Coyotes, cars killing desert tortoises moved from Fort Irwin

Government scientists tracking 158 desert tortoises relocated nearly two years ago from the Army’s Fort Irwin in California to make way for military maneuvers say that nearly half of the animals have died, mostly from coyote attacks.

The death rate, disclosed at a scientific symposium last weekend, raises concern about relocating tortoises, a species threatened with extinction.

The success or failure of the effort is important because more relocations are expected as companies develop wind and solar energy on public land in the Mojave Desert. In addition, the Army intends to move as many as 1,200 more to protect them from artillery fire, tanks and other dangers, and has invested millions of dollars in the effort.

The Army has not decided whether to go forward with another round of relocations that had been planned this spring. The military wants to make way for expanded live-fire exercises at Fort Irwin, where troops train in preparation for deployment to the Middle East.

In spring 2008, in a much-publicized undertaking, the Army moved 556 tortoises to public land a few miles from the base. Many of the animals were outfitted with radio transmitters, and three teams of scientists each tracked a group.

Ecologist Tim Gowan and biologist Kristin Berry, both with the U.S. Geological Survey, followed the fates of 158 tortoises outfitted with radio transmitters. Of those, 70 -- 44 percent -- have died; another 20 cannot be located.

The death rates among the other two tortoise groups, one tracked by an Army contractor and the other by a different USGS team, have not been released.

However, Army and U.S. Fish and Wildlife officials said they believe that moving tortoises does not make them more vulnerable to coyotes. Drought conditions during the past two years have made rabbits and other normal prey scarce, so coyotes are eating tortoises, they said.

They also said the tortoises observed by Gowan and Berry were released near the town of Yermo, where coyotes are more active because they are attracted to people’s trash as a food source.

William Boarman, a wildlife biologist under contract to the Army, said the death rate reported by Gowan is “disturbingly high, but it has more do with human activity.”

Roy C. Averill-Murray, the Reno-based desert tortoise recovery coordinator for the U.S. Fish and Wildlife Service, said a study by Boarman and other scientists examining 2008 tortoise deaths in the Fort Irwin area will detail how relocated tortoises are killed at the same rate as resident tortoises.

“The tortoises are getting slammed wherever they are,” Averill-Murray said.

Speaking at the annual Desert Tortoise Council symposium last weekend in Ontario, Gowan reported that of the 70 tortoises he and Berry found dead in 2008 and 2009, only seven had not been attacked by predators. Among the other deaths, two had been crushed by vehicles and one had been bitten by a snake.

Most of the deaths -- 43 of them -- occurred in 2008, the months after the relocation, when the animals were unsettled and walking longer distances, he said.

“The tortoises that are moving around appear more vulnerable to predators,” Gowan said during the presentation.

Females were killed at a higher frequency during the first year, while more males died the second, he said. Fourteen of the dead tortoises, which all had been healthy before the move, had contracted a respiratory disease, although that was not the cause of death.

No one is certain how much the tortoise population has declined, but researchers who have been studying certain communities of the reptiles for decades have seen as much as a 90 percent decline in some places.

The Army has said it may spend as much as $75 million to protect endangered and threatened species found at Fort Irwin. In 2008, the Army estimated the tortoise relocation cost at $8.5 million, including the cost of scientific research on disease and deaths among the animals that were moved and those that already lived in the relocation areas.

Updated figures were not available this week, but based on the 2008 estimate and the number moved and those still to be relocated, the cost works out to about $4,800 per animal moved.