response to Yosemite’s changing preventative measures.

From the years 1915 to 1919, roughly 13 percent of bear diets was derived from human food; from 1928 to 1939, the proportion was 27 percent; from 1975 to 1985 the proportion was 35 percent; and the proportion has slumped back down to 13 percent again for 2001 to 2007, a favorable result.

“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,” Koch said.

The study found that human foods have decreased in bears’ diets in response to Yosemite’s preventative measure, yet Yosemite management still must grapple with the bear-human conflicts arise when these bears seek out human food. Hopkins explained that this issue is ultimately a people problem— humans enter into the the bears’ territory and introduce foods like Nutella and Cheetos, and the black bears respond by using these calorie dense options for themselves.

When these bears investigate a great-smelling situation and get a high calorie reward to boot, they will probably come back. As bears become accustomed to consuming human foods in lieu of grass,  berries, and meats (foods that require a significant amount of energy for the bear to obtain), bears become habituated to human environments, and that’s where the conflict derives.

“The primary concern about bears eating human food is that they may learn to recognize it as an easy way to find a tasty and calorie-rich meal with little effort … we often find humans where we find human food. As a result, it places bears in increasing contact with people. This invariably leads to conflict. Because these bears are wild animals, their behavior isn’t completely predictable. Property damage from bears breaking into cars and houses or cabins often upsets people. And on occasions when bears may be dangerous to humans, it’s the bears who lose out,” said Paul Todd, a UC Davis assistant professor of wildlife biology.

According to Hopkins, if you reduce the availability of human food on the landscape, then you reduce the problems between humans and bears. The key is to prevent bears from ever becoming accustomed to consuming human foods in the first place. To do this, Yosemite visitors must store goodies in the proper food storage containers and take action to keep any human foods out of bears’ reach. Through taking these actions, the number of unwanted human-bear interactions may fall and fewer bears will need to be exterminated as a result.