The US Geological Survey just released a documentary on the Desert Tortoise and the Federal Government's efforts to study its status and factors affecting its survival in the Mojave Desert. The documentary--titled "The Heat is On: Desert Tortoise and Survival"-- notes the importance of the Desert Tortoise to the entire Mojave ecosystem. Although the website is a bit slow (I wish they would post it on youtube!) you can also download the movie file separately or read the transcript at this site here or here. On the second link in the previous sentence there is an option on the right side of the page to download the full movie or transcript.
I've started the full download, but I have only watched the first quarter of it online so far. What I can say so far is that I do appreciate hearing from the field experts working to understand and, ultimately, to save the desert tortoise. Kudos to the USGS for reaching out to the public and trying to educate us about the plight of this species and America's efforts to preserve it for future generations.