California researchers said they analyzed hair and bone samples of Yosemite National Park bears to track the presence of human food in their diets. The researchers, from the University of California, Santa Cruz, said they analyzed chemical isotopes in the hair and bone samples to track changes in the diets of the bears over the years and they found there were major changes following the National Park Service's 1999 push to keep human food out of their mouths of bears. Yosemite has a rich history of bear management practices as a result of shifting goals over the years," said Jack Hopkins, lead author of the paper and a research fellow at UC Santa Cruz. "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." The researchers, writing in the March issue of Frontiers in Ecology and the Environment, said the presence of human food in the diet of bears decreased by about 63 percent following the 1999 push, which involved purchasing bear-resistant storage containers, enforcing their use, hiring extra staff to deal with bear issues and increased education for campground and hotel visitors.