Chinese researchers observing wild giant pandas roaming a mountain range in the country’s northwest have discovered the reason why, when temperatures drop, the animals suddenly develop an interest in piles of horse dung, sometimes rubbing it all over their bodies.

The manure contains chemicals that inhibit pandas’ ability to sense cold, giving the animals a greater tolerance for chilly weather, says a new study published Tuesday in the academic journal Proceedings of the National Academy of Sciences.

The team of Chinese researchers studied wild pandas in the Qinling mountains, an area in Shaanxi province where horses are still used for transport. Using infrared cameras, they captured 38 instances of male and female pandas engaging in what they call “horse manure rolling behavior,” which ranges from careful sniffing to minutes-long sessions where the animals cover their bodies with the equine droppings.

The pandas were almost exclusively interested in horse dung that had been excreted within the last 10 days because, the researchers found, it is richer in two types of chemicals naturally found in plants: BCP and BCPO. Tests with pandas in the Beijing Zoo confirmed the chemicals’ attractiveness to the animals.

Another clue to why pandas like horse dung has to do with the cold temperatures: They mostly display the behavior when the mercury falls below 15 degrees Celsius. Lab tests showed that mice with BCP/BCPO applied to their paws had a much higher cold tolerance, too. Lead researcher Wei Fuwen told Sixth Tone that the temperature-regulating receptors affected by the chemicals in fresh horse manure are found in all kinds of mammals, including humans.

Wei said that there might yet be other reasons why giant pandas like an occasional frolic in some feces. “Although temperature regulation serves as one possible explanation for the giant panda’s dung-rubbing behavior, this may not be the only explanation,” he said.

Editor: Kevin Schoenmakers.

(Header image: A wild panda in Foping, Shaanxi province. Courtesy of Wei Fuwen)