Changing Diets Among Black Bears Reveal Reliance on Human Food

Human food is apparently desirable among some animal species. Black Bears in Yosemite National Park have been found to incessantly search for human food, whether that means traveling far to find it or committing robbery to obtain it.

The diets of black bears were examined by Jack Hopkins and his research team at the University of California, Santa Cruz through the collection of hair samples from bears in Yosemite National Park. They also obtained hair and bone samples of bears from four different time periods to note the changes.

These samples revealed how much of the bears' diets consisted of human food. The research dates all the way back to 1915, which was 25 years after Yosemite National Park opened. Between 1915-1919, the bears' diets consisted of 13% of human food; compared with 27% between 1928-1939; 35% for 1975 to 1985; and back down to 13% for 2001-2007. The study's findings were published in the March issue of Frontiers in Ecology and the Environment.

But why has there been such a fluctuation in the bears' diets?

Hopkins obtained information that revealed the behavior of the bears dating back to the first hair and bone samples. The park reported that bears would break into nearby cars and cabins for human food. Dating back to 1915, the bears were raiding garbage dumps in the park for a short while in search of human food before the park began killing them when they became disruptive. Then in 1923, the park began feeding the bears where the park visitors can see the animals in action. Additionally, between 1927 and 1956 the bears had access to a fish hatchery where they would capture and eat fresh trout. Over these time periods (1923-1975), the percentage of human food in their diets was increasing.

When the last feeding area and fish hatchery were closed, the bears did not give up their search for human food. They were known to travel to campgrounds and hotels to search for it. Because once bears are exposed to human food, they will continue to search for it no matter how scarce it is, Hopkins noted in his study in a news release.

"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," said Hopkins in the same news release.

According to the published study, Hopkins and the researchers used carbon and nitrogen isotopes derived from the tissues of the Black Bears' hair and bone samples in order to determine their dietary habits. Their human food consumption has reverted back to the original all-time low.