Unblinking red eyes glide along the silent black surface of the tropical river like faintly glowing embers in the dusk. Hoarse barkings nearby always remind cameraman and biologist Rainer Bergomaz that he is close to one of the biggest living reptiles on earth- the black caiman. Up to seven meters long and more than one ton weight it tops bison or grizzly bear. The black caiman is probably the largest predator of the Americas and definitely the least studied.