JACKSON - Conflicting scientific reports could play a role in a lawsuit challenging the supplemental winter feeding of elk on the National Elk Refuge.

One report concludes that ending feeding could cause elk numbers to decline by more than half. Another report says that even without feeding, the greater Jackson area is capable of supporting at least as many elk as there are now.

Five environmental groups filed suit June 4, saying the U.S. Fish and Wildlife Service has turned the refuge into a breeding ground for diseases harmful to wildlife and livestock. The lawsuit challenges a 2007 management plan that continued supplemental feeding on the refuge to help elk survive the winter.

Under the plan, wildlife managers hope to reduce the number of elk that spend the winter on the refuge by 1,000-2,000 animals to around 5,000 animals.

Feeding supporters with the group Sportsmen for Fish and Wildlife point to a paper by retired biologist Garvice Roby, who spent 20 years studying Jackson Hole elk. Roby's report concluded that ending supplemental feeding would cause at least a 57 percent reduction in current elk numbers, which last winter topped 12,000 animals.

About two-thirds of those elk spent the winter on the refuge.

A Sportsmen for Fish and Wildlife summary of the Roby report said that ending supplemental feeding would cause elk as well as bison to seek forage on private land also used by cattle.

"Large scale brucellosis transmission will be inevitable," the summary said.

Authors of the refuge plan relied heavily on studies by N. Thompson Hobbs, an ecology professor at Colorado State University, who concluded that the Jackson elk herd could sustain 9,300-11,000 animals without supplemental feeding.

But the report also predicted that drought followed by deep snow could result in "high mortality of elk" without supplemental feeding.

The Greater Yellowstone Coalition, meanwhile, has released a study of forage availability in the Gros Ventre drainage. Conservation groups say elk don't use that area as much as they could, although in the past more than 4,500 elk have spent winters there.

The report concluded that between 4,419 and 6,628 elk can survive the winter without supplemental feeding in the Gros Ventre drainage. That doesn't include remaining winter range in Jackson Hole, including the elk refuge.

"By phasing out elk feeding in this region, we can capitalize on the natural bounty that exists, essentially for free, which ensures healthy wildlife and healthy habitat," said Lloyd Dorsey, a Greater Yellowstone Coalition representative who wrote the report.

"The climate is a Rocky Mountain climate, but let's not forget these are Rocky Mountain elk," Dorsey said. "All other states in this region, from Colorado through the Canadian Rockies, have bountiful herds of elk and other big game without feeding."

The Greater Yellowstone Coalition is one of the groups suing. The other groups in the lawsuit are Defenders of Wildlife, the Jackson Hole Conservation Alliance, National Wildlife Refuge Association and the Wyoming Outdoor Council.