ABSTRACT: To evaluate the feasibility of desert tortoise relocation as a mitigation tool, and relocation as a viable component of habitat conservation plans for the species, a study was designed to assess the effects of relocation on tortoise health and survival.
In 1989, 72 desert tortoises, Gopherus agassizii, were removed from a section (one square mile, 2.59 km²) of habitat in Cantil, California, on the western edge of the Mojave Desert. Tortoises were relocated to a diagonally adjacent section of fenced habitat in the Desert Tortoise Natural Area. Supplemental irrigation was added to half the study site to assess whether the additional water would positively affect the survival and health of both the relocated tortoises and the original resident population of tortoises. Relocated and resident tortoises were studied for three years after the relocation.
Data from the study indicate that the relocated tortoises were less likely to survive than the resident tortoises. The negative impact on survival was most pronounced in the first year after the relocation. That year was the driest year of the study and was the last year of an extended drought throughout the area. The survival of tortoises improved in the irrigated half of the study site only in this first, driest year. Males had significantly higher survivorship than females, but it was again apparent only in the first year of the study. Results indicate that the survival of the resident population of tortoises was not negatively affected by the addition of new tortoises onto their range.