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.
To do this, he recruited young scientists. Winnie Kiiru had just finished grad school in biology and returned to her native Kenya. She was told to tie a piece of twine around her waist and walk through the forest in a straight line, with the twine trailing behind.
"And you'd walk in a straight line. It didn't matter whether there was a river, a ravine, stinging nettles, buffalo, whatever. You just kept going," Kiiru says.
Just to the north and just to the south of her were other young scientists also trailing their twine through the brush, literally slicing the forest into samples. What Kiiru and the others were counting was not elephants they move around a lot and tend to hide but rather, a different kind of evidence: poop.
The poop serves as a kind of clock, a way of tracking the elephants in space and time. It allowed Barnes to build a model of elephants' numbers and movement through the forest.
"You'd then ... figure out how old the dung pile was. So if it is completely fresh you'd give it an A. If it was slightly more decayed then you'd give it a B. You'd give it a C if you could actually see the dung beetles already because dung beetles ... spread out the dung, so you'd see this one maybe has been there a little longer. So we graded the dung piles according to age," Kiiru says.
It wasn't only age but also other factors, like how much sunlight was there that could be making the dung decay faster or how much vegetation might be hiding other dung on the forest floor she couldn't see.
"It was so exciting because here were these huge animals a lot of times you would walk through the forest, you didn't see them. You smelled them, but you didn't see them, and yet, you were so powerful you could actually count them or get a sense of how many they are," Kiiru says.
Think how exciting this was: Scientists since the time of Anton van Leeuwenhoek in the 17th century have been looking into lenses to gaze at microscopic organisms. And yet up until this moment near the end of the 20th century, something as proverbially unmissable as an elephant was for all intents and purposes invisible in its natural habitat.
"In the forest you don't see them," Kiiru says. But counting the poop, they weren't so invisible.
"You knew they were there. Sometimes the dung was steaming! You knew that the elephant that dropped that poop was not very far," she says.
Kiiru is no longer walking through the forest, but other young scientists are. And those surveys have found that just in the past decade, 62 percent of Africa's forest elephants have died. Kiiru is now a doctor of biology and director of the group Conservation Kenya, trying to save those that are left. But she still gets goose bumps remembering her days as poll-taker in the forest.
"Sometimes you are walking through these really thick forests and you know what? You step one step out, and you're in this beautiful gladelike Sound of Music type of thing, and you're like, you have to stop and dance," she says.