Sweat streamed down my back, thorny shrubs cut my arms, and we were losing them again. The wild chimpanzees my colleagues and I had been following for nearly five hours had stopped their grunting, hooting and screeching. Usually these calls helped us follow the animals through Uganda's Kibale Forest. For three large males to quiet abruptly surely meant trouble. Suddenly, as we approached a small clearing, we spotted them standing below a massive fig tree and looking up at a troop of red colobus monkeys eating and playing in the treetop.