We Now Know Why Bearcats Smell Like Buttered Popcorn

Nature has produced some delightfully clever mimics, from orchids that dress like fuzzy bees to slow lorises that pretend to be cobras. These knockoffs are sophisticated, but they make sense; the orchids' ruse gets them pollinated, and a cobra costume will help a slow loris live another day. Then there's the binturong, which marks its territory with a scent that bears an uncanny resemblance to the aroma of buttered popcorn. This fact has historically delighted trivia buffs, but left researchers scratching their heads. Now, scientists say they've at least found out how—if not why—the backsides of these animals smell like movie theaters. Their research was published in the journal The Science of Nature.

The binturong (Arctictis binturong), also known as the bearcat, is a clever member of the viverrid family. These sturdy critters make their homes in the forests of South and Southeast Asia, where they can reach more than 3 feet long. When marking their territory, binturongs spray urine on the terrain, as well as on their feet and tails. Then, they use their pee-soggy tails like brushes, painting popcorn-scented markings on every tree they come across.

Scientists had previously attempted—and failed—to identify the chemical components producing the bearcats' buttery calling card. Evolutionary anthropologist Christine Drea and her colleagues decided to try again. They collected urine samples from 33 captive bearcats (13 females and 20 males) at a North Carolina wildlife sanctuary. They then examined the urine samples using a technique called gas chromatography, which can identify and measure the individual chemicals in any given sample.

The bearcats' pee contained 29 different chemicals, but each animal's urine sample was unique. Only one compound appeared in all the samples: 2-acetyl-1-pyrroline, or 2-AP—which just so happens to be the chemical responsible for the smell of buttered popcorn. That is, binturong pee doesn't just smell like buttered popcorn; it smells exactly like buttered popcorn.

But finding 2-AP just raised more questions. In addition to popcorn, the compound is also a part of the aromas of cooked rice and toasted bread. Notice anything funny about those three smells? They all involve cooking.

"If you were to make this compound, you would have to use temperatures above what most animals can achieve physiologically," Drea said. "How does this animal make a cooking smell, but without cooking?"

The researchers became concerned that the 2-AP was not a binturong chemical at all, but the product of the cooked and processed Iams Chunks kibble the captive bearcats were fed. But sampling the chow revealed no trace of 2-AP.

The scientists' best guess is that the bearcats aren't actually producing cooked chemicals at all—their bacteria are. Previous studies have shown that a common bacterium called Bacillus cereus can use fermentation to make 2-AP.