Multiyear monitoring of survival following mitigation-driven translocation of a long-lived threatened reptile.

Translocation is used by managers to mitigate the negative impacts of development on species. Moving individuals to a new location is challenging, and many translocation attempts have failed. Robust, posttranslocation monitoring is therefore important for evaluating effects of translocation on target species. We evaluated the efficacy of a translocation designed to mitigate the effects of a utility-scale solar energy project on the U.S. federally listed Mojave desert tortoise (Gopherus agassizii). The species is a long-lived reptile threatened by a variety of factors, including habitat loss due to renewable energy development in the Mojave Desert and portions of the Colorado Desert in southern California (southwestern United States). We translocated 58 individual tortoises away from the project's construction site and intensively monitored them over 5 years (2012-2017). We monitored these individuals and tortoises located in the translocation release area (resident tortoises; n = 112) and control tortoises (n = 149) in a nearby location. We used our tortoise encounter data and known-fate survival models to estimate annual and cumulative survival. Translocated tortoises in each of 2 size classes (120-160 mm, >160 mm) did not survive at lower rates than resident and control tortoises over the study period. For models with different sets of biotic and abiotic covariates, annual and cumulative estimates of survival were always >0.87 and >0.56, respectively. Larger tortoises tended to have higher survival, but translocated tortoises were not differentially affected by the covariates used to model variation in survival. Based on these findings, our translocation design and study protocols could inform other translocation projects for desert species. Our case study highlights the benefits of combining rigorous scientific monitoring with well-designed, mitigation-driven management actions to reduce the negative effects of development on species of conservation concern.

Monitoreo Multianual de la Supervivencia de un Reptil Longevo en Peligro después de una Reubicación por Mitigación Resumen Los administradores utilizan la reubicación para mitigar los impactos negativos que el desarrollo tiene sobre las especies. El traslado de individuos hacia una nueva ubicación es todo un reto y muchos intentos de reubicación han fallado. Por esto el monitoreo robusto post-reubicación es importante para la evaluación de los efectos de la reubicación sobre las especies. Evaluamos la eficiencia de una reubicación diseñada para mitigar los efectos de un proyecto de energía solar fotovoltaica sobre la tortuga terrestre del desierto de Mojave (Gopherus agassizii), una especie en la lista federal estadunidense de especies en peligro. Los reptiles de esta especie son longevos y se encuentran en peligro por una variedad de factores, incluyendo la pérdida del hábitat por el desarrollo de energías renovables en el desierto de Mojave y en porciones del desierto del Colorado en el sur de California (suroeste de los Estados Unidos). Reubicamos a 58 individuos de esta especie para alejarlos del sitio de construcción del proyecto y los monitoreamos intensivamente durante cinco años (2012 - 2017). Monitoreamos a estos individuos y a las tortugas que ya se encontraban en el sitio de liberación (tortugas residentes; n = 112), así como a un grupo control de tortugas (n = 149) en una ubicación cercana. Usamos nuestros datos de encuentro con tortugas y modelos de supervivencia con destino conocido para estimar la supervivencia anual y acumulativa. Las tortugas reubicadas en cada una de las dos clases de tamaño (120-160 mm, >160 mm) no sobrevivieron a tasas más bajas que las residentes y las del grupo control durante el periodo de estudio. Para los modelos con conjuntos diferentes de co-variados bióticos y abióticos los estimados anuales y acumulativos de supervivencia fueron siempre >0.87 y >0.56, respectivamente. Las tortugas más grandes tendieron a tener una mayor supervivencia, aunque las tortugas reubicadas no se vieron afectadas diferencialmente por los co-variados que se usaron para modelar la variación de la supervivencia. Con base en estos hallazgos, nuestro diseño de reubicación y nuestros protocolos de estudio podrían informar a otros proyectos de reubicación para especies de desierto. Nuestro estudio de caso resalta los beneficios de la combinación del monitoreo científico riguroso con acciones de manejo bien diseñadas y llevadas por la mitigación para reducir los efectos negativos del desarrollo sobre las especies de importancia para la conservación.

Short-Term Space-Use Patterns of Translocated Mojave Desert Tortoise in Southern California.

Increasingly, renewable energy comprises a larger share of global energy production. Across the western United States, public lands are being developed to support renewable energy production. Where there are conflicts with threatened or endangered species, translocation can be used in an attempt to mitigate negative effects. For the threatened Mojave desert tortoise (Gopherus agassizii), we sought to compare habitat- and space-use patterns between short-distance translocated, resident, and control groups. We tested for differences in home range size based on utilization distributions and used linear mixed-effects models to compare space-use intensity, while controlling for demographic and environmental variables. In addition, we examined mean movement distances as well as home range overlap between years and for male and female tortoises in each study group. During the first active season post-translocation, home range size was greater and space-use intensity was lower for translocated tortoises than resident and control groups. These patterns were not present in the second season. In both years, there was no difference in home range size or space-use intensity between control and resident groups. Translocation typically resulted in one active season of questing followed by a second active season characterized by space-use patterns that were indistinguishable from control tortoises. Across both years, the number of times a tortoise was found in a burrow was positively related to greater space-use intensity. Minimizing the time required for translocated tortoises to exhibit patterns similar to non-translocated individuals may have strong implications for conservation by reducing exposure to adverse environmental conditions and predation. With ongoing development, our results can be used to guide future efforts aimed at understanding how translocation strategies influence patterns of animal space use.