Restoration of the Bolson tortoise in the northern portion of its prehistoric range in the southwestern U.S.A.

Summary

The Bolson tortoise (Gopherus flavomarginatus), the largest and rarest North American land tortoise, now Vulnerable and reduced to perhaps 1,600-2,000 individuals confined to isolated basins in north-central Mexico, was the subject of a 2006 restoration effort by the Turner Endangered Species Fund aiming to re-establish wild populations within the species' prehistoric range in southern New Mexico, using a captive colony founded from 30 adults acquired from a private collection. Coordinated as the Bolson Tortoise Recovery Project across the Armendaris and Ladder Ranches, the Living Desert Zoo in Carlsbad, and the El Paso Zoo, the breeding program housed adults in a large fenced enclosure feeding on native forage, incubated eggs in temperature-controlled incubators, and raised hatchlings in outdoor predator-proof enclosures; the effort produced over 500 hatchlings and an expanding population of more than 400 juveniles up to eight years old. Starting in fall 2012, 87 transmitter-fitted juveniles judged large enough to resist most predators were released into predator-accessible enclosures for monitoring; by fall 2014, 75 of the 87, over 75%, were confirmed alive, mostly settled within 100 meters of their release point and digging or adopting burrows, with the 11 documented deaths attributed largely to coyote predation. Major difficulties included the tortoise's very slow growth requiring years of protected rearing, labor-intensive forage management, ongoing predation risk after release, and the fact that true success cannot be confirmed until wild-born tortoises reach reproductive age, potentially 40 years or more from project start. The project rates itself successful, citing robust captive reproduction, promising post-release survival, and normal growth and behavior in released juveniles.