White-headed langurs: Why their poop is key to their survival

At the Guangxi Chongzuo White-Headed Langur National Nature Reserve, researchers scour the mountainside daily for monkey droppings – a resource pivotal to protecting this endangered species.

High on limestone cliffs in southern China, yellowish-brown stains mark the nighttime shelters of the white-headed langur. These dark brown patches on the cliff, caused by corrosive substances in the primates' feces, guide scientists to collection sites. What many dismiss as waste has become an irreplaceable conservation tool.

Researchers say that by sequencing the genes found in the feces of white-headed langurs, scientists can analyze the composition of their gut microbiota. This allows them to explore how environmental factors might affect the langurs' health.

Also, by measuring cortisol hormone levels in the feces, scientists can assess the hormonal status of langurs and determine whether the monkeys are under long-term stress.

"Human activities may impact the living environment of white-headed langurs, potentially causing elevated levels of cortisol in their bodies, which leads to chronic stress," said Zhou Chunfang from the College of Life Sciences at Guangxi Normal University.

Previous studies have shown that individuals under prolonged stress tend to scratch their skin more frequently. The resulting skin damage increases the risk of infection from bacteria and parasites, which may negatively affect the overall population of white-headed langurs.

By studying the relationship between cortisol levels and human activity, researchers can provide scientific guidance for setting up buffer zones in tourist areas. In this way, the reserve can create a more favorable living environment for the langurs, improve their reproductive success, and support the recovery of the population of this critically endangered species – one of the rarest monkeys in the world.

Thanks to science-led conservation efforts, the langur population – once critically endangered with just 300 individuals in the 1980s – now thrives with over 1,400 individuals.

(The Communication University of China's Wang Zijian, Li Tingxuan, Gao Yixuan, Deng Jiajun, Zhao Deyu, and Zhao Yujie contributed to this story.)