Activist groups have filed a third lawsuit in connection with controversial Colorado Parks and Wildlife research designed to see whether reducing predator numbers could help mule deer numbers.

The latest suit targets the research's primary funding source, the U.S. Fish and Wildlife Service, which authorized more than $3.4 million in federal funding for projects on the Roan Plateau near Rifle and in the Upper Arkansas River Valley. That constituted three-quarters of the money for the work.

The suit was brought last week by the Center for Biological Diversity, the Humane Society of the United States and WildEarth Guardians, which say the Fish and Wildlife Service failed to adequately analyze the impacts of these projects as required by the National Environmental Policy Act.

CPW's research plan includes removing five to 15 mountain lions and 10 to 25 bears a year for three years on about 500 square miles of the Roan Plateau portion of the Piceance Basin over three years. The Upper Arkansas project is focused only on lion reductions, and involves a range of actions covering nine years.

The Piceance project began last year, while CPW planned to start the other one this year. CPW has refused to say how many predators were taken on the Roan Plateau last year under the project.

It has contracted with the federal Wildlife Services agency to remove the predators on the Piceance, while it expects to use a mix of increased public hunting, private contractors and Wildlife Services for the second project. Animals in the Piceance project generally would be captured and killed, although captured families would be relocated.

WildEarth Guardians has sued CPW to try to stop the studies. WildEarth Guardians and the Center for Biological Diversity then sued Wildlife Services over both its involvement in the CPW work and its overall carnivore-killing program in Colorado.

That suit has been suspended after Wildlife Services agreed to complete a revised environmental assessment for its predator management work in Colorado, and to not participate in projects like the two CPW ones until that assessment is done. It's unclear whether the new document will be done in time for CPW to resume its Roan Plateau predator-reduction efforts this spring.

Rather than doing its own environmental assessment, the Fish and Wildlife Service relied on the same Wildlife Services one that activist groups pushed to have revised.

"The same problematic EA is being used twice," said Stuart Wilcox, an attorney with WildEarth Guardians.

Fish and Wildlife Service spokesman Steve Segin said the agency had no comment on the suit.

The agency has agreed to fund about $483,000 of the $644,000 cost of the Roan Plateau project, and $2.95 million of the $3.93 million Upper Arkansas work.

CPW has studied the impacts of oil and gas development in the Piceance Basin, but says the new research is warranted because habitat doesn't appear to be the factor limiting survival rates for young deer.