The lawsuit was filed Tuesday in U.S. District Court by the Hailey, Idaho-based Western Watersheds Project, joined by the Biodiversity Conservation Alliance, Center for Native Ecosystems, Oregon Natural Desert Association and the Sagebrush Sea Campaign.

It's the second lawsuit the groups have filed against the Interior Department agency over North America's smallest rabbit.

The first, filed in 2004, ended in a settlement that required Fish and Wildlife to decide if threats to the tiny bunny warranted a yearlong review that could have led to protection under the Endangered Species Act.

Last year the agency said the petition seeking to protect the pygmy rabbit did not contain enough biological information to warrant a study.

The conservation groups contend the agency decision was ''arbitrary, capricious, and contrary to law.''

Specifically, the conservation groups say the agency ignored scientific evidence that shows pygmy rabbits had suffered a significant reduction in their historical ranges.