The federal government decided this week against protecting the desert tortoise that lives in the Sonoran Desert, although it agrees with environmentalists that it deserves federal protection.

The U.S. Fish and Wildlife Service classified the tortoise Tuesday as "warranted but precluded." That means other imperiled species nationally are of higher priority to the service for listing than desert tortoises living in Arizona and northwestern Mexico.

The Sonoran Desert tortoise will join about 250 other imperiled species on the candidate list. Those are species that the service considers to be in trouble but not in serious enough trouble to make the lists of endangered or threatened species. Species can stay on that list for years while the service weighs their status.

A key reason for the latest decision was that the Wildlife Service bases such decisions on how immediate the threats are to a species, said Steve Spangle, a service field supervisor in Phoenix. That's because of limited finances, service officials say.

"A species more vulnerable to short-term, irreversible losses gets priority over those that are in not as urgent a need for protection," Spangle said.

A Tucson environmentalist said such attitudes amount to waiting for a species to reach the edge of a cliff.

"It would be better to eliminate the threats that are taking tortoises down now, rather than wait for wholesale destruction to take whatever is left," said Greta Anderson, Arizona director of the Western Watersheds Project, one of two environmental groups that petitioned the service in 2008 to list the Sonoran tortoise. The other group is Wild Earth Guardians.

Phil Rosen, a Tucson reptile specialist, said he was surprised that the service thought the tortoise deserved listing. He personally thought this issue was a "tossup," because not all of the evidence needed to support listing was in.

Now, the Wildlife Service will try to re-energize a desert-tortoise team, formed by a group of government agencies, to get it moving on voluntary steps to protect tortoises, Spangle said. Such steps could include saving open space and halting the spread of non-native grasses, he said.

In a Federal Register notice about the decision, the U.S. Fish and Wildlife Service listed seven major threats to the Sonoran tortoise. At the top was the invasion of the desert by non-native grasses such as buffelgrass that can trigger uncontrolled desert wildfires.

Others include:

• Subdivisions, road-building and other development related activity tied to population growth.

• Increasing use of off-road vehicles in tortoise habitat.

• Harvesting of mesquite and ironwood trees in Mexico.

• Improper livestock grazing in Mexico.

• Undocumented human immigration and enforcement activities aimed at curbing illegal immigration in this country.

The tortoise is also threatened because some government agencies have not adequately addressed many of those threats, the service said. In addition, the tortoise has lost appreciable habitat to urban development, agriculture and roads and other infrastructure.

But there's no evidence that any Sonoran tortoise population is imminently threatened with elimination, the wildlife service said. Because deliberate planting of non-native grasses has stopped in the U.S., unlike Mexico, there's considerably less habitat damage from the non-natives in this country. Plus, the bad economy has slowed growth pressures significantly, the service said.

A scientist for the watersheds project, Michael Connor, said Sonoran tortoises are probably in worse shape today than Mojave tortoises because the Sonorans face more threats and exist in many small, isolated populations. Plus, "there are a lot more Mojave Desert tortoises than Sonoran Desert tortoises," he said.

Contact reporter Tony Davis at or 806-7746. Follow Tony Davis on Twitter at tonydavis987.