Winter behavior of desert tortoises in southcentral Nevada

We studied the activity patterns of desert tortoises (Gopherus agassizii) during 4 winters at Yucca Mountain, Nevada, to evaluate methods for protecting tortoises during winter construction activities. Adult males tended to enter and exit hibernacula later than adult females, and juveniles exited hibernacula earlier than other tortoises. Ninety-eight percent of all tortoises entered hibernacula by 15 November, and 98% of tortoises were still in their hibernacula on 15 February. We found tortoises in burrows during 4,102 of 4,119 observations (99.6%) from 15 November to 15 February. About half of the observations of tortoises out of burrows during that period were animals that were handled or otherwise disturbed. Because most tortoises remained inactive, we recommend that daily monitoring of construction equipment and daily searches of sites being cleared of vegetation, excavated, or similarly disturbed are unnecessary in southcentral Nevada from 15 November to 15 February, if sites are thoroughly searched for tortoises during that period, and all tortoises potentially trapped in burrows or otherwise injured are moved to safe, undisturbed areas. To avoid causing tortoises to become active, we also recommend that tortoises be disturbed as little as possible during winter surveys.