katja rudolph is interested in their social behavior and health. requires patience and endurance. katja rudolph: i watch three or four hours in the morning, and four hours in the afternoon. four different animals. when they sleep, i just watch them sleeping for an hour and try not to fall asleep myself. reporter: there are still many questions left unanswered about the behavior of lemurs. but how much time is left to find out more? both the forest and its inhabitants are endangered. peter kappeler: it's easily forgotten in this beautiful forest where everything is still intact and natural. but if you go 10 kilometers away in any direction, there's no more forest at all. that's when you realize how endangered all of this is. reporter: this is 10 kilometers away. at a fork in the road, the residents of a nearby village sell their produce. mostly corn, some melons. the forest provides them sustenance, even as they slowly contribute to its destruction. peter kappeler can't fathom the speed at which it's all happening. peter kappeler: two years ago, thi