boarman: the increase in raven populations in the desert is the beginning of a vortex. their increase is a symbol of the desert being out of whack. berry: where are the lizards? where are the horny toads? it's not just the tortoise. the tortoise is an indicator of what's going on with the rest of the ecosystem. it's a tragedy because i think we're going to have a hollow desert and we are not going to have the rich flora and fauna that this state once had. henen: across the world, whether it's turtles, tortoises, pandas, tigers, elephants--all of those, the main threat ultimately boils down to humans. narrator: in the southwest, the raven problem has gotten bad enough that the government is now resorting to the selective removal of some offending birds. boarman: they are going to raven nests, under which tortoise shells have been found, and they shoot those ravens so tt it' removing the problem ravens. that sort of approach can reduce pressure on tortoise populations, but it won't reduce raven population levels overall. narrator: the best long-term strategy for controlli