Black bears in the Californian Sierra Nevada could be more likely to encounter humans as their natural food sources are threatened, according to an article published in the BioMed Central open access journal Animal Biotelemetry.
Researchers used GPS collars to track the movements of black bears in Sequoia National Park while measuring the their natural food levels. They monitored ten bears in 2005, then in 2006, they tagged five of those again, plus an additional five.
By tracking the bears' movements, researchers were able to relate the levels of food available to the bears, to their whereabouts at different times of the year. In summer, movements fell within a predictable range, but in the fall, the bears' movements varied depending on availability of acorns and sugar pine seeds.
In a year when acorn availability was lower during the fall, the bears remained in their summer range to feed on sugar pine seeds. Whereas in a fall season when acorns were plentiful, the bears travelled further outside their summer ranges to reach this food source.
Both of these important food sources are at risk -- sugar pines are vulnerable to white pine blister rust, a fungal pathogen, while oaks are currently at risk from fire exclusion, mule deer predation and potentially a pathogen causing sudden oak death.
The authors extrapolate that if both of these food sources are reduced, bears will travel farther to find the high-calorie foods they need to survive hibernation. This will put bears increasing in contact with humans, and human-bear incidents will likely increase.
mplications of the variable availability of seasonal foods on the home ranges of black bears, Ursus americanus, in the Sierra Nevada of California
Rachel Mazur, A P Klimley and Karen Folger
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