FORT COLLINS — The gate is open, at last, and 10 bison that have spent the past 11 days in a wooden corral the size of a high school gymnasium are free to leave. But they're not moving. Ten charter bus-loads of spectators stand a hundred yards back behind a yellow rope in Larimer County's Soapstone Prairie Natural Area, a healthy breeze whipping hair in their faces and setting the knee-high grass aquiver.