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29th Annual Meeting and Symposium of the
Desert Tortoise Council, February 20-23, 2004
Abstracts
Preliminary Results of the Desert Tortoise Survey of the Jawbone-Butterbredt Area of Critical Environmental Concern
Kevin Keith1,3, Kristin H. Berry1, James
Weigand2, and Morgan Ruelle3
1U.S. Geological Survey, Western Ecological Research Center,
Moreno Valley, CA
2Bureau of Land Management, Sacramento, CA
3Bureau of Land Management, Ridgecrest Field Office,
Ridgecrest, CA
The Jawbone-Butterbredt Area of Critical Environmental Concern (ACEC) is located in the northwest Mojave Desert, outside of critical habitat for the desert tortoise (Gopherus agassizii). In 2002, a long-term project was established to establish baseline data and monitor status and health of the ecosystem. Objectives for the desert tortoise included: (1) developing a protocol for monitoring tortoise populations on public lands used for off-highway vehicle (OHV) recreation, (2) developing a statistically valid technique for determining distribution and abundance for the species in areas (such as the ACEC) with low to very low densities, (3) determining abundance and distribution of the tortoise and potentially important habitats within the ACEC, and (4) evaluating historical and ongoing anthropogenic uses and their relationships to tortoise abundance. We stratified the ACEC by such attributes as vegetation, topography, and human uses, and then selected 777 one-hectare plots using a systematic random sampling method. Two field biologists searched each plot independently for tortoises and sign and also recorded data on human-related uses. Thirty-six percent of the plots (N = 277) have been surveyed. Live tortoises and sign were found on 25 (9%) in two clusters: a 12 km2 area in the foothills of the Scodie Mountains, and a similar-sized area in and adjacent to Red Rock Canyon State Park. Signs of human disturbance were on every plot. The most common signs were cattle scat (92% of plots), garbage (60% of plots), off-highway vehicle tracks (52% of plots), and bullet casings (47% of plots). Plots with tortoise sign had fewer cattle scat than plots without tortoise sign (ANOVA; F = 13.286, df = 274, P < 0.0005). The survey will be completed in summer of 2004. We thank the California State Off-Highway Vehicle Commission for financial support.
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