Imagine you're flying in a two-seater plane over Africa, and, in an effort to see how elephants are faring, your job is to count all the ones you see. Over the savannah, that's easy. But how do you peer into the forests, where all you see is treetops?
For years, the zoologists who tried to do this just guessed. But in the late 1980s, conservationist Richard Barnes devised a method to take an elephant census in the densest of forests.