"We know for a fact a lot of localized populations have suffered dramatic declines," said Roy Averill-Murray, desert tortoise recovery coordinator for the U.S. Fish and Wildlife Service. "From that, it's probably not too big a leap to think it's probably at least somewhat true across the board."
The long list of threats - urbanization, predators, wildfire, disease - isn't letting up. And that says nothing of the predicted shift toward higher temperatures and less precipitation that could jeopardize the tortoise's food supplies.
"The biggest challenge and unanswered question is the effects of climate change," Averill-Murray said. "That is the wild card for sure."
The agency is proposing to tweak its tortoise recovery plan, mainly by focusing on a more coordinated approach between dozens of state, federal and local agencies that control tortoise habitat.
But some environmentalists complain that the plan is too weak and too vague.
"To me it's a plan that says they're going to do more planning," said Ileene Anderson of the Center for Biological Diversity.
The agency's new proposal, unveiled earlier this month, waters down important measures from a 1994 plan that tried to protect tortoise habitat from disruptions like grazing or off-road vehicle use, she said.
More than $100 million has been spent since 1980 when some of the tortoises in Utah were listed as threatened. In 1990, Mojave tortoises in all their ranges received that designation under the Endangered Species Act.
Desert tortoises spend up to 95 percent of their time in underground burrows, can have shells 15 inches across, bob their heads oddly during courtship and are capable of noises described as hisses, grunts and whoops.
The population is spread over millions of acres, leaving the tortoise vulnerable to a wide variety of threats.
Kristin Berry, a U.S. Geological Survey biologist in California, hasn't seen much success in tortoise recovery in 15 areas that she monitors.
"My study plots in California at least indicate they've continued to plummet and very seriously so," Berry said.
Averill-Murray is pinning some of his recovery hopes on teams scattered throughout the tortoise's range that can identify problems and act on them.
That could mean doing a better job of educating people about keeping off-road vehicles on designated trails and not letting dogs run loose in places where they might snatch up a tortoise, he said.
One of the population's strongholds has long been Red Cliffs Desert Reserve, 97 square miles of protected habitat in southern Utah. But earlier this year, a biologist with the Utah Division of Wildlife Resources said the population there had fallen from 3,200 in 2000 to 1,700 last year - the lowest number since monitoring began there in 1998.
The population has also taken a symbolic hit.
Mojave Max, the Nevada tortoise whose emergence from his burrow was seen as a harbinger of spring each year, died from natural causes in late June. His age was estimated at 65.