The Marine Corps is gearing up to airlift 1,185 desert tortoises from prospective combat training grounds to nearby terrain where they won’t be crushed by military equipment.

One of the largest translocations of tortoises ever to be undertaken is expected to launch this month as mitigation for congressional approval to expand the Marine Corps’ Air Ground Combat Center by about 165 square miles, much of it prime habitat.

But there is concern that the $50-million effort will hasten the disappearance of federally threatened tortoises in California’s drought-stricken Mojave Desert, where the number of breeding adults has fallen by about 50% over the last decade, according to a recent survey by federal biologists.

The region saw similar declines of adult tortoises from the 1970s to the 1990s. Studies of tortoise carcasses at the time revealed many causes of death: trampling by livestock, crushing by vehicles and diseases introduced by pet tortoises released into the wild. A large percentage of animals were shot.