Yosemite bears aren't eating as much human food as in decades past
Black bears in Yosemite National Park aren’t snacking as much on human food as they did decades ago, according to new research.
Researchers analyzed samples of bear bones from museums and bear hair collected from the field to determine the ratio of human-to-wild-food that Yosemite bears consumed as far back as 1915.
Not surprisingly, they found that the proportion of human food rose significantly after the park started feeding bears in 1923 to keep the animals away from developed areas.
The bears also took advantage of a park fish hatchery, dipping into hatchery tanks for helpings of non-native trout.
From 1975 to 1985, human food made up about a third of the diet of pilfering bears, according to the study, published in Frontiers in Ecology and the Environment.
It wasn’t until the park received funding to install bear-proof food lockers and to patrol campgrounds for problem bears that the proportion of human food dropped to 13% of their diets.
[University of California, Santa Cruz research fellow Jack] Hopkins teamed with coauthor Paul Koch, a UC Santa Cruz professor of earth sciences, to analyze carbon and nitrogen stable isotopes derived from bone and hair samples from park bears.
The researchers compared samples from bears that ate only wild food, from bears known to forage for human food and from human hair, including some from the Smithsonian Institution.
Thanks in part to the meat and corn-based products that people eat, isotope ratios differ between wild bear food and human food, creating a record of the bears’ culinary habits.
Hopkins "searched far and wide to get the collection of samples we analyzed, and that collection made the study powerful enough to answer the question of how management practices affect bear diets," Koch said.
Vocabulary Focus
ratio n.
the relationship between two groups or amounts that expresses how much bigger one is than the other
pilfer v.
/ˈpɪlfɚ/
to steal things of little value or in small amounts
- He was caught pilfering.
isotope n.
/ˈaɪsəˌtoʊp/
a form of an atom which has a different atomic mass from other forms of the same atom but the same chemical structure
forage v.
to go searching, especially for food
to go around searching for food or other supplies
culinary adj.
connected with cooking, especially as a developed skill or art
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