Twenty-Fourth Annual Meeting and Symposium of the Desert Tortoise Council, March 5-8, 1999
Abstracts

Experimental translocations of desert tortoises to the Large-Scale Translocation Site (LSTS) near Jean, Nevada began in April of 1997. The objective of the study at the LSTS includes an investigation of the effects that season-of-release have on relocation success; however, within this framework several smaller experiments have taken place. I will discuss the results of an experiment involving regulating the water available to tortoises prior to their release.

Desert tortoises, removed from harm’s way in the Las Vegas Valley, are placed in holding pens at the Desert Tortoise Conservation Center (DTCC) until translocation to the LSTS. Unlike the infrequent and stochastic desert rainfall that tortoises experience upon release, a sprinkler system at the DTCC provides tortoises with water daily. In our translocation experiment half of the experimental tortoises did not receive the usual daily water while in holding pens, thus possibly making them more prepared for conditions they would encounter at the translocation site.

Twenty-eight tortoises with radio transmitters attached were released at the site in April-May 1997. Tortoises were tracked through late fall 1998. Using data on tortoise locations at various times, we were able to analyze tortoise movements. Body mass and carapace measurements were recorded monthly along with a qualitative assessment of general condition.

Six tortoises of the 28 released (21.4%) died in 1997, however, no deaths occurred in 1998. Deaths did not seem to be related to experimental treatments and the mortality rates were comparable to those of both translocated and resident tortoises at a nearby study site. In contrast, tortoise movements away from their release burrows were related to experimental group. Specifically, control group males, those that received water daily while in holding pens, moved farther from their release burrows before settling in an area than did those from the other groups. Total home ranges calculated using the minimum convex polygon method were as large as 7.7 km² in 1997 and 2.7 km² in 1998. The breakdowns of these home ranges as well as an alternative method for calculation will be discussed. Because of frequent rains, which began in late July 1997, tortoises were able to drink and gain body mass. Effects of the pre-release treatment conditions may have been diminished as a result of rain water availability. The results of this study lead to suggestions for future translocations of desert tortoises.