Mitigation-driven translocation effects on temperature, condition, growth, and mortality of Mojave desert tortoise (Gopherus agassizii) in the face of solar energy development

Abstract

Given the rapid pace of renewable energy development, there is need to assess impacts of mitigation-driven translocations on sensitive species, including federally protected Mojave desert tortoise (Gopherus agassizii) distributed widely across a global solar energy hotspot. We monitored 215 tortoises over 3years to evaluate translocation effects on temperature, condition, growth, and mortality of tortoises adjacent to the world's largest solar thermal plant located in southern California. On the basis of generalized estimating equation mixed models, maximum daily tortoise temperature increased with environmental temperature then leveled off at highest environmental temperatures for all three groups (translocated, resident, and control) likely due to behavioral thermoregulation. This pattern was consistent among groups, but translocated tortoises had higher average maximum daily temperature and durations above 35°C than resident and control tortoises in the first month post-translocation, with smaller effects in the second and fourth months, and no differences in subsequent years. During the first year, adult translocated males had higher temperatures than females. Average percent changes in body condition and carapace length increased post-translocation for all groups and there were no differences in mortality probability among groups or years. Based on the relatively short-term thermal effects, and lack of negative effects on condition, growth, or mortality, our study suggests relatively minimal impacts following short-distance translocation releases in spring. Our study also serves as a unique example and first step for science-based, mitigation-driven translocations implemented to evaluate and reduce effects of translocation from solar energy development on sensitive species.