Twenty-Third Annual Meeting and Symposium of the
Desert Tortoise Council, April 3-5, 1998
Abstracts

In 1979, a 7.8 km² study plot was established at the Desert Tortoise Research Natural Area (DTRNA), eastern Kern County, California. The plot was centered on the interpretive center, which was under construction. The plot contains two subplots, a 4.53 km² protected area inside the DTRNA fence and a 3.24 km² unprotected area outside the fence. The entire plot was surveyed in 1979, 1985, 1989, 1993, and 1997 with a 60 day spring survey technique, modified to be a 180-day spring survey to take into account the large size of the plot. Since the study was initiated, the numbers of tortoises registered on the entire plot declined from 593 individuals in 1979 to 77 individuals in 1997. Between 1979 and 1997, densities of all sizes of tortoises declined 90% inside the fence and 94% outside the fence. For adults, the declines were 86% inside the fence and 94% outside the fence. Habitat for the tortoises has continued to decline outside the protected area, while recovery appears to be underway inside the fence. Existing management practices appear to be effective in protecting habitat, but are not effective in protecting individual tortoises or populations. The losses of tortoises both inside and outside the fence are due in large measure to landscape-scale problems (raven predation, disease). In addition, human activities on a local scale contribute to additional sources of mortality outside the fence (vandalism, vehicle kills).