Why do animals eat their own poop—and other animals’ too?
This natural survival strategy, known as coprophagy, reveals how wildlife makes the most of every available resource.
While poop is decidedly not on the menu for us humans, it’s a normal food for many animals.
Scientists have observed deer snacking on Asian elephant dung, dogs and lemurs consuming human poop, and salamanders eating bat droppings. In Spain’s Sierra de Guara mountains, female goats snack on bird guano, while in Brazil’s Atlantic Forest, rats and opossums visit otter latrines to consume feces.
In one study in Tanzania, scientists remarked that hooded vultures showed more interest in protein-rich lion feces than a freshly killed carcass: “The lion had not gone more than 10 meters from the feces when several hooded vultures dropped to the ground and swallowed the feces rapidly,” they wrote.
So why is the act of eating feces, called coprophagy, so widespread? Far from a useless waste material, feces often contain valuable calories and nutrients that weren’t taken up by the host animal. (Read more about the fascinating ways animals use poop.)
Coprophagy may help animals get extra calories when their usual food sources are limited, or acquire nutrients that are hard to come by in their regular diet. Poop might also contain gut bacteria that give digestive systems a boost, kind of like a wild probiotic.
“Feces can have lots of diverse roles” for wildlife, says Hannah Rempel, an ecologist at the University of Texas at Austin.
“Even though this behavior might seem gross to us, clearly it’s a really important thing for them.”
A nutritional boost—from poop
Coprophagy can also mean eating your own poop. Various species of rabbits and hares digest their food again to extract further nutrients that their swift digestive process missed the first time.
When food is scarce, some species, like reindeer in Svalbard, Norway, feed on goose droppings during the short Arctic summer. In winter, plateau pikas in Tibet eat the dung of domestic yaks.
It's likely for similar reasons that red foxes in Scotland’s Cairngorms National Park frequently consume the feces of dogs walked in the area, as evidenced by the presence of dog DNA in fox scats, says ecologist Xavier Lambin of Aberdeen University in the U.K. He and his colleagues’ research shows that fox feces are especially abundant in dog DNA in years when foxes’ usual prey—field voles—are scarce.
Laboratory analysis reveal that dog poop is very nutritious, with a similar calorie content to cooked chickpeas.
“Instead of having years of starvation and years of plenty, [foxes] must be all right every year,” Lambin says.
Vitamin sea
While diving through coral reefs around Bonaire, Rempel saw surgeonfish and parrotfish darting toward fecal pellets drifting down from large schools of brown chromis fish, a behavior previously observed on some Indo-Pacific reefs.
“I have seen two fish fight for the same feces,” Rempel recalls. She and her colleagues counted that almost 85 percent of the observed brown chromis fecal pellets were eaten by fishes, the vast majority of them by parrotfishes and surgeonfishes.
Surgeonfish and parrotfish usually graze on algae, which are relatively poor in micronutrients vital to survival, such as calcium, phosphorus, and zinc. Algae is also low in protein, though the fish do also consume some protein-containing cyanobacteria and detritus attached to algae.
But brown chromis fish, which eat plankton, produce feces chock full of protein—as well as micronutrients.
Rempel likens these pellets to a kind of nutritional supplement—or “vitamin sea”—for the fish, Rempel explains.
A diverse gut is a happy gut
Barbara Drigo, a microbial ecologist at the University of South Australia, suspects that for many bird species, coprophagy also provides beneficial gut bacteria. The logic is similar to fecal transplants in people, in which bacteria-containing stool extracts from healthy people improve the gut flora in those with certain health conditions.
Drigo believes that some migratory bird species, once they arrive in a new area, may consume the droppings of local birds to acquire gut bacteria that help them more effectively digest food from their new environment.
Young Eurasian coot chicks frequently consume their parents’ poop, which may similarly provide them with bacteria needed for processing local food resources.
And in experiments with captive ostrich chicks at a research facility in South Africa, the birds given their parents' feces to eat had more diverse gut flora and matured faster than in chicks raised without feces. At eight weeks of age, the feces-fed chicks were nearly 10 percent heavier and were less likely to die from gut disease.
Exposing the immune system to a rich diversity of gut bacteria is beneficial for health, Drigo says. In general, “the birds that practice coprophagy are much more healthy than the birds that don’t."
Pros and cons
Coprophagy, however, comes with risks. Bird droppings, for instance, may contain dangerous chemicals from sewage, pesticides, or other human-made harmful compounds.
Eating poop could also cause animals to pick up diseases, gut parasites, or harmful bacteria.
But, at least when it comes to natural threats, the benefits of coprophagy might outweigh the risks for many animals.
Animal digestive systems are likely much tougher and resilient to disease, parasites, and harmful bacteria than human ones. Lambin suggests that perhaps people have evolved to find poop inherently disgusting so we won’t eat it and get sick.
“When a dog sees feces, it doesn’t seem to react as if it smells bad,” he says. “If it's good for you at all, you're not going to deem it distasteful.”
