Bearcats entice mates with popcorn-smelling pee

Binturongs use their roasty, popcorn-like aroma as a calling card to say "this is my turf" and find potential mates. (Credit: Gerald Schneider/Flickr)

Bearcats, also known as binturongs, smell just like buttered popcorn. For many zookeepers, the smell wafting from the binturong enclosure is so striking that they name their resident binturongs after the popular snack.

Solitary animals that rarely come face to face, binturongs use their roasty, popcorn-like aroma as a calling card to say “this is my turf” and find potential mates.

Previous studies searched for compounds in secretions from the scent glands under the binturong’s tail that could explain its signature scent, but nothing turned up.

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For a new paper, researchers analyzed urine samples collected during routine physical examinations of 33 binturongs at Carolina Tiger Rescue, a nonprofit wildlife sanctuary in Pittsboro, North Carolina.

Binturongs pee in a squatting position, soaking their feet and bushy tails in the process. They also drag their tails as they move about in the trees, leaving a scent trail on the branches and leaves behind them.

Using a technique called gas chromatography-mass spectrometry, the researchers identified 29 chemical compounds in the animals’ urine. The one compound that emanated from every sample was 2-acetyl-1-pyrroline, or 2-AP—the same compound that gives popcorn its tantalizing scent.

What’s more, 2-AP was among the few compounds that lingered and became more dominant over time, a fact the researchers discovered when a rush airmail shipment of frozen binturong urine was delayed on a hot tarmac en route to coauthor Thomas Goodwin of Hendrix College in Arkansas for analysis.

How do they do it?

Males secrete more 2-AP than females. “The fact that the compound was in every binturong we studied, and at relatively high concentrations, means it could be a signal that says, ‘A binturong was here,’ and whether it was male or female,” says Lydia Greene, a graduate student at Duke University and first author of the study that is published in the journal the Science of Nature.

The compound 2-AP normally forms in popcorn during the popping process, when heat kicks off reactions between sugars and amino acids in the corn kernels. The cooking produces a variety of new odor and flavor molecules in a chemical reaction called the Maillard reaction. The same compound is also responsible for the comforting aromas of toasted bread and cooked rice.

“If you were to make this compound, you would have to use temperatures above what most animals can achieve physiologically,” says Christine Drea, professor of evolutionary anthropology at Duke who led the study. “How does this animal make a cooking smell, but without cooking?”

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It could be that binturong urine smells funny because of something they eat. The team searched for 2-AP in the binturongs’ kibble, the one cooked item in their diet, but they didn’t detect any.

A more likely explanation, is that 2-AP is produced when binturong urine comes in contact with bacteria and other microorganisms that live on the animal’s skin or fur or in its gut.

Bacteria make smelly compounds as they break down sweat in our armpits in much the same way, Drea says.

The time-release action of the microbes could help the binturongs’ urine smell-o-grams last long after the animals move on, an essential mode of communication for solitary animals that rarely encounter each other.

Tim Wallen of the Centers for Disease Control and Prevention and Anneke Moresco of the Cincinnati Zoo are coauthors of the study. Duke, Hendrix College, and the National Science Foundation funded the work.

Source: Duke University