BILLINGS, Mont. (AP) — Yellowstone National Park's chief scientist says seven gray wolves that were collared for research purposes have been shot by hunters in Montana, Idaho and Wyoming. Yellowstone Center for Resources Chief Dave Hallac said Thursday there's been no indication any wolves were taken illegally. He says two were from packs that no longer spend most of their time in the park. Wildlife advocates say the killings underscore the need for a buffer zone around Yellowstone with limits on wolf hunting and trapping. Otherwise, they warn the number of dead park wolves will quickly climb once Montana's trapping season begins next month.  Hallec says the number killed so far does not threaten the park's population of 85-100 wolves. The animals were removed from the endangered species list last year by Congress.