In the predawn damp of a Ugandan rain forest nearly 20 years ago, I stared up through the crowded canopy at a party of eight chimpanzees sleeping overhead. Our team of three researchers and two field assistants had woken up an hour before, wiggling into rubber boots and hastily assembling backpacks before setting out on muddy trails by headlamp. Now at our destination, the lights were off, and we stood there silently, submerged in a black ocean of forest, the surface 30 meters above, listening to the chimps chuffing and shifting in their leafy nests.