BILLINGS, Mont. - A coalition of environmental and animal rights groups are challenging the federal government's removal of gray wolves in the Northern Rockies from the endangered species list.

They say the estimated 1,500 wolves in Idaho, Montana and Wyoming are too few to ensure the species survival - particularly given that the three states intend to sponsor wolf hunts beginning this fall.

State officials have pledged to keep wolves on the landscape. But they want to let hunters kill possibly hundreds of wolves, in part to reduce conflicts with livestock and big game.

Eleven groups, including the Sierra Club and the Humane Society, notified the Department of Interior Wednesday that they plan to sue the agency in federal court after 60 days. That's a required first step under the Endangered Species Act.