The Secret Lives of Animals Revealed Through Their Poo
Not long ago in South Africa’s Soutpansberg, I watched a line of otherwise fastidious visiting high school students standing at a workbench happily sifting with their fingertips through specimens of excrement. Leopard excrement, to be precise. They were picking out hair, teeth, bones, horns, and claws, the undigested remnants of victims of predatory attacks—to be used in identifying the shifting dietary habits of local leopards.
The yuck factor aside, animal excrement—dung, scat, spoor, feces, poop, crap, or just plain shit—is a topic of enormous importance for biologists and for biodiversity. It is also a source of many bad jokes, as anyone who has performed an owl pellet dissection in high school biology may recall.
But never mind that. Let’s start with the biodiversity, or rather, with the story of the honey locust tree. It produces long leathery seedpods, which look completely unappetizing. But the woolly mammoth and a few other ancient megafauna used to gobble them up, dispersing the seeds in their droppings. Then the megafauna went extinct, and the honey locust would inevitably have followed them—except that humans rediscovered the tree and widely dispersed its seeds (by hand) in cities and suburbs around the country.
Other fruiting plants have been less fortunate, and many are on the path to extinction. New Zealand and Hawaii in particular are full of what botanists call “widow plants” because extinctions have taken away the species they depended on to consume their fruit and defecate their seeds.
This form of partnership is common to a huge variety of plant species, which over the course of their evolution have come to depend on a bat, a bird, a fish, a gorilla, or even a crocodile to perform this vital service of dispersal by defecation. Beyond the coevolutionary richness of the connection between species, all sorts of other biodiversity benefits follow. Among other things, a tree that simply dropped its seeds in place would quickly find itself hemmed in by a monoculture of its own seedlings, all squabbling for resources and room to grow. But plants that can reliably disperse their seeds farther away—by means of some animal’s digestive tract—have more surviving offspring and in habitats that are more diverse. Scat is in short the stuff of life.
For biologists, so is scat analysis. It’s not just a way of picking out victims from a leopard’s woolly turd. Using sophisticated laboratory technologies, Sam Wasser at the University of Washington can measure what certain animals have been eating, how they feel, whether they’re stressed, how many pollutants are sequestered in their flesh, and what reproductive state they’re in. That is, fecal samples can answer the most personal questions imaginable—like a blood test at your annual physical—without the researcher ever having to handle, annoy, or even see the animal. Better still, the animal never has to see the person doing the research.
Finding the scat can be a challenge, particularly when the animals in question are whales at sea. So Wasser’s lab has trained dogs as scat hunters, and one, named Tucker, now rides in the bow of a research boat sniffing out the leavings of Pacific marine mammals. With Tucker’s guidance, Wasser and his fellow researchers have recently used fecal analysis to identify levels of DDT, PCB, and other persistent pollutants in killer whales off the coast of Washington and southern British Columbia. Other research has turned up high levels of pollution from the petroleum industry in caribou living near Alberta’s heavily exploited tar sands.
Scatology’s most impressive achievement so far was the result of a 15-year project to gather elephant dung specimens from across Africa and map the DNA for each location. That enabled law enforcement agents to answer a question that has eluded them for more than 30 years: When they seized contraband ivory, they might be able to determine a tusk’s DNA. But it didn’t tell them where the elephant lived and died. That changed dramatically with an article published in June in the journal ScienceExpress. Wasser and his coauthors looked at 28 large ivory seizures and matched up the DNA of those tusks against the DNA map of elephant dung.
“We can take a seizure from anywhere in Africa and place it to within 300 kilometers of where it was poached,” said Wasser. Africa is huge. The U.S. Lower 48 would fit into it five times over. So being able to trace the crime to an area roughly the distance between Seattle and Portland, Oregon, “shows you the power of the tool.”
The study turned the spotlight on just two areas as the dominant sources of the modern war on elephants: About 90 percent of all contraband savanna elephant ivory came from southeast Tanzania or just across the border in Mozambique. In the case of the forest elephant, about 90 percent came from the so-called Tridom, an area on the border of northern Gabon and the Republic of the Congo, and southeastern Central African Republic. (The latter includes the Dzanga-Sangha Protected Areas, site of a notorious 2013 poaching raid.)
The results put governments in those two areas under intense pressure to admit the scale of the problem. As a result, Tanzania last month arrested a Chinese woman law enforcement agents dubbed the “Queen of Ivory” and a Tanzanian man nicknamed “the Devil.” The arrests so far have not touched corrupt government officials, widely believed to have profited from the poaching. But having hard data enables international agencies to push for change and enforcement agencies to focus their efforts on where the problem is at its worst.
It is a testimony to the considerable importance of poop, which is after all no joke.