70 Tortoises Returned To Wild By SD Zoo Emerge From Winter Burrows

SAN DIEGO, CA — Dozens of critically endangered Mojave desert tortoises emerged from their winter burrows Monday after being reintroduced into their native habitat on Edwards Air Force Base in Southern California thanks in part to San Diego Zoo Wildlife Alliance.

The cohort of 70 tortoises was the first in the program to be reintroduced into the wild as a result of a partnership between San Diego Zoo Wildlife Alliance, The Living Desert Zoo and Gardens, Edwards Air Force Base, the U.S. Fish and Wildlife Service and the U.S. Geological Survey. The collaborative effort aims to increase the survival rate of young tortoises.

The tortoises received a combination of an indoor- and outdoor-rearing through the program. Within 24 hours of reentering their native habitat, they constructed new burrows or modified existing burrows for shelter, according to the organizations. Now, six months later, they emerged after winter brumation, a state of deep sleep specific to reptiles.

"We've worked so hard to get here, and we've been through so much together," said Melissa Merrick, associate director of recovery ecology at San Diego Zoo Wildlife Alliance.

"We've had to re-strategize, switch plans, react and adapt to so many emerging situations, and we've all done it successfully to get to this point," Merrick said. "The second group of young headstart tortoises just arrived from The Living Desert and will spend the next six months with us before joining their predecessors in the wild. It’s an exciting time for the program."

Scientists track egg-carrying tortoises, monitor the adult females as they lay eggs in human care and rear the hatchlings for one to two years. The hatchlings are reared indoors at The Living Desert for six months, and then in a protected outdoor environment at Edwards Air Force Base, managed by San Diego Zoo Wildlife Alliance.

By reintroducing the tortoises into native habitat when they are no longer at their most vulnerable, conservationists are giving juvenile tortoises a fighting chance at survival, according to the organizations. Indoor rearing at The Living Desert enables the tortoises to grow to three to five times the size they would at this stage in their native habitat, making them less vulnerable to predation.

Desert tortoise populations have declined by an estimated 90% in the last 20 years. California's Mojave desert tortoise, federally protected in the U.S. since 1989, faces threats including habitat loss and fragmentation, disease, human-subsidized predators, and climate change.

The U.S. Fish and Wildlife Service's evaluation of population trends from 2018 indicates the species is on a path to extinction under current conditions. However, with continued successful efforts to address the threats they face, there is hope this trend can be reversed, according to the organizations.