Mitigating Impacts of Solar Energy Development on Desert Tortoises - Indoor Rearing and Release of Head-Started Desert Tortoises

The Mojave desert tortoise (Gopherus agassizii) is a special-status species whose preservation often conflicts with land use in California’s deserts. This is especially true given the rapid rise of utility-scale solar energy development in the southwestern deserts to meet targets for renewable energy production. Current laws and policies require that negative impacts to protected species like the desert tortoise be either minimized or offset by mitigation actions. Research is needed to identify the most effective mitigation tools for the desert tortoise as well as aid its recovery and streamline future permitting for renewable energy development.

Researchers from the University of California, Davis, and the University of Georgia Savannah River Ecology Laboratory released juvenile desert tortoises reared in captivity using different husbandry methods (head-starting) and for different durations to evaluate the potential value and role of indoor rearing as a way to increase the effectiveness of tortoise head-starting. Results showed that post-release tortoise survival increased with the size of the tortoises when released, regardless of whether they were reared exclusively outdoors or through a combination of indoor and outdoor rearing. Incorporating an indoor-rearing component greatly reduced the time required to produce large juveniles of releasable size with no observed negative effects on either survival or post-release movement behaviors. The observed combination of high survival and high site fidelity increases the likelihood that released tortoises would be recruited into target populations that need recovery.

By shortening the captivity period, indoor head-starting can dramatically reduce the costs of rearing tortoises and increase production of tortoises from head-starting facilities. These improvements facilitate wider implementation of head-starting as a recovery tool for desert tortoises. Implementing more cost-effective recovery actions such as indoor head-starting will also aid mitigations for solar energy development and should increase the probability of delisting the desert tortoise as a special-status species in the future.