Bears have been causing an unusual amount of trouble in the area around Yellowstone, raiding cabins, tents, cars and backpacks in search of food. In recent weeks, at least 15 problem bears have been euthanized and more than 30 have been relocated in Wyoming, Montana and Idaho. Bear problems also have been reported in Colorado and Nevada. Biologists point to a variety of causes ranging from people moving into bear habitat and leaving food out to less natural food for bears. Problems with bears typically worsen as fall approaches and the animals hurry to fatten up before hibernating for the winter. But this year, problems have been ongoing. "We've had a very busy summer," said Sam Sheppard, warden captain for Montana Fish, Wildlife and Parks in Bozeman. Around Big Sky, Sheppard said, bears haven't been able to resist part ial ly eaten lunches left in garbage cans, trash bags left in garages and windows left open. One bear climbed through an open window to get to some freshly cut peaches. Three bears have been euthanized in the Big Sky area. "Every single one early on could've been prevented, but they habituated to the point where there was no hope," Sheppard said. Dozens of black and grizzly bears have been moved this summer in Wyoming, mostly in Teton County near Grand Teton National Park. "Every couple of years it seems like we have similar activity," said Mark Bruscino, bear management officer with the Wyoming Game and Fish Department. "I can't put my finger on it exactly, but it's probably a combination of things." Grand Teton rangers have euthanized four black bears and sent two cubs to a zoo. "It's been one of our most busy years as far as humanbear incidents," park spokeswoman Jackie Skaggs said. "A very active year, a very frustrating year." Yellowstone National Park doesn't face the same nearby development pressure as Grand Teton and has had fewer bear problems, said Yellowstone spokesman Al Nash. "We certainly don't have the same urbanization issues as they have," Nash said. On Friday, however, a grizzly injured a bow hunter we s t o f Gardiner, near Yellowstone. Often, younger bears are the ones getting in trouble. But this year, older bears are causing problems, even though older bears usually are capable of finding food in the wild. "That indicates to me that they're nutritionally stressed," Bruscino said.