When monitoring the health of mammal populations, scientists often use camera traps to observe the animals in their habitats. But weasels are so sneaky they’re rarely caught on camera—leaving scientists with questions about this population of predators.

“We’re a little worried about the weasels,” says Roland Kays, a research professor at North Carolina State University and scientist at the N.C. Museum of Natural Sciences. “We don’t see them very often, but it’s difficult to tell if they’re actually gone or if they’re just so sneaky that we can’t find them. We decided that we needed to better understand the best method to detect them. There wasn’t a great consensus on that.”

That problem is the focus of a new study by Kays and a host of collaborators, which examines what kind of bait is most effective at luring weasels out of hiding.

Between 2022 and 2023, researchers placed 486 camera traps in sites across the central and eastern United States where they knew weasels lived. They baited those traps with seven types of lures to see which ones attracted the most mustelids—a diverse family of carnivores that includes weasels, ferrets and martens.

Red meat outperformed all other baits, especially when supplemented with a bit of salmon oil. Weasels in the south also had a taste for chicken, Kays said. Because red meat is also attractive to most other predators, researchers used a new double-cage system to make it harder for larger animals to reach the bait.

“There is a huge variety of scent lures available, and trappers often make their own from all kinds of ingredients,” he said. “As it turns out, however, just having a chunk of meat works the best.”

Of all the weasel species to worry about, the “least weasel” is the most worrisome. As the world’s smallest carnivore, the least weasel is notoriously difficult to track down and has only been seen in a handful of camera trap surveys. Their range extends into the North Carolina mountains, and Kays hopes to use the findings from this study to survey least weasel populations there.

“Now that we have an understanding of the best ways to lure the weasels, we can be more confident in the findings of our surveys,” he said. “When we have sites where we don’t detect them, we can be much more assured that they aren’t just in hiding, they’re really just not there at all.”

The paper, “Efficacy of baits and lures for weasel detection” is available to read in the open-source journal Wildlife Society Bulletin. The study’s corresponding author is Scott M. Bergeson of Purdue University Fort Wayne.