"We're waiting to hear back from them," the center's Las Vegas-based conservation advocate, Rob Mrowka, said Tuesday about the group's notice of intent to sue.

The notice gives the federal wildlife agency 60 days to respond.

"The preferred alternative would be to come up with a negotiated agreement," said Mrowka, an ecologist.

He said the center fears that the toad's existence is threatened by a number of factors, including wild burros that graze in the marshes, off-road vehicles and tapping groundwater for future solar business development upstream of the marshes that could reduce surface water the toads need for survival.

A decade ago, The Nature Conservancy in Nevada tried to head off the toad's demise by purchasing key habitats of Torrance Ranch and later Parker Ranch and turning them into sanctuaries for the Amargosa toad, the Oasis Valley speckled dace and migratory birds.

In an effort led by wildlife biologist Jim Moore, The Nature Conservancy helped form the Amargosa Toad Working Group, which brought together state and federal wildlife agencies with biologists, private groups and land owners in nearby Beatty to ensure the toad's continued existence, not just on the ranches, but along the Amargosa River and even ponds at a brothel on the outskirts of town.

But as time went on, the Center for Biological Diversity questioned the effectiveness of the working group because, as Mrowka put it, "the group is under no obligations to come up with any actions."

As a result, the center and Public Employees for Environmental Responsibility petitioned the U.S. Fish and Wildlife Service on Feb. 26, 2008, to protect the Amargosa toad by listing it as a threatened or endangered species.

Since then, the Wildlife Service has missed a 90-day deadline to make a finding on the petition's merit and the 12-month deadline for making a determination on listing.

The lack of action triggered the center to file a notice of intent to sue last week.

Bob Williams, Fish and Wildlife Service supervisor for Nevada, said Tuesday the 90-day finding has been drafted and soon will appear in the Federal Register.

Without revealing what the draft documents concludes, Williams said he disagrees that the working group has been ineffective.

In fact, it has "done a stellar job working with the species," he said.

"This is where the center is on pretty weak footing," he said. "I haven't heard of anything specific in terms of loss of habitat or threat of loss of habitat in the recent past."

Moore, too, said based on the center's claims of potential threats that "a significant portion of that petition really isn't valid anymore."

"The petition is at least two years out of date. As for development in the upper watershed, right now there's no talk of any development in Beatty except for Stagecoach Casino," Moore said.

He said the working group is in discussions with the owner to donate additional riparian habitat to ensure the toad's existence.

He said the toad's numbers have been down somewhat "in the last couple years" because of the drought, but the population count "is nowhere near critical. It's still in the thousands."

According to Williams, the toad's mean population from 1998 through 2007 stood at 5,986 and fluctuated between 3,100 to 8,900. In 2007, Amargosa toads numbered 5,179 and last year's count was within range of the previous nine years.

"There is approximately 8,000 acres of toad habitat, mostly on private land but also on public land. The population of toads at the brothel near Beatty continues to persist and is actively surveyed every year," Williams said.

Contact reporter Keith Rogers at krogers@reviewjournal.com or 702-383-0308.