This timeline of bison management from the 1960s to the present shows a consistently growing population despite agency removals and hunting outside the park. In the decades since the IBMP was created, the bison population has ranged between 2,400 and 5,500 animals (the IBMP includes a population guideline of about 3,000 animals). There have been no cases of bison transmitting brucellosis directly to cattle, in part due to efforts by federal and state agencies to maintain separation between these animals. The state of Montana now allows bison to occupy some habitat adjacent to the park that was previously off-limits. However, lack of tolerance for wild bison in most areas outside Yellowstone continues to limit the restoration of this iconic species. Large parts of their historic winter ranges are no longer available due to human development, and because states only allow limited numbers of bison in areas near the park.