|HOW DO YOU SAFELY study Melanosuchus niger, an 18-foot-long black caiman that lives deep in the Amazonian rainforest? Brazilian biologist Ronis Da Silveira, 35, swears by five rules: Keep your hands in the boat; watch the tail; don't follow tracks in the grass unless you're prepared to find something; don't talk unless you have to scream; and don't go swimming—ever.
Carnivorous, cold-blooded, and primarily nocturnal, the black caiman is the largest predator in the Amazon and the largest crocodilian in the Western Hemisphere. It can weigh more than 600 pounds, live for a century, and is one of only a dozen or so species capable of preying on humans. And, thanks to a once-lucrative international skin trade, it's also endangered; until recently, little was known about its life in the wild.
All of which explains why Da Silveira motors out onto Lake Mamirauá at 1 a.m. in his wooden skiff, hoping to catch the toothy reptile. When he spots one, he glides to within an arm's reach, uses a bamboo pole to slip a noose around its neck, ties its jaws shut with string ("They can swing their heads like clubs," he says, "and break your shins in half"), binds its legs, and starts taking measurements: weight, length, girth, and age. Then he releases the beast—carefully.
Despite 3,000 captures over 11 years, Da Silveira has suffered no injuries. "But my assistants are terrified," he says."They think I'm trying to capture the devil."