A timeline of the desert tortoise’s slow and steady decline

Because the desert tortoise's Mojave range is largely on federal land, conservationists believe the U.S. Fish and Wildlife Service (USFWS) should have better managed the animal's recovery once it was listed under the Endangered Species Act in 1989. Instead, the species has steadily declined.

1976 Bureau of Land Management establishes 40-square-mile Desert Tortoise Natural Area in Kern County, Calif.

1980 Beaver Dam Slope colony of desert tortoises near St. George, Utah, listed as "threatened" with 26 square miles designated "critical habitat."

1984 BLM tortoise biologist Kristin Berry releases a report showing an up to 90 percent decline in tortoise numbers across the Mojave in the last century. Causes include military bases, housing, roads, off-road vehicles, predators, fire, invasive plants, guns and pet collection.

1989 Fish and Wildlife lists the species as "endangered" after an outbreak of upper respiratory tract disease, caused by a Mycoplasma bacterium, kills more than 600 animals at the Desert Tortoise Natural Area in Kern County.

1990 Entire Mojave population is listed as "threatened." "Incidental take" permits are granted to Clark County, Nev. developers in exchange for mitigation funding through a habitat conservation plan and creation of the Desert Tortoise Conservation Center, a 222-acre Las Vegas holding facility for displaced tortoises.

1991 USFWS opposes expansion of Fort Irwin National Training Center near Barstow, Calif., due to habitat incursion.

1994 USFWS designates 6.4 million acres in Mojave Desert as "critical habitat" for tortoise: 4,750,000 acres in California, 1,220,000 in Nevada, 339,000 in Arizona and 129,000 in Utah, but most types of development are not prohibited. It also releases a recovery plan that discourages relocating tortoises and urges protecting areas throughout the Mojave to preserve genetic diversity.

1996 26,000 BLM acres near the California border are designated as the "Large Scale Translocation Site" for Las Vegas' Desert Tortoise Conservation Center to begin releasing displaced tortoises.

2001 Congress authorizes Fort Irwin's expansion into 87,000 acres of critical habitat.

2003 Fish and Wildlife's 1994 recovery plan is reviewed and scientists who promote translocation and downplay danger of disease are charged with drafting a new plan.

California produces three habitat conservation plans that include 12 million acres in the Mojave to comply with the Endangered Species Act.

2005 The Federal Energy Policy Act calls for 10,000 megawatts of solar, geothermal and wind energy generation on public lands, including much of the Mojave, by 2015.

2008 Fort Irwin moves 571 desert tortoises to 13 sites. California's habitat conservation plans are superseded by a new "Desert Renewable Energy Conservation Plan."

2009 Fish and Wildlife asks the San Diego Zoo to help clean up over-crowding at the Desert Tortoise Conservation Center, with plans to release all of its animals if it's closed.

The desert tortoise species Gopherus agassizii is split into two species. Tortoises east of the Colorado River are now designated Gopherus morafkai. This concentrates 70 percent of the federally protected species, Gopherus agassizii, west of the Colorado in California, where the greatest declines are reported.

2011 Fish and Wildlife and the San Diego Zoo experimentally translocate juvenile tortoises from the Desert Tortoise Conservation Center to the former Nevada Test Site; survival rates will be monitored.

2012 BLM field offices in California circulate the Desert Renewable Energy Conservation Plan. Fish and Wildlife's Desert Tortoise Recovery Office joins San Diego Zoo in starting to translocate adult tortoises onto BLM land near Las Vegas, anticipating the Center's closure in 2014 but promising to monitor recovery for the next five years. Meanwhile, the U.S. Geological Survey's follow-up study of 158 tortoises relocated from Fort Irwin in 2008 shows a five-year survival rate of less than 50 percent.

• Wildlife