A Colorado-based environmental group has gone to court to force the U.S. Fish and Wildlife Service to place the lesser prairie chicken on the federal endangered species list.

WildEarth Guardians filed the lawsuit Wednesday in U.S. District Court in Denver. The lawsuit comes just three weeks after the Kansas Department of Wildlife and Parks turned aside a request to place the bird on the state's endangered species list.

The lawsuit essentially argues that the prairie chicken has been a candidate for listing for so long, there's virtually no other animal that has a higher priority.

The lawsuit also takes aim at Interior Secretary Ken Salazar for failing to do much to protect endangered species, making only one addition to the endangered species list in his term in office.

While the prairie chicken has been waiting in the wings of the endangered species list since 1998, the U.S. Fish and Wildlife Service in December 2008 downgraded the status of the bird, raising its ranking from an 8 to a 2 -- as high as it can go without being listed.

But it has remained in that spot since then, which is at the heart of the lawsuit filed by Guardians, which has objected to its status each year since 2001.

This year, the group filed notice that it intended to sue if there wasn't any movement.

In 1995, Guardians contends, there were 35 species with an equal or lower ranking as the lesser prairie chicken. Ten have either been listed or are under review for listing, the lawsuit states.

Of the remaining 14, only two have advanced to the 2-rating.

"The lesser prairie chicken is currently among the most imperiled species on the candidate species list," according to the lawsuit. "The lesser prairie chicken has waited on the candidate species list for protection longer than most other similarly situated species."

As well, the lawsuit takes issue with claims the bird is precluded from listing because the agency is making "expeditious progress" in adding other threatened and endangered species to the list.

"Since the current administration took office on Jan. 20, 2009, the secretary has listed only one new species in the continental United States under the ESA," the lawsuit goes on. "The southwest region of the FWS, which is responsible for the lesser prairie chicken, has not listed any species since 2005. The secretary currently has approximately 250 species, including the lesser prairie chicken on his candidate species list. At the present rate of progress it may require more than a hundred years for the Secretary to take final listing action on all the species presently on his candidate species list."