DURANGO — At night, the 225-pound bear B27 crisscrosses Durango, foraging in alleys, raking her claws through fruit trees, devouring apples and plums. Dozing high in a spruce tree by day, B27 evades detection. State workers at the fish hatchery she passes regularly say they haven’t seen any bear. At the public library in the middle of B27’s urban hangout, supervisors said there’s been no bear sighting for a year. The only clue B27 leaves as she shambles about — other than hourly signals from a black leather radio tracking collar — is heaps of scat. “It is amazing to me that, given all the time she spends in town — she is a big bear — she’s never gotten into significant trouble that has resulted in efforts to trap and remove her,” said Colorado Parks and Wildlife researcher Heather Johnson, who tracks B27 as part of an unprecedented five-year project driven by rising bear-human conflicts. B27 reflects the rise of a new class of city bears — 15 to 20 percent of those tracked — that researchers find to be highly adapted to urban terrain and eat human food even when natural food is abundant.