PRESS-ENTERPRISE (Riverside, California) 07 September 10 Study: Relocated Fort Irwin tortoise death rates average (David Danelski)
Scientists tracking hundreds of desert tortoises that were moved from Fort Irwin in 2008 have found that a high death rate among the relocated animals was consistent with deaths of tortoises throughout their Mojave Desert range that year.
Drought conditions in 2008 made normal coyotes food sources such as rabbits scarce, so the hungry canines turned to tortoises, according to a paper published last month in the scientific journal Endangered Species Research.
"The coincidence of a widespread and high predation with the translocation was unfortunate," the paper said.
Drought conditions in 2008 made normal coyotes food sources such as rabbits scarce, so the hungry canines turned to tortoises, according to a study.
But no evidence showed that moving the tortoises made them more likely to be attacked, it said.
Desert tortoises, threatened with extinction and protected by the Endangered Species Act, were moved from Fort Irwin to make way for expanded military training. About 25 percent of the relocated animals died; most of those were killed by coyotes.
Roy C. Averill-Murray, a co-author of the paper and U.S. Fish and Wildlife Service desert tortoise recovery coordinator, cautioned that the research does not prove that tortoise relocation efforts are successful. Tortoises live longer than 50 years, and the Fort Irwin tortoises have been tracked for only two years, he said.
While short-term studies show promise, relocating tortoises is still considered experimental, he said.
The research did, however, show that tortoises in areas closer to homes and businesses were more likely to be attacked. Such areas have more coyotes because they have access to food from trash cans and other human sources. Averill-Murray calls the animals "subsidized predators."
The study likely will be used to steer future tortoise relocations away from such areas, Averill-Murray said. Officials also might encourage residents and businesses near tortoise habitat to store garbage in animal-proof containers, he said.
In spring 2008, the Army commissioned a team of biologists to move 571 desert tortoises from an area sought for tank training.
Of those animals, 357 were outfitted with radio transmitters; 89 of those animals died within a year. The death rate of about 25 percent was comparable to the death rates of other tortoises in the area that scientist also were tracking, the study said.
The researchers also found unusually high death rates -- 12.5 to 30.8 percent -- in areas as far away as Nevada and eastern Riverside County in 2008.
Ileene Anderson, a biologist with the Center for Biological Diversity, said the study offers some lessons.
"It shows they moved tortoises during a bad year, and that they moved some of them to areas that had subsidized predators," she said. "So they need to think about that in the future."
Study: Relocated Fort Irwin tortoise death rates average